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california smog check program | The California Smog Check Program requires vehicles that were manufactured in 1976 or later to participate in the biennial (every two years) smog check program in participating counties. The program's stated aim is to reduce air pollution from vehicles by ensuring that cars with excessive emissions are repaired in accordance with federal and state guidelines. With some exceptions, gasoline-powered vehicles, hybrid vehicles, and alternative-fuel vehicles that are eight model-years old or newer are not required to participate; instead, these vehicles pay a smog abatement fee for the first 8 years in place of being required to pass a smog check. The eight-year exception does not apply to nonresident (previously registered out-of-state) vehicles being registered in California for the first time, diesel vehicles 1998 model or newer and weighing 14,000 lbs or less, or specially constructed vehicles 1976 and newer. The program is a joint effort between the California Air Resources Board, the California Bureau of Automotive Repair, and the California Department of Motor Vehicles.
A Smog Check is not required for electric, diesel powered manufactured before 1998 or weighing over 14,000 lbs, trailers, motorcycles, or gasoline powered vehicles 1975 or older. In April 2015, hybrid vehicles became subject to smog check requirements.Although vehicles 1975 and older are not required to get a smog check, owners of these vehicles must still ensure that their emissions systems are intact.Anyone wishing to sell a vehicle that is over four years old must first have a smog check performed. It is the seller's responsibility to get the smog certificate prior to the sale. If the vehicle is registered in California and was acquired from a spouse, domestic partner, sibling, child, parent, grandparent, or grandchild it is exempt.
California's history with smog
According to the California EPA, "Californians set the pace nationwide in their love affair with cars". The state's 34 million residents own approximately 25 million cars—one for every adult aged 18 years or older.Smog is created when nitrogen oxides (NOx) and hydrocarbon gases (HC) are exposed to sunlight. The five gasses monitored during a smog check are hydrocarbons, carbon monoxide (CO), nitrogen oxides (NOx), carbon dioxide (CO2), and oxygen (O2).
Impact on human health
In 1998 the Air Resource Board identified diesel particulate matter as carcinogenic. Further research revealed that it can cause life-shortening health problems such as respiratory illness, heart problems, asthma, and cancer. Diesel particulate matter is the most common airborne toxin that Californians breathe.Between 2005 and 2007 air pollution led to almost 30,000 hospital and emergency room visits in California for asthma, pneumonia, and other respiratory and cardiovascular ailments. A study by RAND Corporation showed the cost to the state, federal and private health insurers was over $193 million in hospital-based medical care. John Romley lead author of the study. said "California's failure to meet air pollution standards causes a large amount of expensive hospital care." According to the American Lung Association, California's dirty air causes 19,000 premature deaths, 9,400 hospitalizations and more than 300,000 respiratory illnesses including asthma and acute bronchitis.A study of children living in Southern California found that smog can cause asthma. The study of over 3,000 children showed those living in high-smog areas were more likely to develop asthma if they were avid athletes, when compared to children who did not participate in sports.More people in California live in areas that do not meet federal clean air standards than in any other state. A report by the American Lung Association states that some areas in California are the most polluted in the United States, with air quality that is likely damaging the health of millions of people. The report finds that Los Angeles, Bakersfield (CA), and Visalia-Porterville (CA) rank among the five U.S. cities most polluted with particulates and ozone.
Impact on global warming
Carbon dioxide (CO2) is a greenhouse gas that is associated with global warming. Vehicles are a significant source of CO2 emissions and thus contribute to global warming. According to an advocacy group Environmental Defense, in 2004, automobiles from the three largest automakers in the US – Ford, GM, and DaimlerChrysler – contributed CO2 emissions that were comparable to those from the top 11 electric companies.Historically, California was hottest in July and August, but as climate change takes place, the temperature may be extended from July through September, according to a report from the team established by the Air Resource Board. Some climate change simulations indicate the global warming impact on California will be an increase in the frequency of hot daytime and nighttime temperatures. The climate change simulations also indicate that drying in the Sacramento area may be evident by the mid 21st century. The California sea level has risen at about 7 inches per century, but this trend could change with global warming. According to the report by the Climate Action Team, “[t]he sea-level rise projections in the 2008 Impacts Assessment indicate that the rate and total sea-level rise in future decades may increase substantially above the recent historical rates”. While all sectors are vulnerable to rising sea-levels, 70 percent of those at risk are residential areas. Hospitals, schools, water treatment plants, and other buildings may be at risk of flooding.Climate change may also affect California's diverse agricultural sector, since it is likely to change precipitation, temperature averages, pest and weed ranges, and the length of the growing season (this affecting crop productivity). In one study, researchers looked at the possible effects on the agricultural sector in the US and identified some possible effects. Results suggested that climate change will decrease annual crop yields in the long-term, especially for cotton.Climate change in California could also impact energy consumption. Demand patterns for electricity might be affected as the mean temperatures and the frequency of hot days increases, increasing demand for cooling in summertime.
Causes of smog
Air pollution has two primary sources, biogenic and anthropogenic. Biogenic sources are natural sources, such as volcanoes that spew particulate matter, lightning strikes that cause forest fires, and trees and other vegetation that release pollen and spores into the atmosphere.Californian greenhouse gas emissions come mostly from transportation, utilities, and industries including refineries, cement, manufacturing, forestry, and agriculture.
In 2004, transportation accounted for approximately 40 percent of total greenhouse gas emissions in California. About 80 percent of that came from road transportation.Population growth increases air pollution, as more vehicles are on the road. California's large population significantly contributes to the high amount of smog and air pollution in the state. In 1930, California's population was less than six million people and the total registered vehicles were two million.
Topography
California has a unique topography which contributes to some of the problems; the warm, sunny climate is ideal for trapping and forming air pollutants. On hot, sunny days, pollutants from vehicles, industry, and many products may chemically react with each other. In the winter, temperature inversions can trap tiny particles of smoke and exhaust from vehicles and anything else that burns fuel. This keeps pollution closer to the ground.
History of the Smog Check Program
In 1974 American automobiles manufactured on or after 1966 required a smog inspection upon change of ownership in California by a licensed MVPC Class A Installer/Adjuster technician (Smog Check I). An aftermarket "NOx kit" would be installed on all 1966 to 1973 American automobiles to lower Nitrous Oxide emissions. After the 1973 model year, automobile manufacturers were required to factory install NOx devices (usually in the form of EGR valves) on all cars sold in California. HC and CO (hydrocarbon and carbon monoxide) limits at idle were also checked by an infrared exhaust analyzer and manually recorded by the technician. A $50 repair cost limit was imposed on vehicles that did not pass emission standards. The first truly comprehensive “Smog Check” program was implemented in March 1984. It came about as a result of "SB 33" which was passed in 1982. The program included a biennial and change of ownership testing, "BAR 84" emissions test plus a visual and functional inspection of various emission control components, a $50 repair cost limit (unless emission device tampering was noted), licensing shops to perform smog checks and mechanic certification for emissions repair competence. The program is generally known as “BAR 84” program. During the BAR 84 program, the first acceleration simulation mode (ASM) test was implemented which tests for two gases, HC and CO (hydrocarbons and carbon monoxide) while the vehicle was run at 2500 RPM for 30 seconds (static test). EGR device functions were also tested for NOx emissions.
Automobiles with a motor swap performed prior to the March 19, 1984 mandate which was older than the model year of the vehicle e.g. a 1970 LT-1 350 swapped into a 1975 Chevrolet with the 1970 smog gear intact (with documentation e.g. receipts) are considered noncompliant illegal engine swaps including nonstock exhaust swaps e.g. dual catalytic converters with a true dual exhaust not original to the vehicle - this means that the engine swap performed after the date of enactment must be the same model year or newer. Engine swaps which are the same year or newer where the vehicle class did not have it as a manufacturer option (from a Chevrolet S-10 with a late model LSx powertrain transplant with the associated smog gear intact salvaged from the donor vehicle which includes the OBDII diagnostic connections and associated exhaust system with the catalytic converter attached including the secondary downstream oxygen sensor (catalytic converter must be California legal which has a serial number and build date mandated under California state law) must be approved by a 'referee' smog test station where the engine/transmission package is certified where a silver tag is stickered to the door jamb. Although the engine may be newer than the vehicle model year even with an OBDII upgrade the automobile must be tested based on the model year using the test criteria based on the VIN and registration. This means that even with an OBDII powertrain upgrade regardless of the engine swap being 1996 and newer, the vehicle being smogged must be tested using BAR97 criteria, not the OBDII standard procedure.
In 1997 important laws were passed that made significant changes to Smog Check II.
AB 57 created a financial assistance program.
AB 208 provided funding for low-income assistance and vehicle retirement
AB 1492 exempted vehicles less than four years old from the biennial smog check
AB 42 exempted vehicles manufactured before 1978 from smog check testing. Also required that vehicles 20 years old or older be exempt from the Smog Check program starting in 2004. AB 42 established a brief rolling chassis exemption until it was repealed in 2006 where 1976 and newer vehicles were subjected to emission testing.In 1999, “AB 1105” made additional changes to the program. It authorized but did not require the Bureau of Automotive Repairs (BAR) to exempt vehicles up to six years old from the biennial smog check and gave the agency authorization to except additional vehicles by low-emitter profiling (Schwartz). It also created additional changes to the repair assistance program and provided BAR with increased flexibility for how much to pay drivers whose vehicle failed the smog check so that the vehicle may be scrapped.In 2010 the Air Resource Board and the Bureau of Automotive Repair jointly sponsored legislation, "AB 2289", that is designed to improve the program to reduce air pollution through “the use of new technologies that provide considerable time and cost savings to consumers while at the same time improving consumer protections by adopting more stringent fine structures to respond to stations and technicians that perform improper and incomplete inspections”. The bill, which passed and took effect in 2013, will allow for a major upgrade in technologies used to test vehicle emissions. According to ARB Chairman, Mary D. Nichols, “[t]his new and improved program will have the same result as taking 800,000 vehicles away from California residents, also resulting in a more cost effective program for California motorists”. One way the program would reduce costs is by taking advantage of on-board diagnostic (OBDII) technology that has been installed on new vehicles since 1996. The program will eliminate tailpipe testing of post-1999 vehicles and instead use the vehicle's own emissions monitoring systems. This system has saved consumers in 22 states time and money. Vehicles manufactured in the model years between 1976 and 1999 are now required to pass a more stringent dynamometer-based tail-pipe test than was previously required. A high number of vehicles in this range have begun to fail the emissions test with the arrival of their first test-year under the new rule; some question the influence of the automotive industry on the new rule and the inherent push and perceived unfair requirement to purchase a new or near-new vehicle to replace an otherwise functional and OBDII compliant vehicle.
Smog check process
The Department of Motor Vehicles (DMV) sends a registration renewal notice which indicates if a smog check is required. If the DMV requires a smog check for a vehicle, the owner must comply with the notice within 90 days and provide a completed smog check certificate.A smog check inspection is performed by a station that has been licensed by the California Bureau of Automotive Repair (BAR). Depending on the situation, the owner may be required to take the vehicle to one of the following types of smog check stations:
Test-only station, one that can perform the smog check test, but cannot make repairs.
Test-and-repair station, one that can both perform the smog check and repair the vehicle.
Repair-only station, one that can only repair the vehicle, but cannot perform the test itself.
STAR station, one that meets the BAR's higher performance standards. Some STAR stations are test-only stations, while other STAR stations are test-and-repair.Until a smog certificate can be provided registration will not be renewed. If the vehicle fails the smog check, the owner will be required to complete all necessary repairs and pass a smog check retest in order to complete the registration. If the costs of repairing the vehicle outweigh its value, the state may buy it and have it scrapped. The buyback program is part of California's Consumer Assistance Program (CAP) that also offers consumer assistance for repairs related to smog check. The program is administered by the Bureau of Automotive Repair.
Participating counties
Residents in certain counties, primarily rural ones, are normally exempt from the smog inspection requirements.
Policy tools
Air is susceptible to the Tragedy of the Commons, but that can be overcome with policy tools. In their book Environmental Law and Policy, Salzman and Thompson describe these policy tools as the "5 P’s" - Prescriptive Regulation, Property Rights, Penalties, Payments, and Persuasion.Throughout the years there have been some tensions between the US EPA and the California EPA with disagreements centered on California's Smog Check Policy (The Press-Enterprise, 1997). One disagreement has been over where smog checks are performed. The EPA believes that smog checks and smog repairs must be done separately, to avoid conflicts of interest.For years, California has been asking the US EPA to approve a waiver allowing it to enforce its own greenhouse gas emission standards for new motor vehicles. A request was made in December 2005, but denied in March 2008 under the Bush administration, when interpretations of the Clean Air Act found California did not have the need for special emission standards. However, shortly after taking office, president Obama asked the EPA to assess if it was appropriate to deny the waiver and subsequently allowed the waiver. US EPA's interpretation of the Clean Air Act allows California to have its own vehicle emissions program and set greenhouse gas standards due to the state's unique need.Car manufacturers have been strongly opposed to the emission standards set by California, arguing that regulation imposes further costs on consumers. In 2004, California approved the world's most stringent standards to reduce auto emissions, and the auto industry threatened to challenge the regulations in court. The new regulations required car makers to cut exhaust from cars and light trucks by 25% and from larger trucks and SUVs by 18%, standards that must be met by 2016. The auto industry argued that California's Air Resource Board did not have the authority to adopt such regulation and that the new standards could not be met with the current technology. They further argued that it would raise vehicle costs by as much as $3,000. The agency, however, countered that argument by saying that the additional costs would only be about $1,000 by 2016.The Obama administration has proposed setting a national standard for greenhouse gas emissions from vehicles, which could potentially increase fuel efficiency by an average of 5% per year from 2012 to 2016.
Evaluation
According to the California Air Resources Board, the California Smog Check program removes about 400 tons of smog-forming pollutants from California's air every day.On March 12, 2009, the Bureau of Automotive Repair and the Air Resource Board hired Sierra Research, Inc. to analyze the data collected in the BAR's Roadside Inspection Program to evaluate the effectiveness of the Smog Check Program from data collected in 2003–2006. Under the Roadside Inspection Program vehicles are randomly inspected at checkpoints set up by the California Highway Patrol (CHP). One objective of the evaluation was to compare the post smog check performance of pre-1996 (1974–1995) vehicles to the post smog check performance determined from a previous evaluation collected in 2000–2002.
The report made several recommendations to reduce the number of vehicles failing the Roadside test. One was to develop a method for evaluating station performance. The other was to perform inspections immediately following certifications at smog check stations. Finally, the report recommended continued use of the Roadside test to evaluate the effectiveness of the Smog Check program.
References
External links
Official California Smog Check Program website
California DMV Smog Requirements |
suncor energy | Suncor Energy (French: Suncor Énergie) is a Canadian integrated energy company based in Calgary, Alberta. It specializes in production of synthetic crude from oil sands. In the 2020 Forbes Global 2000, Suncor Energy was ranked as the 48th-largest public company in the world.Suncor was created by Sun Oil in 1979 by the merger of its Canadian conventional and heavy oil companies, the Sun Oil Company and Great Canadian Oil Sands. Until 2010, Suncor marketed products and services to retail customers in Ontario through a downstream network of 780 company-owned, and 700 customer-operated retail and Diesel fuel sites, primarily in Ontario under the Sunoco brand (owing to Suncor having originally been established as a subsidiary of Sunoco). In 2009, Suncor acquired the former Crown corporation Petro-Canada, which replaced the Sunoco brand across its existing outlets. Suncor also markets through a retail network of Shell and ExxonMobil branded outlets in the United States.
Predecessor companies
Sun Company of Canada
The Sun Oil Company began operations in Canada in 1919 when it formed the Sun Company of Canada. The company opened offices in Montreal and began importing American products to Canada for sale. On 31 March 1923, Sun incorporated a Canadian subsidiary, the Sun Oil Company Limited. In 1932, the company transferred its headquarters from Montreal to Toronto. In 1950 the Sun Oil Company drilled its first successful Canadian oil well in Alberta. In 1953 it opened a new refinery in Sarnia.
Great Canadian Oil Sands
Great Canadian Oil Sands was incorporated on 29 December 1953, however, the company originated in several previous ventures dating back to 1920. In 1962, GCOS received a permit from the Government of Alberta to build a plant in the Athabasca Oil Sands. The following year, Sun purchased a majority stake in GCOS. The GCOS plant went online in 1967.
History
In 1979, Sun formed Suncor by merging its Canadian refining and retailing interests; Great Canadian Oil Sands (a majority-owned subsidiary, which constructed and operated the first commercial plant to develop Canada's Athabasca oil sands and went on production in 1967); and its conventional oil and gas interests. In 1981, the Government of Ontario purchased a 25% stake in the company; it divested in 1993. In 1995 Sun Oil also divested its interest in the company, although Suncor maintained the Sunoco retail brand in Canada. With these two divestitures, Suncor become an independent, widely held public company.
In 2003, Suncor acquired a refinery and associated Phillips 66 gas stations in Commerce City, Colorado from ConocoPhillips. In 2005, Suncor acquired a second Commerce City refinery from Valero Energy. Suncor moved its retail brand from Phillips 66 to Shell from 2009 to 2013. Suncor added the Exxon and Mobil brands in Colorado and Wyoming in 2015.On March 23, 2009, Suncor announced its intent to acquire Petro-Canada. This merger created a company with a combined market capitalization of C$43.3 billion. On June 4, 2009, a 98% approval rate was reached by Suncor's shareholders for the acquisition of Petro-Canada and the Competition Bureau approved the merger on June 21, 2009. The merger with Canada's 11th largest company was completed on August 1, 2009 in a $21 billion deal to form the second-largest company in Canada (after Royal Bank of Canada) in terms of market capitalization. In December 2009, as a condition of the merger, Suncor sold 98 gas stations in Ontario to Husky Energy, consisting of 68 Sunoco-branded locations and 30 Petro-Canada-branded locations.In 2015 Suncor courted Canadian Oil Sands, the largest owner of the Syncrude project with 37% ownership (compared with Suncor's 12%), with proposals for acquisition and hostile takeover. In January 2016 they reached an agreement with Suncor acquiring COS for C$6.6 billion, raising its Syncrude ownership to 49%.On April 27, 2016, Suncor announced that it had reached a $937-million deal to acquire Murphy Oil's 5% stake in the Syncrude project, growing its interest in Syncrude to nearly 54%, making it the majority shareholder of the project. In fall 2021, Suncor assumed operatorship of the Syncrude Joint Venture oil sands project in a bid to improve its performance. Suncor holds a majority stake in Syncrude with 58.74 per cent.In July 2022, president and CEO Mark Little resigned amid investor pressure and after a series of workplace deaths and safety incidents. Executive vice-president for downstream Kris Smith was named as interim CEO. On February 21, 2023, Suncor announced that former Imperial Oil Ltd. president and CEO Rich Kruger had been named its new chief executive officer after a months-long search. Kruger replaced interim Suncor CEO Kris Smith on April 3, 2023. Smith assumed the role of chief financial officer and executive vice-president of corporate development after Suncor's annual general meeting on May 9, 2023.June 2023 transactions with customers and suppliers were impaired due to a cyber attack. The company stated no customer information was stolen but some of the companies services, such as digital payment, crashed.In October 2023, Suncor Energy acquired TotalEnergies' Canadian operations for C$1.47 billion($1.07 billion).
Operations
In North America, Suncor develops and produces oil and natural gas in Western Canada, Colorado, and offshore drilling in eastern Canada. Its international efforts include offshore developments in the North Sea, and conventional, land-based efforts in Libya, Syria, and Trinidad and Tobago.
Suncor operates refineries in Edmonton, Alberta; Sarnia, Ontario; Montreal, Quebec and Commerce City, Colorado. These refineries supply industrial, retail and commercial consumers. The company is also one of the largest Canadian retailers of petroleum products.: 22
Bitumen, oil and natural gas production
Suncor is the world's largest producer of bitumen, and owns and operates an oil sands upgrading plant near Fort McMurray, Alberta, Canada. Originally developed by Great Canadian Oil Sands, a majority-owned subsidiary of Sun Oil, it is now wholly owned by the independent Suncor. It was the first commercial development on the Athabasca oil sands, although small, earlier projects like that at Bitumount also played a role in development. The company held a 36.75% interest in the Joslyn north oil sands project which was shelved pending an economic review by operator Total S.A. in May 2014. The Joslyn project was sold to CNRL in September 2018. The company also produces conventional oil, heavy crude oil, and natural gas.: 22
Refining
In Canada, Suncor operates refineries in Alberta, Ontario and Quebec. The company's 135,000-barrel-per-day Strathcona, refinery runs entirely on oil sands-based feedstocks and produces a high-yield of light oils. A 137,000-barrel-per-day Montreal Refinery produces gasoline, distillates, asphalts, heavy fuel oil, petrochemicals, solvents and feedstock for lubricants. An 85,000-barrel-per-day refinery in Sarnia, Ontario produces gasoline, kerosene, jet and diesel fuels. A 98,000-barrel-per-day refinery in Commerce City, Colorado produces gasoline, diesel fuel and paving-grade asphalt.: 22
Retail
Suncor's main downstream brand in Canada is Petro-Canada. Suncor previously operated and franchised retail locations under the Sunoco brand, but post-acquisition, nearly all remaining Sunoco stations were converted to Petro-Canada. In addition, the company terminated all of its independent Sunoco franchises, as it planned to implement Petro-Canada's model of requiring franchisees to operate multiple locations. Presently, at least one Sunoco branded station exists, and is located in Port Colborne, Ontario. A group of affected franchisees filed a class-action lawsuit over the matter, claiming that Suncor had violated Ontario's Arthur Wishart Act. However, the case was blocked by an Ontario court.In the United States, it operates retail outlets in Colorado under the Shell and Phillips 66 brands.On April 13, 2012, Suncor paid a $500,000 fine after being found guilty of price-fixing in Ontario.
Aircraft fleet
Suncor Energy owned and operated three Bombardier CRJ900ER aircraft but sold them in late 2016 and now uses Westjet to shuttle Suncor employees to the oilsands.As of February 2023, Suncor Energy owns a Bombardier Global Express (BD-700) and operate as ICAO airline designator JSN, and telephony JETSUN.
Environmental record
According to a Pollution Watch fact sheet, in 2007 Suncor Energy's oil sands operations had the sixth highest greenhouse gas emissions in Canada. While Suncor has reduced the greenhouse gas emissions intensity of its oil sands operations by more than 50% since 1990, total greenhouse gas emissions from the company's operations have increased because of growing oil sands production.
On April 2, 2009, Suncor was fined $675,000 for failing to install pollution control equipment at its Firebag operation near Fort McMurray, Alberta in July 2006. On the same day, Suncor was fined $175,000 for dumping untreated wastewater from a company work camp near Fort McMurray into the Athabasca River in 2007.In the United States, Suncor has also been fined by the Colorado Department of Public Health and Environment. In April 2012, a fine of $2.2 million was assessed for air pollution. Suncor failed to monitor and control emissions a number of times throughout 2009 and 2010, and numerous emissions exceeded regulations. Suncor was also cited for "failure to conduct equipment inspections, train employees, and fully develop standard procedures for operating equipment". Additionally, a benzene leak into Sand Creek was discovered in the fall of 2011. Employees at Suncor and the nearby Metro Wastewater Reclamation District Plant were exposed to benzene through the air and through drinking water. In April 2018, Suncor and ExxonMobil were sued by the city and county of Boulder, and the county of San Miguel over allegations that they were responsible for climate change in the state. The lawsuit was unique as it was one of the first to be based on these effects on a landlocked area, as opposed to those citing Sea level rise as a factor. In 2020, Suncor reached a US$9 million settlement agreement with authorities in Colorado for more than 100 air pollution violations from its Commerce City refinery.By 2009, Suncor was working to reduce the amount of bitumen entering tailings ponds. In 2009, under the auspices of the Natural Sciences and Engineering Research Council of Canada (NSERC), Suncor teamed with the University of Alberta and Matrikon, an Edmonton-based software company, to develop separation-cell technology to potentially reduce the amount of bitumen entering tailings ponds by 50 per cent.By 2009, Suncor operated four wind farms. These wind farms provided 147 megawatts of power, providing an annual CO2 offset of 284,000 tonnes compared to coal-generated electricity. Suncor operates an ethanol facility in St. Clair Township, Ontario. The facility is the largest corn ethanol producer in Canada.
Governance
† Hennigar was killed in a plane crash on 11 January 1983
See also
History of the petroleum industry in Canada (oil sands and heavy oil)
History of the petroleum industry in Canada
Syncrude
Canadian petroleum companies
List of articles about Canadian oil sands
References
External links
Media related to Suncor Energy, Montreal at Wikimedia Commons
Suncor's Official Website
Petro-Canada's Official Website |
orphan wells | Orphan, orphaned or abandoned wells are oil or gas wells that have been abandoned by fossil fuel extraction industries. These wells may have been deactivated because of economic viability, failure to transfer ownerships (especially at bankruptcy of companies), or neglect and thus no longer have legal owners responsible for their care. Decommissioning wells effectively can be expensive, costing millions of dollars, and economic incentives for businesses generally encourage abandonment. This process leaves the wells the burden of government agencies or landowners when a business entity can no longer be held responsible. As climate change mitigation reduces demand and usage of oil and gas, its expected that more wells will be abandoned as stranded assets.Orphan wells are a potent contributor of greenhouse gas emissions, such as methane emissions, causing climate change. Much of this leakage can be attributed to broken plugs, or failure to plug properly. A 2020 estimate of US abandoned wells alone was that methane emissions released from abandoned wells produced greenhouse gas impacts equivalent of 3 weeks of US oil consumption each year. The scale of leaking abandoned wells are well understood in the US and Canada because of public data and regulation; however, a Reuters investigation in 2020 could not find good estimates for Russia, Saudi Arabia and China—the next biggest oil and gas producers. However, they estimate there are 29 million abandoned wells internationally.Abandoned wells also have the potential to contaminate land, air and water around wells, potentially harming ecosystems, wildlife, livestock, and humans. For example, many wells in the United States are situated on farmland, and if not maintained could contaminate important sources of soil and groundwater with toxic contaminants.
Economic limits
A well is said to reach an "economic limit" when its most efficient production rate does not cover the operating expenses, including taxes. When the economic limit is raised, the life of the well is shortened and proven oil reserves are lost. Conversely, when the financial limit is lowered, the life of the well is lengthened. When the economic limit is reached, the well becomes a liability and is abandoned.
At the economic limit, a significant amount of unrecoverable oil is often left in the reservoir. It might be tempting to defer physical abandonment for an extended period, hoping that the oil price will increase or that new supplemental recovery techniques will be perfected. In these cases, temporary plugs will be placed downhole, and locks will be attached to the wellhead to prevent tampering. There are thousands of "abandoned" wells throughout North America, waiting to see what the market will do before permanent abandonment. Often, lease provisions and governmental regulations usually require quick abandonment; liability and tax concerns also may favor abandonment.Theoretically, an abandoned well can be reinstated and re-entered to production (or converted to injection service for supplemental recovery or downhole hydrocarbon storage), but reentry is often difficult mechanically and expensive. Traditionally elastomer and cement plugs have been used with varying degrees of success and reliability. Over time, they may deteriorate, particularly in corrosive environments, due to the materials from which they are manufactured. New tools have been developed that make re-entry easier; these tools offer higher expansion ratios than conventional bridge plugs and higher differential pressure ratings than inflatable packers, all while providing a V0-rated, gas-tight seal that cement cannot provide.
Reclaim and reuse
Some abandoned wells are subsequently plugged and the site is reclaimed; however, the cost of such efforts can be in the millions of dollars. In this process, tubing is removed from the well, and sections of wellbore are filled with concrete to isolate the flow path between gas and water zones from each other, as well as the surface. The surface around the wellhead is then excavated, and the wellhead and casing are cut off, a cap is welded in place and then buried.
Plugging
The primary method of plugging wells is through elastomer and cement plugs. Government-led campaigns to plug wells are expensive but often facilitated by oil and gas taxes, bonds, or other fees applied to production. Environmental non-profit organizations, such as the Well Done Foundation, also carry out well-plugging projects and develop programs alongside government entities.
Plug bonds
Oil and gas companies on public land in the United States must post financial assurance to cover the cost of plugging wells if they go bankrupt or cannot plug the well themselves. The current financial assurance requirement, which has been in place for 60 years, is $10,000 per well. This is significantly less than the cost of plugging a well, ranging from $92,000 to $400,000. As a result, 99% of federal oil and gas leases have a bond that cannot cover the cost of cleanup.
New rules related to the Infrastructure Investment and Jobs Act will increase the financial assurance requirement to a minimum of $150,000 per well. This will help ensure that oil and gas companies have the financial resources to plug wells if they can no longer do so themselves.
CO2 injection
Unused wells, especially from natural gas might be used for carbon capture or storage. However, if not sealed properly, or the storage site is not sufficiently sealed, there is a possibility of leakage.
Geothermal generation
A 2014 study in China evaluated the use of oil wells for geothermal power generation. A similar study followed in 2019 for natural gas wells.
Environmental impacts
Hydraulic fracturing
Hydraulic fracturing, also known as fracking, is the process of fracturing bedrock with pressurized liquids. This process creates cracks in well-formed rock formations to allow natural gas, petroleum, and brine to move more effortlessly. When hydraulic fracturing is done in nearby geographies to an orphaned well it can cause breaches of poorly sealed or unsealed abandoned wells further contaminating local ecosystems. These orphaned wells can allow gas and oil to contaminate groundwater due to improper sealing.
By context
Alberta, Canada
United States
Notes
== References == |
steel | Steel is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels, which are resistant to corrosion and oxidation, typically need an additional 11% chromium. Because of its high tensile strength and low cost, steel is used in buildings, infrastructure, tools, ships, trains, cars, bicycles, machines, electrical appliances, furniture, and weapons.
Iron is the base metal of steel. Depending on the temperature, it can take two crystalline forms (allotropic forms): body-centred cubic and face-centred cubic. The interaction of the allotropes of iron with the alloying elements, primarily carbon, gives steel and cast iron their range of unique properties. In pure iron, the crystal structure has relatively little resistance to the iron atoms slipping past one another, and so pure iron is quite ductile, or soft and easily formed. In steel, small amounts of carbon, other elements, and inclusions within the iron act as hardening agents that prevent the movement of dislocations.
The carbon in typical steel alloys may contribute up to 2.14% of its weight. Varying the amount of carbon and many other alloying elements, as well as controlling their chemical and physical makeup in the final steel (either as solute elements, or as precipitated phases), impedes the movement of the dislocations that make pure iron ductile, and thus controls and enhances its qualities. These qualities include the hardness, quenching behaviour, need for annealing, tempering behaviour, yield strength, and tensile strength of the resulting steel. The increase in steel's strength compared to pure iron is possible only by reducing iron's ductility.
Steel was produced in bloomery furnaces for thousands of years, but its large-scale, industrial use began only after more efficient production methods were devised in the 17th century, with the introduction of the blast furnace and production of crucible steel. This was followed by the Bessemer process in England in the mid-19th century, and then by the open-hearth furnace. With the invention of the Bessemer process, a new era of mass-produced steel began. Mild steel replaced wrought iron. The German states saw major steel prowess over Europe in the 19th century, and the American steel production industry was manufactured in cities such as Pittsburgh and Cleveland until the late 20th century.
Further refinements in the process, such as basic oxygen steelmaking (BOS), largely replaced earlier methods by further lowering the cost of production and increasing the quality of the final product. Today, steel is one of the most commonly manufactured materials in the world, with more than 1.6 billion tons produced annually. Modern steel is generally identified by various grades defined by assorted standards organisations. The modern steel industry is one of the largest manufacturing industries in the world, but also one of the most energy and greenhouse gas emission intense industries, contributing 8% of global emissions. However, steel is also very reusable: it is one of the world's most-recycled materials, with a recycling rate of over 60% globally.
Definitions and related materials
The noun steel originates from the Proto-Germanic adjective stahliją or stakhlijan 'made of steel', which is related to stahlaz or stahliją 'standing firm'.The carbon content of steel is between 0.002% and 2.14% by weight for plain carbon steel (iron-carbon alloys). Too little carbon content leaves (pure) iron quite soft, ductile, and weak. Carbon contents higher than those of steel make a brittle alloy commonly called pig iron. Alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include: manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium. Additional elements, most frequently considered undesirable, are also important in steel: phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper.
Plain carbon-iron alloys with a higher than 2.1% carbon content are known as cast iron. With modern steelmaking techniques such as powder metal forming, it is possible to make very high-carbon (and other alloy material) steels, but such are not common. Cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties. Certain compositions of cast iron, while retaining the economies of melting and casting, can be heat treated after casting to make malleable iron or ductile iron objects. Steel is distinguishable from wrought iron (now largely obsolete), which may contain a small amount of carbon but large amounts of slag.
Material properties
Origins and production
Iron is commonly found in the Earth's crust in the form of an ore, usually an iron oxide, such as magnetite or hematite. Iron is extracted from iron ore by removing the oxygen through its combination with a preferred chemical partner such as carbon which is then lost to the atmosphere as carbon dioxide. This process, known as smelting, was first applied to metals with lower melting points, such as tin, which melts at about 250 °C (482 °F), and copper, which melts at about 1,100 °C (2,010 °F), and the combination, bronze, which has a melting point lower than 1,083 °C (1,981 °F). In comparison, cast iron melts at about 1,375 °C (2,507 °F). Small quantities of iron were smelted in ancient times, in the solid-state, by heating the ore in a charcoal fire and then welding the clumps together with a hammer and in the process squeezing out the impurities. With care, the carbon content could be controlled by moving it around in the fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily.
All of these temperatures could be reached with ancient methods used since the Bronze Age. Since the oxidation rate of iron increases rapidly beyond 800 °C (1,470 °F), it is important that smelting take place in a low-oxygen environment. Smelting, using carbon to reduce iron oxides, results in an alloy (pig iron) that retains too much carbon to be called steel. The excess carbon and other impurities are removed in a subsequent step.
Other materials are often added to the iron/carbon mixture to produce steel with the desired properties. Nickel and manganese in steel add to its tensile strength and make the austenite form of the iron-carbon solution more stable, chromium increases hardness and melting temperature, and vanadium also increases hardness while making it less prone to metal fatigue.To inhibit corrosion, at least 11% chromium can be added to steel so that a hard oxide forms on the metal surface; this is known as stainless steel. Tungsten slows the formation of cementite, keeping carbon in the iron matrix and allowing martensite to preferentially form at slower quench rates, resulting in high-speed steel. The addition of lead and sulfur decrease grain size, thereby making the steel easier to turn, but also more brittle and prone to corrosion. Such alloys are nevertheless frequently used for components such as nuts, bolts, and washers in applications where toughness and corrosion resistance are not paramount. For the most part, however, p-block elements such as sulfur, nitrogen, phosphorus, and lead are considered contaminants that make steel more brittle and are therefore removed from steel during the melting processing.
Properties
The density of steel varies based on the alloying constituents but usually ranges between 7,750 and 8,050 kg/m3 (484 and 503 lb/cu ft), or 7.75 and 8.05 g/cm3 (4.48 and 4.65 oz/cu in).Even in a narrow range of concentrations of mixtures of carbon and iron that make steel, several different metallurgical structures, with very different properties can form. Understanding such properties is essential to making quality steel. At room temperature, the most stable form of pure iron is the body-centred cubic (BCC) structure called alpha iron or α-iron. It is a fairly soft metal that can dissolve only a small concentration of carbon, no more than 0.005% at 0 °C (32 °F) and 0.021 wt% at 723 °C (1,333 °F). The inclusion of carbon in alpha iron is called ferrite. At 910 °C, pure iron transforms into a face-centred cubic (FCC) structure, called gamma iron or γ-iron. The inclusion of carbon in gamma iron is called austenite. The more open FCC structure of austenite can dissolve considerably more carbon, as much as 2.1%, (38 times that of ferrite) carbon at 1,148 °C (2,098 °F), which reflects the upper carbon content of steel, beyond which is cast iron. When carbon moves out of solution with iron, it forms a very hard, but brittle material called cementite (Fe3C).
When steels with exactly 0.8% carbon (known as a eutectoid steel), are cooled, the austenitic phase (FCC) of the mixture attempts to revert to the ferrite phase (BCC). The carbon no longer fits within the FCC austenite structure, resulting in an excess of carbon. One way for carbon to leave the austenite is for it to precipitate out of solution as cementite, leaving behind a surrounding phase of BCC iron called ferrite with a small percentage of carbon in solution. The two, ferrite and cementite, precipitate simultaneously producing a layered structure called pearlite, named for its resemblance to mother of pearl. In a hypereutectoid composition (greater than 0.8% carbon), the carbon will first precipitate out as large inclusions of cementite at the austenite grain boundaries until the percentage of carbon in the grains has decreased to the eutectoid composition (0.8% carbon), at which point the pearlite structure forms. For steels that have less than 0.8% carbon (hypoeutectoid), ferrite will first form within the grains until the remaining composition rises to 0.8% of carbon, at which point the pearlite structure will form. No large inclusions of cementite will form at the boundaries in hypoeutectoid steel. The above assumes that the cooling process is very slow, allowing enough time for the carbon to migrate.
As the rate of cooling is increased the carbon will have less time to migrate to form carbide at the grain boundaries but will have increasingly large amounts of pearlite of a finer and finer structure within the grains; hence the carbide is more widely dispersed and acts to prevent slip of defects within those grains, resulting in hardening of the steel. At the very high cooling rates produced by quenching, the carbon has no time to migrate but is locked within the face-centred austenite and forms martensite. Martensite is a highly strained and stressed, supersaturated form of carbon and iron and is exceedingly hard but brittle. Depending on the carbon content, the martensitic phase takes different forms. Below 0.2% carbon, it takes on a ferrite BCC crystal form, but at higher carbon content it takes a body-centred tetragonal (BCT) structure. There is no thermal activation energy for the transformation from austenite to martensite. There is no compositional change so the atoms generally retain their same neighbors.Martensite has a lower density (it expands during the cooling) than does austenite, so that the transformation between them results in a change of volume. In this case, expansion occurs. Internal stresses from this expansion generally take the form of compression on the crystals of martensite and tension on the remaining ferrite, with a fair amount of shear on both constituents. If quenching is done improperly, the internal stresses can cause a part to shatter as it cools. At the very least, they cause internal work hardening and other microscopic imperfections. It is common for quench cracks to form when steel is water quenched, although they may not always be visible.
Heat treatment
There are many types of heat treating processes available to steel. The most common are annealing, quenching, and tempering.
Annealing is the process of heating the steel to a sufficiently high temperature to relieve local internal stresses. It does not create a general softening of the product but only locally relieves strains and stresses locked up within the material. Annealing goes through three phases: recovery, recrystallization, and grain growth. The temperature required to anneal a particular steel depends on the type of annealing to be achieved and the alloying constituents.Quenching involves heating the steel to create the austenite phase then quenching it in water or oil. This rapid cooling results in a hard but brittle martensitic structure. The steel is then tempered, which is just a specialized type of annealing, to reduce brittleness. In this application the annealing (tempering) process transforms some of the martensite into cementite, or spheroidite and hence it reduces the internal stresses and defects. The result is a more ductile and fracture-resistant steel.
Production
When iron is smelted from its ore, it contains more carbon than is desirable. To become steel, it must be reprocessed to reduce the carbon to the correct amount, at which point other elements can be added. In the past, steel facilities would cast the raw steel product into ingots which would be stored until use in further refinement processes that resulted in the finished product. In modern facilities, the initial product is close to the final composition and is continuously cast into long slabs, cut and shaped into bars and extrusions and heat treated to produce a final product. Today, approximately 96% of steel is continuously cast, while only 4% is produced as ingots.The ingots are then heated in a soaking pit and hot rolled into slabs, billets, or blooms. Slabs are hot or cold rolled into sheet metal or plates. Billets are hot or cold rolled into bars, rods, and wire. Blooms are hot or cold rolled into structural steel, such as I-beams and rails. In modern steel mills these processes often occur in one assembly line, with ore coming in and finished steel products coming out. Sometimes after a steel's final rolling, it is heat treated for strength; however, this is relatively rare.
History
Ancient
Steel was known in antiquity and was produced in bloomeries and crucibles.The earliest known production of steel is seen in pieces of ironware excavated from an archaeological site in Anatolia (Kaman-Kalehöyük) and are nearly 4,000 years old, dating from 1800 BC. Horace identifies steel weapons such as the falcata in the Iberian Peninsula, while Noric steel was used by the Roman military.The reputation of Seric iron of India (wootz steel) grew considerably in the rest of the world. Metal production sites in Sri Lanka employed wind furnaces driven by the monsoon winds, capable of producing high-carbon steel. Large-scale Wootz steel production in India using crucibles occurred by the sixth century BC, the pioneering precursor to modern steel production and metallurgy.The Chinese of the Warring States period (403–221 BC) had quench-hardened steel, while Chinese of the Han dynasty (202 BC—AD 220) created steel by melting together wrought iron with cast iron, thus producing a carbon-intermediate steel by the 1st century AD.There is evidence that carbon steel was made in Western Tanzania by the ancestors of the Haya people as early as 2,000 years ago by a complex process of "pre-heating" allowing temperatures inside a furnace to reach 1300 to 1400 °C.
Wootz and Damascus
Evidence of the earliest production of high carbon steel in India is found in Kodumanal in Tamil Nadu, the Golconda area in Andhra Pradesh and Karnataka, and in the Samanalawewa, Dehigaha Alakanda, areas of Sri Lanka. This came to be known as Wootz steel, produced in South India by about the sixth century BC and exported globally. The steel technology existed prior to 326 BC in the region as they are mentioned in literature of Sangam Tamil, Arabic, and Latin as the finest steel in the world exported to the Romans, Egyptian, Chinese and Arab worlds at that time – what they called Seric Iron. A 200 BC Tamil trade guild in Tissamaharama, in the South East of Sri Lanka, brought with them some of the oldest iron and steel artifacts and production processes to the island from the classical period. The Chinese and locals in Anuradhapura, Sri Lanka had also adopted the production methods of creating Wootz steel from the Chera Dynasty Tamils of South India by the 5th century AD. In Sri Lanka, this early steel-making method employed a unique wind furnace, driven by the monsoon winds, capable of producing high-carbon steel. Since the technology was acquired from the Tamilians from South India, the origin of steel technology in India can be conservatively estimated at 400–500 BC.The manufacture of what came to be called Wootz, or Damascus steel, famous for its durability and ability to hold an edge, may have been taken by the Arabs from Persia, who took it from India. It was originally created from several different materials including various trace elements, apparently ultimately from the writings of Zosimos of Panopolis. In 327 BC, Alexander the Great was rewarded by the defeated King Porus, not with gold or silver but with 30 pounds of steel. A recent study has speculated that carbon nanotubes were included in its structure, which might explain some of its legendary qualities, though, given the technology of that time, such qualities were produced by chance rather than by design. Natural wind was used where the soil containing iron was heated by the use of wood. The ancient Sinhalese managed to extract a ton of steel for every 2 tons of soil, a remarkable feat at the time. One such furnace was found in Samanalawewa and archaeologists were able to produce steel as the ancients did.Crucible steel, formed by slowly heating and cooling pure iron and carbon (typically in the form of charcoal) in a crucible, was produced in Merv by the 9th to 10th century AD. In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, inhomogeneous steel, and a precursor to the modern Bessemer process that used partial decarburization via repeated forging under a cold blast.
Modern
Since the 17th century, the first step in European steel production has been the smelting of iron ore into pig iron in a blast furnace. Originally employing charcoal, modern methods use coke, which has proven more economical.
Processes starting from bar iron
In these processes, pig iron was refined (fined) in a finery forge to produce bar iron, which was then used in steel-making.The production of steel by the cementation process was described in a treatise published in Prague in 1574 and was in use in Nuremberg from 1601. A similar process for case hardening armor and files was described in a book published in Naples in 1589. The process was introduced to England in about 1614 and used to produce such steel by Sir Basil Brooke at Coalbrookdale during the 1610s.The raw material for this process were bars of iron. During the 17th century, it was realized that the best steel came from oregrounds iron of a region north of Stockholm, Sweden. This was still the usual raw material source in the 19th century, almost as long as the process was used.Crucible steel is steel that has been melted in a crucible rather than having been forged, with the result that it is more homogeneous. Most previous furnaces could not reach high enough temperatures to melt the steel. The early modern crucible steel industry resulted from the invention of Benjamin Huntsman in the 1740s. Blister steel (made as above) was melted in a crucible or in a furnace, and cast (usually) into ingots.
Processes starting from pig iron
The modern era in steelmaking began with the introduction of Henry Bessemer's process in 1855, the raw material for which was pig iron. His method let him produce steel in large quantities cheaply, thus mild steel came to be used for most purposes for which wrought iron was formerly used. The Gilchrist-Thomas process (or basic Bessemer process) was an improvement to the Bessemer process, made by lining the converter with a basic material to remove phosphorus.
Another 19th-century steelmaking process was the Siemens-Martin process, which complemented the Bessemer process. It consisted of co-melting bar iron (or steel scrap) with pig iron.
These methods of steel production were rendered obsolete by the Linz-Donawitz process of basic oxygen steelmaking (BOS), developed in 1952, and other oxygen steel making methods. Basic oxygen steelmaking is superior to previous steelmaking methods because the oxygen pumped into the furnace limited impurities, primarily nitrogen, that previously had entered from the air used, and because, with respect to the open hearth process, the same quantity of steel from a BOS process is manufactured in one-twelfth the time. Today, electric arc furnaces (EAF) are a common method of reprocessing scrap metal to create new steel. They can also be used for converting pig iron to steel, but they use a lot of electrical energy (about 440 kWh per metric ton), and are thus generally only economical when there is a plentiful supply of cheap electricity.
Industry
The steel industry is often considered an indicator of economic progress, because of the critical role played by steel in infrastructural and overall economic development. In 1980, there were more than 500,000 U.S. steelworkers. By 2000, the number of steelworkers had fallen to 224,000.The economic boom in China and India caused a massive increase in the demand for steel. Between 2000 and 2005, world steel demand increased by 6%. Since 2000, several Indian and Chinese steel firms have risen to prominence, such as Tata Steel (which bought Corus Group in 2007), Baosteel Group and Shagang Group. As of 2017, though, ArcelorMittal is the world's largest steel producer. In 2005, the British Geological Survey stated China was the top steel producer with about one-third of the world share; Japan, Russia, and the US followed respectively. The large production capacity of steel results also in a significant amount of carbon dioxide emissions inherent related to the main production route. In 2021, it was estimated that around 7% of the global greenhouse gas emissions resulted from the steel industry. Reduction of these emissions are expected to come from a shift in the main production route using cokes, more recycling of steel and the application of carbon capture and storage or carbon capture and utilization technology.
At the end of 2008, the steel industry faced a sharp downturn that led to many cut-backs.
Recycling
Steel is one of the world's most-recycled materials, with a recycling rate of over 60% globally; in the United States alone, over 82,000,000 metric tons (81,000,000 long tons; 90,000,000 short tons) were recycled in the year 2008, for an overall recycling rate of 83%.As more steel is produced than is scrapped, the amount of recycled raw materials is about 40% of the total of steel produced - in 2016, 1,628,000,000 tonnes (1.602×109 long tons; 1.795×109 short tons) of crude steel was produced globally, with 630,000,000 tonnes (620,000,000 long tons; 690,000,000 short tons) recycled.
Contemporary
Carbon
Modern steels are made with varying combinations of alloy metals to fulfill many purposes. Carbon steel, composed simply of iron and carbon, accounts for 90% of steel production. Low alloy steel is alloyed with other elements, usually molybdenum, manganese, chromium, or nickel, in amounts of up to 10% by weight to improve the hardenability of thick sections. High strength low alloy steel has small additions (usually < 2% by weight) of other elements, typically 1.5% manganese, to provide additional strength for a modest price increase.Recent Corporate Average Fuel Economy (CAFE) regulations have given rise to a new variety of steel known as Advanced High Strength Steel (AHSS). This material is both strong and ductile so that vehicle structures can maintain their current safety levels while using less material. There are several commercially available grades of AHSS, such as dual-phase steel, which is heat treated to contain both a ferritic and martensitic microstructure to produce a formable, high strength steel. Transformation Induced Plasticity (TRIP) steel involves special alloying and heat treatments to stabilize amounts of austenite at room temperature in normally austenite-free low-alloy ferritic steels. By applying strain, the austenite undergoes a phase transition to martensite without the addition of heat. Twinning Induced Plasticity (TWIP) steel uses a specific type of strain to increase the effectiveness of work hardening on the alloy.Carbon Steels are often galvanized, through hot-dip or electroplating in zinc for protection against rust.
Alloy
Stainless steels contain a minimum of 11% chromium, often combined with nickel, to resist corrosion. Some stainless steels, such as the ferritic stainless steels are magnetic, while others, such as the austenitic, are nonmagnetic. Corrosion-resistant steels are abbreviated as CRES.
Alloy steels are plain-carbon steels in which small amounts of alloying elements like chromium and vanadium have been added. Some more modern steels include tool steels, which are alloyed with large amounts of tungsten and cobalt or other elements to maximize solution hardening. This also allows the use of precipitation hardening and improves the alloy's temperature resistance. Tool steel is generally used in axes, drills, and other devices that need a sharp, long-lasting cutting edge. Other special-purpose alloys include weathering steels such as Cor-ten, which weather by acquiring a stable, rusted surface, and so can be used un-painted. Maraging steel is alloyed with nickel and other elements, but unlike most steel contains little carbon (0.01%). This creates a very strong but still malleable steel.Eglin steel uses a combination of over a dozen different elements in varying amounts to create a relatively low-cost steel for use in bunker buster weapons. Hadfield steel (after Sir Robert Hadfield) or manganese steel contains 12–14% manganese which when abraded strain-hardens to form a very hard skin which resists wearing. Examples include tank tracks, bulldozer blade edges, and cutting blades on the jaws of life.
Standards
Most of the more commonly used steel alloys are categorized into various grades by standards organizations. For example, the Society of Automotive Engineers has a series of grades defining many types of steel. The American Society for Testing and Materials has a separate set of standards, which define alloys such as A36 steel, the most commonly used structural steel in the United States. The JIS also defines a series of steel grades that are being used extensively in Japan as well as in developing countries.
Uses
Iron and steel are used widely in the construction of roads, railways, other infrastructure, appliances, and buildings. Most large modern structures, such as stadiums and skyscrapers, bridges, and airports, are supported by a steel skeleton. Even those with a concrete structure employ steel for reinforcing. It sees widespread use in major appliances and cars. Despite the growth in usage of aluminium, steel is still the main material for car bodies. Steel is used in a variety of other construction materials, such as bolts, nails and screws and other household products and cooking utensils.Other common applications include shipbuilding, pipelines, mining, offshore construction, aerospace, white goods (e.g. washing machines), heavy equipment such as bulldozers, office furniture, steel wool, tool, and armour in the form of personal vests or vehicle armour (better known as rolled homogeneous armour in this role).
Historical
Before the introduction of the Bessemer process and other modern production techniques, steel was expensive and was only used where no cheaper alternative existed, particularly for the cutting edge of knives, razors, swords, and other items where a hard, sharp edge was needed. It was also used for springs, including those used in clocks and watches.With the advent of speedier and thriftier production methods, steel has become easier to obtain and much cheaper. It has replaced wrought iron for a multitude of purposes. However, the availability of plastics in the latter part of the 20th century allowed these materials to replace steel in some applications due to their lower fabrication cost and weight. Carbon fiber is replacing steel in some cost insensitive applications such as sports equipment and high-end automobiles.
Long
As reinforcing bars and mesh in reinforced concrete
Railroad tracks
Structural steel in modern buildings and bridges
Wires
Input to reforging applications
Flat carbon
Major appliances
Magnetic cores
The inside and outside body of automobiles, trains, and ships.
Weathering (COR-TEN)
Intermodal containers
Outdoor sculptures
Architecture
Highliner train cars
Stainless
Low-background
Steel manufactured after World War II became contaminated with radionuclides by nuclear weapons testing. Low-background steel, steel manufactured prior to 1945, is used for certain radiation-sensitive applications such as Geiger counters and radiation shielding.
See also
References
Bibliography
Ashby, Michael F.; Jones, David Rayner Hunkin (1992). An introduction to microstructures, processing and design. Butterworth-Heinemann.
Barraclough, K. C. (1984). Steel before Bessemer: I Blister Steel: the birth of an industry. London: The Metals Society.
Bugayev, K.; Konovalov, Y.; Bychkov, Y.; Tretyakov, E.; Savin, Ivan V. (2001). Iron and Steel Production. The Minerva Group, Inc. ISBN 978-0-89499-109-7.
Davidson, H. R. Ellis (1994). The Sword in Anglo-Saxon England: Its Archaeology and Literature. Woodbridge, Suffolk, UK: Boydell Press. ISBN 0-85115-355-0.
Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003). Materials and Processes in Manufacturing (9th ed.). Wiley. ISBN 0-471-65653-4.
Fruehan, R. J.; Wakelin, David H. (1998). The Making, Shaping, and Treating of Steel (11th ed.). Pittsburgh, PA: AISE Steel Foundation. ISBN 0-930767-03-9.
Verein Deutscher Eisenhüttenleute (Ed.). Steel – A Handbook for Materials Research and Engineering, Volume 1: Fundamentals. Springer-Verlag Berlin, Heidelberg and Verlag Stahleisen, Düsseldorf 1992, 737 p. ISBN 3-540-52968-3, 3-514-00377-7.
Verein Deutscher Eisenhüttenleute (Ed.). Steel – A Handbook for Materials Research and Engineering, Volume 2: Applications. Springer-Verlag Berlin, Heidelberg and Verlag Stahleisen, Düsseldorf 1993, 839 pages, ISBN 3-540-54075-X, 3-514-00378-5.
Smith, William F.; Hashemi, Javad (2006). Foundations of Materials Science and Engineering (4th ed.). McGraw-Hill. ISBN 0-07-295358-6.
Further reading
Mark Reutter, Making Steel: Sparrows Point and the Rise and Ruin of American Industrial Might. University of Illinois Press, 2005.
Duncan Burn, The Economic History of Steelmaking, 1867–1939: A Study in Competition. Cambridge University Press, 1961.
Harukiyu Hasegawa, The Steel Industry in Japan: A Comparison with Britain. Routledge, 1996.
J.C. Carr and W. Taplin, History of the British Steel Industry. Harvard University Press, 1962.
H. Lee Scamehorn, Mill & Mine: The Cf&I in the Twentieth Century. University of Nebraska Press, 1992.
Warren, Kenneth, Big Steel: The First Century of the United States Steel Corporation, 1901–2001. University of Pittsburgh Press, 2001.
External links
Official website of the World Steel Association (worldsteel)
steeluniversity.org: Online steel education resources, an initiative of World Steel Association
Metallurgy for the Non-Metallurgist from the American Society for Metals
MATDAT Database of Properties of Unalloyed, Low-Alloy and High-Alloy Steels – obtained from published results of material testing |
hydrogen internal combustion engine vehicle | A hydrogen internal combustion engine vehicle (HICEV) is a type of hydrogen vehicle using an internal combustion engine. Hydrogen internal combustion engine vehicles are different from hydrogen fuel cell vehicles (which utilize hydrogen electrochemically rather than through combustion). Instead, the hydrogen internal combustion engine is simply a modified version of the traditional gasoline-powered internal combustion engine. The absence of carbon means that no CO2 is produced, which eliminates the main greenhouse gas emission of a conventional petroleum engine.
As pure hydrogen does not contain carbon, there are no carbon-based pollutants, such as carbon monoxide (CO) or hydrocarbons (HC), nor is there any carbon dioxide (CO2) in the exhaust. As hydrogen combustion occurs in an atmosphere containing nitrogen and oxygen, however, it can produce oxides of nitrogen known as NOx. In this way, the combustion process is much like other high temperature combustion fuels, such as kerosene, gasoline, diesel or natural gas. As such hydrogen combustion engines are not considered zero emission.
A downside is that hydrogen is difficult to handle. Due to the very small size of the hydrogen molecule, hydrogen is able to leak through many apparently solid materials in a process called hydrogen embrittlement. Escaped hydrogen gas mixed with air is potentially explosive.
History
Francois Isaac de Rivaz designed in 1806 the De Rivaz engine, the first internal combustion engine, which ran on a hydrogen/oxygen mixture. Étienne Lenoir produced the Hippomobile in 1863. In 1970, Paul Dieges patented a modified internal combustion engine which allow a gasoline-powered engine to run on hydrogen.Tokyo City University have been developing hydrogen internal combustion engines since 1970. They recently developed a hydrogen fueled bus and truck.
Mazda has developed Wankel engines that burn hydrogen. The advantage of using ICE (internal combustion engine) such as Wankel and piston engines is that the cost of retooling for production is much lower. Existing-technology ICE can still be used to solve those problems where fuel cells are not a viable solution as yet, for example in cold-weather applications.
In 1990 an electric solar vehicle was converted to hydrogen using a 107 ml 4-stroke engine. It was used in a research project examining and measuring losses from the power conversions sun -> electricity -> electrolysis -> storage -> motor -> transmission -> wheels. Compared to its previous battery-electric mode, the range proved higher but the system efficiency lower and the available alkaline hydrogen generator too large to be carried on-board. It was powered by a stationary solar installation and the produced hydrogen stored in pressure bottles.Between 2005 - 2007, BMW tested a luxury car named the BMW Hydrogen 7, powered by a hydrogen ICE, which achieved 301 km/h (187 mph) in tests. At least two of these concepts have been manufactured.HICE forklift trucks have been demonstrated based on converted diesel internal combustion engines with direct injection.Alset GmbH developed a hybrid hydrogen systems that allows vehicle to use petrol and hydrogen fuels individually or at the same time with an internal combustion engine. This technology was used with Aston Martin Rapide S during the 24 Hours Nürburgring race. The Rapide S was the first vehicle to finish the race with hydrogen technology.Hydrogen internal combustion engine development has been receiving more interest recently, particularly for heavy duty commercial vehicles. Part of the motivation for this is as a bridging technology to meet future climate CO2 emission goals, and as technology more compatible with existing automotive knowledge and manufacturing.In September 2022, Kawasaki unveiled a hydrogen combustion engine developed using the same injector as the hydrogen Corolla, based on the Ninja H2.In May 2023, Yamaha, Honda, Kawasaki and Suzuki received approval from Japan's Ministry of Economy, Trade and Industry (METI) to form a technological research association called HySE (Hydrogen Small mobility & Engine technology) for developing hydrogen-powered engines for small mobility.
Records and motor sport
In the year 2000, a Shelby Cobra was converted to run on hydrogen in a project led by James W. Heffel (principal engineer at the time for the University of California, Riverside CE-CERT). The hydrogen conversion was done with the aim of making a vehicle capable of beating the current land speed record for hydrogen powered vehicles. It achieved a respectable 108.16 mph, missing the world record for hydrogen powered vehicles by 0.1 mph.In May 2021, Toyota Corolla Sport, which is equipped with hydrogen engine entered the Super Taikyu Series race round 3 "NAPAC Fuji Super TEC 24 Hours", and completed the 24 hours race.
Toyota intends to apply its safety technologies and know-how that it has accumulated through the development of fuel cell vehicles and the commercialization of the Mirai.
In November 2021, five automotive manufacturers in Japan (Kawasaki Heavy Industries, Subaru, Toyota, Mazda and Yamaha Motor) jointly announced that they will take on the challenge of expanding fuel options through the use of internal combustion engines to achieve carbon neutrality, at the (three-hour) Super Taikyu race Round 6 held at Okayama International Circuit.
Their common view is that the enemy is not internal combustion engines, and we need diverse solutions toward challenging carbon neutrality.
At the event, Yamaha Motor unveiled 5.0-liter V8 Hydrogen engine which is based on Lexus 2UR engine.In June 2022, Toyota revealed the progress of its efforts in the Super Taikyu Series at the ENEOS Super Taikyu Series 2022. They say
cruising range was improved by approximately 20%, power output was improved by approx. 20% and torque was improved by approx. 30%. Also, Hydrogen suppliers are added and its transporting became more efficient to support the race.
In July 2022, Isuzu, Denso, Toyota, Hino Motors, and Commercial Japan Partnership Technologies Corporation (CJPT) announced that they have started planning and foundational research on hydrogen engines for heavy-duty commercial vehicles with the aim of further utilizing internal combustion engines as one option to achieve carbon neutrality.In August 2022, Toyota conducted demonstration run of GR Yaris H2, a special hydrogen-engine version of Toyota GR Yaris, during the ninth round of the World Rally Championship (WRC) in Ypres.In May 2023, Toyota Corolla Sport which is equipped with liquid hydrogen engine entered the Super Taikyu Series race round 2 "NNAPAC Fuji SUPER TEC 24 Hours Race", and completed the 24 hours race. It was the first time that a car running on liquid hydrogen has entered a race anywhere in the world.In June 2023, Toyota unveiled a hydrogen race car "GR H2 Racing Concept" built for 24 Hours of Le Mans.
Efficiency
The thermal efficiency of an ideal Otto Cycle depends on the compression ratio and improves from 47% to 56% when this is raised from 8 to 15. Engines in practical vehicles achieve 50-75% of this, with about 60% is suggested as an unlimited-cost limit. However, a conference presentation by Oak Ridge claims that the theoretical efficiency limit is 100%, based on it being an open cycle engine and therefore not limited by Carnot efficiency. In comparison, the efficiency of a fuel cell is limited by the Gibbs free energy, which is typically higher than that of Carnot. The determination of a fuel cell’s performance depends on the thermodynamic evaluation. Using hydrogen’s lower heating value, the maximum fuel cell efficiency would be 94.5%.The efficiency of a hydrogen combustion engine can be similar to that of a traditional combustion engine. If well optimized, slightly higher efficiencies can be achieved. The comparison with a hydrogen fuel cell is interesting. The fuel cell has a high efficiency peak at low load, while at high load the efficiency drops. The hydrogen combustion engine has a peak at high load and can achieve similar efficiency levels as a hydrogen fuel cell. From this, one can deduct that hydrogen combustion engines are a match in terms of efficiency for fuel cells for heavy duty applications.
Efficiency decreases for small internal combustion engines. A 67 ml 4-stroke engine converted to hydrogen and tested with a dynamometer at the best operating point (3000 rpm, 14 NLM (normal liters per minute), 2.5 times stoichiometric air/fuel ratio) achieved 520 W and 21% efficiency. In order to measure the vehicular efficiency an also converted similar 107 ml engine (Honda GX110 with best gasoline efficiency 26%) was installed in a lightweight vehicle and driven up known gradients while measuring speed and hydrogen flow. Calculations gave as results 3.5% to 5.9% average efficiencies and 7.5% peak efficiency. The consumption measured on a level road was 24 NLM/km at a speed of 25 km/h and 31 NLM/km at 43 km/h.
Pollutant emissions
The combustion of hydrogen with oxygen produces water vapor as its only product:
2H2 + O2 → 2H2OHowever, air is a mixture of gases, and the most abundant gas in air is nitrogen. Therefore, the combustion of hydrogen in air produces oxides of nitrogen, known as NOx. In this respect, the combustion process is much like other high temperature combustion fuels, such as kerosene, gasoline, diesel or natural gas. This problem is exascerbated by the very high temperatures generated by the combustion of hydrogen. As such hydrogen combustion engines are not considered zero emission.
At the end of 2021, almost 96% of the global hydrogen production was from natural gas (47%), coal (27%) and oil (22%) and only around 4% came from electrolysis. Emissions from burning hydrogen can be negligible but emissions from producing hydrogen are currently higher than direct combustion of the source.Hydrogen has a wide flammability range (3–70% H2 in air) in comparison with other fuels. As a result, it can be combusted in an internal combustion engine over a wide range of fuel-air mixtures. An advantage of this is the engine can be run using a lean fuel-air mixture.
Such a mixture is one in which the amount of fuel is less than the theoretical, stoichiometric or chemically ideal amount needed for combustion with a given amount of air.
Fuel economy is then greater and the combustion reaction is more complete. Also, the combustion temperature is usually lower, which reduces the amount of pollutants (e.g. nitrogen oxides) emitted.The European emission standards measure emissions of carbon monoxide, hydrocarbon, non-methane hydrocarbons, nitrogen oxides (NOx), atmospheric particulate matter, and particle numbers.
As with any internal combustion engine, small amounts of the engine oil needed for lubrication can enter the combustion chamber, and take part in the combustion process. The exhaust gases can therefore contain small amounts of the products of combustion of this oil. Typically very minute quantities of CO, CO2, SO2, HC and particulates can be found in the exhaust gases. These are several orders of magnitude lower than what would be seen in the exhaust gases of a gasoline or diesel engine.
Tuning a hydrogen engine in 1976 to produce the greatest amount of emissions possible resulted in emissions comparable with consumer operated gasoline engines from that period. More modern engines however often come equipped with exhaust gas recirculation (EGR). Equation when ignoring EGR:
H2 + O2 + N2 → H2O + NOx This technology potentially benefits hydrogen combustion also in terms of NOx emissions.Since hydrogen combustion is not zero emission but has zero CO2 emissions, it is attractive to consider hydrogen internal combustion engines as part of a hybrid powertrain. In this configuration, the vehicle is able to offer short-term zero emission capabilities such as operating in city zero emission zones.
Adaptation of existing engines
The differences between a hydrogen ICE and a traditional gasoline engine include hardened valves and valve seats, stronger connecting rods, non-platinum tipped spark plugs, a higher voltage ignition coil, fuel injectors designed for a gas instead of a liquid, larger crankshaft damper, stronger head gasket material, modified (for supercharger) intake manifold, positive pressure supercharger, and high temperature engine oil. All modifications would amount to about one point five times (1.5) the current cost of a gasoline engine. These hydrogen engines burn fuel in the same manner that gasoline engines do.
The theoretical maximum power output from a hydrogen engine depends on the air/fuel ratio and fuel injection method used. The stoichiometric air/fuel ratio for hydrogen is 34:1. At this air/fuel ratio, hydrogen will displace 29% of the combustion chamber leaving only 71% for the air. As a result, the energy content of this mixture will be less than it would be if the fuel were gasoline. Since both the carbureted and port injection methods mix the fuel and air prior to it entering the combustion chamber, these systems limit the maximum theoretical power obtainable to approximately 85% of that of gasoline engines. For direct injection systems, which mix the fuel with the air after the intake valve has closed (and thus the combustion chamber has 100% air), the maximum output of the engine can be approximately 15% higher than that for gasoline engines.
Therefore, depending on how the fuel is metered, the maximum output for a hydrogen engine can be either 15% higher or 15% less than that of gasoline if a stoichiometric air/fuel ratio is used. However, at a stoichiometric air/fuel ratio, the combustion temperature is very high and as a result it will form a large amount of nitrogen oxides (NOx), which is a criteria pollutant. Since one of the reasons for using hydrogen is low exhaust emissions, hydrogen engines are not normally designed to run at a stoichiometric air/fuel ratio.
Typically hydrogen engines are designed to use about twice as much air as theoretically required for complete combustion. At this air/fuel ratio, the formation of NOx is reduced to near zero. Unfortunately, this also reduces the power output to about half that of a similarly sized gasoline engine. To make up for the power loss, hydrogen engines are usually larger than gasoline engines, and/or are equipped with turbochargers or superchargers. A small amount of hydrogen can be burned outside the combustion chamber and reach into the air/fuel mixture in the chamber to ignite the main combustion.In the Netherlands, research organisation TNO has been working with industrial partners for the development of hydrogen internal combustion engines.
See also
Bi-fuel vehicle: a possible solution to overcome the lack of H2 stations
Classic car fuel conversions
Fuel gas-powered scooter
Formic acid
Hydrogen fuel enhancement
Home hydrogen fueling station
Liquid nitrogen vehicle
List of hydrogen internal combustion engine vehicles
Phase-out of fossil fuel vehicles
Timeline of hydrogen technologies
References
External links
EERE-Hydrogen internal combustion engine vehicle |
exhaust gas | Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack, or propelling nozzle. It often disperses downwind in a pattern called an exhaust plume.
It is a major component of motor vehicle emissions (and from stationary internal combustion engines), which can also include crankcase blow-by and evaporation of unused gasoline.
Motor vehicle emissions are a common source of air pollution and are a major ingredient in the creation of smog in some large cities. A 2013 study by the Massachusetts Institute of Technology (MIT) indicates that 53,000 early deaths occur per year in the United States alone because of vehicle emissions. According to another study from the same university, traffic fumes alone cause the death of 5,000 people every year just in the United Kingdom.
Composition
The largest part of most combustion gas is nitrogen (N2), water vapor (H2O) (except with pure-carbon fuels), and carbon dioxide (CO2) (except for fuels without carbon); these are not toxic or noxious (although water vapor and carbon dioxide are greenhouse gases that contribute to climate change). A relatively small part of combustion gas is undesirable, noxious, or toxic substances, such as carbon monoxide (CO) from incomplete combustion, hydrocarbons (properly indicated as CxHy, but typically shown simply as "HC" on emissions-test slips) from unburnt fuel, nitrogen oxides (NOx) from excessive combustion temperatures, and particulate matter (mostly soot).
Exhaust gas temperature
Exhaust gas temperature (EGT) is important to the functioning of the catalytic converter of an internal combustion engine. It may be measured by an exhaust gas temperature gauge. EGT is also a measure of engine health in gas-turbine engines (see below).
Cold engines
During the first two minutes after starting the engine of a car that has not been operated for several hours, the amount of emissions can be very high. This occurs for two main reasons:
Rich air-fuel ratio requirement in cold engines: When a cold engine is started, the fuel does not vaporize completely, creating higher emissions of hydrocarbons and carbon monoxide, which diminishes only as the engine reaches operating temperature. The duration of this start-up phase has been reduced by advances in materials and technology, including computer-controlled fuel injection, shorter intake lengths, and pre-heating of fuel and/or inducted air.
Inefficient catalytic converter under cold conditions: Catalytic converters are very inefficient until warmed up to their operating temperature. This time has been much reduced by moving the converter closer to the exhaust manifold and even more so placing a small yet quick-to-heat-up converter directly at the exhaust manifold. The small converter handles the start-up emissions, which allows enough time for the larger main converter to heat up. Further improvements can be realised in many ways, including electric heating, thermal battery, chemical reaction preheating, flame heating and superinsulation.
Passenger car emissions summary
Comparable with the European emission standards EURO III as it was applied on October 2000
In 2000, the United States Environmental Protection Agency began to implement more stringent emissions standards for light duty vehicles. The requirements were phased in beginning with 2004 vehicles and all new cars and light trucks were required to meet the updated standards by the end of 2007.
Types
Internal-combustion engines
Spark-ignition and Diesel engines
In spark-ignition engines the gases resulting from combustion of the fuel and air mix are called exhaust gases. The composition varies from petrol to diesel engines, but is around these levels:
The 10% oxygen for "diesel" is likely if the engine was idling, e.g. in a test rig. It is much less if the engine is running under load, although diesel engines always operate with an excess of air over fuel.
The CO content for petrol engines varies from ~ 15 ppm for well tuned engine with fuel injection and a catalytic converter up to 100,000 ppm (10%) for a richly tuned carburetor engine, such as typically found on small generators and garden equipment.
Nitromethane additive
Exhaust gas from an internal combustion engine whose fuel includes nitromethane will contain nitric acid vapour, which is corrosive, and when inhaled causes a muscular reaction making it impossible to breathe. People who are likely to be exposed to it should wear a gas mask.
Diesel engines
Gas-turbine engines
In aircraft gas turbine engines, "exhaust gas temperature" (EGT) is a primary measure of engine health. Typically the EGT is compared with a primary engine power indication called "engine pressure ratio" (EPR). For example: at full power EPR there will be a maximum permitted EGT limit. Once an engine reaches a stage in its life where it reaches this EGT limit, the engine will require specific maintenance in order to rectify the problem. The amount the EGT is below the EGT limit is called EGT margin. The EGT margin of an engine will be greatest when the engine is new, or has been overhauled. For most airlines, this information is also monitored remotely by the airline maintenance department by means of ACARS.
Jet engines and rocket engines
In jet engines and rocket engines, exhaust from propelling nozzles which in some applications shows shock diamonds.
Other types
From burning coal
Flue gas
Steam engines
In steam engine terminology the exhaust is steam that is now so low in pressure that it can no longer do useful work.
Main motor vehicle emissions
NOx
Mono-nitrogen oxides NO and NO2 (NOx)(whether produced this way or naturally by lightning) react with ammonia, moisture, and other compounds to form nitric acid vapor and related particles. Small particles can penetrate deeply into sensitive lung tissue and damage it, causing premature death in extreme cases. Inhalation of NO species increases the risk of lung cancer and colorectal cancer. and inhalation of such particles may cause or worsen respiratory diseases such as emphysema and bronchitis and heart disease.In a 2005 U.S. EPA study the largest emissions of NOx came from on road motor vehicles, with the second largest contributor being non-road equipment which is mostly gasoline and diesel stations.The resulting nitric acid may be washed into soil, where it becomes nitrate, which is useful to growing plants.
Volatile organic compounds
When oxides of nitrogen (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight, ground level ozone is formed, a primary ingredient in smog. A 2005 U.S. EPA report gives road vehicles as the second largest source of VOCs in the U.S. at 26% and 19% are from non road equipment which is mostly gasoline and diesel stations. 27% of VOC emissions are from solvents which are used in the manufacturer of paints and paint thinners and other uses.
Ozone
Ozone is beneficial in the upper atmosphere, but at ground level ozone irritates the respiratory system, causing coughing, choking, and reduced lung capacity. It also has many negative effects throughout the ecosystem.
Carbon monoxide (CO)
Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. Carbon monoxide is colorless, odorless and tasteless, but highly toxic. It combines with hemoglobin to produce carboxyhemoglobin, which blocks the transport of oxygen. At concentrations above 1000ppm it is considered immediately dangerous and is the most immediate health hazard from running engines in a poorly ventilated space. In 2011, 52% of carbon monoxide emissions were created by mobile vehicles in the U.S.
Hazardous air pollutants (toxics)
Chronic (long-term) exposure to benzene (C6H6) damages bone marrow. It can also cause excessive bleeding and depress the immune system, increasing the chance of infection. Benzene causes leukemia and is associated with other blood cancers and pre-cancers of the blood.
Particulate matter (PM10 and PM2.5)
The health effects of inhaling airborne particulate matter have been widely studied in humans and animals and include asthma, lung cancer, cardiovascular issues, premature death. Because of the size of the particles, they can penetrate the deepest part of the lungs. A 2011 UK study estimates 90 deaths per year due to passenger vehicle PM. In a 2006 publication, the U.S. Federal Highway Administration (FHWA) state that in 2002 about 1 per-cent of all PM10 and 2 per-cent of all PM2.5 emissions came from the exhaust of on-road motor vehicles (mostly from diesel engines). In Chinese, European, and Indian markets, both diesel and gasoline vehicles are required to have a tailpipe filter installed, while the United States has mandated it for diesel only. In 2022, British testing specialist Emissions Analytics estimated that the 300 million or so gasoline vehicles in the US over the subsequent decade would emit around 1.6 septillion harmful particles.
Carbon dioxide (CO2)
Carbon dioxide is a greenhouse gas. Motor vehicle CO2 emissions are part of the anthropogenic contribution to the growth of CO2 concentrations in the atmosphere which according to the vast majority of the scientific community is causing climate change. Motor vehicles are calculated to generate about 20% of the European Union's man-made CO2 emissions, with passenger cars contributing about 12%. European emission standards limit the CO2 emissions of new passenger cars and light vehicles. The European Union average new car CO2 emissions figure dropped by 5.4% in the year to the first quarter of 2010, down to 145.6 g/km.
Water vapour
Vehicle exhaust contains much water vapour.
Water recovery
There has been research into ways that troops in deserts can recover drinkable water from their vehicles' exhaust gases.
Pollution reduction
Emission standards focus on reducing pollutants contained in the exhaust gases from vehicles as well as from industrial flue gas stacks and other air pollution exhaust sources in various large-scale industrial facilities such as petroleum refineries, natural gas processing plants, petrochemical plants and chemical production plants. However, these are often referred to as flue gases. Catalytic converters in cars intend to break down the pollution of exhaust gases using a catalyst. Scrubbers in ships intend to remove the sulfur dioxide (SO2) of marine exhaust gases. The regulations on marine sulfur dioxide emissions are tightening, however only a small number of special areas worldwide have been designated for low sulfur diesel fuel use only.
One of the advantages claimed for advanced steam technology engines is that they produce smaller quantities of toxic pollutants (e.g. oxides of nitrogen) than petrol and diesel engines of the same power. They produce larger quantities of carbon dioxide but less carbon monoxide due to more efficient combustion.
Health studies
Researchers from the University of California, Los Angeles School of Public Health say preliminary results of their statistical study of children listed in the California Cancer Registry born between 1998 and 2007 found that traffic pollution may be associated with a 5% to 15% increase in the likelihood of some cancers. A World Health Organization study found that diesel fumes cause an increase in lung cancer.
Localised effects
The California Air Resources Board found in studies that 50% or more of the air pollution (smog) in Southern California is due to car emissions. Concentrations of pollutants emitted from combustion engines may be particularly high around signalized intersections because of idling and accelerations. Computer models often miss this kind of detail.
See also
References
External links
Health and Air Pollution Publication of the California Air Resources Board
Cone, Tracie (13 November 2008). "California Air Pollution Kills More People Than Car Crashes, Study Shows". Huffington Post.
"Automotive Exhaust Chemicals: disease causing effects". Alpha Online. Environmed Research Inc. Archived from the original on 5 July 2014.
"Cars, Trucks, and Air Pollution". Clean Vehicles. Union of Concerned Scientists. 3 September 2013.
About diesel exhaust:
U.S. Department of Labor Occupational Safety & Health Administration: Safety and Health Topics: Diesel Exhaust
Partial List of Chemicals Associated with Diesel Exhaust
Diesel Exhaust Particulates: Reasonably Anticipated to Be A Human Carcinogen
Scientific Study of Harmful Effects of Diesel Exhaust: Acute Inflammatory Responses in the Airways and Peripheral Blood After Short-Term Exposure to Diesel Exhaust in Healthy Human Volunteers
Diesel exhaust: what you need to know |
wind power | Wind power is the use of wind energy to generate useful work. Historically, wind power was used by sails, windmills and windpumps, but today it is mostly used to generate electricity. This article deals only with wind power for electricity generation.
Today, wind power is generated almost completely with wind turbines, generally grouped into wind farms and connected to the electrical grid.
In 2022, wind supplied over 2000 TWh of electricity, which was over 7% of world electricity: 58 and about 2% of world energy. With about 100 GW added during 2021, mostly in China and the United States, global installed wind power capacity exceeded 800 GW. To help meet the Paris Agreement goals to limit climate change, analysts say it should expand much faster - by over 1% of electricity generation per year.Wind power is considered a sustainable, renewable energy source, and has a much smaller impact on the environment compared to burning fossil fuels.
Wind power is variable, so it needs energy storage or other dispatchable generation energy sources to attain a reliable supply of electricity.
Land-based (onshore) wind farms have a greater visual impact on the landscape than most other power stations per energy produced. Wind farms sited offshore have less visual impact and have higher capacity factors, although they are generally more expensive. Offshore wind power currently has a share of about 10% of new installations.Wind power is one of the lowest-cost electricity sources per unit of energy produced.
In many locations, new onshore wind farms are cheaper than new coal or gas plants.Regions in the higher northern and southern latitudes have the highest potential for wind power. In most regions, wind power generation is higher in nighttime, and in winter when solar power output is low. For this reason, combinations of wind and solar power are suitable in many countries.
Wind energy resources
Wind is air movement in the earth's atmosphere. In a unit of time, say 1 second, the volume of air that had passed an area
A
A
is
A
v
{\displaystyle Av}
. If the air density is
r
r
, the mass of this volume of air is
M
=
r
A
v
{\displaystyle M=rAv}
, and the power transfer, or energy transfer per second is
P
=
1
2
M
v
2
=
1
2
A
r
v
3
{\displaystyle P={\frac {1}{2}}Mv^{2}={\frac {1}{2}}Arv^{3}}
. Wind power is thus proportional to the third power of the wind speed; the available power increases eightfold when the wind speed doubles. Change of wind speed by a factor of 2.1544 increases the wind power by one order of magnitude (multiply by 10).
The global wind kinetic energy averaged approximately 1.50 MJ/m2 over the period from 1979 to 2010, 1.31 MJ/m2 in the Northern Hemisphere with 1.70 MJ/m2 in the Southern Hemisphere. The atmosphere acts as a thermal engine, absorbing heat at higher temperatures, releasing heat at lower temperatures. The process is responsible for the production of wind kinetic energy at a rate of 2.46 W/m2 thus sustaining the circulation of the atmosphere against friction.Through wind resource assessment, it is possible to estimate wind power potential globally, by country or region, or for a specific site. The Global Wind Atlas provided by the Technical University of Denmark in partnership with the World Bank provides a global assessment of wind power potential.
Unlike 'static' wind resource atlases which average estimates of wind speed and power density across multiple years, tools such as Renewables.ninja provide time-varying simulations of wind speed and power output from different wind turbine models at an hourly resolution. More detailed, site-specific assessments of wind resource potential can be obtained from specialist commercial providers, and many of the larger wind developers have in-house modeling capabilities.
The total amount of economically extractable power available from the wind is considerably more than present human power use from all sources. The strength of wind varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there.
To assess prospective wind power sites, a probability distribution function is often fit to the observed wind speed data. Different locations will have different wind speed distributions. The Weibull model closely mirrors the actual distribution of hourly/ten-minute wind speeds at many locations. The Weibull factor is often close to 2 and therefore a Rayleigh distribution can be used as a less accurate, but simpler model.
Wind farms
A wind farm is a group of wind turbines in the same location. A large wind farm may consist of several hundred individual wind turbines distributed over an extended area. The land between the turbines may be used for agricultural or other purposes. A wind farm may also be located offshore. Almost all large wind turbines have the same design — a horizontal axis wind turbine having an upwind rotor with 3 blades, attached to a nacelle on top of a tall tubular tower.
In a wind farm, individual turbines are interconnected with a medium voltage (often 34.5 kV) power collection system and communications network. In general, a distance of 7D (7 times the rotor diameter of the wind turbine) is set between each turbine in a fully developed wind farm. At a substation, this medium-voltage electric current is increased in voltage with a transformer for connection to the high voltage electric power transmission system.
Generator characteristics and stability
Most modern turbines use variable speed generators combined with either a partial or full-scale power converter between the turbine generator and the collector system, which generally have more desirable properties for grid interconnection and have low voltage ride through-capabilities. Modern turbines use either doubly fed electric machines with partial-scale converters or squirrel-cage induction generators or synchronous generators (both permanently and electrically excited) with full-scale converters. Black start is possible and is being further developed for places (such as Iowa) which generate most of their electricity from wind.Transmission system operators will supply a wind farm developer with a grid code to specify the requirements for interconnection to the transmission grid. This will include the power factor, the constancy of frequency, and the dynamic behaviour of the wind farm turbines during a system fault.
Offshore wind power
Offshore wind power is wind farms in large bodies of water, usually the sea. These installations can use the more frequent and powerful winds that are available in these locations and have less visual impact on the landscape than land-based projects. However, the construction and maintenance costs are considerably higher.As of November 2021, the Hornsea Wind Farm in the United Kingdom is the largest offshore wind farm in the world at 1,218 MW.
Collection and transmission network
Near offshore wind farms may be connected by AC and far offshore by HVDC.Wind power resources are not always located near to high population density. As transmission lines become longer, the losses associated with power transmission increase, as modes of losses at lower lengths are exacerbated and new modes of losses are no longer negligible as the length is increased; making it harder to transport large loads over large distances.When the transmission capacity does not meet the generation capacity, wind farms are forced to produce below their full potential or stop running altogether, in a process known as curtailment. While this leads to potential renewable generation left untapped, it prevents possible grid overload or risk to reliable service.One of the biggest current challenges to wind power grid integration in some countries is the necessity of developing new transmission lines to carry power from wind farms, usually in remote lowly populated areas due to availability of wind, to high load locations, usually on the coasts where population density is higher. Any existing transmission lines in remote locations may not have been designed for the transport of large amounts of energy. In particular geographic regions, peak wind speeds may not coincide with peak demand for electrical power, whether offshore or onshore. A possible future option may be to interconnect widely dispersed geographic areas with an HVDC super grid.
Wind power capacity and production
Growth trends
In 2020, wind supplied almost 1600 TWh of electricity, which was over 5% of worldwide electrical generation and about 2% of energy consumption. With over 100 GW added during 2020, mostly in China, global installed wind power capacity reached more than 730 GW. But to help meet the Paris Agreement's goals to limit climate change, analysts say it should expand much faster - by over 1% of electricity generation per year. Expansion of wind power is being hindered by fossil fuel subsidies.The actual amount of electric power that wind can generate is calculated by multiplying the nameplate capacity by the capacity factor, which varies according to equipment and location. Estimates of the capacity factors for wind installations are in the range of 35% to 44%.
Capacity factor
Since wind speed is not constant, a wind farm's annual energy production is never as much as the sum of the generator nameplate ratings multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor. Online data is available for some locations, and the capacity factor can be calculated from the yearly output.
Penetration
Wind energy penetration is the fraction of energy produced by wind compared with the total generation. Wind power's share of worldwide electricity usage in 2021 was almost 7%, up from 3.5% in 2015.There is no generally accepted maximum level of wind penetration. The limit for a particular grid will depend on the existing generating plants, pricing mechanisms, capacity for energy storage, demand management, and other factors. An interconnected electric power grid will already include reserve generating and transmission capacity to allow for equipment failures. This reserve capacity can also serve to compensate for the varying power generation produced by wind stations. Studies have indicated that 20% of the total annual electrical energy consumption may be incorporated with minimal difficulty. These studies have been for locations with geographically dispersed wind farms, some degree of dispatchable energy or hydropower with storage capacity, demand management, and interconnected to a large grid area enabling the export of electric power when needed. Electrical utilities continue to study the effects of large-scale penetration of wind generation on system stability.A wind energy penetration figure can be specified for different duration of time but is often quoted annually. To generate almost all electricity from wind annually requires substantial interconnection to other systems, for example some wind power in Scotland is sent to the rest of the British grid. On a monthly, weekly, daily, or hourly basis—or less—wind might supply as much as or more than 100% of current use, with the rest stored, exported or curtailed. The seasonal industry might then take advantage of high wind and low usage times such as at night when wind output can exceed normal demand. Such industry might include the production of silicon, aluminum, steel, or natural gas, and hydrogen, and using future long-term storage to facilitate 100% energy from variable renewable energy. Homes and businesses can also be programmed to vary electricity demand, for example by remotely turning up water heater thermostats.
Variability
Wind power is variable, and during low wind periods, it may need to be replaced by other power sources. Transmission networks presently cope with outages of other generation plants and daily changes in electrical demand, but the variability of intermittent power sources such as wind power is more frequent than those of conventional power generation plants which, when scheduled to be operating, may be able to deliver their nameplate capacity around 95% of the time.
Electric power generated from wind power can be highly variable at several different timescales: hourly, daily, or seasonally. Annual variation also exists but is not as significant. Because instantaneous electrical generation and consumption must remain in balance to maintain grid stability, this variability can present substantial challenges to incorporating large amounts of wind power into a grid system. Intermittency and the non-dispatchable nature of wind energy production can raise costs for regulation, incremental operating reserve, and (at high penetration levels) could require an increase in the already existing energy demand management, load shedding, storage solutions, or system interconnection with HVDC cables.
Fluctuations in load and allowance for the failure of large fossil-fuel generating units require operating reserve capacity, which can be increased to compensate for the variability of wind generation.
Utility-scale batteries are often used to balance hourly and shorter timescale variation, but car batteries may gain ground from the mid-2020s. Wind power advocates argue that periods of low wind can be dealt with by simply restarting existing power stations that have been held in readiness, or interlinking with HVDC.The combination of diversifying variable renewables by type and location, forecasting their variation, and integrating them with dispatchable renewables, flexible fueled generators, and demand response can create a power system that has the potential to meet power supply needs reliably. Integrating ever-higher levels of renewables is being successfully demonstrated in the real world.
Solar power tends to be complementary to wind. On daily to weekly timescales, high-pressure areas tend to bring clear skies and low surface winds, whereas low-pressure areas tend to be windier and cloudier. On seasonal timescales, solar energy peaks in summer, whereas in many areas wind energy is lower in summer and higher in winter. Thus the seasonal variation of wind and solar power tend to cancel each other somewhat. Wind hybrid power systems are becoming more popular.
Predictability
For any particular generator, there is an 80% chance that wind output will change less than 10% in an hour and a 40% chance that it will change 10% or more in 5 hours.In summer 2021, wind power in the United Kingdom fell due to the lowest winds in seventy years, In the future, smoothing peaks by producing green hydrogen may help when wind has a larger share of generation.While the output from a single turbine can vary greatly and rapidly as local wind speeds vary, as more turbines are connected over larger and larger areas the average power output becomes less variable and more predictable. Weather forecasting permits the electric-power network to be readied for the predictable variations in production that occur.It is thought that the most reliable low-carbon electricity systems will include a large share of wind power.
Energy storage
Typically, conventional hydroelectricity complements wind power very well. When the wind is blowing strongly, nearby hydroelectric stations can temporarily hold back their water. When the wind drops they can, provided they have the generation capacity, rapidly increase production to compensate. This gives a very even overall power supply and virtually no loss of energy and uses no more water.
Alternatively, where a suitable head of water is not available, pumped-storage hydroelectricity or other forms of grid energy storage such as compressed air energy storage and thermal energy storage can store energy developed by high-wind periods and release it when needed. The type of storage needed depends on the wind penetration level – low penetration requires daily storage, and high penetration requires both short- and long-term storage – as long as a month or more. Stored energy increases the economic value of wind energy since it can be shifted to displace higher-cost generation during peak demand periods. The potential revenue from this arbitrage can offset the cost and losses of storage. Although pumped-storage power systems are only about 75% efficient and have high installation costs, their low running costs and ability to reduce the required electrical base-load can save both fuel and total electrical generation costs.
Energy payback
The energy needed to build a wind farm divided into the total output over its life, Energy Return on Energy Invested, of wind power varies, but averages about 20–25. Thus, the energy payback time is typically around a year.
Economics
Onshore wind is an inexpensive source of electric power, cheaper than coal plants and new gas plants. According to BusinessGreen, wind turbines reached grid parity (the point at which the cost of wind power matches traditional sources) in some areas of Europe in the mid-2000s, and in the US around the same time. Falling prices continue to drive the Levelized cost down and it has been suggested that it has reached general grid parity in Europe in 2010, and will reach the same point in the US around 2016 due to an expected reduction in capital costs of about 12%. In 2021, the CEO of Siemens Gamesa warned that increased demand for low-cost wind turbines combined with high input costs and high costs of steel result in increased pressure on the manufacturers and decreasing profit margins.Northern Eurasia, Canada, some parts of the United States, and Patagonia in Argentina are the best areas for onshore wind: whereas in other parts of the world solar power, or a combination of wind and solar, tend to be cheaper.: 8
Electric power cost and trends
Wind power is capital intensive but has no fuel costs. The price of wind power is therefore much more stable than the volatile prices of fossil fuel sources. However, the estimated average cost per unit of electric power must incorporate the cost of construction of the turbine and transmission facilities, borrowed funds, return to investors (including the cost of risk), estimated annual production, and other components, averaged over the projected useful life of the equipment, which may be more than 20 years. Energy cost estimates are highly dependent on these assumptions so published cost figures can differ substantially.
The presence of wind energy, even when subsidized, can reduce costs for consumers (€5 billion/yr in Germany) by reducing the marginal price, by minimizing the use of expensive peaking power plants.The cost has decreased as wind turbine technology has improved. There are now longer and lighter wind turbine blades, improvements in turbine performance, and increased power generation efficiency. Also, wind project capital expenditure costs and maintenance costs have continued to decline.In 2021, a Lazard study of unsubsidized electricity said that wind power levelized cost of electricity continues to fall but more slowly than before. The study estimated new wind-generated electricity cost from $26 to $50/MWh, compared to new gas power from $45 to $74/MWh. The median cost of fully deprecated existing coal power was $42/MWh, nuclear $29/MWh and gas $24/MWh. The study estimated offshore wind at around $83/MWh. Compound annual growth rate was 4% per year from 2016 to 2021, compared to 10% per year from 2009 to 2021.
Incentives and community benefits
Turbine prices have fallen significantly in recent years due to tougher competitive conditions such as the increased use of energy auctions, and the elimination of subsidies in many markets. As of 2021, subsidies are still often given to offshore wind. But they are generally no longer necessary for onshore wind in countries with even a very low carbon price such as China, provided there are no competing fossil fuel subsidies.Secondary market forces provide incentives for businesses to use wind-generated power, even if there is a premium price for the electricity. For example, socially responsible manufacturers pay utility companies a premium that goes to subsidize and build new wind power infrastructure. Companies use wind-generated power, and in return, they can claim that they are undertaking strong "green" efforts. Wind projects provide local taxes, or payments in place of taxes and strengthen the economy of rural communities by providing income to farmers with wind turbines on their land.The wind energy sector can also produce jobs during the construction and operating phase. Jobs include the manufacturing of wind turbines and the construction process, which includes transporting, installing, and then maintaining the turbines. An estimated 1.25 million people were employed in wind power in 2020.
Small-scale wind power
Small-scale wind power is the name given to wind generation systems with the capacity to produce up to 50 kW of electrical power. Isolated communities, that may otherwise rely on diesel generators, may use wind turbines as an alternative. Individuals may purchase these systems to reduce or eliminate their dependence on grid electric power for economic reasons, or to reduce their carbon footprint. Wind turbines have been used for household electric power generation in conjunction with battery storage over many decades in remote areas.Examples of small-scale wind power projects in an urban setting can be found in New York City, where, since 2009, several building projects have capped their roofs with Gorlov-type helical wind turbines. Although the energy they generate is small compared to the buildings' overall consumption, they help to reinforce the building's 'green' credentials in ways that "showing people your high-tech boiler" cannot, with some of the projects also receiving the direct support of the New York State Energy Research and Development Authority.Grid-connected domestic wind turbines may use grid energy storage, thus replacing purchased electric power with locally produced power when available. The surplus power produced by domestic microgenerators can, in some jurisdictions, be fed into the network and sold to the utility company, producing a retail credit for the microgenerators' owners to offset their energy costs.Off-grid system users can either adapt to intermittent power or use batteries, photovoltaic, or diesel systems to supplement the wind turbine. Equipment such as parking meters, traffic warning signs, street lighting, or wireless Internet gateways may be powered by a small wind turbine, possibly combined with a photovoltaic system, that charges a small battery replacing the need for a connection to the power grid.Airborne wind turbines, such as kites, can be used in places at risk of hurricanes, as they can be taken down in advance.
Impact on environment and landscape
The environmental impact of electricity generation from wind power is minor when compared to that of fossil fuel power. Wind turbines have some of the lowest life-cycle greenhouse-gas emissions of energy sources: far less greenhouse gas is emitted than for the average unit of electricity, so wind power helps limit climate change. Use of engineered wood may allow carbon negative wind power. Wind power consumes no fuel, and emits no local air pollution, unlike fossil fuel power sources.
Onshore wind farms can have a significant visual impact. Due to a very low surface power density and spacing requirements, wind farms typically need to be spread over more land than other power stations. Their network of turbines, access roads, transmission lines, and substations can result in "energy sprawl"; although land between the turbines and roads can still be used for agriculture. Some wind farms are opposed for potentially spoiling protected scenic areas, archaeological landscapes and heritage sites. A report by the Mountaineering Council of Scotland concluded that wind farms harmed tourism in areas known for natural landscapes and panoramic views.Habitat loss and fragmentation are the greatest potential impacts on wildlife of onshore wind farms, but the worldwide ecological impact is minimal. Thousands of birds and bats, including rare species, have been killed by wind turbine blades, though wind turbines are responsible for far fewer bird deaths than fossil-fueled power stations. This can be mitigated with proper wildlife monitoring.Many wind turbine blades are made of fiberglass, and have a lifetime of 20 years. Blades are hollow: some blades are crushed to reduce their volume and then landfilled. However, as they can take a lot of weight they can be made into long lasting small bridges for walkers or cyclists. Blade end-of-life is complicated, and blades manufactured in the 2020s are more likely to be designed to be completely recyclable.Wind turbines also generate noise. At a distance of 300 metres (980 ft), this may be around 45 dB, which is slightly louder than a refrigerator. At 1.5 km (1 mi), they become inaudible. There are anecdotal reports of negative health effects on people who live very close to wind turbines. Peer-reviewed research has generally not supported these claims.
Politics
Central government
Although wind turbines with fixed bases are a mature technology and new installations are generally no longer subsidized, floating wind turbines are a relatively new technology so some governments subsidize them, for example to use deeper waters.Fossil fuel subsidies by some governments are slowing the growth of renewables.Permitting of wind farms can take years and some governments are trying to speed up - the wind industry says this will help limit climate change and increase energy security - sometimes groups such as fishers resist this but governments say that rules protecting biodiversity will still be followed.
Public opinion
Surveys of public attitudes across Europe and in many other countries show strong public support for wind power. Bakker et al. (2012) found in their study that residents who did not want turbines built near them suffered significantly more stress than those who "benefited economically from wind turbines".Although wind power is a popular form of energy generation, onshore or near offshore wind farms are sometimes opposed for their impact on the landscape (especially scenic areas, heritage areas and archaeological landscapes), as well as noise, and impact on tourism.In other cases, there is direct community ownership of wind farms. The hundreds of thousands of people who have become involved in Germany's small and medium-sized wind farms demonstrate such support there.A 2010 Harris Poll found strong support for wind power in Germany, other European countries, and the United States.Public support in the United States has decreased from 75% in 2020 to 62% in 2021, with the Democrat Party supporting the use of wind energy twice as much as the Republican Party. President Biden has signed an executive order to begin building large scale wind farms.In China, Shen et al. (2019) found that Chinese city-dwellers may be resistant to building wind turbines in urban areas, with a surprisingly high proportion of people citing an unfounded fear of radiation as driving their concerns. Also, the study finds that like their counterparts in OECD countries, urban Chinese respondents are sensitive to direct costs and wildlife externalities. Distributing relevant information about turbines to the public may alleviate resistance.
Community
Many wind power companies work with local communities to reduce environmental and other concerns associated with particular wind farms.
In other cases there is direct community ownership of wind farm projects. Appropriate government consultation, planning and approval procedures also help to minimize environmental risks.
Some may still object to wind farms but many say their concerns should be weighed against the need to address the threats posed by air pollution, climate change and the opinions of the broader community.In the US, wind power projects are reported to boost local tax bases, helping to pay for schools, roads, and hospitals, and to revitalize the economies of rural communities by providing steady income to farmers and other landowners.In the UK, both the National Trust and the Campaign to Protect Rural England have expressed concerns about the effects on the rural landscape caused by inappropriately sited wind turbines and wind farms.
Some wind farms have become tourist attractions. The Whitelee Wind Farm Visitor Centre has an exhibition room, a learning hub, a café with a viewing deck and also a shop. It is run by the Glasgow Science Centre.In Denmark, a loss-of-value scheme gives people the right to claim compensation for loss of value of their property if it is caused by proximity to a wind turbine. The loss must be at least 1% of the property's value.Despite this general support for the concept of wind power in the public at large, local opposition often exists and has delayed or aborted a number of projects.
As well as concerns about the landscape, there are concerns that some installations can produce excessive sound and vibration levels leading to a decrease in property values. A study of 50,000 home sales near wind turbines found no statistical evidence that prices were affected.While aesthetic issues are subjective and some find wind farms pleasant and optimistic, or symbols of energy independence and local prosperity, protest groups are often formed to attempt to block some wind power stations for various reasons.Some opposition to wind farms is dismissed as NIMBYism, but research carried out in 2009 found that there is little evidence to support the belief that residents only object to wind farms because of a "Not in my Back Yard" attitude.
Geopolitics
Wind cannot be cut off unlike oil and gas so can contribute to energy security.
Turbine design
Wind turbines are devices that convert the wind's kinetic energy into electrical power. The result of over a millennium of windmill development and modern engineering, today's wind turbines are manufactured in a wide range of horizontal axis and vertical axis types. The smallest turbines are used for applications such as battery charging for auxiliary power. Slightly larger turbines can be used for making small contributions to a domestic power supply while selling unused power back to the utility supplier via the electrical grid. Arrays of large turbines, known as wind farms, have become an increasingly important source of renewable energy and are used in many countries as part of a strategy to reduce their reliance on fossil fuels.
Wind turbine design is the process of defining the form and specifications of a wind turbine to extract energy from the wind.
A wind turbine installation consists of the necessary systems needed to capture the wind's energy, point the turbine into the wind, convert mechanical rotation into electrical power, and other systems to start, stop, and control the turbine.
In 1919, the German physicist Albert Betz showed that for a hypothetical ideal wind-energy extraction machine, the fundamental laws of conservation of mass and energy allowed no more than 16/27 (59%) of the kinetic energy of the wind to be captured. This Betz limit can be approached in modern turbine designs, which may reach 70 to 80% of the theoretical Betz limit.The aerodynamics of a wind turbine are not straightforward. The airflow at the blades is not the same as the airflow far away from the turbine. The very nature of how energy is extracted from the air also causes air to be deflected by the turbine. This affects the objects or other turbines downstream, which is known as "wake effect". Also, the aerodynamics of a wind turbine at the rotor surface exhibit phenomena that are rarely seen in other aerodynamic fields. The shape and dimensions of the blades of the wind turbine are determined by the aerodynamic performance required to efficiently extract energy from the wind, and by the strength required to resist the forces on the blade.In addition to the aerodynamic design of the blades, the design of a complete wind power system must also address the design of the installation's rotor hub, nacelle, tower structure, generator, controls, and foundation.
History
Wind power has been used as long as humans have put sails into the wind. King Hammurabi's Codex (reign 1792 - 1750 BC) already mentioned windmills for generating mechanical energy. Wind-powered machines used to grind grain and pump water, the windmill and wind pump, were developed in what is now Iran, Afghanistan, and Pakistan by the 9th century. Wind power was widely available and not confined to the banks of fast-flowing streams, or later, requiring sources of fuel. Wind-powered pumps drained the polders of the Netherlands, and in arid regions such as the American mid-west or the Australian outback, wind pumps provided water for livestock and steam engines.
The first windmill used for the production of electric power was built in Scotland in July 1887 by Prof James Blyth of Anderson's College, Glasgow (the precursor of Strathclyde University). Blyth's 10 metres (33 ft) high cloth-sailed wind turbine was installed in the garden of his holiday cottage at Marykirk in Kincardineshire, and was used to charge accumulators developed by the Frenchman Camille Alphonse Faure, to power the lighting in the cottage, thus making it the first house in the world to have its electric power supplied by wind power. Blyth offered the surplus electric power to the people of Marykirk for lighting the main street, however, they turned down the offer as they thought electric power was "the work of the devil." Although he later built a wind turbine to supply emergency power to the local Lunatic Asylum, Infirmary, and Dispensary of Montrose, the invention never really caught on as the technology was not considered to be economically viable.Across the Atlantic, in Cleveland, Ohio, a larger and heavily engineered machine was designed and constructed in the winter of 1887–1888 by Charles F. Brush. This was built by his engineering company at his home and operated from 1886 until 1900. The Brush wind turbine had a rotor 17 metres (56 ft) in diameter and was mounted on an 18 metres (59 ft) tower. Although large by today's standards, the machine was only rated at 12 kW. The connected dynamo was used either to charge a bank of batteries or to operate up to 100 incandescent light bulbs, three arc lamps, and various motors in Brush's laboratory.
With the development of electric power, wind power found new applications in lighting buildings remote from centrally generated power. Throughout the 20th century parallel paths developed small wind stations suitable for farms or residences.
From 1932 many isolated properties in Australia ran their lighting and electric fans from batteries, charged by a "Freelite" wind-driven generator, producing 100 watts of electrical power from as little wind speed as 10 miles per hour (16 km/h).The 1973 oil crisis triggered the investigation in Denmark and the United States that led to larger utility-scale wind generators that could be connected to electric power grids for remote use of power. By 2008, the U.S. installed capacity had reached 25.4 gigawatts, and by 2012 the installed capacity was 60 gigawatts. Today, wind-powered generators operate in every size range between tiny stations for battery charging at isolated residences, up to gigawatt-sized offshore wind farms that provide electric power to national electrical networks.
See also
Notes
References
External links
Official website of Global Wind Energy Council (GWEC)
Wind from Project Regeneration
Official website of World Wind Energy Association (WWEA)
Dynamic Data Dashboard from the International Energy Agency
Current global map of wind power density |
one-tonne challenge | The One-Tonne Challenge was a challenge presented by the Government of Canada in March 2004 for Canadians to reduce their greenhouse gas emissions by one tonne each year. The figure represented 20% of total greenhouse gas output by Canadians at the time and aimed to help the country reach its Kyoto Protocol emission reduction targets. The Liberal Government under Jean Chrétien and Paul Martin approved over $45 million to fund the program from 2003 to 2006.To promote this program, the government placed television and print ads featuring comedian Rick Mercer. In one commercial, he described Canadians as wanting to take the challenge. "C’mon... we’re Canadian... we’re up for a challenge!"
The government urged Canadians to do such things as:
take public transit more often
idle vehicles less
use programmable thermostats
seal windows with caulking and weather-stripping
compost organic kitchen waste
support green energy
water and energy conservation
purchase electronics that are labelled with Energy Star logo
recyclingThe program received a lukewarm reception from the public, and has been criticized as ineffective and wasteful.This program was started by the Liberal Party of Canada. However, with the election of Stephen Harper's Conservative Government in 2006, the One Tonne Challenge was scrapped.
See also
Air pollution
Chlorofluorocarbons
Recycling
References
External links
Government of Canada - One-Tonne Challenge
Yukon News - Conservatives Nix One Tonne Challenge |
geologic time scale | The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (a scientific branch of geology that aims to determine the age of rocks). It is used primarily by Earth scientists (including geologists, paleontologists, geophysicists, geochemists, and paleoclimatologists) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardised international units of geologic time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) that are used to define divisions of geologic time. The chronostratigraphic divisions are in turn used to define geochronologic units.While some regional terms are still in use, the table of geologic time presented in this article conforms to the nomenclature, ages, and colour codes set forth by the ICS.
Principles
The geologic time scale is a way of representing deep time based on events that have occurred throughout Earth's history, a time span of about 4.54 ± 0.05 Ga (4.54 billion years). It chronologically organises strata, and subsequently time, by observing fundamental changes in stratigraphy that correspond to major geological or paleontological events. For example, the Cretaceous–Paleogene extinction event, marks the lower boundary of the Paleogene System/Period and thus the boundary between the Cretaceous and Paleogene systems/periods. For divisions prior to the Cryogenian, arbitrary numeric boundary definitions (Global Standard Stratigraphic Ages, GSSAs) are used to divide geologic time. Proposals have been made to better reconcile these divisions with the rock record.Historically, regional geologic time scales were used due to the litho- and biostratigraphic differences around the world in time equivalent rocks. The ICS has long worked to reconcile conflicting terminology by standardising globally significant and identifiable stratigraphic horizons that can be used to define the lower boundaries of chronostratigraphic units. Defining chronostratigraphic units in such a manner allows for the use of global, standardised nomenclature. The ICC represents this ongoing effort.
The relative relationships of rocks for determining their chronostratigraphic positions use the overriding principles of:
Superposition – Newer rock beds will lie on top of older rock beds unless the succession has been overturned.
Horizontality – All rock layers were originally deposited horizontally.
Lateral continuity – Originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer.
Biologic succession (where applicable) – This states that each stratum in a succession contains a distinctive set of fossils. This allows for a correlation of the stratum even when the horizon between them is not continuous.
Cross-cutting relationships – A rock feature that cuts across another feature must be younger than the rock it cuts across.
Inclusion – Small fragments of one type of rock but embedded in a second type of rock must have formed first, and were included when the second rock was forming.
Relationships of unconformities – Geologic features representing periods of erosion or non-deposition, indicating non-continuous sediment deposition.
Terminology
The GTS is divided into chronostratigraphic units and their corresponding geochronologic units. These are represented on the ICC published by the ICS; however, regional terms are still in use in some areas.
Chronostratigraphy is the element of stratigraphy that deals with the relation between rock bodies and the relative measurement of geological time. It is the process where distinct strata between defined stratigraphic horizons are assigned to represent a relative interval of geologic time.
A chronostratigraphic unit is a body of rock, layered or unlayered, that is defined between specified stratigraphic horizons which represent specified intervals of geologic time. They include all rocks representative of a specific interval of geologic time, and only this time span.
Eonothem, erathem, system, series, subseries, stage, and substage are the hierarchical chronostratigraphic units.Geochronology is the scientific branch of geology that aims to determine the age of rocks, fossils, and sediments either through absolute (e.g., radiometric dating) or relative means (e.g., stratigraphic position, Paleomagnetism, stable isotope ratios).A geochronologic unit is a subdivision of geologic time. It is a numeric representation of an intangible property (time). Eon, era, period, epoch, subepoch, age, and subage are the hierarchical geochronologic units. Geochronometry is the field of geochronology that numerically quantifies geologic time.A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundaries of stages on the geologic time scale. (Recently this has been used to define the base of a system)A Global Standard Stratigraphic Age (GSSA) is a numeric only, chronologic reference point used to define the base of geochronologic units prior to the Cryogenian. These points are arbitrarily defined. They are used where GSSPs have not yet been established. Research is ongoing to define GSSPs for the base of all units that are currently defined by GSSAs.
The numeric (geochronometric) representation of a geochronologic unit can, and is more often subject to change when geochronology refines the geochronometry, while the equivalent chronostratigraphic unit remains the same, and their revision is less common. For example, in early 2022 the boundary between the Ediacaran and Cambrian periods (geochronologic units) was revised from 541 Ma to 538.8 Ma but the rock definition of the boundary (GSSP) at the base of the Cambrian, and thus the boundary between the Ediacaran and Cambrian systems (chronostratigraphic units) has not changed, merely the geochronometry has been refined.
The numeric values on the ICC are represented by the unit Ma (megaannum) meaning "million years", i.e., 201.4 ± 0.2 Ma, the lower boundary of the Jurassic Period, is defined as 201,400,000 years old with an uncertainty of 200,000 years. Other SI prefix units commonly used by geologists are Ga (gigaannum, billion years), and ka (kiloannum, thousand years), with the latter often represented in calibrated units (before present).
Divisions of geologic time
An eon is the largest geochronologic time unit and is equivalent to a chronostratigraphic eonothem. There are four formally defined eons: the Hadean, Archean, Proterozoic and Phanerozoic.An era is the second largest geochronologic time unit and is equivalent to a chronostratigraphic erathem. There are ten defined eras: the Eoarchean, Paleoarchean, Mesoarchean, Neoarchean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Paleozoic, Mesozoic and Cenozoic, with none from the Hadean eon.A period is equivalent to a chronostratigraphic system. There are 22 defined periods. As an exception two subperiods are used for the Carboniferous Period.An epoch is the second smallest geochronologic unit. It is equivalent to a chronostratigraphic series. There are 37 defined epochs and one informal one. There are also 11 subepochs which are all within the Neogene and Quaternary. The use of subepochs as formal units in international chronostratigraphy was ratified in 2022.An age is the smallest hierarchical geochronologic unit and is equivalent to a chronostratigraphic stage. There are 96 formal and five informal ages.A chron is a non-hierarchical formal geochronology unit of unspecified rank and is equivalent to a chronostratigraphic chronozone. These correlate with magnetostratigraphic, lithostratigraphic, or biostratigraphic units as they are based on previously defined stratigraphic units or geologic features.The Early and Late subdivisions are used as the geochronologic equivalents of the chronostratigraphic Lower and Upper, e.g., Early Triassic Period (geochronologic unit) is used in place of Lower Triassic Series (chronostratigraphic unit).
Rocks representing a given chronostratigraphic unit are that chronostratigraphic unit, and the time they were laid down in is the geochronologic unit, i.e., the rocks that represent the Silurian Series are the Silurian Series and they were deposited during the Silurian Period.
Naming of geologic time
The names of geologic time units are defined for chronostratigraphic units with the corresponding geochronologic unit sharing the same name with a change to the latter (e.g. Phanerozoic Eonothem becomes the Phanerozoic Eon). Names of erathems in the Phanerozoic were chosen to reflect major changes in the history of life on Earth: Paleozoic (old life), Mesozoic (middle life), and Cenozoic (new life). Names of systems are diverse in origin, with some indicating chronologic position (e.g., Paleogene), while others are named for lithology (e.g., Cretaceous), geography (e.g., Permian), or are tribal (e.g., Ordovician) in origin. Most currently recognised series and subseries are named for their position within a system/series (early/middle/late); however, the ICS advocates for all new series and subseries to be named for a geographic feature in the vicinity of its stratotype or type locality. The name of stages should also be derived from a geographic feature in the locality of its stratotype or type locality.Informally, the time before the Cambrian is often referred to as the Precambrian or pre-Cambrian (Supereon).
History of the geologic time scale
Early history
While a modern geological time scale was not formulated until 1911 by Arthur Holmes, the broader concept that rocks and time are related can be traced back to (at least) the philosophers of Ancient Greece. Xenophanes of Colophon (c. 570–487 BCE) observed rock beds with fossils of shells located above the sea-level, viewed them as once living organisms, and used this to imply an unstable relationship in which the sea had at times transgressed over the land and at other times had regressed. This view was shared by a few of Xenophanes' contemporaries and those that followed, including Aristotle (384–322 BCE) who (with additional observations) reasoned that the positions of land and sea had changed over long periods of time. The concept of deep time was also recognised by Chinese naturalist Shen Kuo (1031–1095) and Islamic scientist-philosophers, notably the Brothers of Purity, who wrote on the processes of stratification over the passage of time in their treatises. Their work likely inspired that of the 11th-century Persian polymath Avicenna (Ibn Sînâ, 980–1037) who wrote in The Book of Healing (1027) on the concept of stratification and superposition, pre-dating Nicolas Steno by more than six centuries. Avicenna also recognised fossils as "petrifications of the bodies of plants and animals", with the 13th-century Dominican bishop Albertus Magnus (c. 1200–1280) extending this into a theory of a petrifying fluid. These works appeared to have little influence on scholars in Medieval Europe who looked to the Bible to explain the origins of fossils and sea-level changes, often attributing these to the 'Deluge', including Ristoro d'Arezzo in 1282. It was not until the Italian Renaissance when Leonardo da Vinci (1452–1519) would reinvigorate the relationships between stratification, relative sea-level change, and time, denouncing attribution of fossils to the 'Deluge':
Of the stupidity and ignorance of those who imagine that these creatures were carried to such places distant from the sea by the Deluge...Why do we find so many fragments and whole shells between the different layers of stone unless they had been upon the shore and had been covered over by earth newly thrown up by the sea which then became petrified? And if the above-mentioned Deluge had carried them to these places from the sea, you would find the shells at the edge of one layer of rock only, not at the edge of many where may be counted the winters of the years during which the sea multiplied the layers of sand and mud brought down by the neighboring rivers and spread them over its shores. And if you wish to say that there must have been many deluges in order to produce these layers and the shells among them it would then become necessary for you to affirm that such a deluge took place every year.
These views of da Vinci remained unpublished, and thus lacked influence at the time; however, questions of fossils and their significance were pursued and, while views against Genesis were not readily accepted and dissent from religious doctrine was in some places unwise, scholars such as Girolamo Fracastoro shared da Vinci's views, and found the attribution of fossils to the 'Deluge' absurd.
Establishment of primary principles
Niels Stensen, more commonly known as Nicolas Steno (1638–1686), is credited with establishing four of the guiding principles of stratigraphy. In De solido intra solidum naturaliter contento dissertationis prodromus Steno states:
When any given stratum was being formed, all the matter resting on it was fluid and, therefore, when the lowest stratum was being formed, none of the upper strata existed.
...strata which are either perpendicular to the horizon or inclined to it were at one time parallel to the horizon.
When any given stratum was being formed, it was either encompassed at its edges by another solid substance or it covered the whole globe of the earth. Hence, it follows that wherever bared edges of strata are seen, either a continuation of the same strata must be looked for or another solid substance must be found that kept the material of the strata from being dispersed.
If a body or discontinuity cuts across a stratum, it must have formed after that stratum.
Respectively, these are the principles of superposition, original horizontality, lateral continuity, and cross-cutting relationships. From this Steno reasoned that strata were laid down in succession and inferred relative time (in Steno's belief, time from Creation). While Steno's principles were simple and attracted much attention, applying them proved challenging. These basic principles, albeit with improved and more nuanced interpretations, still form the foundational principles of determining the correlation of strata relative to geologic time.
Over the course of the 18th-century geologists realised that:
Sequences of strata often become eroded, distorted, tilted, or even inverted after deposition
Strata laid down at the same time in different areas could have entirely different appearances
The strata of any given area represented only part of Earth's long history
Formulation of a modern geologic time scale
The apparent, earliest formal division of the geologic record with respect to time was introduced by Thomas Burnet who applied a two-fold terminology to mountains by identifying "montes primarii" for rock formed at the time of the 'Deluge', and younger "monticulos secundarios" formed later from the debris of the "primarii". This attribution to the 'Deluge', while questioned earlier by the likes of da Vinci, was the foundation of Abraham Gottlob Werner's (1749–1817) Neptunism theory in which all rocks precipitated out of a single flood. A competing theory, Plutonism, was developed by Anton Moro (1687–1784) and also used primary and secondary divisions for rock units. In this early version of the Plutonism theory, the interior of Earth was seen as hot, and this drove the creation of primary igneous and metamorphic rocks and secondary rocks formed contorted and fossiliferous sediments. These primary and secondary divisions were expanded on by Giovanni Targioni Tozzetti (1712–1783) and Giovanni Arduino (1713–1795) to include tertiary and quaternary divisions. These divisions were used to describe both the time during which the rocks were laid down, and the collection of rocks themselves (i.e., it was correct to say Tertiary rocks, and Tertiary Period). Only the Quaternary division is retained in the modern geologic time scale, while the Tertiary division was in use until the early 21st century. The Neptunism and Plutonism theories would compete into the early 19th century with a key driver for resolution of this debate being the work of James Hutton (1726–1797), in particular his Theory of the Earth, first presented before the Royal Society of Edinburgh in 1785. Hutton's theory would later become known as uniformitarianism, popularised by John Playfair (1748–1819) and later Charles Lyell (1797–1875) in his Principles of Geology. Their theories strongly contested the 6,000 year age of the Earth as suggested determined by James Ussher via Biblical chronology that was accepted at the time by western religion. Instead, using geological evidence, they contested Earth to be much older, cementing the concept of deep time.
During the early 19th century William Smith, Georges Cuvier, Jean d'Omalius d'Halloy, and Alexandre Brongniart pioneered the systematic division of rocks by stratigraphy and fossil assemblages. These geologists began to use the local names given to rock units in a wider sense, correlating strata across national and continental boundaries based on their similarity to each other. Many of the names below erathem/era rank in use on the modern ICC/GTS were determined during the early to mid-19th century.
The advent of geochronometry
During the 19th century, the debate regarding Earth's age was renewed, with geologists estimating ages based on denudation rates and sedimentary thicknesses or ocean chemistry, and physicists determining ages for the cooling of the Earth or the Sun using basic thermodynamics or orbital physics. These estimations varied from 15,000 million years to 0.075 million years depending on method and author, but the estimations of Lord Kelvin and Clarence King were held in high regard at the time due to their pre-eminence in physics and geology. All of these early geochronometric determinations would later prove to be incorrect.
The discovery of radioactive decay by Henri Becquerel, Marie Curie, and Pierre Curie laid the ground work for radiometric dating, but the knowledge and tools required for accurate determination of radiometric ages would not be in place until the mid-1950s. Early attempts at determining ages of uranium minerals and rocks by Ernest Rutherford, Bertram Boltwood, Robert Strutt, and Arthur Holmes, would culminate in what are considered the first international geological time scales by Holmes in 1911 and 1913. The discovery of isotopes in 1913 by Frederick Soddy, and the developments in mass spectrometry pioneered by Francis William Aston, Arthur Jeffrey Dempster, and Alfred O. C. Nier during the early to mid-20th century would finally allow for the accurate determination of radiometric ages, with Holmes publishing several revisions to his geological time-scale with his final version in 1960.
Modern international geologic time scale
The establishment of the IUGS in 1961 and acceptance of the Commission on Stratigraphy (applied in 1965) to become a member commission of IUGS led to the founding of the ICS. One of the primary objectives of the ICS is "the establishment, publication and revision of the ICS International Chronostratigraphic Chart which is the standard, reference global Geological Time Scale to include the ratified Commission decisions".Following on from Holmes, several A Geological Time Scale books were published in 1982, 1989, 2004, 2008, 2012, 2016, and 2020. However, since 2013, the ICS has taken responsibility for producing and distributing the ICC citing the commercial nature, independent creation, and lack of oversight by the ICS on the prior published GTS versions (GTS books prior to 2013) although these versions were published in close association with the ICS. Subsequent Geologic Time Scale books (2016 and 2020) are commercial publications with no oversight from the ICS, and do not entirely conform to the chart produced by the ICS. The ICS produced GTS charts are versioned (year/month) beginning at v2013/01. At least one new version is published each year incorporating any changes ratified by the ICS since the prior version.
The following five timelines show the geologic time scale to scale. The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon. The second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in the third timeline, the most recent period is expanded in the fourth timeline, and the most recent epoch is expanded in the fifth timeline.
Major proposed revisions to the ICC
Proposed Anthropocene Series/Epoch
First suggested in 2000, the Anthropocene is a proposed epoch/series for the most recent time in Earth's history. While still informal, it is a widely used term to denote the present geologic time interval, in which many conditions and processes on Earth are profoundly altered by human impact. As of April 2022 the Anthropocene has not been ratified by the ICS; however, in May 2019 the Anthropocene Working Group voted in favour of submitting a formal proposal to the ICS for the establishment of the Anthropocene Series/Epoch. Nevertheless, the definition of the Anthropocene as a geologic time period rather than a geologic event remains controversial and difficult.
Proposals for revisions to pre-Cryogenian timeline
Shields et al. 2021
An international working group of the ICS on pre-Cryogenian chronostratigraphic subdivision have outlined a template to improve the pre-Cryogenian geologic time scale based on the rock record to bring it in line with the post-Tonian geologic time scale. This work assessed the geologic history of the currently defined eons and eras of the pre-Cambrian, and the proposals in the "Geological Time Scale" books 2004, 2012, and 2020. Their recommend revisions of the pre-Cryogenian geologic time scale were (changes from the current scale [v2023/09] are italicised):
Three divisions of the Archean instead of four by dropping Eoarchean, and revisions to their geochronometric definition, along with the repositioning of the Siderian into the latest Neoarchean, and a potential Kratian division in the Neoarchean.
Archean (4000–2450 Ma)
Paleoarchean (4000–3500 Ma)
Mesoarchean (3500–3000 Ma)
Neoarchean (3000–2450 Ma)
Kratian (no fixed time given, prior to the Siderian) – from Greek word κράτος (krátos), meaning strength.
Siderian (?–2450 Ma) – moved from Proterozoic to end of Archean, no start time given, base of Paleoproterozoic defines the end of the Siderian
Refinement of geochronometric divisions of the Proterozoic, Paleoproterozoic, repositioning of the Statherian into the Mesoproterozoic, new Skourian period/system in the Paleoproterozoic, new Kleisian or Syndian period/system in the Neoproterozoic.
Paleoproterozoic (2450–1800 Ma)
Skourian (2450–2300 Ma) – from the Greek word σκουριά (skouriá), meaning 'rust'.
Rhyacian (2300–2050 Ma)
Orosirian (2050–1800 Ma)
Mesoproterozoic (1800–1000 Ma)
Statherian (1800–1600 Ma)
Calymmian (1600–1400 Ma)
Ectasian (1400-1200 Ma)
Stenian (1200–1000 Ma)
Neoproterozoic (1000–538.8 Ma)Kleisian or Syndian (1000–800 Ma) – respectively from the Greek words κλείσιμο (kleísimo) meaning 'closure', and σύνδεση (sýndesi) meaning 'connection'.
Tonian (800–720 Ma)
Cryogenian (720–635 Ma)
Ediacaran (635–538.8 Ma)Proposed pre-Cambrian timeline (Shield et al. 2021, ICS working group on pre-Cryogenian chronostratigraphy), shown to scale:
Current ICC pre-Cambrian timeline (v2023/09), shown to scale:
Van Kranendonk et al. 2012 (GTS2012)
The book, Geologic Time Scale 2012, was the last commercial publication of an international chronostratigraphic chart that was closely associated with the ICS. It included a proposal to substantially revise the pre-Cryogenian time scale to reflect important events such as the formation of the Solar System and the Great Oxidation Event, among others, while at the same time maintaining most of the previous chronostratigraphic nomenclature for the pertinent time span. As of April 2022 these proposed changes have not been accepted by the ICS. The proposed changes (changes from the current scale [v2023/09]) are italicised:
Hadean Eon (4567–4030 Ma)
Chaotian Era/Erathem (4567–4404 Ma) – the name alluding both to the mythological Chaos and the chaotic phase of planet formation.
Jack Hillsian or Zirconian Era/Erathem (4404–4030 Ma) – both names allude to the Jack Hills Greenstone Belt which provided the oldest mineral grains on Earth, zircons.
Archean Eon/Eonothem (4030–2420 Ma)
Paleoarchean Era/Erathem (4030–3490 Ma)
Acastan Period/System (4030–3810 Ma) – named after the Acasta Gneiss, one of the oldest preserved pieces of continental crust.
Isuan Period (3810–3490 Ma) – named after the Isua Greenstone Belt.
Mesoarchean Era/Erathem (3490–2780 Ma)
Vaalbaran Period/System (3490–3020 Ma) – based on the names of the Kapvaal (Southern Africa) and Pilbara (Western Australia) cratons, to reflect the growth of stable continental nuclei or proto-cratonic kernels.
Pongolan Period/System (3020–2780 Ma) – named after the Pongola Supergroup, in reference to the well preserved evidence of terrestrial microbial communities in those rocks.
Neoarchean Era/Erathem (2780–2420 Ma)
Methanian Period/System (2780–2630 Ma) – named for the inferred predominance of methanotrophic prokaryotes
Siderian Period/System (2630–2420 Ma) – named for the voluminous banded iron formations formed within its duration.
Proterozoic Eon/Eonothem (2420–538.8 Ma)Paleoproterozoic Era/Erathem (2420–1780 Ma)
Oxygenian Period/System (2420–2250 Ma) – named for displaying the first evidence for a global oxidising atmosphere.
Jatulian or Eukaryian Period/System (2250–2060 Ma) – names are respectively for the Lomagundi–Jatuli δ13C isotopic excursion event spanning its duration, and for the (proposed) first fossil appearance of eukaryotes.
Columbian Period/System (2060–1780 Ma) – named after the supercontinent Columbia.
Mesoproterozoic Era/Erathem (1780–850 Ma)
Rodinian Period/System (1780–850 Ma) – named after the supercontinent Rodinia, stable environment.Proposed pre-Cambrian timeline (GTS2012), shown to scale:
Current ICC pre-Cambrian timeline (v2023/09), shown to scale:
Table of geologic time
The following table summarises the major events and characteristics of the divisions making up the geologic time scale of Earth. This table is arranged with the most recent geologic periods at the top, and the oldest at the bottom. The height of each table entry does not correspond to the duration of each subdivision of time. As such, this table is not to scale and does not accurately represent the relative time-spans of each geochronologic unit. While the Phanerozoic Eon looks longer than the rest, it merely spans ~539 million years (~12% of Earth's history), whilst the previous three eons collectively span ~3,461 million years (~76% of Earth's history). This bias toward the most recent eon is in part due to the relative lack of information about events that occurred during the first three eons compared to the current eon (the Phanerozoic). The use of subseries/subepochs has been ratified by the ICS.The content of the table is based on the official ICC produced and maintained by the ICS who also provide an online interactive version of this chart. The interactive version is based on a service delivering a machine-readable Resource Description Framework/Web Ontology Language representation of the time scale, which is available through the Commission for the Management and Application of Geoscience Information GeoSciML project as a service and at a SPARQL end-point.
Non-Earth based geologic time scales
Some other planets and satellites in the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars and the Earth's Moon. Dominantly fluid planets, such as the gas giants, do not comparably preserve their history. Apart from the Late Heavy Bombardment, events on other planets probably had little direct influence on the Earth, and events on Earth had correspondingly little effect on those planets. Construction of a time scale that links the planets is, therefore, of only limited relevance to the Earth's time scale, except in a Solar System context. The existence, timing, and terrestrial effects of the Late Heavy Bombardment are still a matter of debate.
Lunar (selenological) time scale
The geologic history of Earth's Moon has been divided into a time scale based on geomorphological markers, namely impact cratering, volcanism, and erosion. This process of dividing the Moon's history in this manner means that the time scale boundaries do not imply fundamental changes in geological processes, unlike Earth's geologic time scale. Five geologic systems/periods (Pre-Nectarian, Nectarian, Imbrian, Eratosthenian, Copernican), with the Imbrian divided into two series/epochs (Early and Late) were defined in the latest Lunar geologic time scale. The Moon is unique in the Solar System in that it is the only other body from which we have rock samples with a known geological context.
Martian geologic time scale
The geological history of Mars has been divided into two alternate time scales. The first time scale for Mars was developed by studying the impact crater densities on the Martian surface. Through this method four periods have been defined, the Pre-Noachian (~4,500–4,100 Ma), Noachian (~4,100–3,700 Ma), Hesperian (~3,700–3,000 Ma), and Amazonian (~3,000 Ma to present).
A second time scale based on mineral alteration observed by the OMEGA spectrometer on-board the Mars Express. Using this method, three periods were defined, the Phyllocian (~4,500–4,000 Ma), Theiikian (~4,000–3,500 Ma), and Siderikian (~3,500 Ma to present).
See also
Notes
References
Further reading
Aubry, Marie-Pierre; Van Couvering, John A.; Christie-Blick, Nicholas; Landing, Ed; Pratt, Brian R.; Owen, Donald E.; Ferrusquia-Villafranca, Ismael (2009). "Terminology of geological time: Establishment of a community standard". Stratigraphy. 6 (2): 100–105. doi:10.7916/D8DR35JQ.
Gradstein, F. M.; Ogg, J. G. (2004). "A Geologic Time scale 2004 – Why, How and Where Next!" (PDF). Lethaia. 37 (2): 175–181. doi:10.1080/00241160410006483. Archived from the original (PDF) on 17 April 2018. Retrieved 30 November 2018.
Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2004). A Geologic Time Scale 2004. Cambridge, UK: Cambridge University Press. ISBN 978-0-521-78142-8. Retrieved 18 November 2011.
Gradstein, Felix M.; Ogg, James G.; Smith, Alan G.; Bleeker, Wouter; Laurens, Lucas, J. (June 2004). "A new Geologic Time Scale, with special reference to Precambrian and Neogene". Episodes. 27 (2): 83–100. doi:10.18814/epiiugs/2004/v27i2/002.{{cite journal}}: CS1 maint: multiple names: authors list (link)
Ialenti, Vincent (28 September 2014). "Embracing 'Deep Time' Thinking". NPR. NPR Cosmos & Culture.
Ialenti, Vincent (21 September 2014). "Pondering 'Deep Time' Could Inspire New Ways To View Climate Change". NPR. NPR Cosmos & Culture.
Knoll, Andrew H.; Walter, Malcolm R.; Narbonne, Guy M.; Christie-Blick, Nicholas (30 July 2004). "A New Period for the Geologic Time Scale" (PDF). Science. 305 (5684): 621–622. doi:10.1126/science.1098803. PMID 15286353. S2CID 32763298. Archived (PDF) from the original on 15 December 2011. Retrieved 18 November 2011.
Levin, Harold L. (2010). "Time and Geology". The Earth Through Time. Hoboken, New Jersey: John Wiley & Sons. ISBN 978-0-470-38774-0. Retrieved 18 November 2011.
Montenari, Michael (2016). Stratigraphy and Timescales (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-811549-7.
Montenari, Michael (2017). Advances in Sequence Stratigraphy (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-813077-3.
Montenari, Michael (2018). Cyclostratigraphy and Astrochronology (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-815098-6.
Montenari, Michael (2019). Case Studies in Isotope Stratigraphy (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-817552-1.
Montenari, Michael (2020). Carbon Isotope Stratigraphy (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-820991-2.
Montenari, Michael (2021). Calcareous Nannofossil Biostratigraphy (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-824624-5.
Nichols, Gary (2013). Sedimentology and Stratigraphy (2nd ed.). Hoboken: Wiley-Blackwell. ISBN 978-1-4051-3592-4
Williams, Aiden (2019). Sedimentology and Stratigraphy (1st ed.). Forest Hills, NY: Callisto Reference. ISBN 978-1-64116-075-9
External links
The current version of the International Chronostratigraphic Chart can be found at stratigraphy.org/chart
Interactive version of the International Chronostratigraphic Chart is found at stratigraphy.org/timescale
A list of current Global Boundary Stratotype and Section Points is found at stratigraphy.org/gssps
NASA: Geologic Time (archived 18 April 2005)
GSA: Geologic Time Scale (archived 20 January 2019)
British Geological Survey: Geological Timechart
GeoWhen Database (archived 23 June 2004)
National Museum of Natural History – Geologic Time (archived 11 November 2005)
SeeGrid: Geological Time Systems. Archived 23 July 2008 at the Wayback Machine. Information model for the geologic time scale.
Exploring Time from Planck Time to the lifespan of the universe
Episodes, Gradstein, Felix M. et al. (2004) A new Geologic Time Scale, with special reference to Precambrian and Neogene, Episodes, Vol. 27, no. 2 June 2004 (pdf)
Lane, Alfred C, and Marble, John Putman 1937. Report of the Committee on the measurement of geologic time
Lessons for Children on Geologic Time (archived 14 July 2011)
Deep Time – A History of the Earth : Interactive Infographic
Geology Buzz: Geologic Time Scale. Archived 12 August 2021 at the Wayback Machine. |
list of archaeological periods | The names for archaeological periods in the list of archaeological periods vary enormously from region to region. This is a list of the main divisions by continent and region. Dating also varies considerably and those given are broad approximations across wide areas.
The three-age system has been used in many areas, referring to the prehistorical and historical periods identified by tool manufacture and use, of Stone Age, Bronze Age and Iron Age. Since these ages are distinguished by the development of technology, it is natural that the dates to which these refer vary in different parts of the world. In many regions, the term Stone Age is no longer used, as it has been replaced by more specific geological periods. For some regions, there is need for an intermediate Chalcolithic period between the Stone Age and Bronze Age. For cultures where indigenous metal tools were in less widespread use, other classifications, such as the lithic stage, archaic stage and formative stage refer to the development of other types of technology and social organization.
Historical periods denotes periods of human development with the advantage of the development of writing. Written records tend to provide more socio-political insight into the dominant nations, and hence allow categorization according to the ruling empires and cultures, such as Hellenistic, Roman, Viking. Inevitably these definitions of periods only relate to the region of that empire or culture.
The Industrial Age or Modern era is generally taken to refer to post-1800. From this time, the industrial revolution which began in Western Europe resulted in global trade and greatly increased cultural exchange.
Archaeological period articles – by continent and region
See also
List of time periods |
quaternary | The Quaternary ( kwə-TUR-nə-ree, KWOT-ər-nerr-ee) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ago to the present. As of 2023, the Quaternary Period is divided into two epochs: the Pleistocene (2.58 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to today); a third epoch, the Anthropocene, has recently been proposed, but it is not officially recognised by the ICS.The Quaternary Period is typically defined by the cyclic growth and decay of continental ice sheets related to the Milankovitch cycles and the associated climate and environmental changes that they caused.
Research history
In 1759 Giovanni Arduino proposed that the geological strata of northern Italy could be divided into four successive formations or "orders" (Italian: quattro ordini). The term "quaternary" was introduced by Jules Desnoyers in 1829 for sediments of France's Seine Basin that clearly seemed to be younger than Tertiary Period rocks.The Quaternary Period follows the Neogene Period and extends to the present. The Quaternary covers the time span of glaciations classified as the Pleistocene, and includes the present interglacial time-period, the Holocene.
This places the start of the Quaternary at the onset of Northern Hemisphere glaciation approximately 2.6 million years ago (mya). Prior to 2009, the Pleistocene was defined to be from 1.805 million years ago to the present, so the current definition of the Pleistocene includes a portion of what was, prior to 2009, defined as the Pliocene.
Quaternary stratigraphers usually worked with regional subdivisions. From the 1970s, the International Commission on Stratigraphy (ICS) tried to make a single geologic time scale based on GSSP's, which could be used internationally. The Quaternary subdivisions were defined based on biostratigraphy instead of paleoclimate.
This led to the problem that the proposed base of the Pleistocene was at 1.805 million years ago, long after the start of the major glaciations of the northern hemisphere. The ICS then proposed to abolish use of the name Quaternary altogether, which appeared unacceptable to the International Union for Quaternary Research (INQUA).
In 2009, it was decided to make the Quaternary the youngest period of the Cenozoic Era with its base at 2.588 mya and including the Gelasian Stage, which was formerly considered part of the Neogene Period and Pliocene Epoch. This was later revised to 2.58 mya.The Anthropocene has been proposed as a third epoch as a mark of the anthropogenic impact on the global environment starting with the Industrial Revolution, or about 200 years ago. The Anthropocene is not officially designated by the ICS, but a working group has been working on a proposal for the creation of an epoch or sub-period.
Geology
The 2.58 million years of the Quaternary represents the time during which recognisable humans existed. Over this geologically short time period there has been relatively little change in the distribution of the continents due to plate tectonics.
The Quaternary geological record is preserved in greater detail than that for earlier periods.
The major geographical changes during this time period included the emergence of the Strait of Bosphorus and Skagerrak during glacial epochs, which respectively turned the Black Sea and Baltic Sea into fresh water lakes, followed by their flooding (and return to salt water) by rising sea level; the periodic filling of the English Channel, forming a land bridge between Britain and the European mainland; the periodic closing of the Bering Strait, forming the land bridge between Asia and North America; and the periodic flash flooding of Scablands of the American Northwest by glacial water.The current extent of Hudson Bay, the Great Lakes and other major lakes of North America are a consequence of the Canadian Shield's readjustment since the last ice age; different shorelines have existed over the course of Quaternary time.
Climate
The climate was one of periodic glaciations with continental glaciers moving as far from the poles as 40 degrees latitude. Glaciation took place repeatedly during the Quaternary Ice age – a term coined by Schimper in 1839 that began with the start of the Quaternary about 2.58 Mya and continues to the present day.In 1821, a Swiss engineer, Ignaz Venetz, presented an article in which he suggested the presence of traces of the passage of a glacier at a considerable distance from the Alps. This idea was initially disputed by another Swiss scientist, Louis Agassiz, but when he undertook to disprove it, he ended up affirming his colleague's hypothesis. A year later, Agassiz raised the hypothesis of a great glacial period that would have had long-reaching general effects. This idea gained him international fame and led to the establishment of the Glacial Theory.
In time, thanks to the refinement of geology, it has been demonstrated that there were several periods of glacial advance and retreat and that past temperatures on Earth were very different from today.
In particular, the Milankovitch cycles of Milutin Milankovitch are based on the premise that variations in incoming solar radiation are a fundamental factor controlling Earth's climate.
During this time, substantial glaciers advanced and retreated over much of North America and Europe, parts of South America and Asia, and all of Antarctica.
Flora and Fauna
There was a major extinction of large mammals in Northern areas at the end of the Pleistocene Epoch. Many forms such as sabre-toothed cats, mammoths, mastodons, glyptodonts, etc., became extinct worldwide. Others, including horses, camels and American cheetahs became extinct in North America.The Great Lakes formed and giant mammals thrived in parts of North America and Eurasia not covered in ice. These mammals became extinct when the glacial period ended about 11,700 years ago. Modern humans evolved about 315,000 years ago. During the Quaternary Period, mammals, flowering plants, and insects dominated the land.
See also
List of Quaternary volcanic eruptions
References
External links
Subcommission on Quaternary Stratigraphy
Stratigraphical charts for the Quaternary
Version history of the global Quaternary chronostratigraphical charts (from 2004b)
Silva, P.G. C. Zazo, T. Bardají, J. Baena, J. Lario, A. Rosas, J. Van der Made. 2009, "Tabla Cronoestratigrafíca del Cuaternario en la Península Ibérica - V.2". [Versión PDF, 3.6 Mb]. Asociación Española para el Estudio del Cuaternario (AEQUA), Departamento de Geología, Universidad de Salamanca, Spain. (Correlation chart of European Quaternary and cultural stages and fossils)
Welcome to the XVIII INQUA-Congress, Bern, 2011 Archived 21 March 2012 at the Wayback Machine
Quaternary (chronostratigraphy scale)
Media related to Quaternary at Wikimedia Commons |
jurassic | The Jurassic ( juu-RASS-ik) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period 201.4 million years ago (Mya) to the beginning of the Cretaceous Period, approximately 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era and is named after the Jura Mountains, where limestone strata from the period were first identified.
The start of the Jurassic was marked by the major Triassic–Jurassic extinction event, associated with the eruption of the Central Atlantic Magmatic Province (CAMP). The beginning of the Toarcian Stage started around 183 million years ago and is marked by the Toarcian Oceanic Anoxic Event, a global episode of oceanic anoxia, ocean acidification, and elevated global temperatures associated with extinctions, likely caused by the eruption of the Karoo-Ferrar large igneous provinces. The end of the Jurassic, however, has no clear, definitive boundary with the Cretaceous and is the only boundary between geological periods to remain formally undefined.
By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses: Laurasia to the north and Gondwana to the south. The climate of the Jurassic was warmer than the present, and there were no ice caps. Forests grew close to the poles, with large arid expanses in the lower latitudes.
On land, the fauna transitioned from the Triassic fauna, dominated jointly by dinosauromorph and pseudosuchian archosaurs, to one dominated by dinosaurs alone. The first birds appeared during the Jurassic, evolving from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards and the evolution of therian mammals. Crocodylomorphs made the transition from a terrestrial to an aquatic life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates. The first sharks, rays and crabs also first appeared during the period.
Etymology and history
The chronostratigraphic term "Jurassic" is linked to the Jura Mountains, a forested mountain range that mainly follows the France–Switzerland border. The name "Jura" is derived from the Celtic root *jor via Gaulish *iuris "wooded mountain", which was borrowed into Latin as a name of a place and evolved into Juria and finally Jura.
During a tour of the region in 1795, German naturalist Alexander von Humboldt recognized carbonate deposits within the Jura Mountains as geologically distinct from the Triassic aged Muschelkalk of southern Germany, but he erroneously concluded that they were older. He then named them Jura-Kalkstein ('Jura limestone') in 1799.In 1829, the French naturalist Alexandre Brongniart published a book entitled Description of the Terrains that Constitute the Crust of the Earth or Essay on the Structure of the Known Lands of the Earth. In this book, Brongniart used the phrase terrains jurassiques when correlating the "Jura-Kalkstein" of Humboldt with similarly aged oolitic limestones in Britain, thus coining and publishing the term "Jurassic".The German geologist Leopold von Buch in 1839 established the three-fold division of the Jurassic, originally named from oldest to the youngest: the Black Jurassic, Brown Jurassic, and White Jurassic. The term "Lias" had previously been used for strata of equivalent age to the Black Jurassic in England by William Conybeare and William Phillips in 1822.
The French palaeontologist Alcide d'Orbigny in papers between 1842 and 1852 divided the Jurassic into ten stages based on ammonite and other fossil assemblages in England and France, of which seven are still used, but none has retained its original definition. The German geologist and palaeontologist Friedrich August von Quenstedt in 1858 divided the three series of von Buch in the Swabian Jura into six subdivisions defined by ammonites and other fossils.
The German palaeontologist Albert Oppel in his studies between 1856 and 1858 altered d'Orbigny's original scheme and further subdivided the stages into biostratigraphic zones, based primarily on ammonites. Most of the modern stages of the Jurassic were formalized at the Colloque du Jurassique à Luxembourg in 1962.
Geology
The Jurassic Period is divided into three epochs: Early, Middle, and Late. Similarly, in stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, and Upper Jurassic series. Geologists divide the rocks of the Jurassic into a stratigraphic set of units called stages, each formed during corresponding time intervals called ages.
Stages can be defined globally or regionally. For global stratigraphic correlation, the International Commission on Stratigraphy (ICS) ratify global stages based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype) identifying the lower boundary of the stage. The ages of the Jurassic from youngest to oldest are as follows:
Stratigraphy
Jurassic stratigraphy is primarily based on the use of ammonites as index fossils. The first appearance datum of specific ammonite taxa is used to mark the beginnings of stages, as well as smaller timespans within stages, referred to as "ammonite zones"; these, in turn, are also sometimes subdivided further into subzones. Global stratigraphy is based on standard European ammonite zones, with other regions being calibrated to the European successions.
Early Jurassic
The oldest part of the Jurassic Period has historically been referred to as the Lias or Liassic, roughly equivalent in extent to the Early Jurassic, but also including part of the preceding Rhaetian. The Hettangian Stage was named by Swiss palaeontologist Eugène Renevier in 1864 after Hettange-Grande in north-eastern France. The GSSP for the base of the Hettangian is located at the Kuhjoch Pass, Karwendel Mountains, Northern Calcareous Alps, Austria; it was ratified in 2010. The beginning of the Hettangian, and thus the Jurassic as a whole, is marked by the first appearance of the ammonite Psiloceras spelae tirolicum in the Kendlbach Formation exposed at Kuhjoch. The base of the Jurassic was previously defined as the first appearance of Psiloceras planorbis by Albert Oppel in 1856–58, but this was changed as the appearance was seen as too localised an event for an international boundary.The Sinemurian Stage was first defined and introduced into scientific literature by Alcide d'Orbigny in 1842. It takes its name from the French town of Semur-en-Auxois, near Dijon. The original definition of Sinemurian included what is now the Hettangian. The GSSP of the Sinemurian is located at a cliff face north of the hamlet of East Quantoxhead, 6 kilometres east of Watchet, Somerset, England, within the Blue Lias, and was ratified in 2000. The beginning of the Sinemurian is defined by the first appearance of the ammonite Vermiceras quantoxense.Albert Oppel in 1858 named the Pliensbachian Stage after the hamlet of Pliensbach in the community of Zell unter Aichelberg in the Swabian Alb, near Stuttgart, Germany. The GSSP for the base of the Pliensbachian is found at the Wine Haven locality in Robin Hood's Bay, Yorkshire, England, in the Redcar Mudstone Formation, and was ratified in 2005. The beginning of the Pliensbachian is defined by the first appearance of the ammonite Bifericeras donovani.The village Thouars (Latin: Toarcium), just south of Saumur in the Loire Valley of France, lends its name to the Toarcian Stage. The Toarcian was named by Alcide d'Orbigny in 1842, with the original locality being Vrines quarry around 2 km northwest of Thouars. The GSSP for the base of the Toarcian is located at Peniche, Portugal, and was ratified in 2014. The boundary is defined by the first appearance of ammonites belonging to the subgenus Dactylioceras (Eodactylites).
Middle Jurassic
The Aalenian is named after the city of Aalen in Germany. The Aalenian was defined by Swiss geologist Karl Mayer-Eymar in 1864. The lower boundary was originally between the dark clays of the Black Jurassic and the overlying clayey sandstone and ferruginous oolite of the Brown Jurassic sequences of southwestern Germany. The GSSP for the base of the Aalenian is located at Fuentelsaz in the Iberian range near Guadalajara, Spain, and was ratified in 2000. The base of the Aalenian is defined by the first appearance of the ammonite Leioceras opalinum.Alcide d'Orbigny in 1842 named the Bajocian Stage after the town of Bayeux (Latin: Bajoce) in Normandy, France. The GSSP for the base of the Bajocian is located in the Murtinheira section at Cabo Mondego, Portugal; it was ratified in 1997. The base of the Bajocian is defined by the first appearance of the ammonite Hyperlioceras mundum.The Bathonian is named after the city of Bath, England, introduced by Belgian geologist d'Omalius d'Halloy in 1843, after an incomplete section of oolitic limestones in several quarries in the region. The GSSP for the base of the Bathonian is Ravin du Bès, Bas-Auran area, Alpes de Haute Provence, France; it was ratified in 2009. The base of the Bathonian is defined by the first appearance of the ammonite Gonolkites convergens, at the base of the Zigzagiceras zigzag ammonite zone.The Callovian is derived from the Latinized name of the village of Kellaways in Wiltshire, England, and was named by Alcide d'Orbigny in 1852, originally the base at the contact between the Forest Marble Formation and the Cornbrash Formation. However, this boundary was later found to be within the upper part of the Bathonian. The base of the Callovian does not yet have a certified GSSP. The working definition for the base of the Callovian is the first appearance of ammonites belonging to the genus Kepplerites.
Late Jurassic
The Oxfordian is named after the city of Oxford in England and was named by Alcide d'Orbigny in 1844 in reference to the Oxford Clay. The base of the Oxfordian lacks a defined GSSP. W. J. Arkell in studies in 1939 and 1946 placed the lower boundary of the Oxfordian as the first appearance of the ammonite Quenstedtoceras mariae (then placed in the genus Vertumniceras). Subsequent proposals have suggested the first appearance of Cardioceras redcliffense as the lower boundary.The village of Kimmeridge on the coast of Dorset, England, is the origin of the name of the Kimmeridgian. The stage was named by Alcide d'Orbigny in 1842 in reference to the Kimmeridge Clay. The GSSP for the base of the Kimmeridgian is the Flodigarry section at Staffin Bay on the Isle of Skye, Scotland, which was ratified in 2021. The boundary is defined by the first appearance of ammonites marking the boreal Bauhini Zone and the subboreal Baylei Zone.The Tithonian was introduced in scientific literature by Albert Oppel in 1865. The name Tithonian is unusual in geological stage names because it is derived from Greek mythology rather than a place name. Tithonus was the son of Laomedon of Troy and fell in love with Eos, the Greek goddess of dawn. His name was chosen by Albert Oppel for this stratigraphical stage because the Tithonian finds itself hand in hand with the dawn of the Cretaceous. The base of the Tithonian currently lacks a GSSP. The working definition for the base of the Tithonian is the first appearance of the ammonite genus Gravesia.The upper boundary of the Jurassic is currently undefined, and the Jurassic–Cretaceous boundary is currently the only system boundary to lack a defined GSSP. Placing a GSSP for this boundary has been difficult because of the strong regionality of most biostratigraphic markers, and lack of any chemostratigraphic events, such as isotope excursions (large sudden changes in ratios of isotopes), that could be used to define or correlate a boundary. Calpionellids, an enigmatic group of planktonic protists with urn-shaped calcitic tests briefly abundant during the latest Jurassic to earliest Cretaceous, have been suggested to represent the most promising candidates for fixing the Jurassic–Cretaceous boundary In particular, the first appearance Calpionella alpina, co-inciding with the base of the eponymous Alpina subzone, has been proposed as the definition of the base of the Cretaceous. The working definition for the boundary has often been placed as the first appearance of the ammonite Strambergella jacobi, formerly placed in the genus Berriasella, but its use as a stratigraphic indicator has been questioned, as its first appearance does not correlate with that of C. alpina.
Mineral and hydrocarbon deposits
The Kimmeridge Clay and equivalents are the major source rock for the North Sea oil. The Arabian Intrashelf Basin, deposited during the Middle and Late Jurassic, is the setting of the world's largest oil reserves, including the Ghawar Field, the world's largest oil field. The Jurassic-aged Sargelu and Naokelekan formations are major source rocks for oil in Iraq. Over 1500 gigatons of Jurassic coal reserves are found in north-west China, primarily in the Turpan-Hami Basin and the Ordos Basin.
Impact structures
Major impact structures include the Morokweng impact structure, a 70 km diameter impact structure buried beneath the Kalahari desert in northern South Africa. The impact is dated to the Tithonian, approximately 146.06 ± 0.16 Mya. Another major structure is the Puchezh-Katunki crater, 40 kilometres in diameter, buried beneath Nizhny Novgorod Oblast in western Russia. The impact has been dated to the Sinemurian, 195.9 ± 1.0 Ma.
Paleogeography and tectonics
At the beginning of the Jurassic, all of the world's major landmasses were coalesced into the supercontinent Pangaea, which during the Early Jurassic began to break up into northern supercontinent Laurasia and the southern supercontinent Gondwana. The rifting between North America and Africa was the first to initiate, beginning in the early Jurassic, associated with the emplacement of the Central Atlantic Magmatic Province.During the Jurassic, the North Atlantic Ocean remained relatively narrow, while the South Atlantic did not open until the Cretaceous. The continents were surrounded by Panthalassa, with the Tethys Ocean between Gondwana and Asia. At the end of the Triassic, there was a marine transgression in Europe, flooding most parts of central and western Europe transforming it into an archipelago of islands surrounded by shallow seas. During the Jurassic, both the North and South Pole were covered by oceans. Beginning in the Early Jurassic, the Boreal Ocean was connected to the proto-Atlantic by the "Viking corridor" or Transcontinental Laurasian Seaway, a passage between the Baltic Shield and Greenland several hundred kilometers wide. During the Callovian, the Turgai Epicontinental Sea formed, creating a marine barrier between Europe and Asia.Madagascar and Antarctica began to rift away from Africa during the late Early Jurassic in association with the eruption of the Karoo-Ferrar large igneous provinces, opening the western Indian Ocean and beginning the fragmentation of Gondwana. At the beginning of the Jurassic, North and South America remained connected, but by the beginning of the Late Jurassic they had rifted apart to form the Caribbean Seaway, also known as the Hispanic Corridor, which connected the North Atlantic Ocean with eastern Panthalassa. Palaeontological data suggest that the seaway had been open since the Early Jurassic.As part of the Nevadan orogeny, which began during the Triassic, the Cache Creek Ocean closed, and various terranes including the large Wrangellia Terrane accreted onto the western margin of North America. By the Middle Jurassic the Siberian plate and the North China-Amuria block had collided, resulting in the closure of the Mongol-Okhotsk Ocean.
During the Early Jurassic, around 190 million years ago, the Pacific Plate originated at the triple junction of the Farallon, Phoenix, and Izanagi tectonic plates, the three main oceanic plates of Panthalassa. The previously stable triple junction had converted to an unstable arrangement surrounded on all sides by transform faults because of a kink in one of the plate boundaries, resulting in the formation of the Pacific Plate at the centre of the junction. During the Middle to early Late Jurassic, the Sundance Seaway, a shallow epicontinental sea, covered much of northwest North America.The eustatic sea level is estimated to have been close to present levels during the Hettangian and Sinemurian, rising several tens of metres during the late Sinemurian–Pliensbachian before regressing to near present levels by the late Pliensbachian. There seems to have been a gradual rise to a peak of ~75 m above present sea level during the Toarcian. During the latest part of the Toarcian, the sea level again dropped by several tens of metres. It progressively rose from the Aalenian onwards, aside from dips of a few tens of metres in the Bajocian and around the Callovian–Oxfordian boundary, peaking possibly as high as 140 metres above present sea level at the Kimmeridgian–Tithonian boundary. The sea levels falls in the late Tithonian, perhaps to around 100 metres, before rebounding to around 110 metres at the Tithonian–Berriasian boundary.
The sea level within the long-term trends across the Jurassic was cyclical, with 64 fluctuations, 15 of which were over 75 metres. The most noted cyclicity in Jurassic rocks is fourth order, with a periodicity of approximately 410,000 years.During the Early Jurassic the world's oceans transitioned from an aragonite sea to a calcite sea chemistry, favouring the dissolution of aragonite and precipitation of calcite. The rise of calcareous plankton during the Middle Jurassic profoundly altered ocean chemistry, with the deposition of biomineralized plankton on the ocean floor acting as a buffer against large CO2 emissions.
Climate
The climate of the Jurassic was generally warmer than that of present, by around 5 °C to 10 °C, with atmospheric carbon dioxide likely about four times higher. Intermittent "cold snap" intervals are known to have occurred during this time period, however, interrupting the otherwise warm greenhouse climate. Forests likely grew near the poles, where they experienced warm summers and cold, sometimes snowy winters; there were unlikely to have been ice sheets given the high summer temperatures that prevented the accumulation of snow, though there may have been mountain glaciers. Dropstones and glendonites in northeastern Siberia during the Early to Middle Jurassic indicate cold winters. The ocean depths were likely 8 °C warmer than present, and coral reefs grew 10° of latitude further north and south. The Intertropical Convergence Zone likely existed over the oceans, resulting in large areas of desert and scrubland in the lower latitudes between 40° N and S of the equator. Tropical rainforest and tundra biomes are likely to have been rare or absent. The Jurassic also witnessed the decline of the Pangaean megamonsoon that had characterised the preceding Permian and Triassic periods. Variation in the frequency of wildfire activity in the Jurassic was governed by the 405 kyr eccentricity cycle. Thanks to the breakup of Pangaea, the hydrological cycle during the Jurassic was significantly enhanced.The beginning of the Jurassic was likely marked by a thermal spike corresponding to the Triassic–Jurassic extinction and eruption of the Central Atlantic magmatic province. The first part of the Jurassic was marked by the Early Jurassic Cool Interval between 199 and 183 million years ago. It has been proposed that glaciation was present in the Northern Hemisphere during both the early Pliensbachian and the latest Pliensbachian. There was a spike in global temperatures of around 4–8 °C during the early part of the Toarcian corresponding to the Toarcian Oceanic Anoxic Event and the eruption of the Karoo-Ferrar large igneous provinces in southern Gondwana, with the warm interval extending to the end of the Toarcian around 174 million years ago. During the Toarcian Warm Interval, ocean surface temperatures likely exceeded 30 °C, and equatorial and subtropical (30°N–30°S) regions are likely to have been extremely arid, with temperatures in the interior of Pangea likely in excess of 40 °C. The Toarcian Warm Interval is followed by the Middle Jurassic Cool Interval (MJCI) between 174 and 164 million years ago, which may have been punctuated by brief, ephemeral icehouse intervals. A transient ice age possibly occurred in the late Bajocian. The Callovian-Oxfordian boundary at the end of the MJCI witnessed particularly notable global cooling, potentially even an ice age. This is followed by the Kimmeridgian Warm Interval (KWI) between 164 and 150 million years ago. Based on fossil wood distribution, this was one of the wettest intervals of the Jurassic. The Pangaean interior had less severe seasonal swings than in previous warm periods as the expansion of the Central Atlantic and Western Indian Ocean provided new sources of moisture. A prominent drop in temperatures occurred during the Tithonian, known as the Early Tithonian Cooling Event (ETCE). The end of the Jurassic was marked by the Tithonian–early Barremian Cool Interval (TBCI), beginning 150 million years ago and continuing into the Early Cretaceous.
Climatic events
Toarcian Oceanic Anoxic Event
The Toarcian Oceanic Anoxic Event (TOAE), also known as the Jenkyns Event, was an episode of widespread oceanic anoxia during the early part of the Toarcian Age, c. 183 Mya. It is marked by a globally documented high amplitude negative carbon isotope excursion, as well as the deposition of black shales and the extinction and collapse of carbonate-producing marine organisms, associated with a major rise in global temperatures.The TOAE is often attributed to the eruption of the Karoo-Ferrar large igneous provinces and the associated increase of carbon dioxide concentration in the atmosphere, as well as the possible associated release of methane clathrates. This likely accelerated the hydrological cycle and increased silicate weathering, as evidenced by an increased amount of organic matter of terrestrial origin found in marine deposits during the TOAE. Groups affected include ammonites, ostracods, foraminifera, bivalves, cnidarians, and especially brachiopods, for which the TOAE represented one of the most severe extinctions in their evolutionary history. While the event had significant impact on marine invertebrates, it had little effect on marine reptiles. During the TOAE, the Sichuan Basin was transformed into a giant lake, probably three times the size of modern-day Lake Superior, represented by the Da’anzhai Member of the Ziliujing Formation. The lake likely sequestered ~460 gigatons (Gt) of organic carbon and ~1,200 Gt of inorganic carbon during the event. Seawater pH, which had already substantially decreased prior to the event, increased slightly during the early stages of the TOAE, before dropping to its lowest point around the middle of the event. This ocean acidification is the probable cause of the collapse of carbonate production. Additionally, anoxic conditions were exacerbated by enhanced recycling of phosphorus back into ocean water as a result of high ocean acidity and temperature inhibiting its mineralisation into apatite; the abundance of phosphorus in marine environments caused further eutrophication and consequent anoxia in a positive feedback loop.
End-Jurassic transition
The end-Jurassic transition was originally considered one of eight mass extinctions, but is now considered to be a complex interval of faunal turnover, with the increase in diversity of some groups and decline in others, though the evidence for this is primarily European, probably controlled by changes in eustatic sea level.
Flora
End-Triassic extinction
There is no evidence of a mass extinction of plants at the Triassic–Jurassic boundary. At the Triassic–Jurassic boundary in Greenland, the sporomorph (pollen and spores) record suggests a complete floral turnover. An analysis of macrofossil floral communities in Europe suggests that changes were mainly due to local ecological succession. At the end of the Triassic, the Peltaspermaceae became extinct in most parts of the world, with Lepidopteris persisting into the Early Jurassic in Patagonia. Dicroidium, a corystosperm seed fern that was a dominant part of Gondwanan floral communities during the Triassic, also declined at the Triassic–Jurassic boundary, surviving as a relict in Antarctica into the Early Jurassic.
Floral composition
Conifers
Conifers formed a dominant component of Jurassic floras. The Late Triassic and Jurassic was a major time of diversification of conifers, with most modern conifer groups appearing in the fossil record by the end of the Jurassic, having evolved from voltzialean ancestors.Araucarian conifers have their first unambiguous records during the Early Jurassic, and members of the modern genus Araucaria were widespread across both hemispheres by the Middle Jurassic.Also abundant during the Jurassic is the extinct family Cheirolepidiaceae, often recognised through their highly distinctive Classopolis pollen. Jurassic representatives include the pollen cone Classostrobus and the seed cone Pararaucaria. Araucarian and Cheirolepidiaceae conifers often occur in association.The oldest definitive record of the cypress family (Cupressaceae) is Austrohamia minuta from the Early Jurassic (Pliensbachian) of Patagonia, known from many parts of the plant. The reproductive structures of Austrohamia have strong similarities to those of the primitive living cypress genera Taiwania and Cunninghamia. By the Middle to Late Jurassic Cupressaceae were abundant in warm temperate–tropical regions of the Northern Hemisphere, most abundantly represented by the genus Elatides. The Jurassic also saw the first appearances of some modern genera of cypresses, such as Sequoia.Members of the extinct genus Schizolepidopsis which likely represent a stem-group to the pine family (Pinaceae), were widely distributed across Eurasia during the Jurassic. The oldest unambiguous record of Pinaceae is the pine cone Eathiestrobus, known from the Late Jurassic (Kimmeridgian) of Scotland, which remains the only known unequivocal fossil of the group before the Cretaceous. Despite being the earliest known member of the Pinaceae, Eathiestrobus appears to be a member of the pinoid clade of the family, suggesting that the initial diversification of Pinaceae occurred earlier than has been found in the fossil record.The earliest record of the yew family (Taxaceae) is Palaeotaxus rediviva, from the Hettangian of Sweden, suggested to be closely related to the living Austrotaxus, while Marskea jurassica from the Middle Jurassic of Yorkshire, England and material from the Callovian–Oxfordian Daohugou Bed in China are thought to be closely related to Amentotaxus, with the latter material assigned to the modern genus, indicating that Taxaceae had substantially diversified by the end of the Jurassic.The oldest unambiguous members of Podocarpaceae are known from the Jurassic, found across both hemispheres, including Scarburgia and Harrisiocarpus from the Middle Jurassic of England, as well as unnamed species from the Middle-Late Jurassic of Patagonia.During the Early Jurassic, the flora of the mid-latitudes of Eastern Asia were dominated by the extinct deciduous broad leafed conifer Podozamites, which appears to not be closely related to any living family of conifer. Its range extended northwards into polar latitudes of Siberia and then contracted northward in the Middle to Late Jurassic, corresponding to the increasing aridity of the region.
Ginkgoales
Ginkgoales, of which the sole living species is Ginkgo biloba, were more diverse during the Jurassic: they were among the most important components of Eurasian Jurassic floras and were adapted to a wide variety of climatic conditions. The earliest representatives of the genus Ginkgo, represented by ovulate and pollen organs similar to those of the modern species, are known from the Middle Jurassic in the Northern Hemisphere. Several other lineages of ginkgoaleans are known from Jurassic rocks, including Yimaia, Grenana, Nagrenia and Karkenia. These lineages are associated with Ginkgo-like leaves, but are distinguished from living and fossil representatives of Ginkgo by having differently arranged reproductive structures. Umaltolepis from the Jurassic of Asia has strap-shaped ginkgo-like leaves with highly distinct reproductive structures with similarities to those of peltasperm and corystosperm seed ferns, has been suggested to be a member of Ginkgoales sensu lato.
Bennettitales
Bennettitales, having first become widespread during the preceding Triassic, were diverse and abundant members of Jurassic floras across both hemispheres. The foliage of Bennettitales bears strong similarities to those of cycads, to such a degree that they cannot be reliably distinguished on the basis of morphology alone. Leaves of Bennettitales can be distinguished from those of cycads their different arrangement of stomata, and the two groups are not thought to be closely related. Jurassic Bennettitales predominantly belong to the group Williamsoniaceae, which grew as shrubs and small trees. The Williamsoniaceae are thought to have had a divaricate branching habit, similar to that of living Banksia, and adapted to growing in open habitats with poor soil nutrient conditions. Bennettitales exhibit complex, flower-like reproductive structures some of which are thought to have been pollinated by insects. Several groups of insects that bear long proboscis, including extinct families such as kalligrammatid lacewings and extant ones such as acrocerid flies, are suggested to have been pollinators of bennettitales, feeding on nectar produced by bennettitalean cones.
Cycads
Cycads reached their apex of diversity during the Jurassic and Cretaceous Periods. Despite the Mesozoic sometimes being called the "Age of Cycads", cycads are thought to have been a relatively minor component of mid-Mesozoic floras, with the Bennettitales and Nilssoniales, which have cycad-like foliage, being dominant. The Nilssoniales have often been considered cycads or cycad relatives, but have been found to be distinct on chemical grounds, and perhaps more closely allied with Bennettitales. The relationships of most Mesozoic cycads to living groups are ambiguous, with no Jurassic cycads belonging to either of the two modern groups of cycads, though some Jurassic cycads possibly represent stem-group relatives of modern Cycadaceae, like the leaf genus Paracycas known Europe, and Zamiaceae, like some European species of the leaf genus Pseudoctenis. Also widespread during the Jurassic was the extinct Ctenis lineage, which appears to be distantly related to modern cycads. Modern cycads are pollinated by beetles, and such an association is thought to have formed by the Early Jurassic.
Other seed plants
Although there have been several claimed records, there are no widely accepted Jurassic fossil records of flowering plants, which make up 90% of living plant species, and fossil evidence suggests that the group diversified during the following Cretaceous.
The earliest known gnetophytes, one of the four main living groups of gymnosperms, appeared by the end of the Jurassic, with the oldest unequivocal gnetophyte being the seed Dayvaultia from the Late Jurassic of North America."Seed ferns" (Pteridospermatophyta) is a collective term to refer to disparate lineages of fern like plants that produce seeds but have uncertain affinities to living seed plant groups. A prominent group of Jurassic seed ferns is the Caytoniales, which reached their zenith during the Jurassic, with widespread records in the Northern Hemisphere, though records in the Southern Hemisphere remain rare. Due to their berry-like seed-bearing capsules, they have often been suggested to have been closely related or perhaps ancestral to flowering plants, but the evidence for this is inconclusive. Corystosperm-aligned seed ferns, such as Pachypteris and Komlopteris were widespread across both hemispheres during the Jurassic.Czekanowskiales, also known as Leptostrobales, are a group of seed plants uncertain affinities with persistent heavily dissected leaves borne on deciduous short shoots, subtended by scale-like leaves, known from the Late Triassic (possibly Late Permian) to Cretaceous. They are thought to have had a tree- or shrub-like habit and formed a conspicuous component of Northern Hemisphere Mesozoic temperate and warm-temperate floras. The genus Phoenicopsis was widespread in Early-Middle Jurassic floras of Eastern Asia and Siberia.The Pentoxylales, a small but clearly distinct group of liana-like seed plants of obscure affinities, first appeared during the Jurassic. Their distribution appears to have been confined to Eastern Gondwana.
Ferns and allies
Living families of ferns widespread during the Jurassic include Dipteridaceae, Matoniaceae, Gleicheniaceae, Osmundaceae and Marattiaceae. Polypodiales, which make up 80% of living fern diversity, have no record from the Jurassic and are thought to have diversified in the Cretaceous, though the widespread Jurassic herbaceous fern genus Coniopteris, historically interpreted as a close relative of tree ferns of the family Dicksoniaceae, has recently been reinterpreted as an early relative of the group.The Cyatheales, the group containing most modern tree ferns, appeared during the Late Jurassic, represented by members of the genus Cyathocaulis, which are suggested to be early members of Cyatheaceae on the basis of cladistic analysis. Only a handful of possible records exist of the Hymenophyllaceae from the Jurassic, including Hymenophyllites macrosporangiatus from the Russian Jurassic.The oldest remains of modern horsetails of the genus Equisetum first appear in the Early Jurassic, represented by Equisetum dimorphum from the Early Jurassic of Patagonia and Equisetum laterale from the Early to Middle Jurassic of Australia. Silicified remains of Equisetum thermale from the Late Jurassic of Argentina exhibit all the morphological characters of modern members of the genus. The estimated split between Equisetum bogotense and all other living Equisetum is estimated to have occurred no later than the Early Jurassic.
Lower plants
Quillworts virtually identical to modern species are known from the Jurassic onwards. Isoetites rolandii from the Middle Jurassic of Oregon is the earliest known species to represent all major morphological features of modern Isoetes. More primitive forms such as Nathorstiana, which retain an elongated stem, persisted into the Early Cretaceous.The moss Kulindobryum from the Middle Jurassic of Russia, which was found associated with dinosaur bones, is thought to be related to the Splachnaceae, which grow on animal caracasses. Bryokhutuliinia from the same region is thought to be related to Dicranales. Heinrichsiella from the Jurassic of Patagonia is thought to belong to either Polytrichaceae or Timmiellaceae.The liverwort Pellites hamiensis from the Middle Jurassic Xishanyao Formation of China is the oldest record of the family Pelliaceae. Pallaviciniites sandaolingensis from the same deposit is thought to belong to the subclass Pallaviciniineae within the Pallaviciniales. Ricciopsis sandaolingensis, also from the same deposit, is the only Jurassic record of Ricciaceae.
Fauna
Reptiles
Crocodylomorphs
The Triassic–Jurassic extinction decimated pseudosuchian diversity, with crocodylomorphs, which originated during the early Late Triassic, being the only group of pseudosuchians to survive. All other pseudosuchians, including the herbivorous aetosaurs and carnivorous "rauisuchians", became extinct. The morphological diversity of crocodylomorphs during the Early Jurassic was around the same as that of Late Triassic pseudosuchians, but they occupied different areas of morphospace, suggesting that they occupied different ecological niches to their Triassic counterparts and that there was an extensive and rapid radiation of crocodylomorphs during this interval. While living crocodilians are mostly confined to an aquatic ambush predator lifestyle, Jurassic crocodylomorphs exhibited a wide variety of life habits. An unnamed protosuchid known from teeth from the Early Jurassic of Arizona represents the earliest known herbivorous crocodylomorph, an adaptation that appeared several times during the Mesozoic.The Thalattosuchia, a clade of predominantly marine crocodylomorphs, first appeared during the Early Jurassic and became a prominent part of marine ecosystems. Within Thalattosuchia, the Metriorhynchidae became highly adapted for life in the open ocean, including the transformation of limbs into flippers, the development of a tail fluke, and smooth, scaleless skin. The morphological diversity of crocodylomorphs during the Early and Middle Jurassic was relatively low compared to that in later time periods and was dominated by terrestrial small-bodied, long-legged sphenosuchians, early crocodyliforms and thalattosuchians. The Neosuchia, a major group of crocodylomorphs, first appeared during the Early to Middle Jurassic. The Neosuchia represents the transition from an ancestrally terrestrial lifestyle to a freshwater aquatic ecology similar to that occupied by modern crocodilians. The timing of the origin of Neosuchia is disputed. The oldest record of Neosuchians has been suggested to be Calsoyasuchus, from the Early Jurassic of Arizona, which in many analyses has been recovered as the earliest branching member of the neosuchian family Goniopholididae, which radically alters times of diversification for crocodylomorphs. However, this placement has been disputed, with some analyses finding it outside Neosuchia, which would place the oldest records of Neosuchia in the Middle Jurassic. Razanandrongobe from the Middle Jurassic of Madagascar has been suggested the represent the oldest record of Notosuchia, a primarily Gondwanan clade of mostly terrestrial crocodylomorphs, otherwise known from the Cretaceous and Cenozoic.
Turtles
Stem-group turtles (Testudinata) diversified during the Jurassic. Jurassic stem-turtles belong to two progressively more advanced clades, the Mesochelydia and Perichelydia. It is thought that the ancestral condition for mesochelydians is aquatic, as opposed to terrestrial for testudinates. The two modern groups of turtles (Testudines), Pleurodira and Cryptodira, diverged by the beginning of the Late Jurassic. The oldest known pleurodires, the Platychelyidae, are known from the Late Jurassic of Europe and the Americas, while the oldest unambiguous cryptodire, Sinaspideretes, an early relative of softshell turtles, is known from the Late Jurassic of China. The Thalassochelydia, a diverse lineage of marine turtles unrelated to modern sea turtles, are known from the Late Jurassic of Europe and South America.
Lepidosaurs
Rhynchocephalians (the sole living representative being the tuatara) had achieved a global distribution by the beginning of the Jurassic. Rhynchocephalians reached their highest morphological diversity in their evolutionary history during the Jurassic, occupying a wide range of lifestyles, including the aquatic pleurosaurs with long snake-like bodies and reduced limbs, the specialized herbivorous eilenodontines, as well as Oenosaurus, which had broad tooth plates indicative of durophagy. Rhynchocephalians disappeared from Asia after the Early Jurassic. The last common ancestor of living squamates (which includes lizards and snakes) is estimated to have lived around 190 million years ago during the Early Jurassic, with the major divergences between modern squamate lineages estimated to have occurred during the Early to Middle Jurassic. Squamates first appear in the fossil record during the Middle Jurassic including members of modern clades such as Scincomorpha, though many Jurassic squamates have unclear relationships to living groups. Eichstaettisaurus from the Late Jurassic of Germany has been suggested to be an early relative of geckos and displays adaptations for climbing. Dorsetisaurus from the Late Jurassic of North America and Europe represents the oldest widely accepted record of Anguimorpha. Tamaulipasaurus from Early Jurassic of Mexico and Marmoretta from the Middle Jurassic of Britain represents late surviving lepidosauromorphs outside both Rhynchocephalia and Squamata.
Choristoderes
The earliest known remains of Choristodera, a group of freshwater aquatic reptiles with uncertain affinities to other reptile groups, are found in the Middle Jurassic. Only two genera of choristodere are known from the Jurassic. One is the small lizard-like Cteniogenys, thought to be the most basal known choristodere; it is known from the Middle to Late Jurassic of Europe and Late Jurassic of North America, with similar remains also known from the upper Middle Jurassic of Kyrgyzstan and western Siberia. The other is Coeruleodraco from the Late Jurassic of China, which is a more advanced choristodere, though still small and lizard-like in morphology.
Ichthyosaurs
Ichthyosaurs suffered an evolutionary bottleneck during the end-Triassic extinction, with all non-neoichthyosaurians becoming extinct. Ichthyosaurs reached their apex of species diversity during the Early Jurassic, with an array of morphologies including the huge apex predator Temnodontosaurus and swordfish-like Eurhinosaurus, though Early Jurassic ichthyosaurs were significantly less morphologically diverse than their Triassic counterparts. At the Early–Middle Jurassic boundary, between the end of the Toarcian and the beginning of the Bajocian, most lineages of ichythosaur appear to have become extinct, with the first appearance of the Ophthalmosauridae, the clade that would encompass almost all ichthyosaurs from then on, during the early Bajocian. Ophthalmosaurids were diverse by the Late Jurassic, but failed to fill many of the niches that had been occupied by ichthyosaurs during the Early Jurassic.
Plesiosaurs
Plesiosaurs originated at the end of the Triassic (Rhaetian). By the end of the Triassic, all other sauropterygians, including placodonts and nothosaurs, had become extinct. At least six lineages of plesiosaur crossed the Triassic–Jurassic boundary. Plesiosaurs were already diverse in the earliest Jurassic, with the majority of plesiosaurs in the Hettangian-aged Blue Lias belonging to the Rhomaleosauridae. Early plesiosaurs were generally small-bodied, with body size increasing into the Toarcian. There appears to have been a strong turnover around the Early–Middle Jurassic boundary, with microcleidids and rhomaleosaurids becoming extinct and nearly extinct respectively after the end of the Toarcian with the first appearance of the dominant clade of plesiosaurs of the latter half of the Jurassic, the Cryptoclididae during the Bajocian. The Middle Jurassic saw the evolution of short-necked and large-headed thalassophonean pliosaurs from ancestrally small-headed, long-necked forms. Some thalassophonean pliosaurs, such as some species of Pliosaurus, had skulls up to two metres in length with body lengths estimated around 10–12 metres, making them the apex predators of Late Jurassic oceans. Plesiosaurs invaded freshwater environments during the Jurassic, with indeterminate remains of small-bodied pleisosaurs known from freshwater sediments from the Jurassic of China and Australia.
Pterosaurs
Pterosaurs first appeared in the Late Triassic. A major radiation of Jurassic pterosaurs is the Rhamphorhynchidae, which first appeared in the late Early Jurassic (Toarcian); they are thought to been piscivorous. Anurognathids, which first appeared in the Middle Jurassic, possessed short heads and densely furred bodies, and are thought to have been insectivores. Derived monofenestratan pterosaurs such as wukongopterids appeared in the late Middle Jurassic. Advanced short-tailed pterodactyloids first appeared at the Middle–Late Jurassic boundary. Jurassic pterodactyloids include the ctenochasmatids, like Ctenochasma, which have closely spaced needle-like teeth that were presumably used for filter feeding. The bizarre Late Jurassic ctenochasmatoid Cycnorhamphus had a jaw with teeth only at the tips, with bent jaws like those of living openbill storks that may have been used to hold and crush hard invertebrates.
Dinosaurs
Dinosaurs, which had morphologically diversified in the Late Triassic, experienced a major increase in diversity and abundance during the Early Jurassic in the aftermath of the end-Triassic extinction and the extinction of other reptile groups, becoming the dominant vertebrates in terrestrial ecosystems. Chilesaurus, a morphologically aberrant herbivorous dinosaur from the Late Jurassic of South America, has uncertain relationships to the three main groups of dinosaurs, having been recovered as a member of all three in different analyses.
Theropods
Advanced theropods belonging to Neotheropoda first appeared in the Late Triassic. Basal neotheropods, such as coelophysoids and dilophosaurs, persisted into the Early Jurassic, but became extinct by the Middle Jurassic. The earliest averostrans appear during the Early Jurassic, with the earliest known member of Ceratosauria being Saltriovenator from the early Sinemurian (199.3–197.5 million years ago) of Italy. The unusual ceratosaur Limusaurus from the Late Jurassic of China had a herbivorous diet, with adults having edentulous beaked jaws, making it the earliest known theropod to have converted from an ancestrally carnivorous diet. The earliest members of the Tetanurae appeared during the late Early Jurassic or early Middle Jurassic. The Megalosauridae represent the oldest radiation of the Tetanurae, first appearing in Europe during the Bajocian. The oldest member of Allosauroidea has been suggested to be Asfaltovenator from the Middle Jurassic of South America. Coelurosaurs first appeared during the Middle Jurassic, including early tyrannosaurs such as Proceratosaurus from the Bathonian of Britain. Some coelurosaurs from the Late Jurassic of China including Shishugounykus and Haplocheirus are suggested to represent early alvarezsaurs, however, this has been questioned. Scansoriopterygids, a group of small feathered coelurosaurs with membraneous, bat-like wings for gliding, are known from the Middle to Late Jurassic of China. The oldest record of troodontids is suggested to be Hesperornithoides from the Late Jurassic of North America. Tooth remains suggested to represent those of dromaeosaurs are known from the Jurassic, but no body remains are known until the Cretaceous.
Birds
The earliest avialans, which include birds and their ancestors, appear during the Middle to Late Jurassic, definitively represented by Archaeopteryx from the Late Jurassic of Germany. Avialans belong to the clade Paraves within Coelurosauria, which also includes dromaeosaurs and troodontids. The Anchiornithidae from the Middle-Late Jurassic of Eurasia have frequently suggested to be avialans, but have also alternatively found as a separate lineage of paravians.
Ornithischians
The earliest definitive ornithischians appear during the Early Jurassic, represented by basal ornithischians like Lesothosaurus, heterodontosaurids, and early members of Thyreophora. The earliest members of Ankylosauria and Stegosauria appear during the Middle Jurassic. The basal neornithischian Kulindadromeus from the Middle Jurassic of Russia indicates that at least some ornithischians were covered in protofeathers. The earliest members of Ankylopollexia, which become prominent in the Cretaceous, appeared during the Late Jurassic, represented by bipedal forms such as Camptosaurus. Ceratopsians first appeared in the Late Jurassic of China, represented by members of Chaoyangsauridae.
Sauropodomorphs
Sauropods became the dominant large herbivores in terrestrial ecosystems during the Jurassic. Some Jurassic sauropods reached gigantic sizes, becoming the largest organisms to have ever lived on land.Basal bipedal sauropodomorphs, such as massospondylids, continued to exist into the Early Jurassic, but became extinct by the beginning of the Middle Jurassic. Quadrupedal sauropomorphs appeared during the Late Triassic. The quadrupedal Ledumahadi from the earliest Jurassic of South Africa reached an estimated weight of 12 tons, far in excess of other known basal sauropodomorphs. Gravisaurian sauropods first appeared during the Early Jurassic, with the oldest definitive record being Vulcanodon from Zimbabwe, likely of Sinemurian age. Eusauropods first appeared during the late Early Jurassic (Toarcian) and diversified during the Middle Jurassic; these included cetiosaurids, turiasaurs, and mamenchisaurs. Neosauropods such as macronarians and diplodocoids first appeared during the Middle Jurassic, before becoming abundant and globally distributed during the Late Jurassic.
Amphibians
The diversity of temnospondyls had progressively declined through the Late Triassic, with only brachyopoids surviving into the Jurassic and beyond. Members of the family Brachyopidae are known from Jurassic deposits in Asia, while the chigutisaurid Siderops is known from the Early Jurassic of Australia. Modern lissamphibians began to diversify during the Jurassic. The Early Jurassic Prosalirus thought to represent the first frog relative with a morphology capable of hopping like living frogs. Morphologically recognisable stem-frogs like the South American Notobatrachus are known from the Middle Jurassic, with modern crown-group frogs like Enneabatrachus and Rhadinosteus appearing by the Late Jurassic. While the earliest salamander-line amphibians are known from the Triassic, crown group salamanders first appear during the Middle to Late Jurassic in Eurasia, alongside stem-group relatives. Many Jurassic stem-group salamanders, such as Marmorerpeton and Kokartus, are thought to have been neotenic. Early representatives of crown group salamanders include Chunerpeton, Pangerpeton and Linglongtriton from the Middle to Late Jurassic Yanliao Biota of China. These belong to the Cryptobranchoidea, which contains living Asiatic and giant salamanders. Beiyanerpeton, and Qinglongtriton from the same biota are thought to be early members of Salamandroidea, the group which contains all other living salamanders. Salamanders dispersed into North America by the end of the Jurassic, as evidenced by Iridotriton, found in the Late Jurassic Morrison Formation. The stem-caecilian Eocaecilia is known from the Early Jurassic of Arizona. The fourth group of lissamphibians, the extinct albanerpetontids, first appeared in the Middle Jurassic, represented by Anoualerpeton priscus from the Bathonian of Britain, as well as indeterminate remains from equivalently aged sediments in France and the Anoual Formation of Morocco.
Mammaliaformes
Mammaliaformes, having originated from cynodonts at the end of the Triassic, diversified extensively during the Jurassic. Important groups of Jurassic Mammaliaformes include Morganucodonta, Docodonta, Eutriconodonta, Dryolestida, Haramiyida and Multituberculata. While most Jurassic mammalaliaformes are solely known from isolated teeth and jaw fragments, exceptionally preserved remains have revealed a variety of lifestyles. The docodontan Castorocauda was adapted to aquatic life, similarly to the platypus and otters. Some members of Haramiyida and the eutriconodontan tribe Volaticotherini had a patagium akin to those of flying squirrels, allowing them to glide through the air. The aardvark-like mammal Fruitafossor, of uncertain taxonomy, was likely a specialist on colonial insects, similarly to living anteaters. Australosphenida, a group of mammals possibly related to monotremes, first appeared in the Middle Jurassic of Gondwana. Therian mammals, represented today by living placentals and marsupials, appear during the early Late Jurassic, represented by Juramaia, a eutherian mammal closer to the ancestry of placentals than marsupials. Juramaia is much more advanced than expected for its age, as other therian mammals are not known until the Early Cretaceous. Two groups of non-mammalian cynodonts persisted beyond the end of the Triassic. The insectiviorous Tritheledontidae has a few records from the Early Jurassic. The Tritylodontidae, a herbiviorous group of cynodonts that first appeared during the Rhaetian, has abundant records from the Jurassic, overwhelmingly from the Northern Hemisphere.
Fish
Jawless fish
The last known species of conodont, a class of jawless fish whose hard, tooth-like elements are key index fossils, finally became extinct during the earliest Jurassic after over 300 million years of evolutionary history, with an asynchronous extinction occurring first in the Tethys and eastern Panthalassa and survivors persisting into the earliest Hettangian of Hungary and central Panthalassa. End-Triassic conodonts were represented by only a handful of species and had been progressively declining through the Middle and Late Triassic. Yanliaomyzon from the Middle Jurassic of China represents the oldest post Paleozoic lamprey, and the oldest lamprey to have the toothed feeding apparatus and likely the three stage life cycle typical of modern members of the group.
Sarcopterygii
Lungfish (Dipnoi) were present in freshwater environments of both hemispheres during the Jurassic. Genera include Ceratodus and Ptychoceratodus, which are more closely related to living South American and African lungfish than Queensland lungfish, and Ferganoceratodus from the Jurassic of Asia, which is not closely related to either group of living lungfish. Mawsoniids, a marine and freshwater/brackish group of coelacanths, which first appeared in North America during the Triassic, expanded into Europe and South America by the end of the Jurassic. The marine Latimeriidae, which contains the living coelacanths of the genus Latimeria, were also present in the Jurassic, having originated in the Triassic.
Actinopterygii
Ray-finned fish (Actinopterygii) were major components of Jurassic freshwater and marine ecosystems. Archaic "palaeoniscoid" fish, which were common in both marine and freshwater habitats during the preceding Triassic declined during the Jurassic, being largely replaced by more derived actinopterygian lineages. The oldest known Acipenseriformes, the group that contains living sturgeon and paddlefish, are from the Early Jurassic. Amiiform fish (which today only includes the bowfin) first appeared during the Early Jurassic, represented by Caturus from the Pliensbachian of Britain; after their appearance in the western Tethys, they expanded to Africa, North America and Southeast and East Asia by the end of the Jurassic, with the modern family Amiidae appearing during the Late Jurassic. Pycnodontiformes, which first appeared in the western Tethys during the Late Triassic, expanded to South America and Southeast Asia by the end of the Jurassic, having a high diversity in Europe during the Late Jurassic. During the Jurassic, the Ginglymodi, the only living representatives being gars (Lepisosteidae) were diverse in both freshwater and marine environments. The oldest known representatives of anatomically modern gars appeared during the Upper Jurassic. Stem-group teleosts, which make up over 99% of living Actinopterygii, had first appeared during the Triassic in the western Tethys; they underwent a major diversification beginning in the Late Jurassic, with early representatives of modern teleost clades such as Elopomorpha and Osteoglossoidei appearing during this time. The Pachycormiformes, a group of marine stem-teleosts, first appeared in the Early Jurassic and included both tuna-like predatory and filter-feeding forms, the latter included the largest bony fish known to have existed: Leedsichthys, with an estimated maximum length of over 15 metres, known from the late Middle to Late Jurassic.
Chondrichthyes
During the Early Jurassic, the shark-like hybodonts, which represented the dominant group of chondrichthyans during the preceding Triassic, were common in both marine and freshwater settings; however, by the Late Jurassic, hybodonts had become minor components of most marine communities, having been largely replaced by modern neoselachians, but remained common in freshwater and restricted marine environments. The Neoselachii, which contains all living sharks and rays, radiated beginning in the Early Jurassic. The oldest known ray (Batoidea) is Antiquaobatis from the Pliensbachian of Germany. Jurassic batoids known from complete remains retain a conservative, guitarfish-like morphology. The oldest known Hexanchiformes and carpet sharks (Orectolobiformes) are from the Early Jurassic (Pliensbachian & Toarcian, respectively) of Europe. The oldest known members of the Heterodontiformes, the only living member of which is the bullhead shark (Heterodontus), first appeared in the Early Jurassic, with representatives of the living genus appearing during the Late Jurassic. The oldest known mackerel sharks (Lamniformes) are from the Middle Jurassic, represented by the genus Palaeocarcharias, which has an orectolobiform-like body but shares key similarities in tooth histology with lamniformes, including the absence of orthodentine. The oldest record of angelsharks (Squatiniformes) is Pseudorhina from the Late Jurassic (Oxfordian–Tithonian) of Europe, which already has a bodyform similar to living members of the order. The oldest known remains of Carcharhiniformes, the largest order of living sharks, first appear in the late Middle Jurassic (Bathonian) of the western Tethys (England and Morocco). Known dental and exceptionally preserved body remains of Jurassic Carchariniformes are similar to those of living catsharks. Synechodontiformes, an extinct group of sharks closely related to Neoselachii, were also widespread during the Jurassic. The oldest remains of modern chimaeras are from the Early Jurassic of Europe, with members of the living family Callorhinchidae appearing during the Middle Jurassic. Unlike living chimaeras, these were found in shallow water settings. The closely related Squaloraja and myriacanthoids are also known from the Jurassic of Europe.
Insects and arachnids
There appears to have been no major extinction of insects at the Triassic–Jurassic boundary. Many important insect fossil localities are known from the Jurassic of Eurasia, the most important being the Karabastau Formation of Kazakhstan and the various Yanliao Biota deposits in Inner Mongolia, China, such as the Daohugou Bed, dating to the Callovian–Oxfordian. The diversity of insects stagnated throughout the Early and Middle Jurassic, but during the latter third of the Jurassic origination rates increased substantially while extinction rates remained flat. The increasing diversity of insects in the Middle–Late Jurassic corresponds with a substantial increase in the diversity of insect mouthparts. The Middle to Late Jurassic was a time of major diversification for beetles. Weevils first appear in the fossil record during the Middle to Late Jurassic, but are suspected to have originated during the Late Triassic to Early Jurassic. The oldest known lepidopterans (the group containing butterflies and moths) are known from the Triassic–Jurassic boundary, with wing scales belonging to the suborder Glossata and Micropterigidae-grade moths from the deposits of this age in Germany. Modern representatives of both dragonflies and damselflies also first appeared during the Jurassic. Although modern representatives are not known until the Cenozoic, ectoparasitic insects thought to represent primitive fleas, belonging to the family Pseudopulicidae, are known from the Middle Jurassic of Asia. These insects are substantially different from modern fleas, lacking the specialised morphology of the latter and being larger. Parasitoid wasps (Apocrita) first appeared during the Early Jurassic and subsequently became widespread, reshaping terrestrial food webs. The Jurassic saw also saw the first appearances of several other groups of insects, including Phasmatodea (stick insects), Mantophasmatidae, Embioptera (webspinners), and Raphidioptera (snakeflies).
Only a handful of records of mites are known from the Jurassic, including Jureremus, an oribatid mite belonging to the family Cymbaeremaeidae known from the Late Jurassic of Britain and Russia, and a member of the still living orbatid genus Hydrozetes from the Early Jurassic of Sweden. Spiders diversified through the Jurassic. The Early Jurassic Seppo koponeni may represent a stem group to Palpimanoidea. Eoplectreurys from the Middle Jurassic of China is considered a stem lineage of Synspermiata. The oldest member of the family Archaeidae, Patarchaea, is known from the Middle Jurassic of China. Mongolarachne from the Middle Jurassic of China is among the largest known fossil spiders, with legs over 5 centimetres long. The only scorpion known from the Jurassic is Liassoscorpionides from the Early Jurassic of Germany, of uncertain placement. Eupnoi harvestmen (Opiliones) are known from the Middle Jurassic of China, including members of the family Sclerosomatidae.
Marine invertebrates
End-Triassic extinction
During the end-Triassic extinction, 46%–72% of all marine genera became extinct. The effects of the end Triassic extinction were greatest at tropical latitudes and were more severe in Panthalassa than the Tethys or Boreal oceans. Tropical reef ecosystems collapsed during the event, and would not fully recover until much later in the Jurassic. Sessile filter feeders and photosymbiotic organisms were among most severely affected.
Marine ecosystems
Having declined at the Triassic–Jurassic boundary, reefs substantially expanded during the Late Jurassic, including both sponge reefs and scleractinian coral reefs. Late Jurassic reefs were similar in form to modern reefs but had more microbial carbonates and hypercalcified sponges, and had weak biogenic binding. Reefs sharply declined at the close of the Jurassic, which caused an associated drop in diversity in decapod crustaceans. The earliest planktonic foraminifera, which constitute the suborder Globigerinina, are known from the late Early Jurassic (mid-Toarcian) of the western Tethys, expanding across the whole Tethys by the Middle Jurassic and becoming globally distributed in tropical latitudes by the Late Jurassic. Coccolithophores and dinoflagellates, which had first appeared during the Triassic, radiated during the Early to Middle Jurassic, becoming prominent members of the phytoplankton. Microconchid tube worms, the last remaining order of Tentaculita, a group of animals of uncertain affinities that were convergent on Spirorbis tube worms, were rare after the Triassic and had become reduced to the single genus Punctaconchus, which became extinct in the late Bathonian. The oldest known diatom is from Late Jurassic–aged amber from Thailand, assigned to the living genus Hemiaulus.
Echinoderms
Crinoids diversified throughout the Jurassic, reaching their peak Mesozoic diversity during the Late Jurassic, primarily due to the radiation of sessile forms belonging to the orders Cyrtocrinida and Millericrinida. Echinoids (sea urchins) underwent substantial diversification beginning in the Early Jurassic, primarily driven by the radiation of irregular (asymmetrical) forms, which were adapting to deposit feeding. Rates of diversification sharply dropped during the Late Jurassic.
Crustaceans
The Jurassic was a significant time for the evolution of decapods. The first true crabs (Brachyura) are known from the Early Jurassic, with the earliest being Eocarcinus praecursor from the early Pliensbachian of England, which lacked the crab-like morphology (carcinisation) of modern crabs, and Eoprosopon klugi from the late Pliensbachian of Germany, which may belong to the living family Homolodromiidae. Most Jurassic crabs are known only from carapace pieces, which makes it difficult to determine their relationships. While rare in the Early and Middle Jurassic, crabs became abundant during the Late Jurassic as they expanded from their ancestral silty sea floor habitat into hard substrate habitats like reefs, with crevices in reefs providing refuge from predators. Hermit crabs also first appeared during the Jurassic, with the earliest known being Schobertella hoelderi from the late Hettangian of Germany. Early hermit crabs are associated with ammonite shells rather than those of gastropods. Glypheids, which today are only known from two species, reached their peak diversity during the Jurassic, with around 150 species out of a total fossil record of 250 known from the period. Jurassic barnacles were of low diversity compared to present, but several important evolutionary innovations are known, including the first appearances of calcite shelled forms and species with an epiplanktonic mode of life.
Brachiopods
Brachiopod diversity declined during the Triassic–Jurassic extinction. Spire-bearing brachiopods (Spiriferinida and Athyridida) did not recover their biodiversity, becoming extinct in the TOAE. Rhynchonellida and Terebratulida also declined during the Triassic–Jurassic extinction but rebounded during the Early Jurassic; neither clade underwent much morphological variation. Brachiopods substantially declined in the Late Jurassic; the causes are poorly understood. Proposed reasons include increased predation, competition with bivalves, enhanced bioturbation or increased grazing pressure.
Bryozoans
Like the preceding Triassic, bryozoan diversity was relatively low compared to the Paleozoic. The vast majority of Jurassic bryozoans are members of Cyclostomatida, which experienced a radiation during the Middle Jurassic, with all Jurassic representatives belonging to the suborders Tubuliporina and Cerioporina. Cheilostomata, the dominant group of modern bryozoans, first appeared during the Late Jurassic.
Molluscs
Bivalves
The end-Triassic extinction had a severe impact on bivalve diversity, though it had little impact on bivalve ecological diversity. The extinction was selective, having less of an impact on deep burrowers, but there is no evidence of a differential impact between surface-living (epifaunal) and burrowing (infaunal) bivalves. Bivalve family level diversity after the Early Jurassic was static, though genus diversity experienced a gradual increase throughout the period. Rudists, the dominant reef-building organisms of the Cretaceous, first appeared in the Late Jurassic (mid-Oxfordian) in the northern margin of the western Tethys, expanding to the eastern Tethys by the end of the Jurassic.
Cephalopods
Ammonites were devastated by the end-Triassic extinction, with only a handful of genera belonging to the family Psiloceratidae of the suborder Phylloceratina surviving and becoming ancestral to all later Jurassic and Cretaceous ammonites. Ammonites explosively diversified during the Early Jurassic, with the orders Psiloceratina, Ammonitina, Lytoceratina, Haploceratina, Perisphinctina and Ancyloceratina all appearing during the Jurassic. Ammonite faunas during the Jurassic were regional, being divided into around 20 distinguishable provinces and subprovinces in two realms, the northern high latitude Pan-Boreal realm, consisting of the Arctic, northern Panthalassa and northern Atlantic regions, and the equatorial–southern Pan-Tethyan realm, which included the Tethys and most of Panthalassa. Ammonite diversifications occurred coevally with marine transgressions, while their diversity nadirs occurred during marine regressions.The oldest definitive records of the squid-like belemnites are from the earliest Jurassic (Hettangian–Sinemurian) of Europe and Japan; they expanded worldwide during the Jurassic. Belemnites were shallow-water dwellers, inhabiting the upper 200 metres of the water column on the continental shelves and in the littoral zone. They were key components of Jurassic ecosystems, both as predators and prey, as evidenced by the abundance of belemnite guards in Jurassic rocks.The earliest vampyromorphs, of which the only living member is the vampire squid, first appeared during the Early Jurassic. The earliest octopuses appeared during the Middle Jurassic, having split from their closest living relatives, the vampyromorphs, during the Triassic to Early Jurassic. All Jurassic octopuses are solely known from the hard gladius. Octopuses likely originated from bottom-dwelling (benthic) ancestors which lived in shallow environments. Proteroctopus from the late Middle Jurassic La Voulte-sur-Rhône lagerstätte, previously interpreted as an early octopus, is now thought to be a basal taxon outside the clade containing vampyromorphs and octopuses.
References
Citations
External links
Examples of Jurassic Fossils
Jurassic (chronostratigraphy scale)
Jurassic fossils in Harbury, Warwickshire
Jurassic Microfossils: 65+ images of Foraminifera
"Jurassic" . Encyclopædia Britannica. Vol. 15 (11th ed.). 1911. With map and table. |
permian | The Permian ( PUR-mee-ən) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the region of Perm in Russia.The Permian witnessed the diversification of the two groups of amniotes, the synapsids and the sauropsids (reptiles). The world at the time was dominated by the supercontinent Pangaea, which had formed due to the collision of Euramerica and Gondwana during the Carboniferous. Pangaea was surrounded by the superocean Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior. Amniotes, which could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors.
Various authors recognise at least three, and possibly four extinction events in the Permian. The end of the Early Permian (Cisuralian) saw a major faunal turnover, with most lineages of primitive "pelycosaur" synapsids becoming extinct, being replaced by more advanced therapsids. The end of the Capitanian Stage of the Permian was marked by the major Capitanian mass extinction event, associated with the eruption of the Emeishan Traps. The Permian (along with the Paleozoic) ended with the Permian–Triassic extinction event, the largest mass extinction in Earth's history (which is the last of the three or four crises that occurred in the Permian), in which nearly 81% of marine species and 70% of terrestrial species died out, associated with the eruption of the Siberian Traps. It took well into the Triassic for life to recover from this catastrophe; on land, ecosystems took 30 million years to recover.
Etymology and history
Prior to the introduction of the term "Permian", rocks of equivalent age in Germany had been named the Rotliegend and Zechstein, and in Great Britain as the New Red Sandstone.The term "Permian" was introduced into geology in 1841 by Sir Roderick Impey Murchison, president of the Geological Society of London, after extensive Russian explorations undertaken with Édouard de Verneuil in the vicinity of the Ural Mountains in the years 1840 and 1841. Murchison identified "vast series of beds of marl, schist, limestone, sandstone and conglomerate" that succeeded Carboniferous strata in the region. Murchison, in collaboration with Russian geologists, named the period after the surrounding Russian region of Perm, which takes its name from the medieval kingdom of Permia that occupied the same area hundreds of years prior, and which is now located in the Perm Krai administrative region. Between 1853 and 1867, Jules Marcou recognised Permian strata in a large area of North America from the Mississippi River to the Colorado River and proposed the name "Dyassic", from "Dyas" and "Trias", though Murchison rejected this in 1871. The Permian system was controversial for over a century after its original naming, with the United States Geological Survey until 1941 considering the Permian a subsystem of the Carboniferous equivalent to the Mississippian and Pennsylvanian.
Geology
The Permian Period is divided into three epochs, from oldest to youngest, the Cisuralian, Guadalupian, and Lopingian. Geologists divide the rocks of the Permian into a stratigraphic set of smaller units called stages, each formed during corresponding time intervals called ages. Stages can be defined globally or regionally. For global stratigraphic correlation, the International Commission on Stratigraphy (ICS) ratify global stages based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype) identifying the lower boundary of the stage. The ages of the Permian, from youngest to oldest, are:
For most of the 20th century, the Permian was divided into the Early and Late Permian, with the Kungurian being the last stage of the Early Permian. Glenister and colleagues in 1992 proposed a tripartite scheme, advocating that the Roadian-Capitanian was distinct from the rest of the Late Permian, and should be regarded as a separate epoch. The tripartite split was adopted after a formal proposal by Glenister et al. (1999).Historically, most marine biostratigraphy of the Permian was based on ammonoids; however, ammonoid localities are rare in Permian stratigraphic sections, and species characterise relatively long periods of time. All GSSPs for the Permian are based around the first appearance datum of specific species of conodont, an enigmatic group of jawless chordates with hard tooth-like oral elements. Conodonts are used as index fossils for most of the Palaeozoic and the Triassic.
Cisuralian
The Cisuralian Series is named after the strata exposed on the western slopes of the Ural Mountains in Russia and Kazakhstan. The name was proposed by J. B. Waterhouse in 1982 to comprise the Asselian, Sakmarian, and Artinskian stages. The Kungurian was later added to conform to the Russian "Lower Permian". Albert Auguste Cochon de Lapparent in 1900 had proposed the "Uralian Series", but the subsequent inconsistent usage of this term meant that it was later abandoned.The Asselian was named by the Russian stratigrapher V.E. Ruzhenchev in 1954, after the Assel River in the southern Ural Mountains. The GSSP for the base of the Asselian is located in the Aidaralash River valley near Aqtöbe, Kazakhstan, which was ratified in 1996. The beginning of the stage is defined by the first appearance of Streptognathodus postfusus.The Sakmarian is named in reference to the Sakmara River in the southern Urals, and was coined by Alexander Karpinsky in 1874. The GSSP for the base of the Sakmarian is located at the Usolka section in the southern Urals, which was ratified in 2018. The GSSP is defined by the first appearance of Sweetognathus binodosus.The Artinskian was named after the city of Arti in Sverdlovsk Oblast, Russia. It was named by Karpinsky in 1874. The Artinskian currently lacks a defined GSSP. The proposed definition for the base of the Artinskian is the first appearance of Sweetognathus aff. S. whitei.
The Kungurian takes its name after Kungur, a city in Perm Krai. The stage was introduced by Alexandr Antonovich Stukenberg in 1890. The Kungurian currently lacks a defined GSSP. Recent proposals have suggested the appearance of Neostreptognathodus pnevi as the lower boundary.
Guadalupian
The Guadalupian Series is named after the Guadalupe Mountains in Texas and New Mexico, where extensive marine sequences of this age are exposed. It was named by George Herbert Girty in 1902.The Roadian was named in 1968 in reference to the Road Canyon Member of the Word Formation in Texas. The GSSP for the base of the Roadian is located 42.7m above the base of the Cutoff Formation in Stratotype Canyon, Guadalupe Mountains, Texas, and was ratified in 2001. The beginning of the stage is defined by the first appearance of Jinogondolella nankingensis.The Wordian was named in reference to the Word Formation by Johan August Udden in 1916, Glenister and Furnish in 1961 was the first publication to use it as a chronostratigraphic term as a substage of the Guadalupian Stage. The GSSP for the base of the Wordian is located in Guadalupe Pass, Texas, within the sediments of the Getaway Limestone Member of the Cherry Canyon Formation, which was ratified in 2001. The base of the Wordian is defined by the first appearance of the conodont Jinogondolella aserrata.The Capitanian is named after the Capitan Reef in the Guadalupe Mountains of Texas, named by George Burr Richardson in 1904, and first used in a chronostratigraphic sense by Glenister and Furnish in 1961 as a substage of the Guadalupian Stage. The Capitanian was ratified as an international stage by the ICS in 2001. The GSSP for the base of the Capitanian is located at Nipple Hill in the southeast Guadalupe Mountains of Texas, and was ratified in 2001, the beginning of the stage is defined by the first appearance of Jinogondolella postserrata.
Lopingian
The Lopingian was first introduced by Amadeus William Grabau in 1923 as the "Loping Series" after Leping, Jiangxi, China. Originally used as a lithostraphic unit, T.K. Huang in 1932 raised the Lopingian to a series, including all Permian deposits in South China that overlie the Maokou Limestone. In 1995, a vote by the Subcommission on Permian Stratigraphy of the ICS adopted the Lopingian as an international standard chronostratigraphic unit.
The Wuchiapinginan and Changhsingian were first introduced in 1962, by J. Z. Sheng as the "Wuchiaping Formation" and "Changhsing Formation" within the Lopingian series. The GSSP for the base of the Wuchiapingian is located at Penglaitan, Guangxi, China and was ratified in 2004. The boundary is defined by the first appearance of Clarkina postbitteri postbitteri The Changhsingian was originally derived from the Changxing Limestone, a geological unit first named by the Grabau in 1923, ultimately deriving from Changxing County, Zhejiang .The GSSP for the base of the Changhsingian is located 88 cm above the base of the Changxing Limestone in the Meishan D section, Zhejiang, China and was ratified in 2005, the boundary is defined by the first appearance of Clarkina wangi.The GSSP for the base of the Triassic is located at the base of Bed 27c at the Meishan D section, and was ratified in 2001. The GSSP is defined by the first appearance of the conodont Hindeodus parvus.
Regional stages
The Russian Tatarian Stage includes the Lopingian, Capitanian and part of the Wordian, while the underlying Kazanian includes the rest of the Wordian as well at the Roadian. In North America, the Permian is divided into the Wolfcampian (which includes the Nealian and the Lenoxian stages); the Leonardian (Hessian and Cathedralian stages); the Guadalupian; and the Ochoan, corresponding to the Lopingian.
Paleogeography
During the Permian, all the Earth's major landmasses were collected into a single supercontinent known as Pangaea, with the microcontinental terranes of Cathaysia to the east. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean ("Panthalassa", the "universal sea"), and the Paleo-Tethys Ocean, a large ocean that existed between Asia and Gondwana. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys Ocean to shrink. A new ocean was growing on its southern end, the Neotethys Ocean, an ocean that would dominate much of the Mesozoic Era. The Central Pangean Mountains, which began forming due to the collision of Laurasia and Gondwana during the Carboniferous, reached their maximum height during the early Permian around 295 million years ago, comparable to the present Himalayas, but became heavily eroded as the Permian progressed. The Kazakhstania block collided with Baltica during the Cisuralian, while the North China Craton, the South China Block and Indochina fused to each other and Pangea by the end of the Permian. The Zechstein Sea, a hypersaline epicontinental sea, existed in what is now northwestern Europe.Large continental landmass interiors experience climates with extreme variations of heat and cold ("continental climate") and monsoon conditions with highly seasonal rainfall patterns. Deserts seem to have been widespread on Pangaea. Such dry conditions favored gymnosperms, plants with seeds enclosed in a protective cover, over plants such as ferns that disperse spores in a wetter environment. The first modern trees (conifers, ginkgos and cycads) appeared in the Permian.
Three general areas are especially noted for their extensive Permian deposits—the Ural Mountains (where Perm itself is located), China, and the southwest of North America, including the Texas red beds. The Permian Basin in the U.S. states of Texas and New Mexico is so named because it has one of the thickest deposits of Permian rocks in the world.
Paleoceanography
Sea levels dropped slightly during the earliest Permian (Asselian). The sea level was stable at several tens of metres above present during the Early Permian, but there was a sharp drop beginning during the Roadian, culminating in the lowest sea level of the entire Palaeozoic at around present sea level during the Wuchiapingian, followed by a slight rise during the Changhsingian.
Climate
The Permian was cool in comparison to most other geologic time periods, with modest pole to Equator temperature gradients. At the start of the Permian, the Earth was still in the Late Paleozoic icehouse (LPIA), which began in the latest Devonian and spanned the entire Carboniferous period, with its most intense phase occurring during the latter part of the Pennsylvanian epoch. A significant trend of increasing aridification can be observed over the course of the Cisuralian. Early Permian aridification was most notable in Pangaean localities at near-equatorial latitudes. At the Carboniferous-Permian boundary, a warming event occurred. In addition to becoming warmer, the climate became notably more arid at the end of the Carboniferous and beginning of the Permian. Nonetheless, temperatures continued to cool during most of the Asselian and Sakmarian, during which the LPIA peaked. By 287 million years ago, temperatures warmed and the South Pole ice cap retreated in what was known as the Artinskian Warming Event (AWE), though glaciers remained present in the uplands of eastern Australia, and perhaps also the mountainous regions of far northern Siberia. The AWE also witnessed aridification of a particularly great magnitude. In the late Kungurian, cooling resumed, resulting in a cool glacial interval that lasted into the early Capitanian, though average temperatures were still much higher than during the beginning of the Cisuralian. Another cool period began around the middle Capitanian. This was interrupted by the Emeishan Thermal Excursion in the late part of the Capitanian, around 260 million years ago, corresponding to the eruption of the Emeishan Traps. This interval of rapid climate change was responsible for the Capitanian mass extinction event. During the early Wuchiapingian, following the emplacement of the Emeishan Traps, global temperatures declined as carbon dioxide was weathered out of the atmosphere by the large igneous province's emplaced basalts. The late Wuchiapingian saw the finale of the Late Palaeozoic Ice Age, when the last Australian glaciers melted. The end of the Permian is marked by a temperature excursion, much larger than the Emeishan Thermal Excursion, at the Permian-Triassic boundary, corresponding to the eruption of the Siberian Traps, which released more than 5 teratonnes of CO2, more than doubling the atmospheric carbon dioxide concentration. This extremely rapid interval of greenhouse gas release caused the Permian-Triassic mass extinction, as well as ushering in an extreme hothouse that persisted for several million years into the next geologic epoch, the Triassic.The Permian climate was also extremely seasonal and characterised by megamonsoons, which produced high aridity and extreme seasonality in Pangaea's interiors. Precipitation along the western margins of the Palaeo-Tethys Ocean was very high. Evidence for the megamonsoon includes the presence of megamonsoonal rainforests in the Qiangtang Basin of Tibet, enormous seasonal variation in sedimentation, bioturbation, and ichnofossil deposition recorded in sedimentary facies in the Sydney Basin, and palaeoclimatic models of the Earth's climate based on the behaviour of modern weather patterns showing that such a megamonsoon would occur given the continental arrangement of the Permian. The aforementioned increasing equatorial aridity was likely driven by the development and intensification of this Pangaean megamonsoon.
Life
Marine biota
Permian marine deposits are rich in fossil mollusks, brachiopods, and echinoderms. Brachiopods were highly diverse during the Permian. The extinct order Productida was the predominant group of Permian brachiopods, accounting for up to about half of all Permian brachiopod genera. Amongst ammonoids, Goniatitida were a major group during the Early-Mid Permian, but declined during the Late Permian. Members of the order Prolecanitida were less diverse. The Ceratitida originated from the family Daraelitidae within Prolecanitida during the mid-Permian, and extensively diversified during the Late Permian. Only three families of trilobite are known from the Permian, Proetidae, Brachymetopidae and Phillipsiidae. Diversity, origination and extinction rates during the Early Permian were low. Trilobites underwent a diversification during the Kungurian-Wordian, the last in their evolutionary history, before declining during the Late Permian. By the Changhsingian, only a handful (4-6) genera remained.
Terrestrial biota
Terrestrial life in the Permian included diverse plants, fungi, arthropods, and various types of tetrapods. The period saw a massive desert covering the interior of Pangaea. The warm zone spread in the northern hemisphere, where extensive dry desert appeared. The rocks formed at that time were stained red by iron oxides, the result of intense heating by the sun of a surface devoid of vegetation cover. A number of older types of plants and animals died out or became marginal elements.
The Permian began with the Carboniferous flora still flourishing. About the middle of the Permian a major transition in vegetation began. The swamp-loving lycopod trees of the Carboniferous, such as Lepidodendron and Sigillaria, were progressively replaced in the continental interior by the more advanced seed ferns and early conifers as a result of the Carboniferous rainforest collapse. At the close of the Permian, lycopod and equisete swamps reminiscent of Carboniferous flora survived only on a series of equatorial islands in the Paleo-Tethys Ocean that later would become South China.The Permian saw the radiation of many important conifer groups, including the ancestors of many present-day families. Rich forests were present in many areas, with a diverse mix of plant groups. The southern continent saw extensive seed fern forests of the Glossopteris flora. Oxygen levels were probably high there. The ginkgos and cycads also appeared during this period.
Insects
Insects, which had first appeared and become abundant during the preceding Carboniferous, experienced a dramatic increase in diversification during the Early Permian. Towards the end of the Permian, there was a substantial drop in both origination and extinction rates. The dominant insects during the Permian Period were early representatives of Paleoptera, Polyneoptera, and Paraneoptera. Palaeodictyopteroidea, which had represented the dominant group of insects during the Carboniferous, declined during the Permian. This is likely due to competition by Hemiptera, due to their similar mouthparts and therefore ecology. Primitive relatives of damselflies and dragonflies (Meganisoptera), which include the largest flying insects of all time, also declined during the Permian. Holometabola, the largest group of modern insects, also diversified during this time. The earliest known beetles appear at the beginning of the Permian. Early beetles such as members of Permocupedidae likely xylophagous feeding on decaying wood. Several lineages, such as Schizophoridae expanded into aquatic habitats by the Late Permian. Members of the modern orders Archostemata and Adephaga are known from the Late Permian. Complex wood boring traces found in the Late Permian of China suggest that members of Polyphaga, the most diverse group of modern beetles, were also present in the Permian. Based on molecular evidence, Phasmatodea likely originated sometime in the Permian, in conjunction with the spread of insectivory among tetrapods.
Tetrapods
The terrestrial fossil record of the Permian is patchy and temporally discontinuous. Early Permian records are dominated by equatorial Europe and North America, while those of the Middle and Late Permian are dominated by temperate Karoo Supergroup sediments of South Africa and the Ural region of European Russia. Early Permian terrestrial faunas of North America and Europe were dominated by primitive pelycosaur synapsids including the herbivorous edaphosaurids, and carnivorous sphenacodontids, diadectids and amphibians. Early Permian reptiles, such as acleistorhinids, were mostly small insectivores.
Amniotes
Synapsids (the group that would later include mammals) thrived and diversified greatly during the Cisuralian. Permian synapsids included some large members such as Dimetrodon. The special adaptations of synapsids enabled them to flourish in the drier climate of the Permian and they grew to dominate the vertebrates. A faunal turnover occurred at the transition between the Cisuralian and Guadalupian, with the decline of amphibians and the replacement of pelycosaurs with more advanced therapsids. If terrestrial deposition ended around the end of the Cisuralian in North America and began in Russia during the early Guadalupian, a continuous record of the transition is not preserved. Uncertain dating has led to suggestions that there is a global hiatus in the terrestrial fossil record during the late Kungurian and early Roadian, referred to as "Olson's Gap" that obscures the nature of the transition. Other proposals have suggested that the North American and Russian records overlap, with the latest terrestrial North American deposition occurring during the Roadian, suggesting that there was an extinction event, dubbed "Olson's Extinction". The Middle Permian faunas of South Africa and Russia are dominated by therapsids, most abundantly by the diverse Dinocephalia. Dinocephalians become extinct at the end of the Middle Permian, during the Capitanian mass extinction event. Late Permian faunas are dominated by advanced therapsids such as the predatory sabertoothed gorgonopsians and herbivorous beaked dicynodonts, alongside large herbivorous pareiasaur parareptiles. The Archosauromorpha, the group of reptiles that would give rise to the pseudosuchians, dinosaurs, and pterosaurs in the following Triassic, first appeared and diversified during the Late Permian, including the first appearance of the Archosauriformes during the latest Permian. Cynodonts, the group of therapsids ancestral to modern mammals, first appeared and gained a worldwide distribution during the Late Permian. Another group of therapsids, the therocephalians (such as Lycosuchus), arose in the Middle Permian. There were no flying vertebrates, though the extinct lizard-like reptile family Weigeltisauridae from the Late Permian had extendable wings like modern gliding lizards, and are the oldest known gliding vertebrates.
Amphibians
Permian stem-amniotes consisted of temnospondyli, lepospondyli and batrachosaurs. Temnospondyls reached a peak of diversity in the Cisuralian, with a substantial decline during the Guadalupian-Lopingian following Olson's extinction, with the family diversity dropping below Carboniferous levels.Embolomeres, a group of aquatic crocodile-like reptilliomorphs that previously had its last records in the Cisuralian, are now known to have persisted into the Lopingian in China.Modern amphibians (lissamphibians) are suggested to have originated during Permian, descending from a lineage of dissorophoid temnospondyls.
Fish
The diversity of fish during the Permian is relatively low compared to the following Triassic. The dominant group of bony fishes during the Permian were the "Paleopterygii" a paraphyletic grouping of Actinopterygii that lie outside of Neopterygii. The earliest unequivocal members of Neopterygii appear during the Early Triassic, but a Permian origin is suspected. The diversity of coelacanths is relatively low throughout the Permian in comparison to other marine fishes, though there is an increase in diversity during the terminal Permian (Changhsingian), corresponding with the highest diversity in their evolutionary history during the Early Triassic. Diversity of freshwater fish faunas was generally low and dominated by lungfish and "Paleopterygians". The last common ancestor of all living lungfish is thought to have existed during the Early Permian. Though the fossil record is fragmentary, lungfish appear to have undergone an evolutionary diversification and size increase in freshwater habitats during the Early Permian, but subsequently declined during the middle and late Permian. Conodonts experienced their lowest diversity of their entire evolutionary history during the Permian. Permian chondrichthyan faunas are poorly known. Members of the chondrichthyan clade Holocephali, which contains living chimaeras, reached their apex of diversity during the Carboniferous-Permian, the most famous Permian representative being the "buzz-saw shark" Helicoprion, known for its unusual spiral shaped spiral tooth whorl in the lower jaw. Hybodonts, a group of shark-like chondrichtyans, were widespread and abundant members of marine and freshwater faunas throughout the Permian. Xenacanthiformes, another extinct group of shark-like chondrichtyans, were common in freshwater habitats, and represented the apex predators of freshwater ecosystems.
Flora
Four floristic provinces in the Permian are recognised, the Angaran, Euramerican, Gondwanan, and Cathaysian realms. The Carboniferous Rainforest Collapse would result in the replacement of lycopsid-dominated forests with tree-fern dominated ones during the late Carboniferous in Euramerica, and result in the differentiation of the Cathaysian floras from those of Euramerica. The Gondwanan floristic region was dominated by Glossopteridales, a group of woody gymnosperm plants, for most of the Permian, extending to high southern latitudes. The ecology of the most prominent glossopterid, Glossopteris, has been compared to that of bald cypress, living in mires with waterlogged soils. The tree-like calamites, distant relatives of modern horsetails, lived in coal swamps and grew in bamboo-like vertical thickets. A mostly complete specimen of Arthropitys from the Early Permian Chemnitz petrified forest of Germany demonstrates that they had complex branching patterns similar to modern angiosperm trees.
The oldest likely record of Ginkgoales (the group containing Ginkgo and its close relatives) is Trichopitys heteromorpha from the earliest Permian of France. The oldest known fossils definitively assignable to modern cycads are known from the Late Permian. In Cathaysia, where a wet tropical frost-free climate prevailed, the Noeggerathiales, an extinct group of tree fern-like progymnosperms were a common component of the flora The earliest Permian (~ 298 million years ago) Cathyasian Wuda Tuff flora, representing a coal swamp community, has an upper canopy consisting of lycopsid tree Sigillaria, with a lower canopy consisting of Marattialean tree ferns, and Noeggerathiales. Early conifers appeared in the Late Carboniferous, represented by primitive walchian conifers, but were replaced with more derived voltzialeans during the Permian. Permian conifers were very similar morphologically to their modern counterparts, and were adapted to stressed dry or seasonally dry climatic conditions. The increasing aridity, especially at low latitudes, facilitated the spread of conifers and their increasing prevalence throughout terrestrial ecosystems. Bennettitales, which would go on to become in widespread the Mesozoic, first appeared during the Cisuralian in China. Lyginopterids, which had declined in the late Pennsylvanian and subsequently have a patchy fossil record, survived into the Late Permian in Cathaysia and equatorial east Gondwana.
Permian–Triassic extinction event
The Permian ended with the most extensive extinction event recorded in paleontology: the Permian–Triassic extinction event. 90 to 95% of marine species became extinct, as well as 70% of all land organisms. It is also the only known mass extinction of insects. Recovery from the Permian–Triassic extinction event was protracted; on land, ecosystems took 30 million years to recover. Trilobites, which had thrived since Cambrian times, finally became extinct before the end of the Permian. Nautiloids, a subclass of cephalopods, surprisingly survived this occurrence.
There is evidence that magma, in the form of flood basalt, poured onto the Earth's surface in what is now called the Siberian Traps, for thousands of years, contributing to the environmental stress that led to mass extinction. The reduced coastal habitat and highly increased aridity probably also contributed. Based on the amount of lava estimated to have been produced during this period, the worst-case scenario is the release of enough carbon dioxide from the eruptions to raise world temperatures five degrees Celsius.Another hypothesis involves ocean venting of hydrogen sulfide gas. Portions of the deep ocean will periodically lose all of its dissolved oxygen allowing bacteria that live without oxygen to flourish and produce hydrogen sulfide gas. If enough hydrogen sulfide accumulates in an anoxic zone, the gas can rise into the atmosphere. Oxidizing gases in the atmosphere would destroy the toxic gas, but the hydrogen sulfide would soon consume all of the atmospheric gas available. Hydrogen sulfide levels might have increased dramatically over a few hundred years. Models of such an event indicate that the gas would destroy ozone in the upper atmosphere allowing ultraviolet radiation to kill off species that had survived the toxic gas. There are species that can metabolize hydrogen sulfide.
Another hypothesis builds on the flood basalt eruption theory. An increase in temperature of five degrees Celsius would not be enough to explain the death of 95% of life. But such warming could slowly raise ocean temperatures until frozen methane reservoirs below the ocean floor near coastlines melted, expelling enough methane (among the most potent greenhouse gases) into the atmosphere to raise world temperatures an additional five degrees Celsius. The frozen methane hypothesis helps explain the increase in carbon-12 levels found midway in the Permian–Triassic boundary layer. It also helps explain why the first phase of the layer's extinctions was land-based, the second was marine-based (and starting right after the increase in C-12 levels), and the third land-based again.
See also
List of fossil sites (with link directory)
Olson's Extinction
List of Permian tetrapods
References
Further reading
Ogg, Jim (June 2004). "Overview of Global Boundary Stratotype Sections and Points (GSSP's)". stratigraphy.org. Archived from the original on 2004-02-19. Retrieved April 30, 2006.
External links
University of California offers a more modern Permian stratigraphy
Classic Permian strata in the Glass Mountains of the Permian Basin
"International Commission on Stratigraphy (ICS)". Geologic Time Scale 2004. Retrieved September 19, 2005.
Examples of Permian Fossils
Permian (chronostratigraphy scale)
Schneebeli-Hermann, Elke (2012), "Extinguishing a Permian World", Geology, 40 (3): 287–288, Bibcode:2012Geo....40..287S, doi:10.1130/focus032012.1 |
ordovician | The Ordovician ( or-də-VISH-ee-ən, -doh-, -VISH-ən) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 million years ago (Ma) to the start of the Silurian Period 443.8 Mya.The Ordovician, named after the Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in North Wales in the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician received international approval in 1960 (forty years after Lapworth's death), when it was adopted as an official period of the Paleozoic Era by the International Geological Congress.
Life continued to flourish during the Ordovician as it did in the earlier Cambrian Period, although the end of the period was marked by the Ordovician–Silurian extinction events. Invertebrates, namely molluscs and arthropods, dominated the oceans, with members of the latter group probably starting their establishment on land during this time, becoming fully established by the Devonian. The first land plants are known from this period. The Great Ordovician Biodiversification Event considerably increased the diversity of life. Fish, the world's first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period. About 100 times as many meteorites struck the Earth per year during the Ordovician compared with today.
Subdivisions
A number of regional terms have been used to subdivide the Ordovician Period. In 2008, the ICS erected a formal international system of subdivisions. There exist Baltoscandic, British, Siberian, North American, Australian, Chinese, Mediterranean and North-Gondwanan regional stratigraphic schemes.
ICS (global) subdivisions
Upper Ordovician epoch (458.4 Ma – 443.8 Ma)
Hirnantian stage/age (445.2 Ma – 443.8 Ma)
Katian stage/age (453.0 Ma – 445.2 Ma)
Sandbian stage/age (458.4 Ma – 453.0 Ma)
Middle Ordovician epoch (470.0 Ma – 458.4 Ma)
Darriwilian stage/age (467.3 Ma – 458.4 Ma)
Dapingian stage/age (470.0 Ma – 467.3 Ma)
Lower Ordovician epoch (485.4 Ma – 470.0 Ma)
Floian stage/age (477.7 Ma – 470.0 Ma)
Tremadocian stage/age (485.4 Ma – 477.7 Ma)
British stages and ages
The Ordovician Period in Britain was traditionally broken into Early (Tremadocian and Arenig), Middle (Llanvirn (subdivided into Abereiddian and Llandeilian) and Llandeilo) and Late (Caradoc and Ashgill) epochs. The corresponding rocks of the Ordovician System are referred to as coming from the Lower, Middle, or Upper part of the column.
The Tremadoc corresponds to the (modern) Tremadocian. The Floian corresponds to the early Arenig; the Arenig continues until the early Darriwilian, subsuming the Dapingian. The Llanvirn occupies the rest of the Darriwilian, and terminates with it at the start of the Late Ordovician.
The Sandbian represents the first half of the Caradoc; the Caradoc ends in the mid-Katian, and the Ashgill represents the last half of the Katian, plus the Hirnantian.
The British ages (subdivisions of epochs) from youngest to oldest are:
"Late Ordovician"
Hirnantian/Gamach (Ashgill)
Rawtheyan/Richmond (Ashgill)
Cautleyan/Richmond (Ashgill)
Pusgillian/Maysville/Richmond (Ashgill)"Middle Ordovician"
Trenton (Caradoc)
Onnian/Maysville/Eden (Caradoc)
Actonian/Eden (Caradoc)
Marshbrookian/Sherman (Caradoc)
Longvillian/Sherman (Caradoc)
Soudleyan/Kirkfield (Caradoc)
Harnagian/Rockland (Caradoc)
Costonian/Black River (Caradoc)
Chazy (Llandeilo)
Llandeilo (Llandeilo)
Whiterock (Llanvirn)
Llanvirn (Llanvirn)"Early Ordovician"
Cassinian (Arenig)
Arenig/Jefferson/Castleman (Arenig)
Tremadoc/Deming/Gaconadian (Tremadoc)The Tremadoc corresponds to the (modern) Tremadocian. The Floian corresponds to the lower Arenig; the Arenig continues until the early Darriwilian, subsuming the Dapingian. The Llanvirn occupies the rest of the Darriwilian, and terminates with it at the base of the Late Ordovician.
The Sandbian represents the first half of the Caradoc; the Caradoc ends in the mid-Katian, and the Ashgill represents the last half of the Katian, plus the Hirnantian.
Paleogeography and tectonics
During the Ordovician, the southern continents were assembled into Gondwana, which reached from north of the equator to the South Pole. The Panthalassic Ocean, centered in the northern hemisphere, covered over half the globe. At the start of the period, the continents of Laurentia (in present-day North America), Siberia, and Baltica (present-day northern Europe) were separated from Gondwana by over 5,000 kilometres (3,100 mi) of ocean. These smaller continents were also sufficiently widely separated from each other to develop distinct communities of benthic organisms. The small continent of Avalonia had just rifted from Gondwana and began to move north towards Baltica and Laurentia, opening the Rheic Ocean between Gondwana and Avalonia. Avalonia collided with Baltica towards the end of Ordovician.Other geographic features of the Ordovician world included the Tornquist Sea, which separated Avalonia from Baltica; the Aegir Ocean, which separated Baltica from Siberia; and an oceanic area between Siberia, Baltica, and Gondwana which expanded to become the Paleoasian Ocean in Carboniferous time. The Mongol-Okhotsk Ocean formed a deep embayment between Siberia and the Central Mongolian terranes. Most of the terranes of central Asia were part of an equatorial archipelago whose geometry is poorly constrained by the available evidence.The period was one of extensive, widespread tectonism and volcanism. However, orogenesis (mountain-building) was not primarily due to continent-continent collisions. Instead, mountains arose along active continental margins during accretion of arc terranes or ribbon microcontinents. Accretion of new crust was limited to the Iapetus margin of Laurentia; elsewhere, the pattern was of rifting in back-arc basins followed by remerger. This reflected episodic switching from extension to compression. The initiation of new subduction reflected a global reorganization of tectonic plates centered on the amalgamation of Gondwana.The Taconic orogeny, a major mountain-building episode, was well under way in Cambrian times. This continued into the Ordovician, when at least two volcanic island arcs collided with Laurentia to form the Appalachian Mountains. Laurentia was otherwise tectonically stable. An island arc accreted to South China during the period, while subduction along north China (Sulinheer) resulted in the emplacement of ophiolites.The ash fall of the Millburg/Big Bentonite bed, at about 454 Ma, was the largest in the last 590 million years. This had a dense rock equivalent volume of as much as 1,140 cubic kilometres (270 cu mi). Remarkably, this appears to have had little impact on life.There was vigorous tectonic activity along northwest margin of Gondwana during the Floian, 478 Ma, recorded in the Central Iberian Zone of Spain. The activity reached as far as Turkey by the end of Ordovician. The opposite margin of Gondwana, in Australia, faced a set of island arcs. The accretion of these arcs to the eastern margin of Gondwana was responsible for the Benambran Orogeny of eastern Australia. Subduction also took place along what is now Argentina (Famatinian Orogeny) at 450 Ma. This involved significant back arc rifting. The interior of Gondwana was tectonically quiet until the Triassic.Towards the end of the period, Gondwana began to drift across the South Pole. This contributed to the Hibernian glaciation and the associated extinction event.
Ordovician meteor event
The Ordovician meteor event is a proposed shower of meteors that occurred during the Middle Ordovician Epoch, about 467.5 ± 0.28 million years ago, due to the break-up of the L chondrite parent body. It is not associated with any major extinction event.
Geochemistry
The Ordovician was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Carbonate hardgrounds were thus very common, along with calcitic ooids, calcitic cements, and invertebrate faunas with dominantly calcitic skeletons. Biogenic aragonite, like that composing the shells of most molluscs, dissolved rapidly on the sea floor after death.Unlike Cambrian times, when calcite production was dominated by microbial and non-biological processes, animals (and macroalgae) became a dominant source of calcareous material in Ordovician deposits.
Climate and sea level
The Early Ordovician climate was very hot, with intense greenhouse conditions and sea surface temperatures comparable to those during the Early Eocene Climatic Optimum. By the late Early Ordovician, the Earth cooled, giving way to a more temperate climate in the Middle Ordovician, with the Earth likely entering the Early Palaeozoic Ice Age during the Sandbian, and possibly as early as the Darriwilian or even the Floian. Evidence suggests that global temperatures rose briefly in the early Katian (Boda Event), depositing bioherms and radiating fauna across Europe. Further cooling during the Hirnantian, at the end of the Ordovician, led to the Late Ordovician glaciation.The Ordovician saw the highest sea levels of the Paleozoic, and the low relief of the continents led to many shelf deposits being formed under hundreds of metres of water. The sea level rose more or less continuously throughout the Early Ordovician, leveling off somewhat during the middle of the period. Locally, some regressions occurred, but the sea level rise continued in the beginning of the Late Ordovician. Sea levels fell steadily due to the cooling temperatures for about 3 million years leading up to the Hirnantian glaciation. During this icy stage, sea level seems to have risen and dropped somewhat. Despite much study, the details remain unresolved. In particular, some researches interpret the fluctuations in sea level as pre-Hibernian glaciation, but sedimentary evidence of glaciation is lacking until the end of the period. There is evidence of glaciers during the Hirnantian on the land we now know as Africa and South America, which were near the South Pole at the time, facilitating the formation of the ice caps of the Hirnantian glaciation.
As with North America and Europe, Gondwana was largely covered with shallow seas during the Ordovician. Shallow clear waters over continental shelves encouraged the growth of organisms that deposit calcium carbonates in their shells and hard parts. The Panthalassic Ocean covered much of the Northern Hemisphere, and other minor oceans included Proto-Tethys, Paleo-Tethys, Khanty Ocean, which was closed off by the Late Ordovician, Iapetus Ocean, and the new Rheic Ocean.
Life
For most of the Late Ordovician life continued to flourish, but at and near the end of the period there were mass-extinction events that seriously affected conodonts and planktonic forms like graptolites. The trilobites Agnostida and Ptychopariida completely died out, and the Asaphida were much reduced. Brachiopods, bryozoans and echinoderms were also heavily affected, and the endocerid cephalopods died out completely, except for possible rare Silurian forms. The Ordovician–Silurian extinction events may have been caused by an ice age that occurred at the end of the Ordovician Period, due to the expansion of the first terrestrial plants, as the end of the Late Ordovician was one of the coldest times in the last 600 million years of Earth's history.
Fauna
On the whole, the fauna that emerged in the Ordovician were the template for the remainder of the Palaeozoic. The fauna was dominated by tiered communities of suspension feeders, mainly with short food chains. The ecological system reached a new grade of complexity far beyond that of the Cambrian fauna, which has persisted until the present day. Though less famous than the Cambrian explosion, the Ordovician radiation (also known as the Great Ordovician Biodiversification Event) was no less remarkable; marine faunal genera increased fourfold, resulting in 12% of all known Phanerozoic marine fauna. Several animals also went through a miniaturization process, becoming much smaller than their Cambrian counterparts. Another change in the fauna was the strong increase in filter-feeding organisms. The trilobite, inarticulate brachiopod, archaeocyathid, and eocrinoid faunas of the Cambrian were succeeded by those that dominated the rest of the Paleozoic, such as articulate brachiopods, cephalopods, and crinoids. Articulate brachiopods, in particular, largely replaced trilobites in shelf communities. Their success epitomizes the greatly increased diversity of carbonate shell-secreting organisms in the Ordovician compared to the Cambrian.Ordovician geography had its effect on the diversity of fauna; Ordovician invertebrates displayed a very high degree of provincialism. The widely separated continents of Laurentia and Baltica, then positioned close to the tropics and boasting many shallow seas rich in life, developed distinct trilobite faunas from the trilobite fauna of Gondwana, and Gondwana developed distinct fauna in its tropical and temperature zones. The Tien Shan terrane maintained a biogeographic affinity with Gondwana, and the Alborz margin of Gondwana was linked biogeographically to South China. Southeast Asia's fauna also maintained strong affinities to Gondwana's. North China was biogeographically connected to Laurentia and the Argentinian margin of Gondwana. A Celtic biogeographic province also existed, separate from the Laurentian and Baltican ones. However, tropical articulate brachiopods had a more cosmopolitan distribution, with less diversity on different continents. During the Middle Ordovician, beta diversity began a significant decline as marine taxa began to disperse widely across space. Faunas become less provincial later in the Ordovician, partly due to the narrowing of the Iapetus Ocean, though they were still distinguishable into the late Ordovician.
Trilobites in particular were rich and diverse. Trilobites in the Ordovician were very different from their predecessors in the Cambrian. Many trilobites developed bizarre spines and nodules to defend against predators such as primitive eurypterids and nautiloids while other trilobites such as Aeglina prisca evolved to become swimming forms. Some trilobites even developed shovel-like snouts for ploughing through muddy sea bottoms. Another unusual clade of trilobites known as the trinucleids developed a broad pitted margin around their head shields. Some trilobites such as Asaphus kowalewski evolved long eyestalks to assist in detecting predators whereas other trilobite eyes in contrast disappeared completely. Molecular clock analyses suggest that early arachnids started living on land by the end of the Ordovician. Although solitary corals date back to at least the Cambrian, reef-forming corals appeared in the early Ordovician, including the earliest known octocorals, corresponding to an increase in the stability of carbonate and thus a new abundance of calcifying animals. Brachiopods surged in diversity, adapting to almost every type of marine environment. Even after GOBE, there is evidence suggesting that Ordovician brachiopods maintained elevated rates of speciation. Molluscs, which appeared during the Cambrian or even the Ediacaran, became common and varied, especially bivalves, gastropods, and nautiloid cephalopods. Cephalopods diversified from shallow marine tropical environments to dominate almost all marine environments. Graptolites, which evolved in the preceding Cambrian period, thrived in the oceans. This includes the distinctive Nemagraptus gracilis graptolite fauna, which was distributed widely during peak sea levels in the Sandbian. Some new cystoids and crinoids appeared. It was long thought that the first true vertebrates (fish — Ostracoderms) appeared in the Ordovician, but recent discoveries in China reveal that they probably originated in the Early Cambrian. The first gnathostome (jawed fish) may have appeared in the Late Ordovician epoch. Chitinozoans, which first appeared late in the Wuliuan, exploded in diversity during the Tremadocian, quickly becoming globally widespread. Several groups of endobiotic symbionts appeared in the Ordovician.In the Early Ordovician, trilobites were joined by many new types of organisms, including tabulate corals, strophomenid, rhynchonellid, and many new orthid brachiopods, bryozoans, planktonic graptolites and conodonts, and many types of molluscs and echinoderms, including the ophiuroids ("brittle stars") and the first sea stars. Nevertheless, the arthropods remained abundant; all the Late Cambrian orders continued, and were joined by the new group Phacopida. The first evidence of land plants also appeared (see evolutionary history of life).
In the Middle Ordovician, the trilobite-dominated Early Ordovician communities were replaced by generally more mixed ecosystems, in which brachiopods, bryozoans, molluscs, cornulitids, tentaculitids and echinoderms all flourished, tabulate corals diversified and the first rugose corals appeared. The planktonic graptolites remained diverse, with the Diplograptina making their appearance. One of the earliest known armoured agnathan ("ostracoderm") vertebrates, Arandaspis, dates from the Middle Ordovician. During the Middle Ordovician there was a large increase in the intensity and diversity of bioeroding organisms. This is known as the Ordovician Bioerosion Revolution. It is marked by a sudden abundance of hard substrate trace fossils such as Trypanites, Palaeosabella, Petroxestes and Osprioneides. Bioerosion became an important process, particularly in the thick calcitic skeletons of corals, bryozoans and brachiopods, and on the extensive carbonate hardgrounds that appear in abundance at this time.
Flora
Green algae were common in the Late Cambrian (perhaps earlier) and in the Ordovician. Terrestrial plants probably evolved from green algae, first appearing as tiny non-vascular forms resembling liverworts, in the middle to late Ordovician. Fossil spores found in Ordovician sedimentary rock are typical of bryophytes.
Among the first land fungi may have been arbuscular mycorrhiza fungi (Glomerales), playing a crucial role in facilitating the colonization of land by plants through mycorrhizal symbiosis, which makes mineral nutrients available to plant cells; such fossilized fungal hyphae and spores from the Ordovician of Wisconsin have been found with an age of about 460 million years ago, a time when the land flora most likely only consisted of plants similar to non-vascular bryophytes.
End of the period
The Ordovician came to a close in a series of extinction events that, taken together, comprise the second largest of the five major extinction events in Earth's history in terms of percentage of genera that became extinct. The only larger one was the Permian–Triassic extinction event.
The extinctions occurred approximately 447–444 million years ago and mark the boundary between the Ordovician and the following Silurian Period. At that time all complex multicellular organisms lived in the sea, and about 49% of genera of fauna disappeared forever; brachiopods and bryozoans were greatly reduced, along with many trilobite, conodont and graptolite families.
The most commonly accepted theory is that these events were triggered by the onset of cold conditions in the late Katian, followed by an ice age, in the Hirnantian faunal stage, that ended the long, stable greenhouse conditions typical of the Ordovician.
The ice age was possibly not long-lasting. Oxygen isotopes in fossil brachiopods show its duration may have been only 0.5 to 1.5 million years. Other researchers (Page et al.) estimate more temperate conditions did not return until the late Silurian.
The late Ordovician glaciation event was preceded by a fall in atmospheric carbon dioxide (from 7000 ppm to 4400 ppm). The dip may have been caused by a burst of volcanic activity that deposited new silicate rocks, which draw CO2 out of the air as they erode. Another possibility is that bryophytes and lichens, which colonized land in the middle to late Ordovician, may have increased weathering enough to draw down CO2 levels. The drop in CO2 selectively affected the shallow seas where most organisms lived. As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it, which have been detected in Upper Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time.
As glaciers grew, the sea level dropped, and the vast shallow intra-continental Ordovician seas withdrew, which eliminated many ecological niches. When they returned, they carried diminished founder populations that lacked many whole families of organisms. They then withdrew again with the next pulse of glaciation, eliminating biological diversity with each change. Species limited to a single epicontinental sea on a given landmass were severely affected. Tropical lifeforms were hit particularly hard in the first wave of extinction, while cool-water species were hit worst in the second pulse.Those species able to adapt to the changing conditions survived to fill the ecological niches left by the extinctions. For example, there is evidence the oceans became more deeply oxygenated during the glaciation, allowing unusual benthic organisms (Hirnantian fauna) to colonize the depths. These organisms were cosmopolitan in distribution and present at most latitudes.At the end of the second event, melting glaciers caused the sea level to rise and stabilise once more. The rebound of life's diversity with the permanent re-flooding of continental shelves at the onset of the Silurian saw increased biodiversity within the surviving Orders. Recovery was characterized by an unusual number of "Lazarus taxa", disappearing during the extinction and reappearing well into the Silurian, which suggests that the taxa survived in small numbers in refugia.An alternate extinction hypothesis suggested that a ten-second gamma-ray burst could have destroyed the ozone layer and exposed terrestrial and marine surface-dwelling life to deadly ultraviolet radiation and initiated global cooling.Recent work considering the sequence stratigraphy of the Late Ordovician argues that the mass extinction was a single protracted episode lasting several hundred thousand years, with abrupt changes in water depth and sedimentation rate producing two pulses of last occurrences of species.
References
External links
Ogg, Jim (June 2004). "Overview of Global Boundary Stratotype Sections and Points (GSSP's)". Archived from the original on 2006-04-23. Retrieved 2006-04-30.
Mehrtens, Charlotte. "Chazy Reef at Isle La Motte". An Ordovician reef in Vermont.
Ordovician fossils of the famous Cincinnatian Group
Ordovician (chronostratigraphy scale) |
orosirian | The Orosirian Period ( ; Ancient Greek: ὀροσειρά, romanized: oroseirá, meaning "mountain range") is the third geologic period in the Paleoproterozoic Era and lasted from 2050 Mya to 1800 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
The later half of the period was an episode of intensive orogeny on virtually all continents.
Two of the largest known impact events on Earth occurred during the Orosirian. Early in the period, 2023 Mya, a large asteroid collision created the Vredefort impact structure. The event that created the Sudbury Basin structure occurred near the end of the period, 1850 Mya.
For the time period from about 2060 to 1780 Mya, an alternative period based on stratigraphy rather than chronometry, named the Columbian, was suggested in the geological timescale review 2012 edited by Gradstein et al., but as of February 2022, this has not yet been officially adopted by the IUGS.
Paleogeography
The supercontinent Columbia formed at the end of this period.
References
"Orosirian Period". GeoWhen Database. Retrieved July 8, 2011.
James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492. |
cryogenian | The Cryogenian (from Ancient Greek: κρύος, romanized: krýos, meaning "cold" and γένεσις, romanized: génesis, meaning "birth") is a geologic period that lasted from 720 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
The Cryogenian was a time of drastic biosphere changes. After the previous Boring Billion years of stability, at the beginning of Cryogenian the severe Sturtian glaciation began, freezing the entire Earth in a planetary state known as a Snowball Earth. After 70 million years it ended, but was quickly followed by the Marinoan glaciation, which was also a global event. These events are the subject of much scientific controversy specifically over whether these glaciations covered the entire planet or a band of open sea survived near the equator (termed "slushball Earth").
Ratification
The Cryogenian Period was ratified in 1990 by the International Commission on Stratigraphy. In contrast to most other time periods, the beginning of the Cryogenian is not linked to a globally observable and documented event. Instead, the base of the period is defined by a fixed rock age, that was originally set at 850 million years, but changed in 2015 to 720 million years.This could cause ambiguity because estimates of rock ages are variable and are subject to laboratory error. For instance, the time scale of the Cambrian Period is not reckoned by rock younger than a given age (538.8 million years), but by the appearance of the worldwide Treptichnus pedum diagnostic trace fossil assemblages. This means that rocks can be recognized as Cambrian in the field, without extensive lab testing.
Currently, there is no consensus on what global event is a suitable candidate to mark the start of the Cryogenian Period, but a global glaciation would be a likely candidate.
Climate
The name of the geologic period refers to the very cold global climate of the Cryogenian.
Characteristic glacial deposits indicate that Earth suffered the most severe ice ages in its history during this period (Sturtian and Marinoan). According to Eyles and Young, "Late Proterozoic glaciogenic deposits are known from all the continents. They provide evidence of the most widespread and long-ranging glaciation on Earth." Several glacial periods are evident, interspersed with periods of relatively warm climate, with glaciers reaching sea level in low paleolatitudes.Glaciers extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator.
The Cryogenian is generally considered to be divisible into at least two major worldwide glaciations. The Sturtian glaciation persisted from 720 to 660 million years ago, and the Marinoan glaciation which ended approximately 635 Ma, at the end of the Cryogenian. The deposits of glacial tillite also occur in places that were at low latitudes during the Cryogenian, a phenomenon which led to the hypothesis of deeply frozen planetary oceans called "Snowball Earth". Between the Sturtian and Marinoan glaciations was a so-called "Cryogenian interglacial period" marked by relatively warm climate and anoxic oceans, along with marine transgression.
Paleogeography
Before the start of the Cryogenian, around 750 Ma, the cratons that made up the supercontinent Rodinia started to rift apart. The superocean Mirovia began to close while the superocean Panthalassa began to form. The cratons (possibly) later assembled into another supercontinent called Pannotia, in the Ediacaran.
Eyles and Young state, "Most Neoproterozoic glacial deposits accumulated as glacially influenced marine strata along rifted continental margins or interiors." Worldwide deposition of dolomite might have reduced atmospheric carbon dioxide. The break up along the margins of Laurentia at about 750 Ma occurs at about the same time as the deposition of the Rapitan Group in North America, contemporaneously with the Sturtian in Australia. A similar period of rifting at about 650 Ma occurred with the deposition of the Ice Brook Formation in North America, contemporaneously with the Marinoan in Australia. The Sturtian and Marinoan are local divisions within the Adelaide Rift Complex.
Cryogenian biota and fossils
Between the Sturtian and Marinoan glaciations, global biodiversity was very low.Fossils of testate amoeba (or Arcellinida) first appear during the Cryogenian Period. Since 2009, some researchers have argued that during the Cryogenian Period, potentially the oldest known fossils of sponges, and therefore animals, were formed. However, it is unclear whether these fossils actually belong to sponges, though the authors do not rule out the possibility of such fossils to represent proto-sponges or complex microbial precursors to sponge-grade organisms.
The issue of whether or not biology was impacted by this event has not been settled, for example Porter (2000) suggests that new groups of life evolved during this period, including the red algae and green algae, stramenopiles, ciliates, dinoflagellates, and testate amoeba.The end of the period also saw the origin of heterotrophic plankton, which would feed on unicellular algae and prokaryotes, ending the bacterial dominance of the oceans.
See also
Timeline of glaciation – Chronology of the major ice ages of the Earth
References
Further reading
"Cryogenian Period". GeoWhen Database. Archived from the original on December 2, 2005. Retrieved January 5, 2006.
James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492.
Brain, C. K.; Prave, A. R.; Hoffmann, K. H.; Fallick, A. E.; Herd, D. A.; Sturrock, C.; Young, I.; Condon, D. J.; Allison, S. G. (2012). "The first animals: ca. 760-million-year-old sponge-like fossils from Namibia" (PDF). South African Journal of Science. 108: 1–8. doi:10.4102/sajs.v108i1/2.658.
Hoffman, Paul F.; Abbot, Dorian S.; et al. (November 8, 2017). "Snowball Earth climate dynamics and Cryogenian geology-geobiology". Science Advances. American Association for the Advancement of Science. 3 (11): e1600983. Bibcode:2017SciA....3E0983H. doi:10.1126/sciadv.1600983. PMC 5677351. PMID 29134193. S2CID 1465316.
External links
The Time Travellers Guide to Australia (2012) at IMDb
Miracle Planet : Snowball Earth on YouTube (2010s) BBC/CBC/NHK |
triassic | The Triassic ( try-ASS-ik; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. The Triassic Period is subdivided into three epochs: Early Triassic, Middle Triassic and Late Triassic.
The Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Three categories of organisms can be distinguished in the Triassic record: survivors from the extinction event, new groups that flourished briefly, and other new groups that went on to dominate the Mesozoic Era. Reptiles, especially archosaurs, were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period. Archosaurs that became dominant in this period were primarily pseudosuchians, ancestors of modern crocodilians, while some archosaurs specialized in flight, the first time among vertebrates, becoming the pterosaurs.
Therapsids, the dominant vertebrates of the preceding Permian period, declined throughout the period. The first true mammals, themselves a specialized subgroup of therapsids, also evolved during this period. The vast supercontinent of Pangaea dominated the globe during the Triassic, but in the following Jurassic period it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south.
The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups, including most pseudosuchians, and allowed dinosaurs to assume dominance in the Jurassic.
Etymology
The Triassic was named in 1834 by Friedrich August von Alberti, after a succession of three distinct rock layers (Greek triás meaning 'triad') that are widespread in southern Germany: the lower Buntsandstein (colourful sandstone), the middle Muschelkalk (shell-bearing limestone) and the upper Keuper (coloured clay).
Dating and subdivisions
On the geologic time scale, the Triassic is usually divided into Early, Middle, and Late Triassic Epochs, and the corresponding rocks are referred to as Lower, Middle, or Upper Triassic. The faunal stages from the youngest to oldest are:
Paleogeography
During the Triassic, almost all the Earth's land mass was concentrated into a single supercontinent, Pangaea (lit. 'entire land'). This supercontinent was more-or-less centered on the equator and extended between the poles, though it did drift northwards as the period progressed. Southern Pangea, also known as Gondwana, was made up by closely-appressed cratons corresponding to modern South America, Africa, Madagascar, India, Antarctica, and Australia. North Pangea, also known as Laurussia or Laurasia, corresponds to modern-day North America and the fragmented predecessors of Eurasia.
The western edge of Pangea lay at the margin of an enormous ocean, Panthalassa (lit. 'entire sea'), which roughly corresponds to the modern Pacific Ocean. Practically all deep-ocean crust present during the Triassic has been recycled through the subduction of oceanic plates, so very little is known about the open ocean from this time period. Most information on Panthalassan geology and marine life is derived from island arcs and rare seafloor sediments accreted onto surrounding land masses, such as present-day Japan and western North America.
The eastern edge of Pangea was encroached upon by a pair of extensive oceanic basins: The Neo-Tethys (or simply Tethys) and Paleo-Tethys Oceans. These extended from China to Iberia, hosting abundant marine life along their shallow tropical peripheries. They were divided from each other by a long string of microcontinents known as the Cimmerian terranes. Cimmerian crust had detached from Gondwana in the early Permian and drifted northwards during the Triassic, enlarging the Neo-Tethys Ocean which formed in their wake. At the same time, they forced the Paleo-Tethys Ocean to shrink as it was being subducted under Asia. By the end of the Triassic, the Paleo-Tethys Ocean occupied a small area and the Cimmerian terranes began to collide with southern Asia. This collision, known as the Cimmerian Orogeny, continued into the Jurassic and Cretaceous to produce a chain of mountain ranges stretching from Turkey to Malaysia.Pangaea was fractured by widespread faulting and rift basins during the Triassic—especially late in that period—but had not yet separated. The first nonmarine sediments in the rift that marks the initial break-up of Pangaea, which separated eastern North America from Morocco, are of Late Triassic age; in the United States, these thick sediments comprise the Newark Supergroup. Rift basins are also common in South America, Europe, and Africa. Terrestrial environments are particularly well-represented in the South Africa, Russia, central Europe, and the southwest United States. Terrestrial Triassic biostratigraphy is mostly based on terrestrial and freshwater tetrapods, as well as conchostracans ("clam shrimps"), a type of fast-breeding crustacean which lived in lakes and hypersaline environments.
Because a supercontinent has less shoreline compared to a series of smaller continents, Triassic marine deposits are relatively uncommon on a global scale. A major exception is in Western Europe, where the Triassic was first studied. The northeastern margin of Gondwana was a stable passive margin along the Neo-Tethys Ocean, and marine sediments have been preserved in parts of northern India and Arabia. In North America, marine deposits are limited to a few exposures in the west.
Scandinavia
During the Triassic peneplains are thought to have formed in what is now Norway and southern Sweden. Remnants of this peneplain can be traced as a tilted summit accordance in the Swedish West Coast. In northern Norway Triassic peneplains may have been buried in sediments to be then re-exposed as coastal plains called strandflats. Dating of illite clay from a strandflat of Bømlo, southern Norway, have shown that landscape there became weathered in Late Triassic times (c. 210 million years ago) with the landscape likely also being shaped during that time.
Paleooceanography
Eustatic sea level in the Triassic was consistently low compared to the other geological periods. The beginning of the Triassic was around present sea level, rising to about 10–20 metres (33–66 ft) above present-day sea level during the Early and Middle Triassic. Sea level rise accelerated in the Ladinian, culminating with a sea level up to 50 metres (164 ft) above present-day levels during the Carnian. Sea level began to decline in the Norian, reaching a low of 50 metres (164 ft) below present sea level during the mid-Rhaetian. Low global sea levels persisted into the earliest Jurassic. The long-term sea level trend is superimposed by 22 sea level drop events widespread in the geologic record, mostly of minor (less than 25-metre (82 ft)) and medium (25–75-metre (82–246 ft)) magnitudes. A lack of evidence for Triassic continental ice sheets suggest that glacial eustasy is unlikely to be the cause of these changes.
Climate
The Triassic continental interior climate was generally hot and dry, so that typical deposits are red bed sandstones and evaporites. There is no evidence of glaciation at or near either pole; in fact, the polar regions were apparently moist and temperate, providing a climate suitable for forests and vertebrates, including reptiles. Pangaea's large size limited the moderating effect of the global ocean; its continental climate was highly seasonal, with very hot summers and cold winters. The strong contrast between the Pangea supercontinent and the global ocean triggered intense cross-equatorial monsoons, sometimes referred to as the Pangean megamonsoons.The Triassic may have mostly been a dry period, but evidence exists that it was punctuated by several episodes of increased rainfall in tropical and subtropical latitudes of the Tethys Sea and its surrounding land. Sediments and fossils suggestive of a more humid climate are known from the Anisian to Ladinian of the Tethysian domain, and from the Carnian and Rhaetian of a larger area that includes also the Boreal domain (e.g., Svalbard Islands), the North American continent, the South China block and Argentina. The best-studied of such episodes of humid climate, and probably the most intense and widespread, was the Carnian Pluvial Event.
Early Triassic
The Early Triassic was the hottest portion of the entire Phanerozoic, seeing as it occurred during and immediately after the discharge of titanic volumes of greenhouse gases from the Siberian Traps. The Early Triassic began with the Permian-Triassic Thermal Maximum (PTTM) and was followed by the brief Dienerian Cooling (DC) from 251 to 249 Ma, which was in turn followed by the Latest Smithian Thermal Maximum (LSTT) around 249 to 248 Ma. During the Latest Olenekian Cooling (LOC), from 248 to 247 Ma, temperatures cooled by about 6 °C.
Middle Triassic
The Middle Triassic was cooler than the Early Triassic, with temperatures falling over most of the Anisian, with the exception of a warming spike in the latter portion of the stage. From 242 to 233 Ma, the Ladinian-Carnian Cooling (LCC) ensued.
Late Triassic
At the beginning of the Carnian, global temperatures continued to be relatively cool. The eruption of the Wrangellia Large Igneous Province around 234 Ma caused abrupt global warming, terminating the cooling trend of the LCC. This warming was responsible for the Carnian Pluvial Event and resulted in an episode of widespread global humidity. The CPE ushered in the Mid-Carnian Warm Interval (MCWI), which lasted from 234 to 227 Ma. From 227 to 217 Ma, there was a relatively cool period known as the Early Norian Cool Interval (ENCI), after which occurred the Mid-Norian Warm Interval (MNWI) from 217 to 209 Ma. The MNWI was briefly interrupted around 214 Ma by a cooling possibly related to the Manicouagan impact. The Rhaetian Cool Interval (RCI) lasted from 209 to 201 Ma. At the terminus of the Triassic, there was an extreme warming event referred to as the End-Triassic Thermal Event (ETTE), which was responsible for the Triassic-Jurassic mass extinction. Bubbles of carbon dioxide in basaltic rocks dating back to the end of the Triassic indicate that volcanic activity from the Central Atlantic Magmatic Province helped trigger climate change in the ETTE.
Flora
Land plants
On land, the surviving vascular plants included the lycophytes, the dominant cycadophytes, ginkgophyta (represented in modern times by Ginkgo biloba), ferns, horsetails and glossopterids. The spermatophytes, or seed plants, came to dominate the terrestrial flora: in the northern hemisphere, conifers, ferns and bennettitales flourished. The seed fern genus Dicroidium would dominate Gondwana throughout the period.
Coal
No known coal deposits date from the start of the Triassic Period. This is known as the Early Triassic "coal gap" and can be seen as part of the Permian–Triassic extinction event. Possible explanations for the coal gap include sharp drops in sea level at the time of the Permo-Triassic boundary; acid rain from the Siberian Traps eruptions or from an impact event that overwhelmed acidic swamps; climate shift to a greenhouse climate that was too hot and dry for peat accumulation; evolution of fungi or herbivores that were more destructive of wetlands; the extinction of all plants adapted to peat swamps, with a hiatus of several million years before new plant species evolved that were adapted to peat swamps; or soil anoxia as oxygen levels plummeted.
Phytoplankton
Before the Permian extinction, Archaeplastida (red and green algae) had been the major marine phytoplanktons since about 659–645 million years ago, when they replaced marine planktonic cyanobacteria, which first appeared about 800 million years ago, as the dominant phytoplankton in the oceans. In the Triassic, secondary endosymbiotic algae became the most important plankton.
Fauna
Marine invertebrates
In marine environments, new modern types of corals appeared in the Early Triassic, forming small patches of reefs of modest extent compared to the great reef systems of Devonian or modern times. At the end of the Carnian, a reef crisis occurred in South China. Serpulids appeared in the Middle Triassic. Microconchids were abundant. The shelled cephalopods called ammonites recovered, diversifying from a single line that survived the Permian extinction. Bivalves began to rapidly diversify during the Middle Triassic, becoming highly abundant in the oceans.
Fish
The fish fauna was remarkably uniform, with many families and genera exhibiting a global distribution in the wake of the Permian-Triassic mass extinction event. Ray-finned fishes (actinopterygians) went through a remarkable diversification during the Triassic, leading to peak diversity during the Middle Triassic; however, the pattern of this diversification is still not well understood due to a taphonomic megabias. Large predatory actinopterygians such as saurichthyids and birgeriids appeared in the Early Triassic and became widespread and successful during the period as a whole. Lakes and rivers were populated by lungfish (Dipnoi), such as Ceratodus, which are mainly known from the dental plates, abundant in the fossils record. Hybodonts, a group of shark-like cartilaginous fish, were dominant in both freshwater and marine environments throughout the Triassic.
Amphibians
Temnospondyl amphibians were among those groups that survived the Permian–Triassic extinction. Once abundant in both terrestrial and aquatic environments, the terrestrial species had mostly died out during the extinction event. The Triassic survivors were aquatic or semi-aquatic, and were represented by Tupilakosaurus, Thabanchuia, Branchiosauridae and Micropholis, all of which died out in Early Triassic, and the successful Stereospondyli, with survivors into the Cretaceous Period. The largest Triassic stereospondyls, such as Mastodonsaurus, were up to 4 to 6 metres (13 to 20 ft) in length. Some lineages (e.g. trematosaurs) flourished briefly in the Early Triassic, while others (e.g. capitosaurs) remained successful throughout the whole period, or only came to prominence in the Late Triassic (e.g. Plagiosaurus, metoposaurs).
The first Lissamphibians (modern amphibians) appear in the Triassic, with the progenitors of the first frogs already present by the Early Triassic. However, the group as a whole did not become common until the Jurassic, when the temnospondyls had become very rare.
Most of the Reptiliomorpha, stem-amniotes that gave rise to the amniotes, disappeared in the Triassic, but two water-dwelling groups survived: Embolomeri that only survived into the early part of the period, and the Chroniosuchia, which survived until the end of the Triassic.
Reptiles
Archosauromorphs
The Permian–Triassic extinction devastated terrestrial life. Biodiversity rebounded as the surviving species repopulated empty terrain, but these were short-lived. Diverse communities with complex food-web structures took 30 million years to reestablish. Archosauromorph reptiles, which had already appeared and diversified to an extent in the Permian Period, exploded in diversity as an adaptive radiation in response to the Permian-Triassic mass extinction. By the Early Triassic, several major archosauromorph groups had appeared. Long-necked, lizard-like early archosauromorphs were known as protorosaurs, which is likely a paraphyletic group rather than a true clade. Tanystropheids were a family of protorosaurs which elevated their neck size to extremes, with the largest genus Tanystropheus having a neck longer than its body. The protorosaur family Sharovipterygidae used their elongated hindlimbs for gliding. Other archosauromorphs, such as rhynchosaurs and allokotosaurs, were mostly stocky-bodied herbivores with specialized jaw structures.
Rhynchosaurs, barrel-gutted herbivores, thrived for only a short period of time, becoming extinct about 220 million years ago. They were exceptionally abundant in the middle of the Triassic, as the primary large herbivores in many Carnian-age ecosystems. They sheared plants with premaxillary beaks and plates along the upper jaw with multiple rows of teeth. Allokotosaurs were iguana-like reptiles, including Trilophosaurus (a common Late Triassic reptile with three-crowned teeth), Teraterpeton (which had a long beak-like snout), and Shringasaurus (a horned herbivore which reached a body length of 3–4 metres (9.8–13.1 ft).
One group of archosauromorphs, the archosauriforms, were distinguished by their active predatory lifestyle, with serrated teeth and upright limb postures. Archosauriforms were diverse in the Triassic, including various terrestrial and semiaquatic predators of all shapes and sizes. The large-headed and robust erythrosuchids were among the dominant carnivores in the early Triassic. Phytosaurs were a particularly common group which prospered during the Late Triassic. These long-snouted and semiaquatic predators resemble living crocodiles and probably had a similar lifestyle, hunting for fish and small reptiles around the water's edge. However, this resemblance is only superficial and is a prime-case of convergent evolution.
True archosaurs appeared in the early Triassic, splitting into two branches: Avemetatarsalia (the ancestors to birds) and Pseudosuchia (the ancestors to crocodilians). Avemetatarsalians were a minor component of their ecosystems, but eventually produced the earliest pterosaurs and dinosaurs in the Late Triassic. Early long-tailed pterosaurs appeared in the Norian and quickly spread worldwide. Triassic dinosaurs evolved in the Carnian and include early sauropodomorphs and theropods. Most Triassic dinosaurs were small predators and only a few were common, such as Coelophysis, which was 1 to 2 metres (3.3 to 6.6 ft) long. Triassic sauropodomorphs primarily inhabited cooler regions of the world.The large predator Smok was most likely also an archosaur, but it is uncertain if it was a primitive dinosaur or a pseudosuchian.
Pseudosuchians were far more ecologically dominant in the Triassic, including large herbivores (such as aetosaurs), large carnivores ("rauisuchians"), and the first crocodylomorphs ("sphenosuchians"). Aetosaurs were heavily-armored reptiles that were common during the last 30 million years of the Late Triassic until they died out at the Triassic-Jurassic extinction. Most aetosaurs were herbivorous and fed on low-growing plants, but some may have eaten meat. "rauisuchians" (formally known as paracrocodylomorphs) were the keystone predators of most Triassic terrestrial ecosystems. Over 25 species have been found, including giant quadrupedal hunters, sleek bipedal omnivores, and lumbering beasts with deep sails on their backs. They probably occupied the large-predator niche later filled by theropods. "Rauisuchians" were ancestral to small, lightly-built crocodylomorphs, the only pseudosuchians which survived into the Jurassic.
Marine reptiles
There were many types of marine reptiles. These included the Sauropterygia, which featured pachypleurosaurus and nothosaurs (both common during the Middle Triassic, especially in the Tethys region), placodonts, the earliest known herbivorous marine reptile Atopodentatus, and the first plesiosaurs. The first of the lizardlike Thalattosauria (askeptosaurs) and the highly successful ichthyosaurs, which appeared in Early Triassic seas soon diversified, and some eventually developed to huge size during the Late Triassic.
Other reptiles
Among other reptiles, the earliest turtles, like Proganochelys and Proterochersis, appeared during the Norian Age (Stage) of the Late Triassic Period. The Lepidosauromorpha, specifically the Sphenodontia, are first found in the fossil record of the earlier Carnian Age, though the earliest lepidosauromorphs likely occurred in the Permian. The Procolophonidae, the last surviving parareptiles, were an important group of small lizard-like herbivores. The drepanosaurs were a clade of unusual, chameleon-like arboreal reptiles with birdlike heads and specialised claws.
Synapsids
Three therapsid groups survived into the Triassic: dicynodonts, therocephalians, and cynodonts. The cynodont Cynognathus was a characteristic top predator in the Olenekian and Anisian of Gondwana. Both kannemeyeriiform dicynodonts and gomphodont cynodonts remained important herbivores during much of the period. Therocephalians included both large predators (Moschorhinus) and herbivorous forms (bauriids) until their extinction midway through the period. Ecteniniid cynodonts played a role as large-sized, cursorial predators in the Late Triassic. During the Carnian (early part of the Late Triassic), some advanced cynodonts gave rise to the first mammals.
During the Triassic, archosaurs displaced therapsids as the largest and most ecologically prolific terrestrial amniotes. This "Triassic Takeover" may have contributed to the evolution of mammals by forcing the surviving therapsids and their mammaliaform successors to live as small, mainly nocturnal insectivores. Nocturnal life may have forced the mammaliaforms to develop fur and a higher metabolic rate.
Lagerstätten
Two Early Triassic lagerstätten (high-quality fossil beds), the Dienerian aged Guiyang biota and the earliest Spathian aged Paris biota stand out due to their exceptional preservation and diversity. They represent the earliest lagerstätten of the Mesozoic era and provide insight into the biotic recovery from the Permian-Triassic mass extinction event.
The Monte San Giorgio lagerstätte, now in the Lake Lugano region of northern Italy and southern Switzerland, was in Middle Triassic times a lagoon behind reefs with an anoxic bottom layer, so there were no scavengers and little turbulence to disturb fossilization, a situation that can be compared to the better-known Jurassic Solnhofen Limestone lagerstätte. The remains of fish and various marine reptiles (including the common pachypleurosaur Neusticosaurus, and the bizarre long-necked archosauromorph Tanystropheus), along with some terrestrial forms like Ticinosuchus and Macrocnemus, have been recovered from this locality. All these fossils date from the Anisian and Ladinian ages (about 242 Ma ago).
Triassic–Jurassic extinction event
The Triassic Period ended with a mass extinction, which was particularly severe in the oceans; the conodonts disappeared, as did all the marine reptiles except ichthyosaurs and plesiosaurs. Invertebrates like brachiopods and molluscs (such as gastropods) were severely affected. In the oceans, 22% of marine families and possibly about half of marine genera went missing.
Though the end-Triassic extinction event was not equally devastating in all terrestrial ecosystems, several important clades of crurotarsans (large archosaurian reptiles previously grouped together as the thecodonts) disappeared, as did most of the large labyrinthodont amphibians, groups of small reptiles, and most synapsids. Some of the early, primitive dinosaurs also became extinct, but more adaptive ones survived to evolve into the Jurassic. Surviving plants that went on to dominate the Mesozoic world included modern conifers and cycadeoids.
The cause of the Late Triassic extinction is uncertain. It was accompanied by huge volcanic eruptions that occurred as the supercontinent Pangaea began to break apart about 202 to 191 million years ago (40Ar/39Ar dates), forming the Central Atlantic Magmatic Province (CAMP), one of the largest known inland volcanic events since the planet had first cooled and stabilized. Other possible but less likely causes for the extinction events include global cooling or even a bolide impact, for which an impact crater containing Manicouagan Reservoir in Quebec, Canada, has been singled out. However, the Manicouagan impact melt has been dated to 214±1 Mya. The date of the Triassic-Jurassic boundary has also been more accurately fixed recently, at 201.4 Mya. Both dates are gaining accuracy by using more accurate forms of radiometric dating, in particular the decay of uranium to lead in zircons formed at time of the impact. So, the evidence suggests the Manicouagan impact preceded the end of the Triassic by approximately 10±2 Ma. It could not therefore be the immediate cause of the observed mass extinction.
The number of Late Triassic extinctions is disputed. Some studies suggest that there are at least two periods of extinction towards the end of the Triassic, separated by 12 to 17 million years. But arguing against this is a recent study of North American faunas. In the Petrified Forest of northeast Arizona there is a unique sequence of late Carnian-early Norian terrestrial sediments. An analysis in 2002 found no significant change in the paleoenvironment. Phytosaurs, the most common fossils there, experienced a change-over only at the genus level, and the number of species remained the same. Some aetosaurs, the next most common tetrapods, and early dinosaurs, passed through unchanged. However, both phytosaurs and aetosaurs were among the groups of archosaur reptiles completely wiped out by the end-Triassic extinction event.
It seems likely then that there was some sort of end-Carnian extinction, when several herbivorous archosauromorph groups died out, while the large herbivorous therapsids—the kannemeyeriid dicynodonts and the traversodont cynodonts—were much reduced in the northern half of Pangaea (Laurasia).
These extinctions within the Triassic and at its end allowed the dinosaurs to expand into many niches that had become unoccupied. Dinosaurs became increasingly dominant, abundant and diverse, and remained that way for the next 150 million years. The true "Age of Dinosaurs" is during the following Jurassic and Cretaceous periods, rather than the Triassic.
See also
Geologic time scale
List of fossil sites (with link directory)
Triassic land vertebrate faunachrons
Phylloceratina
Dinosaurs
Notes
References
Emiliani, Cesare. (1992). Planet Earth: Cosmology, Geology, & the Evolution of Life & the Environment. Cambridge University Press. (Paperback Edition ISBN 0-521-40949-7)
Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) Stratigraphy.org, Accessed April 30, 2006
Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6
Sues, Hans-Dieter & Fraser, Nicholas C. Triassic Life on Land: The Great Transition New York: Columbia University Press, 2010. Series: Critical Moments and Perspectives in Earth History and Paleobiology. ISBN 978-0-231-13522-1
van Andel, Tjeerd, (1985) 1994, New Views on an Old Planet: A History of Global Change, Cambridge University Press
External links
Overall introduction
'The Triassic world'
Douglas Henderson's illustrations of Triassic animals
Paleofiles page on the Triassic extinctions
Examples of Triassic Fossils
Triassic (chronostratigraphy scale) |
lunar geologic timescale | The lunar geological timescale (or selenological timescale) divides the history of Earth's Moon into five generally recognized periods: the Copernican, Eratosthenian, Imbrian (Late and Early epochs), Nectarian, and Pre-Nectarian. The boundaries of this time scale are related to large impact events that have modified the lunar surface, changes in crater formation through time, and the size-frequency distribution of craters superposed on geological units. The absolute ages for these periods have been constrained by radiometric dating of samples obtained from the lunar surface. However, there is still much debate concerning the ages of certain key events, because correlating lunar regolith samples with geological units on the Moon is difficult, and most lunar radiometric ages have been highly affected by an intense history of bombardment.
Lunar stratigraphy
The primary geological processes that have modified the lunar surface are impact cratering and volcanism, and by using standard stratigraphic principles (such as the law of superposition) it is possible to order these geological events in time. At one time, it was thought that the mare basalts might represent a single stratigraphic unit with a unique age, but it is now recognized that mare volcanism was an ongoing process, beginning as early as 4.2 Ga (1 Ga = 1 billion years ago) and continuing to perhaps as late as 1.2 Ga. Impact events are by far the most useful for defining a lunar stratigraphy as they are numerous and form in a geological instant. The continued effects of impact cratering over long periods of time modify the morphology of lunar landforms in a quantitative way, and the state of erosion of a landform can also be used to assign a relative age.
The lunar geological time scale has been divided into five periods (Pre-Nectarian, Nectarian, Imbrian, Eratosthenian, and Copernican) with one of these (the Imbrian) being subdivided into two epochs. These divisions of geological time are based on the recognition of convenient geomorphological markers, and as such, they should not be taken to imply that any fundamental changes in geological processes have occurred at these boundaries. The Moon is unique in the Solar System in that it is the only body (other than the Earth) for which we possess rock samples with a known geological context. By correlating the ages of samples obtained from the Apollo missions to known geological units, it has been possible to assign absolute ages to some of these geological periods. The timeline below represents one such attempt, but it is important to note (as is discussed below) that some of the ages are either uncertain, or disputed. In many lunar highland regions, it is not possible to distinguish between Nectarian and Pre-Nectarian materials, and these deposits are sometimes labeled as just Pre-Imbrian.
Pre-Nectarian
The Pre-Nectarian period is defined from the point at which the lunar crust formed, to the time of the Nectaris impact event. Nectaris is a multi-ring impact basin that formed on the near side of the Moon, and its ejecta blanket serves as a useful stratigraphic marker. 30 impact basins from this period are recognized, the oldest of which is the South Pole–Aitken basin. This geological period has been informally subdivided into the Cryptic and Basin Groups 1–9, but these divisions are not used on any geological maps.
Nectarian
The Nectarian period encompasses all events that occurred between the formation of the Nectaris and Imbrium impact basins. 12 multi-ring impact basins are recognized in the Nectarian period, including the Serenitatis and Crisium basins. One of the scientific objectives of the Apollo 16 mission was to date material excavated by the Nectaris impact basin. Nevertheless, the age of the Nectaris basin is somewhat contentious, with the most frequently cited numbers being 3.92 Ga, and less frequently 3.85 Ga. Recently, it has been suggested that the Nectaris basin could be, in fact, much older at ~4.1 Ga.
Imbrian
The Imbrian period has been subdivided into Late and Early epochs. The Early Imbrian is defined as the time between the formation of the Imbrium and Orientale impact basins. The Imbrium basin is believed to have formed at 3.85 Ga, though a minority opinion places this event at 3.77 Ga. The Schrödinger basin is the only other multi-ring basin that is Lower Imbrian in age, and no large multi-ring basins formed after this epoch.
The Late Imbrian is defined as the time between the formation of the Orientale basin, and the time at which craters of a certain size (DL) have been obliterated by erosional processes. The age of the Orientale basin has not been directly determined, though it must be older than 3.72 Ga (based on Upper Imbrian ages of mare basalts) and could be as old as 3.84 Ga based on the size-frequency distributions of craters superposed on Orientale ejecta. About two-thirds of the Moon's mare basalts erupted within the Upper Imbrian Series, with many of these lavas filling the depressions associated with older impact basins.
Eratosthenian
The base of the Eratosthenian period is defined by the time at which craters on a geological unit of a certain size DL have been almost obliterated by erosional processes. The principal erosional agent on the Moon is impact cratering itself, though seismic modification could play a minor role as well. The absolute age of this boundary is not well defined, but is commonly quoted as being near 3.2 Ga. The younger boundary of this period is defined based on the recognition that freshly excavated materials on the lunar surface are generally bright and that they become darker over time as a result of space weathering processes. Operationally, this period was originally defined as the time at which impact craters lost their bright ray systems. This definition, however, has recently been subjected to some criticism as some crater rays are bright for compositional reasons that are unrelated to the amount of space weathering they have incurred. In particular, if the ejecta from a crater formed in the highlands (which is composed of bright anorthositic materials) is deposited on the low albedo mare, it will remain bright even after being space weathered.
Copernican
The Copernican period is the youngest geological period of the Moon. Originally, the presence of a bright ray system surrounding an impact crater was used to define Copernican units, but as mentioned above, this is complicated by the presence of compositional ray systems. The base of the Copernican period does not correspond to the formation of the impact crater Copernicus. The age of the base of the Copernican is not well constrained, but a commonly quoted number is 1.1 Ga. The Copernican extends until the present day.
Relationship to Earth's geologic time scale
The divisions of the lunar geologic time scale are based on the recognition of a few convenient geomorphological markers. While these divisions are extremely useful for ordering geological events in a relative manner, it is important to realize that the boundaries do not imply any fundamental change of geological processes. Furthermore, as the oldest geological periods of the Moon are based exclusively on the times of individual impact events (in particular, Nectaris, Imbrium, and Orientale), these punctual events will most likely not correspond to any specific geological event on the other terrestrial planets, such as Mercury, Venus, Earth, or Mars.
Nevertheless, at least one notable scientific work has advocated using the lunar geological time scale to subdivide the Hadean eon of Earth's geologic time scale. In particular, it is sometimes found that the Hadean is subdivided into the Cryptic, Basin Groups 1–9, Nectarian, and Early Imbrian. This notation is not entirely consistent with the above lunar geologic time scale in that the Cryptic and Basin Groups 1–9 (both of which are only informal terms that are not used in geologic maps) comprise the Pre-Nectarian period.
See also
Crater counting
Geology of the Moon
Geologic time scale (Earth)
Impact crater
Late Heavy Bombardment
References
Cited references
General references
Martel, L.M.V. (September 28, 2004). "Lunar Crater Rays Point to a New Lunar Time Scale". Planetary Science Research Discoveries. |
neogene | The Neogene ( NEE-ə-jeen, informally Upper Tertiary or Late Tertiary) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago (Mya) to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene. Some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary. The term "Neogene" was coined in 1853 by the Austrian palaeontologist Moritz Hörnes (1815–1868).During this period, mammals and birds continued to evolve into modern forms, while other groups of life remained relatively unchanged. The first humans (Homo habilis) appeared in Africa near the end of the period. Some continental movements took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the warm ocean currents from the Pacific to the Atlantic Ocean, leaving only the Gulf Stream to transfer heat to the Arctic Ocean. The global climate cooled considerably throughout the Neogene, culminating in a series of continental glaciations in the Quaternary Period that follows.
Divisions
In ICS terminology, from upper (later, more recent) to lower (earlier):
The Pliocene Epoch is subdivided into two ages:
Piacenzian Age, preceded by
Zanclean AgeThe Miocene Epoch is subdivided into six ages:
Messinian Age, preceded by
Tortonian Age
Serravallian Age
Langhian Age
Burdigalian Age
Aquitanian AgeIn different geophysical regions of the world, other regional names are also used for the same or overlapping ages and other timeline subdivisions.
The terms Neogene System (formal) and Upper Tertiary System (informal) describe the rocks deposited during the Neogene Period.
Geography
The continents in the Neogene were very close to their current positions. The Isthmus of Panama formed, connecting North and South America. The Indian subcontinent continued to collide with Asia, forming the Himalayas. Sea levels fell, creating land bridges between Africa and Eurasia and between Eurasia and North America.
Climate
The global climate became more seasonal and continued an overall drying and cooling trend which began during the Paleogene. The Early Miocene was relatively cool; Early Miocene mid-latitude seawater and continental thermal gradients were already very similar to those of the present. During the Middle Miocene, Earth entered a warm phase known as the Middle Miocene Climatic Optimum (MMCO), which was driven by the emplacement of the Columbia River Basalt Group. Around 11 Ma, the Middle Miocene Warm Interval gave way to the much cooler Late Miocene. The ice caps on both poles began to grow and thicken, a process enhanced by positive feedbacks from increased formation of sea ice. Between 7 and 5.3 Ma, a decrease in global temperatures termed the Late Miocene Cooling (LMC) ensued, driven by decreases in carbon dioxide concentrations. During the Middle Pliocene, another warm interval occurred, interrupting the longer-term cooling trend. By the end of the period the first of a series of glaciations of the current Ice Age began.
Flora and fauna
Marine and continental flora and fauna have a modern appearance. The reptile group Choristodera went extinct in the early part of the period, while the amphibians known as Allocaudata disappeared at the end of it. Neogene also marked the end of the reptilian genera Langstonia and Barinasuchus, terrestrial predators that were the last surviving members of Sebecosuchia, a group related to crocodiles. The oceans were dominated by large carnivores like megalodons and livyatans, and 19 million years ago about 70% of all pelagic shark species disappeared. Mammals and birds continued to be the dominant terrestrial vertebrates, and took many forms as they adapted to various habitats. The first hominins, the ancestors of humans may have appeared in southern Europe and migrated into Africa. The first humans (belonging to the species Homo habilis) appeared in Africa near the end of the period.About 20 million years ago gymnosperms in the form of some conifer and cycad groups started to diversify and produce more species due to the changing conditions. In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones and grasslands replaced many forests. Grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses, antelope, and bison. Ice age mammals like the mammoths and woolly rhinoceros were common in Pliocene. With lower levels of CO2 in the atmosphere, C4 plants expanded and reached ecological dominance in grasslands during the last 10 million years. Also Asteraceae (daisies) went through a significant adaptive radiation. Eucalyptus fossil leaves occur in the Miocene of New Zealand, where the genus is not native today, but have been introduced from Australia.
Disagreements
The Neogene traditionally ended at the end of the Pliocene Epoch, just before the older definition of the beginning of the Quaternary Period; many time scales show this division.
However, there was a movement amongst geologists (particularly marine geologists) to also include ongoing geological time (Quaternary) in the Neogene, while others (particularly terrestrial geologists) insist the Quaternary to be a separate period of distinctly different record. The somewhat confusing terminology and disagreement amongst geologists on where to draw what hierarchical boundaries is due to the comparatively fine divisibility of time units as time approaches the present, and due to geological preservation that causes the youngest sedimentary geological record to be preserved over a much larger area and to reflect many more environments than the older geological record. By dividing the Cenozoic Era into three (arguably two) periods (Paleogene, Neogene, Quaternary) instead of seven epochs, the periods are more closely comparable to the duration of periods in the Mesozoic and Paleozoic Eras.
The International Commission on Stratigraphy (ICS) once proposed that the Quaternary be considered a sub-era (sub-erathem) of the Neogene, with a beginning date of 2.58 Ma, namely the start of the Gelasian Stage. In the 2004 proposal of the ICS, the Neogene would have consisted of the Miocene and Pliocene Epochs. The International Union for Quaternary Research (INQUA) counterproposed that the Neogene and the Pliocene end at 2.58 Ma, that the Gelasian be transferred to the Pleistocene, and the Quaternary be recognized as the third period in the Cenozoic, citing key changes in Earth's climate, oceans, and biota that occurred 2.58 Ma and its correspondence to the Gauss-Matuyama magnetostratigraphic boundary. In 2006 ICS and INQUA reached a compromise that made Quaternary a sub-era, subdividing Cenozoic into the old classical Tertiary and Quaternary, a compromise that was rejected by International Union of Geological Sciences because it split both Neogene and Pliocene in two.Following formal discussions at the 2008 International Geological Congress in Oslo, Norway, the ICS decided in May 2009 to make the Quaternary the youngest period of the Cenozoic Era with its base at 2.58 Mya and including the Gelasian Age, which was formerly considered part of the Neogene Period and Pliocene Epoch. Thus the Neogene Period ends bounding the succeeding Quaternary Period at 2.58 Mya.
References
External links
"Digital Atlas of Neogene Life for the Southeastern United States". San Jose State University. Archived from the original on 2013-04-23. Retrieved 21 September 2018. |
list of time periods | The categorisation of the past into discrete, quantified named blocks of time is called periodization. This is a list of such named time periods as defined in various fields of study.
These can be divided broadly into prehistorical periods and historical periods (when written records began to be kept).
In archaeology and anthropology, prehistory is subdivided around the three-age system, this list includes the use of the three-age system as well as a number of various designation used in reference to sub-ages within the traditional three.
The dates for each age can vary by region. On the geologic time scale, the Holocene epoch starts at the end of the last glacial period of the current ice age (c. 10,000 BC) and continues to the present. The beginning of the Mesolithic is usually considered to correspond to the beginning of the Holocene epoch.
Prehistoric periods
Common System
Precambrian
Hadean (or hadaeozoic)
Archean (or archaeozoic)
Proterozoic
Paleoproterozoic
Siderian
Rhyacian
Statherian
Mesoproterozoic
Stenian
Neoproterozoic
Tonian
Cryogenian
Ediacarian
Paleozoic
Cambrian
Cambrian Explosion
Ordovician
Silurian
Devonian
Carboniferous
Permian
Mesozoic
Triassic
Jurassic
Cretaceous
Cenozoic
Paleogene
Paleocene
Eocene
Oligocene
Neogene
Miocene
Pliocene
Quaternary
Pleistocene
Holocene
Greenlandian
Northgrippian
Meghalayan
Anthropocene
Russian Prehistoric Periods
Vendian
General periods
Geologic Time – Period prior to humans. 4.6 billion to 3 million years ago. (See "prehistoric periods" for more detail into this.)
Primatomorphid Era – Period prior to the existence of Primatomorpha
Simian Era – Period prior to the existence of Simiiformes
Hominoid Era – Period prior to the existence of Hominoidea
Hominid Era – Period prior to the existence of Hominidae
Distant signs of Human-like apes
Homininaeid Era – Period prior to the existence of Homininae
Homininid Era – Period prior to the existence of Hominini
Prehistory – Period between the appearance of Homo ("humans"; first stone tools c. three million years ago) and the invention of writing systems (for the Ancient Near East: c. five thousand years ago).
Paleolithic – the earliest period of the Stone Age
Lower Paleolithic – time of archaic human species, predates Homo sapiens
Middle Paleolithic – coexistence of archaic and anatomically modern human species
Upper Paleolithic – worldwide expansion of anatomically modern humans, the disappearance of archaic humans by extinction or admixture with modern humans; earliest evidence for pictorial art.
Mesolithic (Epipaleolithic) – a period in the development of human technology between the Palaeolithic and Neolithic periods.
Neolithic – a period of primitive technological and social development, beginning about 10,200 BC in parts of the Middle East, and later in other parts of the world.
Chalcolithic (or "Eneolithic", "Copper Age") – still largely Neolithic in character, when early copper metallurgy appeared alongside the use of stone tools.
Bronze Age – not part of prehistory for all regions and civilizations who had adopted or developed a writing system.
Ancient Egypt
Iron Age – not part of prehistory for all civilizations who had introduced written records during the Bronze Age.
Ancient history – Aggregate of past events from the beginning of recorded human history and extending as far as the Early Middle Ages or the Postclassical Era. The span of recorded history is roughly five thousand years, beginning with the earliest linguistic records in the third millennium BC in Mesopotamia and Egypt.
Classical antiquity – Broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome, collectively known as the Greco-Roman world. It is the period in which Greek and Roman society flourished and wielded great influence throughout Europe, North Africa and the Middle East.
Post-classical history – Period of time that immediately followed ancient history. Depending on the continent, the era generally falls between the years AD 200–600 and AD 1200–1500. The major classical civilizations that the era follows are Han China (ending in 220), the Western Roman Empire (in 476), the Gupta Empire (in the 550s), and the Sasanian Empire (in 651).
Middle Ages – Lasted from the 5th to the 15th century. It began with the collapse of the Western Roman Empire in 476 and is variously demarcated by historians as ending with the Fall of Constantinople in 1453, or the discovery of America by Columbus in 1492, merging into the Renaissance and the Age of Discovery.
Early Middle Ages
High Middle Ages
Late Middle Ages
Modern history – After the post-classical era
Early modern period – The chronological limits of this period are open to debate. It emerges from the Late Middle Ages (c. 1500), demarcated by historians as beginning with the fall of Constantinople in 1453, in forms such as the Italian Renaissance in the West, the Ming dynasty in the East, and the rise of the Aztecs in the New World. The period ends with the beginning of the Age of Revolutions.
Late modern period – Began approximately in the mid-18th century; notable historical milestones included the French Revolution, the American Revolution, the Industrial Revolution and the Great Divergence
Contemporary history – History within living memory. It shifts forward with the generations, and today is the span of historic events from approximately 1945 that are immediately relevant to the present time.
Forms of modernity
Hominids archaeologically and anatomically similar or identical to modern humans (HAASMHs)
Anatomically modern humans (AMHs)
Technologically modern humans (TMHs)
Technological periods
Prehistory
Paleolithic (Lower, Middle, Upper)
Mesolithic (Epipaleolithic)
Neolithic
Chalcolithic (or "Eneolithic", "Copper Age")
Ancient history (The Bronze and Iron Ages are not part of prehistory for all regions and civilizations who had adopted or developed a writing system.)
Bronze Age
Iron Age
Late Middle Ages
Renaissance
Early modern history
Modern history
Industrial Age (1760–1970)
Machine Age (1880–1945)
Age of Oil (1901–present)
Jet Age (1940s)
Nuclear Age (a.k.a. Atomic Era) (1945/1950–present)
Space Age (1957–present)
Information Age (1970–present)
Internet Age (1990–present)
American (continent) periods
Pre-Columbian America
Classic and Postclassic eras, Central America (200–1519)
Early Intermediate, Middle Horizon, Late Intermediate, Late Horizon (Peru, 200–1534)
Huari, Chimú, Chincha, Chanka people, Tiwanaku, IncaColonial America
Baroque (New World, 1600–1750)
Spanish hegemony (Americas, 1492–1832)
Australian periods
Ancient Australia, History of Indigenous Australians (between 65,000 and 50,000 BCE – 1788 CE)
Age of Discovery European maritime exploration of Australia (1606–1802)
Convict era (1788–1868)
Victorian era (1837–1901)
Federation era (1890–1918)
World War II (1939–1945)
Second Elizabethan era (1952–2022)
Southeast Asian periods
Archaic Southeast Asia
Srivijaya (Indonesia, 3rd – 14th centuries), Tarumanagara (358–723), Sailendra (8th and 9th centuries), Kingdom of Sunda (669–1579), Kingdom of Mataram (752–1045), Kediri (1045–1221), Singhasari (1222–1292), Majapahit (1293–1500)Modern Southeast Asia
Chenla (Cambodia, 630 – 802) and Khmer Empire (Cambodia, 802–1432)
Anterior Lý dynasty and Triệu Việt Vương, Third Chinese domination, Khúc Family, Dương Đình Nghệ, Kiều Công Tiễn, Ngô dynasty, The 12 Lords Rebellion, Đinh dynasty, Prior Lê dynasty, Lý dynasty, Trần dynasty, Hồ dynasty, Fourth Chinese domination (Vietnam, 544–1427)
Chinese periods
Bronze Age China
prechaic china
Three Sovereigns and Five Emperors (2852–2070 BC)earliest dynastic china
Xia dynasty (2070–1600 BC)Archaic China
archaicic china
Shang dynasty (1600–1046 BC)
Zhou dynasty (1046–221 BC)
Western Zhou (1046–771 BC)
Eastern Zhou (771–221 BC)divistates of China
Spring and Autumn period (771–476 BC)
Warring States period (476–221 BC)
Qin dynasty (221–206 BC)Antiquity
mid dynastic periods
Han dynasty (206 BC – 220 AD)
Western Han (206 BC – 2 AD)
Xin dynasty (9–23 AD)
Eastern Han (25–220 AD)
Six Dynasties (220–580)
Three Kingdoms (220–265)
Jin dynasty (266–420)
Southern and Northern Dynasties (420–580)Medieval China
Sui dynasty (580–618)
Tang dynasty (623–907)
Five Dynasties and Ten Kingdoms period (907–960)
Song dynasty (960–1279)
Northern Song (960–1127), Liao dynasty (907–1115)
Western Xia dynasty (1038–1227)
Southern Song (1127–1279), Jin dynasty (1115–1234)Mongol China
Yuan dynasty (1271–1368)Late Dynastic Period
Ming dynasty (1368–1644)
Qing dynasty (1644–1911)Modern China
Republic of China (1912–1949)
Xinhai Revolution (1911–1912)
Warlord Era (1918–1927)Contemporary China
Chinese Civil War (1927–1936/1946–1950)
Second Sino-Japanese War (1937–1945)Post-Contemporary China
People's Republic of China and Taiwan (1949–present)
Central Asian periods
Antiquity
Xiongnu (Mongolia, 220 BC – AD 200)Medieval Central Asia
Rouran Khaganate (Mongolia, Manchuria, Xianbei, AD 330 – 555)
Sixteen Kingdoms (Xianbei, Turkic peoples, 304–439)
Uyghur Khaganate (Mongolia, Manchuria, Tibet, 744–848)
Liao dynasty (Khitan people, 907–1125)Imperial Central Asia
Mongol Empire (Mongolia, 1206–1380)
Yuan Dynasty of China (≈1250 – ≈1350)
Golden Horde (≈1250 – 1380)Modern Central Asia
Qing dynasty (Manchu China, 1692–1911)
Egyptian periods
Prehistoric Egypt (pre-3150 BC)
Dynastic Period
Early Dynastic Period or Archaic Period (two dynasties) (3150 BC – 2686 BC)
Old Kingdom (four dynasties) (2686 BC – 2181 BC)
First Intermediate Period (four dynasties) (2181 BC – 2055 BC)
Middle Kingdom (three dynasties) (2055 BC – 1650 BC)
Second Intermediate Period (four dynasties) (1650 BC – 1550 BC)
New Kingdom (three dynasties) (1550 BC – 1069 BC)
Third Intermediate Period (five dynasties) (1069 BC – 664 BC)Antiquity
Late Period of Ancient Egypt (six dynasties: of these six, two were Persian dynasties that ruled from capitals distant from Egypt) (664 BC – c. 332 BC)
Argead and Ptolemaic dynasties (332 BC – 30 BC)
Aegyptus (fifteen Roman dynasties that ruled from capitals distant from Egypt) (30 BC – 641 AD)
Sasanian Egypt (one dynasty) (619–629)
Coptic period (300 AD – 900 AD)Islamic Egypt
Egypt under four foreign Arabic dynasties that ruled from capitals distant from Egypt.
Rashidun Egypt (641–661)
Umayyad Egypt (661–750)
Abbasid Egypt (750–868 and 905–935)Medieval Egypt
Tulunid dynasty (868–905)
Ikhshidid dynasty (935–969)
Fatimid Dynasty (969–1171)
Ayyubid Dynasty (1171–1250)
Mamluk dynasties (1250–1517)
Bahri dynasty (1250–1382)
Burji dynasty (1382–1517)Modern Egypt
Ottoman Egypt (Turk dynasty that ruled from a capital distant from Egypt) (1517–1867)
Muhammad Ali dynasty (1805–1953)
Khedivate of Egypt (1867–1914)
Sultanate of Egypt (1914–1922)Contemporary Egypt
Kingdom of Egypt (1922–1953)
Republican Egypt (1953–present)
European periods
Bronze Age (c. 3000 BC – c. 1050 BC)
Early Aegean Civilization (Crete, Greece and Near East; c. 3000 BC – c. 1050 BC)
Iron Age (c. 1050 BC – c. 500 AD)
Greek expansion and colonization (c. 1050 BC – 776 BC)
Archaic Greece (776 BC – 480 BC) – begins with the First Olympiad, traditionally dated 776 BC
Archaic period (776 BC – 612 BC) – the establishment of city-states in Greece
Pre-classical period (612 BC – 480 BC) – the fall of Nineveh to the second Persian invasion of Greece
Classical antiquity (480 BC – 476 AD)
Classical Greece (480 BC – 338 BC)
Macedonian era (338 BC – 323 BC)
Hellenistic Greece (323 BC – 146 BC)
Late Roman Republic (147 BC – 27 BC)
Principate of the Roman Empire (27 BC – 284 AD)
Late Antiquity (284 AD – 500 AD)
Migration Period (Europe, 300 AD – 700 AD)
Middle Ages (Europe, 476–1453)
Byzantine era (330–1453)
Early Middle Ages (Europe, 476–1066)
Viking Age (Scandinavia, Europe, 793–1066)
High Middle Ages (Europe, 1066 – c. 1300)
Late Middle Ages (Europe, c. 1300 – 1453)
The Renaissance (Europe, c. 1300 – c. 1601)
Early modern period (Europe, 1453–1789)
Age of Discovery (or Exploration) (Europe, c. 1400 – 1770)
Polish Golden Age (Poland, 1507–1572)
Golden Age of Piracy (1650–1730)
Tudor period (England, 1485–1603)
Elizabethan era (England, 1558–1603)
Stuart period (British Isles, 1603–1714)
Jacobean era (British Isles, 1603–1625)
Caroline era (British Isles, 1625–1649)
British Interregnum (British Isles, 1649–1660)
Stuart Restoration (British Isles, 1660–1714)
Carolean era (British Isles, 1660–1685)
Protestant Reformation (Europe, 16th century)
Classicism (Europe, 16th – 18th centuries)
Industrious Revolution, (Europe, 16th – 18th centuries)
Petrine Era (Russia, 1689–1725)
Age of Enlightenment (or Reason) (Europe, 18th century)
Scientific Revolution (Europe, 18th century)
Long nineteenth century (1789–1914)
Georgian era (the United Kingdom, 1714–1830)
Industrial Revolution (Europe, United States, and elsewhere 18th and 19th centuries, though with its beginnings in Britain)
Age of European colonialism and imperialism
Romantic era (1770–1850)
Napoleonic era (1799–1815)
Victorian era (the United Kingdom, 1837–1901); British hegemony (1815–1914) much of world, around the same time period.
Edwardian era (the United Kingdom, 1901–1914)
First, interwar period and Second World Wars (1914–1945)
Interwar Britain (United Kingdom, 1918–1939)
Cold War (1945–1991)
Post-Cold War (1991–present)
Iranian periods
Prehistoric Iran
Ancient age:
Achaemenid Empire (550 –330 BC)
Greek occupation of Persia (330 –312 BC):
Seleucid Empire (312 – 63 BC)
Parthian Empire (247 BCE – 224 AD)
Sassanid Empire (224 – 651 AD)Medieval age:
Persia under Caliphates (651 – 820 AD)
Iranian Intermezzo (c.820 – 1037): Tahirids (821 to 873), Saffarids (861 to 1003), Samanids (819 to 999) and Buyids (934 to 1062)
Seljuk Empire (1037–1194)
Khwarazmian Empire (1194–1219)
Mongol occupation of Persia (1219 –1256)
Ilkhanate (1256–1335)
Disintegration of the Ilkhanate (1335–1370): Jalayirids, Chobanids, Muzaffarids, Injuids, Sarbadars, and Kartids
Timurid Empire (1370–1507) and Aq Qoyunlu (1378–1501)Modern age:
Safavid Iran (1501–1736)
Afsharid Iran (1736 –c.1750)
Zand Iran (1750–1794)
Qajar Iran (1794–1925)
Pahlavi Iran (1925–1979)
Islamic Republic of Iran (1979–present)
Indian periods
South Asian Stone Age
Pre-Harappan
Mehrgarh
South Asian Bronze Age (3340 BC – 1350 BC)
Indus Valley civilization
Early Harappan
Early Mature Harappan
Mature Harappan
Late Harappan
Punjab Phase
Jhukar Phase
Rangpur Phase
Final Harappan
South Asian Iron Age (1350 BCE – 200 BC)
Vedic period (1350 BC – 500 BC): Mahajanapadas
Magadha period (c.500 BC – c.750 AD): Nandas, Mauryans, Shungas
Classical Age in India (200 BC – 500 AD)
Sangam period (300 BC – 600 AD): Cholas, Chalukyas, Pallavas and Pandyans
Golden period: Kushans (50 AD – 220 AD), Satavahanas (230 BC – 220 AD), Guptas (320 AD – 535 AD) and Vakatakas (300AD – 650 AD)
Medieval Age in India (500–1526)
Tripartite period (c.750 – c.900): Palas, Rashtrakutas and Gurjaras
Muslim period (712–1857): Delhi, Bengal, Bahmani and Gujarat sultanates
Vijayanagara empire (1336–1646), Gajapati empire (1434–1541) and kingdom of Mewar (1325–1448)
Modern Age in India (1526 – present)
Mughal empire (1526–1857)
Maratha empire (1674–1818)
Colonial period: British Raj (1858 – 1947)
Independence (1947 – present)
Japanese periods
Archaic Japan
Jōmon period (10,501 BC – 400 BC)
Yayoi period (450 BC – 250 AD)
Kofun period (250–600)Medieval Japan
Asuka period (643–710)
Nara period (743–794)
Heian period (795–1185)
Kamakura period (1185–1333)Samurai Japan
Muromachi period (1333–1573)
Azuchi–Momoyama period (1573–1603)Modern Japan
Edo period (1603–1868)
Meiji period (1868–1912)
Taishō period (1912–1926)Contemporary Japan
Shōwa period (1926–1989)
Post-occupation era (1952 – present)
Heisei period (1989–2019)
Reiwa period (2019–present)
Iraqi periods
Archaic Period
Mesopotamia
Samarra culture
Hassuna culture
Halaf-Ubaid Transitional period
Ubaid period
Uruk period
Jemdet Nasr period (3100 BC – 2900 BC)
Early Dynastic Period (2900 BC – 2270 BC)
Akkadian Empire (2270 BC – 2083 BC)
Gutian dynasty (2083 BC – 2050 BC)
Ur III period (2050 BC – 1940 BC)
First Babylonian dynasty (1830 BC – 1531 BC), Hittites (1800 BC – 1178 BC)
Kassites (1531 BC – 1135 BC), Mitanni (1500 BC – 1300 BC)
Neo-Assyrian Empire (934 BC – 609 BC)
Neo-Babylonian Empire (626 BC – 539 BC), Medes (678 BC – 549 BC)Imperial Period
Persian Empires (550 BC – 651 AD)
Achaemenid Empire (550 BC – 330 BC)
Conquered by Macedonian Empire (330 BC – 312 BC)
Seleucid Empire (312 BC – 63 BC)
Parthian Empire (247 BC – 224 AD)
Sasanian Empire (224 AD – 651 AD)Islamic Period
Islamicate periods (7th – 21st centuries)
High Caliphate (685–945)
Earlier Middle Period (945–1250)
Later Middle Period (1250–1500)
Rashidun Caliphate (632–661)
Umayyad Caliphate (661–750)
Abbasid Caliphate (750–1258), Fatimid Caliphate (909–1171)
Buyid dynasty (934–1055)
Seljuq dynasty (1055–1171)
Ayyubid dynasty (1171–1341)
Ottoman Empire (1300–1923)
Safavid Empire (1501–1736)
Modern Iraq (1923–present)
Libyan periods
Prehistoric Libya
Prehistoric Libya (pre-600 BC)Early Libya
Carthaginian Libya (600 BC – 200 BC)
Roman Libya (200 BC – 487 AD)
Vandal Libya (487 AD – ≈600 AD)
Islamic Libya (≈600 – ≈1200)
Ottoman Libya (≈1600 – ≈1900)Modern Libya
Colonial Libya (≈1900 – ≈1950)
Libya as an independent country
Early Independent Era
Libyan Arab Republic (September 1969–1977)
Great Socialist People's Libyan Arab Jamahiriya
Contemporary Libya (2011–present)
Mexican periods
Prehistoric Mexico and Ancient Mexico
Mayans (3000 BC – 600 AD)
Aztecs (1000 BC – 1492)Modern Mexico
Spanish Mexico (1492–1850)
Contemporary Mexico (1850–present)
United States historical periods
Pre-Colonial era
Lithic stage
Archaic stage
Formative stage
Classic stage
Post-Classic stageThirteen British Colonies (1607–1775)
United Colonies (1775-1781)
American Revolutionary WarConfederation period (1781-1789)
First Party System (1789–1824)
Federalist Era (1789–1800)
Jeffersonian democracy (1790s–1820s)
Era of Good Feelings (1817–1825)Second Party System (1824–1856)
Jacksonian democracy (1825–1854)
Civil War Era (1849–1865)Third Party System (1856–1896)
Civil War Era (1849–1865)
Reconstruction era (1865–1877) (Some of this time period is known as the "Old West".)
Gilded Age (1877–1896)Fourth Party System (1896–1932)
Progressive Era (1896–1917)
United States in World War I (1917–1918)
Roaring Twenties (1920–1929)Fifth Party System (1932–1980)
Great Depression (1929–1939)
United States home front during World War II (1942–1945)
Post-World War II (1945–1964)
Civil Rights Movement (1954–1968)
United States in the Vietnam War (1955–1973)Sixth Party System (1980–present)
Reagan Era (1980–1991)
Post-Cold War period (1991–2008)
Contemporary United States (2008-present)
See also
Art of Europe
Geologic time scale
List of fossil sites with link directory.
List of timelines around the world.
Logarithmic timeline shows all history on one page in ten lines.
Orders of magnitude (time)
Periodization for a discussion of the tendency to try to fit history into non-overlapping periods.
Time
Planck Time
Jiffy
Second
Millisecond
Microsecond
Nanosecond
Minute
Hour
Day
Week
Fortnight
Month
Year
Olympiad
Lustrum
Decade
Century
Millennium
References
Citations
=== Sources cited === |
siderian | The Siderian Period ( ; Ancient Greek: σίδηρος, romanized: sídēros, meaning "iron") is the first geologic period in the Paleoproterozoic Era and lasted from 2500 Ma to 2300 Ma. Instead of being based on stratigraphy, these dates are defined chronometrically.
The deposition of banded iron formations peaked early in this period. These iron rich formations were formed as anaerobic cyanobacteria produced waste oxygen that combined with iron, forming magnetite (Fe3O4, an iron oxide). This process removed iron from the Earth's oceans, presumably turning greenish seas clear. Eventually, with no remaining iron in the oceans to serve as an oxygen sink, the process allowed the buildup of an oxygen-rich atmosphere. This second, follow-on event is known as the oxygen catastrophe, which, some geologists believe triggered the Huronian glaciation.Since the time period from 2420 Ma to 2250 Ma is well-defined by the lower edge of iron-deposition layers, an alternative period named the Oxygenian, based on stratigraphy instead of chronometry, was suggested in 2012 in a geological timescale review.
References
"Siderian Period". GeoWhen Database. Retrieved May 24, 2015.
"The Siderian". Dinosaurfact.net. Retrieved May 24, 2015. |
black sea | The Black Sea is a marginal mediterranean sea lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Romania, Russia, Turkey, and Ukraine. The Black Sea is supplied by major rivers, principally the Danube, Dnieper and Don. Consequently, while six countries have a coastline on the sea, its drainage basin includes parts of 24 countries in Europe.The Black Sea covers 436,400 km2 (168,500 sq mi) (not including the Sea of Azov), has a maximum depth of 2,212 m (7,257 ft), and a volume of 547,000 km3 (131,000 cu mi).
Most of its coasts ascend rapidly.
These rises are the Pontic Mountains to the south, bar the southwest-facing peninsulas, the Caucasus Mountains to the east, and the Crimean Mountains to the mid-north.
In the west, the coast is generally small floodplains below foothills such as the Strandzha; Cape Emine, a dwindling of the east end of the Balkan Mountains; and the Dobruja Plateau considerably farther north.
The longest east–west extent is about 1,175 km (730 mi).
Important cities along the coast include (clockwise from the Bosporus) Burgas, Varna, Constanța, Odesa, Sevastopol, Novorossiysk, Sochi, Batumi, Trabzon and Samsun.
The Black Sea has a positive water balance, with an annual net outflow of 300 km3 (72 cu mi) per year through the Bosporus and the Dardanelles into the Aegean Sea. While the net flow of water through the Bosporus and Dardanelles (known collectively as the Turkish Straits) is out of the Black Sea, water generally flows in both directions simultaneously: Denser, more saline water from the Aegean flows into the Black Sea underneath the less dense, fresher water that flows out of the Black Sea. This creates a significant and permanent layer of deep water that does not drain or mix and is therefore anoxic. This anoxic layer is responsible for the preservation of ancient shipwrecks which have been found in the Black Sea.
The Black Sea ultimately drains into the Mediterranean Sea, via the Turkish Straits and the Aegean Sea. The Bosporus strait connects it to the small Sea of Marmara which in turn is connected to the Aegean Sea via the strait of the Dardanelles. To the north, the Black Sea is connected to the Sea of Azov by the Kerch Strait.
The water level has varied significantly over geological time. Due to these variations in the water level in the basin, the surrounding shelf and associated aprons have sometimes been dry land. At certain critical water levels, connections with surrounding water bodies can become established. It is through the most active of these connective routes, the Turkish Straits, that the Black Sea joins the World Ocean. During geological periods when this hydrological link was not present, the Black Sea was an endorheic basin, operating independently of the global ocean system (similar to the Caspian Sea today). Currently, the Black Sea water level is relatively high; thus, water is being exchanged with the Mediterranean. The Black Sea undersea river is a current of particularly saline water flowing through the Bosporus Strait and along the seabed of the Black Sea, the first of its kind discovered. The Black Sea is discussed in amongst others in world issues including trade routes.
Name
Modern names
Current names of the sea are usually equivalents of the English name "Black Sea", including these given in the countries bordering the sea:
Abkhaz: Амшын Еиқәа, romanized: Amŝən Ejkʷa, IPA: [ɑmʂɨn ɛjkʷʰɑ]
Adyghe: Хы Шӏуцӏэ, romanized: Xə Šʷʼucʼɛ, IPA: [xɘ ʃʷʼtsʼɜ]
Armenian: Սեւ ծով, romanized: Sev cov, IPA: [sɛv t͡sɔv]
Azerbaijani: Qara dəniz, IPA: [kaˈɾa deniz]
Bulgarian: Чeрно морe, romanized: Čérno moré, IPA: [ˈt͡ʃɛrno moˈrɛ]
Crimean Tatar: Къара денъиз, romanized: Qara deñiz, IPA: [qɑrɑ deŋiz]
Georgian: შავი ზღვა, romanized: shavi zghva, šavi zɣva, IPA: [ʃavi zʁʷa]
Laz and Mingrelian: უჩა ზუღა, romanized: Ucha Zugha, IPA: [ˈutʃä ˈzuɣä], or simply ზუღა, IPA: [ˈzuɣä], "Sea"
Romanian: Marea Neagră, pronounced [ˈmare̯a ˈne̯aɡrə]
Russian: Чёрное мо́ре, romanized: Čórnoje móre, IPA: [ˈt͡ɕɵrnəjə ˈmorʲe]
Turkish: Karadeniz, IPA: [kaˈɾadeniz]
Ukrainian: Чо́рне мо́ре, romanized: Čórne móre, IPA: [ˈt͡ʃɔrne ˈmɔre]Such names have not yet been shown conclusively to predate the 13th century.In Greece, the historical name "Euxine Sea", which holds a different literal meaning (see below), is still widely used:
Greek: Εύξεινος Πόντος, romanized: Éfxinos Póndos, lit. 'Hospitable Sea', [ˈefksinos ˈpondos]; the name Μαύρη Θάλασσα, Mávri Thálassa, 'Black Sea', [ˈmavɾi ˈθalasa], is used, but is much less common.
Historical names and etymology
The earliest known name of the Black Sea is the Sea of Zalpa, so called by both the Hattians and their conquerors the Hittites. The Hattic city of Zalpa was "situated probably at or near the estuary of the Marrassantiya River, the modern Kızıl Irmak, on the Black Sea coast."The principal Greek name Póntos Áxeinos is generally accepted to be a rendering of the Iranian word *axšaina- ("dark colored"). Ancient Greek voyagers adopted the name as Á-xe(i)nos, identified with the Greek word áxeinos (inhospitable). The name Πόντος Ἄξεινος Póntos Áxeinos (Inhospitable Sea), first attested in Pindar (c. 475 BC), was considered an ill omen and was euphemized to its opposite, Εὔξεινος Πόντος Eúxeinos Póntos (Hospitable Sea), also first attested in Pindar. This became the commonly used designation in Greek, although in mythological contexts the "true" name Póntos Áxeinos remained favoured.Strabo's Geographica (1.2.10) reports that in antiquity, the Black Sea was often simply called "the Sea" (ὁ πόντος ho Pontos). He thought that the sea was called the "Inhospitable Sea Πόντος Ἄξεινος Póntos Áxeinos by the inhabitants of the Pontus region of the southern shoreline before Greek colonisation due to its difficult navigation and hostile barbarian natives (7.3.6), and that the name was changed to "hospitable" after the Milesians colonised the region, bringing it into the Greek world.Popular supposition derives "Black Sea" from the dark color of the water or climatic conditions. Some scholars understand the name to be derived from a system of colour symbolism representing the cardinal directions, with black or dark for north, red for south, white for west, and green or light blue for east. Hence "Black Sea" meant "Northern Sea". According to this scheme, the name could only have originated with a people living between the northern (black) and southern (red) seas: this points to the Achaemenids (550–330 BC).In the Greater Bundahishn, a Middle Persian Zoroastrian scripture, the Black Sea is called Siyābun. In the tenth-century Persian geography book Hudud al-'Alam, the Black Sea is called Georgian Sea (daryā-yi Gurz). The Georgian Chronicles use the name zğua sperisa ზღუა სპერისა (Sea of Speri) after the Kartvelian tribe of Speris or Saspers. Other modern names such as Chyornoye more and Karadeniz (both meaning Black Sea) originated during the 13th century. A 1570 map Asiae Nova Descriptio from Abraham Ortelius's Theatrum Orbis Terrarum labels the sea Mar Maggior (Great Sea), compare Latin Mare major.English writers of the 18th century often used Euxine Sea ( or ). During the Ottoman Empire, it was called either Bahr-e Siyah or Karadeniz, both meaning "Black Sea" in Ottoman Turkish, with the former consisting of Perso-Arabic .
Geography
The International Hydrographic Organization defines the limits of the Black Sea as follows:
On the Southwest. The Northeastern limit of the Sea of Marmara [A line joining Cape Rumili with Cape Anatoli (41°13'N)].
In the Kertch Strait. A line joining Cape Takil and Cape Panaghia (45°02'N).The area surrounding the Black Sea is commonly referred to as the Black Sea Region. Its northern part lies within the Chernozem belt (black soil belt) which goes from eastern Croatia (Slavonia), along the Danube (northern Serbia, northern Bulgaria (Danubian Plain) and southern Romania (Wallachian Plain)) to northeast Ukraine and further across the Central Black Earth Region and southern Russia into Siberia.The littoral zone of the Black Sea is often referred to as the Pontic littoral or Pontic zone.The largest bays of the Black Sea are Karkinit Bay in Ukraine; the Gulf of Burgas in Bulgaria; Dnieprovski Bay and Dniestrovski Bay, both in Ukraine; and Sinop Bay and Samsun Bay, both in Turkey.
Coastline and exclusive economic zones
Drainage basin
The largest rivers flowing into the Black Sea are:
These rivers and their tributaries comprise a 2-million km2 (0.77-million sq mi) Black Sea drainage basin that covers wholly or partially 24 countries:
Islands
Some islands in the Black Sea belong to Bulgaria, Romania, Turkey, and Ukraine:
Climate
Short-term climatic variation in the Black Sea region is significantly influenced by the operation of the North Atlantic oscillation, the climatic mechanisms resulting from the interaction between the north Atlantic and mid-latitude air masses. While the exact mechanisms causing the North Atlantic Oscillation remain unclear, it is thought the climate conditions established in western Europe mediate the heat and precipitation fluxes reaching Central Europe and Eurasia, regulating the formation of winter cyclones, which are largely responsible for regional precipitation inputs and influence Mediterranean sea surface temperatures (SSTs).The relative strength of these systems also limits the amount of cold air arriving from northern regions during winter. Other influencing factors include the regional topography, as depressions and storm systems arriving from the Mediterranean are funneled through the low land around the Bosporus, with the Pontic and Caucasus mountain ranges acting as waveguides, limiting the speed and paths of cyclones passing through the region.
Geology and bathymetry
The Black Sea is divided into two depositional basins—the Western Black Sea and Eastern Black Sea—separated by the Mid-Black Sea High, which includes the Andrusov Ridge, Tetyaev High, and Archangelsky High, extending south from the Crimean Peninsula. The basin includes two distinct relict back-arc basins which were initiated by the splitting of an Albian volcanic arc and the subduction of both the Paleo- and Neo-Tethys oceans, but the timings of these events remain uncertain. Arc volcanism and extension occurred as the Neo-Tethys Ocean subducted under the southern margin of Laurasia during the Mesozoic. Uplift and compressional deformation took place as the Neotethys continued to close. Seismic surveys indicate that rifting began in the Western Black Sea in the Barremian and Aptian followed by the formation of oceanic crust 20 million years later in the Santonian. Since its initiation, compressional tectonic environments led to subsidence in the basin, interspersed with extensional phases resulting in large-scale volcanism and numerous orogenies, causing the uplift of the Greater Caucasus, Pontides, southern Crimean Peninsula and Balkanides mountain ranges.
During the Messinian salinity crisis in the neighboring Mediterranean Sea, water levels fell but without drying up the sea. The collision between the Eurasian and African plates and the westward escape of the Anatolian block along the North Anatolian and East Anatolian faults dictates the current tectonic regime, which features enhanced subsidence in the Black Sea basin and significant volcanic activity in the Anatolian region. These geological mechanisms, in the long term, have caused the periodic isolations of the Black Sea from the rest of the global ocean system.
The large shelf to the north of the basin is up to 190 km (120 mi) wide and features a shallow apron with gradients between 1:40 and 1:1000. The southern edge around Turkey and the eastern edge around Georgia, however, are typified by a narrow shelf that rarely exceeds 20 km (12 mi) in width and a steep apron that is typically 1:40 gradient with numerous submarine canyons and channel extensions. The Euxine abyssal plain in the centre of the Black Sea reaches a maximum depth of 2,212 metres (7,257.22 feet) just south of Yalta on the Crimean Peninsula.
Chronostratigraphy
The Paleo-Euxinian is described by the accumulation of eolian silt deposits (related to the Riss glaciation) and the lowering of sea levels (MIS 6, 8 and 10). The Karangat marine transgression occurred during the Eemian Interglacial (MIS 5e). This may have been the highest sea levels reached in the late Pleistocene. Based on this some scholars have suggested that the Crimean Peninsula was isolated from the mainland by a shallow strait during the Eemian Interglacial.The Neoeuxinian transgression began with an inflow of waters from the Caspian Sea. Neoeuxinian deposits are found in the Black Sea below −20 m (−66 ft) water depth in three layers. The upper layers correspond with the peak of the Khvalinian transgression, on the shelf shallow-water sands and coquina mixed with silty sands and brackish-water fauna, and inside the Black Sea Depression hydrotroilite silts. The middle layers on the shelf are sands with brackish-water mollusc shells. Of continental origin, the lower level on the shelf is mostly alluvial sands with pebbles, mixed with less common lacustrine silts and freshwater mollusc shells. Inside the Black Sea Depression they are terrigenous non-carbonate silts, and at the foot of the continental slope turbidite sediments.
Hydrology
The Black Sea is the world's largest body of water with a meromictic basin. The deep waters do not mix with the upper layers of water that receive oxygen from the atmosphere. As a result, over 90% of the deeper Black Sea volume is anoxic water. The Black Sea's circulation patterns are primarily controlled by basin topography and fluvial inputs, which result in a strongly stratified vertical structure. Because of the extreme stratification, it is classified as a salt wedge estuary.
The Black Sea experiences water transfer only with the Mediterranean Sea, so all inflow and outflow occurs through the Bosporus and Dardanelles. Inflow from the Mediterranean has a higher salinity and density than the outflow, creating the classic estuarine circulation. This means that the inflow of dense water from the Mediterranean occurs at the bottom of the basin while the outflow of fresher Black Sea surface-water into the Sea of Marmara occurs near the surface. According to Gregg (2002), the outflow is 16,000 cubic metres per second (570,000 cubic feet per second) or around 500 cubic kilometres per year (120 cubic miles per year), and the inflow is 11,000 m3/s (390,000 cu ft/s) or around 350 km3/a (84 cu mi/a).The following water budget can be estimated:
Water in: 900 km3/a (220 cu mi/a)
Total river discharge: 370 km3/a (90 cu mi/a)
Precipitation: 180 km3/a (40 cu mi/a)
Inflow via Bosporus: 350 km3/a (80 cu mi/a)
Water out: 900 km3/a (220 cu mi/a)
Evaporation: 400 km3/a (100 cu mi/a) (reduced greatly since the 1970s)
Outflow via Bosporus: 500 km3/a (120 cu mi/a)The southern sill of the Bosporus is located at 36.5 m (120 ft) below present sea level (deepest spot of the shallowest cross-section in the Bosporus, located in front of Dolmabahçe Palace) and has a wet section of around 38,000 m2 (410,000 sq ft). Inflow and outflow current speeds are averaged around 0.3 to 0.4 m/s (1.0 to 1.3 ft/s), but much higher speeds are found locally, inducing significant turbulence and vertical shear. This allows for turbulent mixing of the two layers. Surface water leaves the Black Sea with a salinity of 17 practical salinity units (PSU) and reaches the Mediterranean with a salinity of 34 PSU. Likewise, an inflow of the Mediterranean with salinity 38.5 PSU experiences a decrease to about 34 PSU.Mean surface circulation is cyclonic; waters around the perimeter of the Black Sea circulate in a basin-wide shelfbreak gyre known as the Rim Current. The Rim Current has a maximum velocity of about 50–100 cm/s (20–39 in/s). Within this feature, two smaller cyclonic gyres operate, occupying the eastern and western sectors of the basin. The Eastern and Western Gyres are well-organized systems in the winter but dissipate into a series of interconnected eddies in the summer and autumn. Mesoscale activity in the peripheral flow becomes more pronounced during these warmer seasons and is subject to interannual variability.
Outside of the Rim Current, numerous quasi-permanent coastal eddies are formed as a result of upwelling around the coastal apron and "wind curl" mechanisms. The intra-annual strength of these features is controlled by seasonal atmospheric and fluvial variations. During the spring, the Batumi eddy forms in the southeastern corner of the sea.Beneath the surface waters—from about 50 to 100 metres (160 to 330 ft)—there exists a halocline that stops at the Cold Intermediate Layer (CIL). This layer is composed of cool, salty surface waters, which are the result of localized atmospheric cooling and decreased fluvial input during the winter months. It is the remnant of the winter surface mixed layer. The base of the CIL is marked by a major pycnocline at about 100–200 metres (330–660 ft), and this density disparity is the major mechanism for isolation of the deep water.
Below the pycnocline is the Deep Water mass, where salinity increases to 22.3 PSU and temperatures rise to around 8.9 °C (48.0 °F). The hydrochemical environment shifts from oxygenated to anoxic, as bacterial decomposition of sunken biomass utilizes all of the free oxygen. Weak geothermal heating and long residence time create a very thick convective bottom layer.The Black Sea undersea river is a current of particularly saline water flowing through the Bosporus Strait and along the seabed of the Black Sea. The discovery of the river, announced on August 1, 2010, was made by scientists at the University of Leeds and is the first of its kind to be identified. The undersea river stems from salty water spilling through the Bosporus Strait from the Mediterranean Sea into the Black Sea, where the water has a lower salt content.
Hydrochemistry
Because of the anoxic water at depth, organic matter, including anthropogenic artifacts such as boat hulls, are well preserved. During periods of high surface productivity, short-lived algal blooms form organic rich layers known as sapropels. Scientists have reported an annual phytoplankton bloom that can be seen in many NASA images of the region. As a result of these characteristics the Black Sea has gained interest from the field of marine archaeology, as ancient shipwrecks in excellent states of preservation have been discovered, such as the Byzantine wreck Sinop D, located in the anoxic layer off the coast of Sinop, Turkey.
Modelling shows that, in the event of an asteroid impact on the Black Sea, the release of hydrogen sulfide clouds would pose a threat to health—and perhaps even life—for people living on the Black Sea coast.There have been isolated reports of flares on the Black Sea occurring during thunderstorms, possibly caused by lightning igniting combustible gas seeping up from the sea depths.
Ecology
Marine
The Black Sea supports an active and dynamic marine ecosystem, dominated by species suited to the brackish, nutrient-rich, conditions. As with all marine food webs, the Black Sea features a range of trophic groups, with autotrophic algae, including diatoms and dinoflagellates, acting as primary producers. The fluvial systems draining Eurasia and central Europe introduce large volumes of sediment and dissolved nutrients into the Black Sea, but the distribution of these nutrients is controlled by the degree of physiochemical stratification, which is, in turn, dictated by seasonal physiographic development.During winter, strong wind promotes convective overturning and upwelling of nutrients, while high summer temperatures result in a marked vertical stratification and a warm, shallow mixed layer. Day length and insolation intensity also control the extent of the photic zone. Subsurface productivity is limited by nutrient availability, as the anoxic bottom waters act as a sink for reduced nitrate, in the form of ammonia. The benthic zone also plays an important role in Black Sea nutrient cycling, as chemosynthetic organisms and anoxic geochemical pathways recycle nutrients which can be upwelled to the photic zone, enhancing productivity.In total, the Black Sea's biodiversity contains around one-third of the Mediterranean's and is experiencing natural and artificial invasions or "Mediterranizations".
Phytoplankton
The main phytoplankton groups present in the Black Sea are dinoflagellates, diatoms, coccolithophores and cyanobacteria. Generally, the annual cycle of phytoplankton development comprises significant diatom and dinoflagellate-dominated spring production, followed by a weaker mixed assemblage of community development below the seasonal thermocline during summer months, and surface-intensified autumn production. This pattern of productivity is augmented by an Emiliania huxleyi bloom during the late spring and summer months.
DinoflagellatesAnnual dinoflagellate distribution is defined by an extended bloom period in subsurface waters during the late spring and summer. In November, subsurface plankton production is combined with surface production, due to vertical mixing of water masses and nutrients such as nitrite. The major bloom-forming dinoflagellate species in the Black Sea is Gymnodinium sp. Estimates of dinoflagellate diversity in the Black Sea range from 193 to 267 species. This level of species richness is relatively low in comparison to the Mediterranean Sea, which is attributable to the brackish conditions, low water transparency and presence of anoxic bottom waters. It is also possible that the low winter temperatures below 4 °C (39 °F) of the Black Sea prevent thermophilous species from becoming established. The relatively high organic matter content of Black Sea surface water favor the development of heterotrophic (an organism that uses organic carbon for growth) and mixotrophic dinoflagellates species (able to exploit different trophic pathways), relative to autotrophs. Despite its unique hydrographic setting, there are no confirmed endemic dinoflagellate species in the Black Sea.DiatomsThe Black Sea is populated by many species of the marine diatom, which commonly exist as colonies of unicellular, non-motile auto- and heterotrophic algae. The life-cycle of most diatoms can be described as 'boom and bust' and the Black Sea is no exception, with diatom blooms occurring in surface waters throughout the year, most reliably during March. In simple terms, the phase of rapid population growth in diatoms is caused by the in-wash of silicon-bearing terrestrial sediments, and when the supply of silicon is exhausted, the diatoms begin to sink out of the photic zone and produce resting cysts. Additional factors such as predation by zooplankton and ammonium-based regenerated production also have a role to play in the annual diatom cycle. Typically, Proboscia alata blooms during spring and Pseudosolenia calcar-avis blooms during the autumn.CoccolithophoresCoccolithophores are a type of motile, autotrophic phytoplankton that produce CaCO3 plates, known as coccoliths, as part of their life cycle. In the Black Sea, the main period of coccolithophore growth occurs after the bulk of the dinoflagellate growth has taken place. In May, the dinoflagellates move below the seasonal thermocline into deeper waters, where more nutrients are available. This permits coccolithophores to utilize the nutrients in the upper waters, and by the end of May, with favorable light and temperature conditions, growth rates reach their highest. The major bloom-forming species is Emiliania huxleyi, which is also responsible for the release of dimethyl sulfide into the atmosphere. Overall, coccolithophore diversity is low in the Black Sea, and although recent sediments are dominated by E. huxleyi and Braarudosphaera bigelowii, Holocene sediments have been shown to also contain Helicopondosphaera and Discolithina species.CyanobacteriaCyanobacteria are a phylum of picoplanktonic (plankton ranging in size from 0.2 to 2.0 µm) bacteria that obtain their energy via photosynthesis, and are present throughout the world's oceans. They exhibit a range of morphologies, including filamentous colonies and biofilms. In the Black Sea, several species are present, and as an example, Synechococcus spp. can be found throughout the photic zone, although concentration decreases with increasing depth. Other factors which exert an influence on distribution include nutrient availability, predation, and salinity.
Animal species
Zebra musselThe Black Sea along with the Caspian Sea is part of the zebra mussel's native range. The mussel has been accidentally introduced around the world and become an invasive species where it has been introduced.Common carpThe common carp's native range extends to the Black Sea along with the Caspian Sea and Aral Sea. Like the zebra mussel, the common carp is an invasive species when introduced to other habitats.Round gobyAnother native fish that is also found in the Caspian Sea. It preys upon zebra mussels. Like the mussels and common carp, it has become invasive when introduced to other environments, like the Great Lakes in North America.Marine mammals and marine megafaunaMarine mammals present within the basin include two species of dolphin (common and bottlenose) and the harbour porpoise, although all of these are endangered due to pressures and impacts by human activities. All three species have been classified as distinct subspecies from those in the Mediterranean and the Atlantic and are endemic to the Black and Azov seas, and are more active during nights in the Turkish Straits. However, construction of the Crimean Bridge has caused increases in nutrients and planktons in the waters, attracting large numbers of fish and more than 1,000 bottlenose dolphins. However, others claim that construction may cause devastating damages on the ecosystem, including dolphins.
Mediterranean monk seals, now critically endangered, were historically abundant in the Black Sea, and are regarded to have become extinct from the basin in 1997. Monk seals were present at Snake Island, near the Danube Delta, until the 1950s, and several locations such as the Danube Plavni Nature Reserve and Doğankent were the last of the seals' hauling-out sites post-1990. Very few animals still thrive in the Sea of Marmara.
Ongoing Mediterranizations may or may not boost cetacean diversity in the Turkish Straits and hence in the Black and Azov basins.
Various species of pinnipeds, sea otter, and beluga whale were introduced into the Black Sea by mankind and later escaped either by accidental or purported causes. Of these, grey seals and beluga whales have been recorded with successful, long-term occurrences.
Great white sharks are known to reach into the Sea of Marmara and Bosporus Strait and basking sharks into the Dardanelles, although it is unclear whether or not these sharks may reach into the Black and Azov basins.
Ecological effects of pollution
Since the 1960s, rapid industrial expansion along the Black Sea coastline and the construction of a major dam has significantly increased annual variability in the N:P:Si ratio in the basin. In coastal areas, the biological effect of these changes has been an increase in the frequency of monospecific phytoplankton blooms, with diatom bloom frequency increasing by a factor of 2.5 and non-diatom bloom frequency increasing by a factor of 6. The non-diatoms, such as the prymnesiophytes Emiliania huxleyi (coccolithophore), Chromulina sp., and the Euglenophyte Eutreptia lanowii, are able to out-compete diatom species because of the limited availability of silicon, a necessary constituent of diatom frustules. As a consequence of these blooms, benthic macrophyte populations were deprived of light, while anoxia caused mass mortality in marine animals.The decline in macrophytes was further compounded by overfishing during the 1970s, while the invasive ctenophore Mnemiopsis reduced the biomass of copepods and other zooplankton in the late 1980s. Additionally, an alien species—the warty comb jelly (Mnemiopsis leidyi)—was able to establish itself in the basin, exploding from a few individuals to an estimated biomass of one billion metric tons. The change in species composition in Black Sea waters also has consequences for hydrochemistry, as calcium-producing coccolithophores influence salinity and pH, although these ramifications have yet to be fully quantified. In central Black Sea waters, silicon levels were also significantly reduced, due to a decrease in the flux of silicon associated with advection across isopycnal surfaces. This phenomenon demonstrates the potential for localized alterations in Black Sea nutrient input to have basin-wide effects.
Pollution reduction and regulation efforts have led to a partial recovery of the Black Sea ecosystem during the 1990s, and an EU monitoring exercise, 'EROS21', revealed decreased nitrogen and phosphorus values, relative to the 1989 peak. Recently, scientists have noted signs of ecological recovery, in part due to the construction of new sewage treatment plants in Slovakia, Hungary, Romania, and Bulgaria in connection with membership in the European Union. Mnemiopsis leidyi populations have been checked with the arrival of another alien species which feeds on them.
History
Mediterranean connection during the Holocene
The Black Sea is connected to the World Ocean by a chain of two shallow straits, the Dardanelles and the Bosporus. The Dardanelles is 55 m (180 ft) deep, and the Bosporus is as shallow as 36 m (118 ft). By comparison, at the height of the last ice age, sea levels were more than 100 m (330 ft) lower than they are now.
There is evidence that water levels in the Black Sea were considerably lower at some point during the post-glacial period. Some researchers theorize that the Black Sea had been a landlocked freshwater lake (at least in upper layers) during the last glaciation and for some time after.
In the aftermath of the last glacial period, water levels in the Black Sea and the Aegean Sea rose independently until they were high enough to exchange water. The exact timeline of this development is still subject to debate. One possibility is that the Black Sea filled first, with excess freshwater flowing over the Bosporus sill and eventually into the Mediterranean Sea. There are also catastrophic scenarios, such as the "Black Sea deluge hypothesis" put forward by William Ryan, Walter Pitman and Petko Dimitrov.
Deluge hypothesis
The Black Sea deluge is a hypothesized catastrophic rise in the level of the Black Sea c. 5600 BC due to waters from the Mediterranean Sea breaching a sill in the Bosporus Strait. The hypothesis was headlined when The New York Times published it in December 1996, shortly before it was published in an academic journal. While it is agreed that the sequence of events described did occur, there is debate over the suddenness, dating, and magnitude of the events. Relevant to the hypothesis is that its description has led some to connect this catastrophe with prehistoric flood myths.
Archaeology
The Black Sea was sailed by Hittites, Carians, Colchians, Thracians, Greeks, Persians, Cimmerians, Scythians, Romans, Byzantines, Goths, Huns, Avars, Slavs, Varangians, Crusaders, Venetians, Genoese, Georgians, Bulgarians, Tatars and Ottomans.
The concentration of historical powers, combined with the preservative qualities of the deep anoxic waters of the Black Sea, has attracted increased interest from marine archaeologists who have begun to discover a large number of ancient ships and organic remains in a high state of preservation.
Recorded history
The Black Sea was a busy waterway on the crossroads of the ancient world: the Balkans to the west, the Eurasian steppes to the north, the Caucasus and Central Asia to the east, Asia Minor and Mesopotamia to the south, and Greece to the southwest.
The land at the eastern end of the Black Sea, Colchis (in present-day Georgia), marked for the ancient Greeks the edge of the known world.
The Pontic–Caspian steppe to the north of the Black Sea is seen by several researchers as the pre-historic original homeland(Urheimat) of the speakers of the Proto-Indo-European language (PIE).Greek presence in the Black Sea began at least as early as the 9th century BC with colonies scattered along the Black Sea's southern coast, attracting traders and colonists due to the grain grown in the Black Sea hinterland.
By 500 BC, permanent Greek communities existed all around the Black Sea, and a lucrative trade-network connected the entirety of the Black Sea to the wider Mediterranean. While Greek colonies generally maintained very close cultural ties to their founding polis, Greek colonies in the Black Sea began to develop their own Black Sea Greek culture, known today as Pontic. The coastal communities of Black Sea Greeks remained a prominent part of the Greek world for centuries, and the realms of Mithridates of Pontus, Rome and Constantinople spanned the Black Sea to include Crimean territories.
The Black Sea became a virtual Ottoman Navy lake within five years of the Republic of Genoa losing control of the Crimean Peninsula in 1479, after which the only Western merchant vessels to sail its waters were those of Venice's old rival Ragusa. The Black Sea became a trade route of slaves between Crimea and Ottoman Anatolia.
Imperial Russia became a significant Black Sea power in the late-18th century,
occupying the littoral of Novorossiya in 1764 and of Crimea in 1783. Ottoman restrictions on Black Sea navigation were challenged by the Black Sea Fleet (founded in 1783) of the Imperial Russian Navy, and the Ottomans relaxed export controls after the outbreak in 1789 of the French Revolution.
Modern history
The Crimean War, fought between 1853 and 1856, saw naval engagements between the French and British allies and the forces of Nicholas I of Russia. On the 2 March 1855 death of Nicholas I, Alexander II became Tsar. On 15 January 1856, the new tsar took Russia out of the war on the very unfavourable terms of the Treaty of Paris (1856), which included the loss of a naval fleet on the Black Sea, and the provision that the Black Sea was to be a demilitarized zone similar to a contemporaneous region of the Baltic Sea.
World Wars
The Black Sea was a significant naval theatre of World War I (1914–1918) and saw both naval and land battles between 1941 and 1945 during World War II. For example, Sevastopol was obliterated by the Nazis, who even brought Schwerer Gustav to the Siege of Sevastopol (1941–1942). The Soviet naval base was one of the strongest fortifications in the world. Its site, on a deeply eroded, bare limestone promontory at the southwestern tip of the Crimea, made an approach by land forces exceedingly difficult. The high-level cliffs overlooking Severnaya Bay protected the anchorage, making an amphibious landing just as dangerous. The Soviet Navy had built upon these natural defenses by modernizing the port and installing heavy coastal batteries consisting of 180mm and 305mm re-purposed battleship guns which were capable of firing inland as well as out to sea. The artillery emplacements were protected by reinforced concrete fortifications and 9.8-inch thick armored turrets.
21st century
During the Russian invasion of Ukraine, Snake Island was a source of contention. On 24 February 2022, two Russian navy warships attacked and captured Snake Island. It was subsequently bombarded heavily by Ukraine. On 30 June 2022, Ukraine announced that it had driven Russian forces off the island.On 6 May 2022 the flagship of the Black Sea Fleet, Russian cruiser Moskva was sunk by Ukrainian missiles.As early as 29 April 2022 submarines of the Black Sea Fleet were used by Russia to bombard Ukrainian cities with Kalibr SLCMs. The Kalibr missile was so successful that on 10 March 2023 Defense Minister Sergey Shoigu announced plans to broaden the type of ship which carried it, to include the corvette Steregushchiy and the nuclear-powered cruiser Admiral Nakhimov.On the morning of 14 March 2023, a Russian Su-27 fighter jet intercepted and damaged an American MQ-9 Reaper drone, causing the latter to crash into the Black Sea. At 13:20 on 5 May 2023 a Russian Su-35 fighter jet intercepted and threatened the safety of a Polish L-140 Turbolet on a "routine Frontex patrol mission.. and performed 'aggressive and dangerous' manoeuvres". The incident, which occurred "in international airspace over the Black Sea about 60km" east of Romanian airspace, "caused the crew of five Polish border guards to lose control of the plane and lose altitude."
Economy and politics
The Black Sea plays an integral part in the connection between Asia and Europe. In addition to sea ports and fishing, key activities include hydrocarbons exploration for oil and natural gas, and tourism.
According to NATO, the Black Sea is a strategic corridor that provides smuggling channels for moving legal and illegal goods including drugs, radioactive materials, and counterfeit goods that can be used to finance terrorism.
Navigation
According to an International Transport Workers' Federation 2013 study, there were at least 30 operating merchant seaports in the Black Sea (including at least 12 in Ukraine). There were also around 2,400 commercial vessels operating in the Black Sea.
Fishing
The Turkish commercial fishing fleet catches around 300,000 tons of anchovies per year. The fishery is carried out mainly in winter, and the highest portion of the stock is caught between November and December.
Hydrocarbon exploration
In the 1980s, the Soviet Union started offshore drilling for petroleum in the sea's western portion (adjoining Ukraine's coast). Independent Ukraine continued and intensified that effort within its exclusive economic zone, inviting major international oil companies for exploration. Discovery of the new, massive oilfields in the area stimulated an influx of foreign investments. It also provoked a short-term peaceful territorial dispute with Romania which was resolved in 2011 by an international court redefining the exclusive economic zones between the two countries.
The Black Sea contains oil and natural gas resources but exploration in the sea is incomplete. As of 2017, 20 wells are in place. Throughout much of its existence, the Black Sea has had significant oil and gas-forming potential because of significant inflows of sediment and nutrient-rich waters. However, this varies geographically. For example, prospects are poorer off the coast of Bulgaria because of the large influx of sediment from the Danube which obscured sunlight and diluted organic-rich sediments. Many of the discoveries to date have taken place offshore of Romania in the Western Black Sea and only a few discoveries have been made in the Eastern Black Sea.
During the Eocene, the Paratethys Sea was partially isolated and sea levels fell. During this time sand shed off the rising Balkanide, Pontide and Caucasus mountains trapped organic material in the Maykop Suite of rocks through the Oligocene and early Miocene. Natural gas appears in rocks deposited in the Miocene and Pliocene by the paleo-Dnieper and paleo-Dniester rivers, or in deep-water Oligocene-age rocks. Serious exploration began in 1999 with two deep-water wells, Limanköy-1 and Limanköy-2, drilled in Turkish waters. Next, the HPX (Hopa)-1 deepwater well targeted late Miocene sandstone units in Achara-Trialet fold belt (also known as the Gurian fold belt) along the Georgia-Turkey maritime border. Although geologists inferred that these rocks might have hydrocarbons that migrated from the Maykop Suite, the well was unsuccessful. No more drilling happened for five years after the HPX-1 well. Then in 2010, Sinop-1 targeted carbonate reservoirs potentially charged from the nearby Maykop Suite on the Andrusov Ridge, but the well-struck only Cretaceous volcanic rocks. Yassihöyük-1 encountered similar problems. Other Turkish wells, Sürmene-1 and Sile-1 drilled in the Eastern Black Sea in 2011 and 2015 respectively tested four-way closures above Cretaceous volcanoes, with no results in either case. A different Turkish well, Kastamonu-1 drilled in 2011 did successfully find thermogenic gas in Pliocene and Miocene shale-cored anticlines in the Western Black Sea. A year later in 2012, Romania drilled Domino-1 which struck gas prompting the drilling of other wells in the Neptun Deep. In 2016, the Bulgarian well Polshkov-1 targeted Maykop Suite sandstones in the Polshkov High and Russia is in the process of drilling Jurassic carbonates on the Shatsky Ridge as of 2018.In August 2020, Turkey found 320 billion cubic metres (11 trillion cubic feet) of natural gas in the biggest ever discovery in the Black Sea, and hoped to begin production in the Sakarya Gas Field by 2023. The sector is near where Romania has also found gas reserves.
Trans-sea cooperation
Urban areas
Tourism
In the years following the end of the Cold War, the popularity of the Black Sea as a tourist destination steadily increased. Tourism at Black Sea resorts became one of the region's growth industries.The following is a list of notable Black Sea resort towns:
Modern military use
The 1936 Montreux Convention provides for free passage of civilian ships between the international waters of the Black and the Mediterranean seas. However, a single country (Turkey) has complete control over the straits connecting the two seas. Military ships are categorised separately from civilian vessels and can pass through the straits only if the ship belongs to a Black Sea country. Other military ships have the right to pass through the straits if they are not in a war against Turkey and if they stay in the Black Sea basin for a limited time. The 1982 amendments to the Montreux Convention allow Turkey to close the straits at its discretion in both war and peacetime.The Montreux Convention governs the passage of vessels between the Black, the Mediterranean and Aegean seas and the presence of military vessels belonging to non-littoral states in the Black Sea waters.The Russian Black Sea Fleet has its official primary headquarters and facilities in the city of Sevastopol (Sevastopol Naval Base).The Soviet hospital ship Armenia was sunk on 7 November 1941 by German aircraft while evacuating civilians and wounded soldiers from Crimea. It has been estimated that approximately 5,000 to 7,000 people were killed during the sinking, making it one of the deadliest maritime disasters in history. There were only eight survivors.In December 2018, the Kerch Strait incident occurred, in which the Russian navy and coast guard took control of three Ukrainian vessels as the ships were trying to enter the Black Sea.In April 2022, during the Russian invasion of Ukraine, the Russian cruiser Moskva was sunk in the western Black Sea by sea-skimming Neptune missiles of the Ukrainian armed forces while the Russians claimed that an onboard fire had caused munitions to explode and damage the ship extensively. She was the largest ship to be lost in naval combat in Europe since World War II.
See also
1927 Crimean earthquakes
Kerch Strait
Regions of Europe
Sea of Azov
Notes and references
Informational notes
Citations
General and cited references
External links
Space Monitoring of the Black Sea Coastline and Waters
Pictures of the Black sea coast all along the Crimean peninsula
Black Sea Environmental Internet Node
Black Sea-Mediterranean Corridor during the last 30 ky: UNESCO IGCP 521 WG12 |
calymmian | The Calymmian Period (from Ancient Greek: κάλυμμα, romanized: kálymma, meaning "cover") is the first geologic period in the Mesoproterozoic Era and lasted from 1600 Mya to 1400 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
The period is characterised by expansion of existing platform covers, or by new platforms on recently cratonized basements.
The supercontinent Columbia started to break up during the Calymmian some 1500 Mya.
The Volyn biota have been dated to 1500 Mya.
See also
Boring Billion – Earth history, 1.8 to 0.8 billion years ago
Jotnian – Oldest known sediments in the Baltic area that have not been subject to metamorphism
References
"Calymmian Period". GeoWhen Database. Archived from the original on May 12, 2006. Retrieved January 5, 2006.
James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492. |
system (stratigraphy) | A system in stratigraphy is a sequence of strata (rock layers) that were laid down together within the same corresponding geological period. The associated period is a chronological time unit, a part of the geological time scale, while the system is a unit of chronostratigraphy. Systems are unrelated to lithostratigraphy, which subdivides rock layers on their lithology. Systems are subdivisions of erathems and are themselves divided into series and stages.
Systems in the geological timescale
The systems of the Phanerozoic were defined during the 19th century, beginning with the Cretaceous (by Belgian geologist Jean d'Omalius d'Halloy in the Paris Basin) and the Carboniferous (by British geologists William Conybeare and William Phillips) in 1822). The Paleozoic and Mesozoic were divided into the currently used systems before the second half of the 19th century, except for a minor revision when the Ordovician system was added in 1879.
The Cenozoic has seen more recent revisions by the International Commission on Stratigraphy. It has been divided into three systems with the Paleogene and Neogene replacing the former Tertiary System though the succeeding Quaternary remains. The one-time system names of Paleocene, Eocene, Oligocene, Miocene and Pliocene are now series within the Paleogene and Neogene.
Another recent development is the official division of the Proterozoic into systems, which was decided in 2004.
Notes
References
Gehling, James; Jensen, Sören; Droser, Mary; Myrow, Paul; Narbonne, Guy (March 2001). "Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland". Geological Magazine. 138 (2): 213–218. Bibcode:2001GeoM..138..213G. doi:10.1017/S001675680100509X. S2CID 131211543. 1.
Hedberg, H.D., (editor), International stratigraphic guide: A guide to stratigraphic classification, terminology, and procedure, New York, John Wiley and Sons, 1976
International Stratigraphic Chart from the International Commission on Stratigraphy
USA National Park Service
Washington State University
Web Geological Time Machine
Eon or Aeon, Math Words - An alphabetical index
External links
The Global Boundary Stratotype Section and Point (GSSP): overview
Chart of The Global Boundary Stratotype Sections and Points (GSSP): chart
Geotime chart displaying geologic time periods compared to the fossil record - Deals with chronology and classifications for laymen (not GSSPs)
International Commission on Stratigraphy page on Chronostratigraphy : overview |
list of index fossils | Index fossils (also known as guide fossils or indicator fossils) are fossils used to define and identify geologic periods (or faunal stages). Index fossils must have a short vertical range, wide geographic distribution and rapid evolutionary trends. Another term, Zone fossil is used when the fossil have all the characters stated above except wide geographical distribution, they are limited to a zone and can't be used for correlations of strata.
See also
Biostratigraphy#Index fossils
== References == |
cambrian | The Cambrian Period ( KAM-bree-ən, KAYM-; sometimes symbolized Ꞓ) is the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago (mya) to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, and its base, are somewhat in flux.
The period was established as "Cambrian series" by Adam Sedgwick, who named it after Cambria, the Latin name for 'Cymru' (Wales), where Britain's Cambrian rocks are best exposed. Sedgwick identified the layer as part of his task, along with Roderick Murchison, to subdivide the large "Transition Series", although the two geologists disagreed for a while on the appropriate categorization.The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, scientific understanding of the Cambrian biology surpasses that of some later periods.The Cambrian marked a profound change in life on Earth: prior to the Cambrian, the majority of living organisms on the whole were small, unicellular and simple (Ediacaran fauna and earlier Tonian Huainan biota being notable exceptions). Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized – hence readily fossilized – organisms became common.The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla. Phylogenetic analysis has supported the view that before the Cambrian radiation, in the Cryogenian or Tonian, animals (metazoans) evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates.
Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren – with nothing more complex than a microbial soil crust and a few molluscs and arthropods (albeit not terrestrial) that emerged to browse on the microbial biofilm.By the end of the Cambrian, myriapods, arachnids, and hexapods started adapting to the land, along with the first plants. Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia. The seas were relatively warm, and polar ice was absent for much of the period.
Stratigraphy
The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period.
The base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage.
The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is problematic because very similar trace fossils belonging to the Treptichnids group are found well below T. pedum in Namibia, Spain and Newfoundland, and possibly in the western US. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.
Subdivisions
The Cambrian is divided into four epochs (series) and ten ages (stages). Currently only three series and six stages are named and have a GSSP (an internationally agreed-upon stratigraphic reference point).
Because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian (Caerfai or Waucoban, 538.8 ± 0.2 to 509 ± 1.9 mya), Middle Cambrian (St Davids or Albertan, 509 ± 0.2 to 497 ± 1.9 mya) and Late Cambrian (497 ± 0.2 to 485.4 ± 1.9 mya; also known as Merioneth or Croixan).
Trilobite zones allow biostratigraphic correlation in the Cambrian. Rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian.
Each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance:
*Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.
Dating the Cambrian
The International Commission on Stratigraphy lists the Cambrian Period as beginning at 538.8 million years ago and ending at 485.4 million years ago.
The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier, led to calls for a more precisely defined base to the Cambrian Period.Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian Period, which was to be correlated worldwide by the earliest appearance of Treptichnus pedum. Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, and it is the T. pedum ichnofossil assemblage that is now formally used to correlate the base of the Cambrian.This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate. A more precise date using modern radiometric dating yield a date of 538.8 ± 0.2 million years ago. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, and to the disappearance of distinctive Ediacaran fossils (Namacalathus, Cloudina). Nevertheless, there are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata – which would mean that dates from other sections, ranging from 544 or 542 Ma, are more suitable.
Paleogeography
Plate reconstructions suggest a global supercontinent, Pannotia, was in the process of breaking up early in the Cambrian, with Laurentia (North America), Baltica, and Siberia having separated from the main supercontinent of Gondwana to form isolated land masses. Most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian.With a lack of sea ice – the great glaciers of the Marinoan Snowball Earth were long melted – the sea level was high, which led to large areas of the continents being flooded in warm, shallow seas ideal for sea life. The sea levels fluctuated somewhat, suggesting there were "ice ages", associated with pulses of expansion and contraction of a south polar ice cap.In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into an epicontinental sea.
Climate
Glaciers likely existed during the earliest Cambrian at high and possibly even at middle palaeolatitudes, possibly due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents. Middle Terreneuvian deposits, corresponding to the boundary between the Fortunian and Stage 2, show evidence of glaciation. However, other authors believe these very early, pretrilobitic glacial deposits may not even be of Cambrian age at all but instead date back to the Neoproterozoic, an era characterised by numerous severe icehouse periods.The beginning of Stage 3 was relatively cool, with the period between 521 and 517 Ma being known as the Cambrian Arthropod Radiation Cool Event (CARCE). The Earth was generally very warm during Stage 4; its climate was comparable to the hot greenhouse of the Late Cretaceous and Early Palaeogene, as evidenced by a maximum in continental weathering rates over the last 900 million years and the presence of tropical, lateritic palaeosols at high palaeolatitudes during this time.The Archaecyathid Extinction Warm Event (AEWE), lasting from 511 to 510.5 Ma, was particularly warm. Another warm event, the Redlichiid-Olenid Extinction Warm Event, occurred at the beginning of the Wuliuan. It became even warmer towards the end of the period, and sea levels rose dramatically. This warming trend continued into the Early Ordovician, the start of which was characterised by an extremely hot global climate.
Flora
The Cambrian flora was little different from the Ediacaran. The principal taxa were the marine macroalgae Fuxianospira, Sinocylindra, and Marpolia. No calcareous macroalgae are known from the period.No land plant (embryophyte) fossils are known from the Cambrian. However, biofilms and microbial mats were well developed on Cambrian tidal flats and beaches 500 mya, and microbes forming microbial Earth ecosystems, comparable with modern soil crust of desert regions, contributing to soil formation. Although molecular clock estimates suggest terrestrial plants may have first emerged during the Middle or Late Cambrian, the consequent large-scale removal of the greenhouse gas CO2 from the atmosphere through sequestration did not begin until the Ordovician.
Oceanic life
The Cambrian explosion was a period of rapid multicellular growth. Most animal life during the Cambrian was aquatic. Trilobites were once assumed to be the dominant life form at that time, but this has proven to be incorrect. Arthropods were by far the most dominant animals in the ocean, but trilobites were only a minor part of the total arthropod diversity. What made them so apparently abundant was their heavy armor reinforced by calcium carbonate (CaCO3), which fossilized far more easily than the fragile chitinous exoskeletons of other arthropods, leaving numerous preserved remains.The period marked a steep change in the diversity and composition of Earth's biosphere. The Ediacaran biota suffered a mass extinction at the start of the Cambrian Period, which corresponded with an increase in the abundance and complexity of burrowing behaviour. This behaviour had a profound and irreversible effect on the substrate which transformed the seabed ecosystems. Before the Cambrian, the sea floor was covered by microbial mats. By the end of the Cambrian, burrowing animals had destroyed the mats in many areas through bioturbation. As a consequence, many of those organisms that were dependent on the mats became extinct, while the other species adapted to the changed environment that now offered new ecological niches. Around the same time there was a seemingly rapid appearance of representatives of all the mineralized phyla, including the Bryozoa, which were once thought to have only appeared in the Lower Ordovician. However, many of those phyla were represented only by stem-group forms; and since mineralized phyla generally have a benthic origin, they may not be a good proxy for (more abundant) non-mineralized phyla.
While the early Cambrian showed such diversification that it has been named the Cambrian Explosion, this changed later in the period, when there occurred a sharp drop in biodiversity. About 515 million years ago, the number of species going extinct exceeded the number of new species appearing. Five million years later, the number of genera had dropped from an earlier peak of about 600 to just 450. Also, the speciation rate in many groups was reduced to between a fifth and a third of previous levels. 500 million years ago, oxygen levels fell dramatically in the oceans, leading to hypoxia, while the level of poisonous hydrogen sulfide simultaneously increased, causing another extinction. The later half of Cambrian was surprisingly barren and showed evidence of several rapid extinction events; the stromatolites which had been replaced by reef building sponges known as Archaeocyatha, returned once more as the archaeocyathids became extinct. This declining trend did not change until the Great Ordovician Biodiversification Event.Some Cambrian organisms ventured onto land, producing the trace fossils Protichnites and Climactichnites. Fossil evidence suggests that euthycarcinoids, an extinct group of arthropods, produced at least some of the Protichnites. Fossils of the track-maker of Climactichnites have not been found; however, fossil trackways and resting traces suggest a large, slug-like mollusc.In contrast to later periods, the Cambrian fauna was somewhat restricted; free-floating organisms were rare, with the majority living on or close to the sea floor; and mineralizing animals were rarer than in future periods, in part due to the unfavourable ocean chemistry.Many modes of preservation are unique to the Cambrian, and some preserve soft body parts, resulting in an abundance of Lagerstätten. These include Sirius Passet, the Sinsk Algal Lens, the Maotianshan Shales, the Emu Bay Shale, and the Burgess Shale,.
Symbol
The United States Federal Geographic Data Committee uses a "barred capital C" ⟨Ꞓ⟩ character to represent the Cambrian Period.
The Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR.
Gallery
See also
Cambrian–Ordovician extinction event – circa 488 mya
Dresbachian extinction event—circa 499 mya
End Botomian extinction event—circa 513 mya
List of fossil sites (with link directory)
Type locality (geology), the locality where a particular rock type, stratigraphic unit, fossil or mineral species is first identified
References
Further reading
Amthor, J. E.; Grotzinger, John P.; Schröder, Stefan; Bowring, Samuel A.; Ramezani, Jahandar; Martin, Mark W.; Matter, Albert (2003). "Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian boundary in Oman". Geology. 31 (5): 431–434. Bibcode:2003Geo....31..431A. doi:10.1130/0091-7613(2003)031<0431:EOCANA>2.0.CO;2.
Collette, J. H.; Gass, K. C.; Hagadorn, J. W. (2012). "Protichnites eremita unshelled? Experimental model-based neoichnology and new evidence for a euthycarcinoid affinity for this ichnospecies". Journal of Paleontology. 86 (3): 442–454. Bibcode:2012JPal...86..442C. doi:10.1666/11-056.1. S2CID 129234373.
Collette, J. H.; Hagadorn, J. W. (2010). "Three-dimensionally preserved arthropods from Cambrian Lagerstatten of Quebec and Wisconsin". Journal of Paleontology. 84 (4): 646–667. doi:10.1666/09-075.1. S2CID 130064618.
Getty, P. R.; Hagadorn, J. W. (2008). "Reinterpretation of Climactichnites Logan 1860 to include subsurface burrows, and erection of Musculopodus for resting traces of the trailmaker". Journal of Paleontology. 82 (6): 1161–1172. Bibcode:2008JPal...82.1161G. doi:10.1666/08-004.1. S2CID 129732925.
Gould, S. J. (1989). Wonderful Life: the Burgess Shale and the Nature of Life. New York: Norton. ISBN 9780393027051.
Howe, John Allen (1911). "Cambrian System" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 05 (11th ed.). Cambridge University Press. pp. 86–89.
Ogg, J. (June 2004). "Overview of Global Boundary Stratotype Sections and Points (GSSPs)". Archived from the original on 23 April 2006. Retrieved 30 April 2006.
Owen, R. (1852). "Description of the impressions and footprints of the Protichnites from the Potsdam sandstone of Canada". Geological Society of London Quarterly Journal. 8 (1–2): 214–225. doi:10.1144/GSL.JGS.1852.008.01-02.26. S2CID 130712914.
Peng, S.; Babcock, L.E.; Cooper, R.A. (2012). "The Cambrian Period" (PDF). The Geologic Time Scale. Archived from the original (PDF) on 12 February 2015. Retrieved 14 January 2015.
Schieber, J.; Bose, P. K.; Eriksson, P. G.; Banerjee, S.; Sarkar, S.; Altermann, W.; Catuneau, O. (2007). Atlas of Microbial Mat Features Preserved within the Clastic Rock Record. Elsevier. pp. 53–71. ISBN 9780444528599.
Yochelson, E. L.; Fedonkin, M. A. (1993). "Paleobiology of Climactichnites, and Enigmatic Late Cambrian Fossil". Smithsonian Contributions to Paleobiology. 74 (74): 1–74. doi:10.5479/si.00810266.74.1.
External links
Cambrian period on In Our Time at the BBC
Biostratigraphy – includes information on Cambrian trilobite biostratigraphy
Sam Gon's trilobite pages (contains numerous Cambrian trilobites)
Examples of Cambrian Fossils
Paleomap Project
Report on the web on Amthor and others from Geology vol. 31
Weird Life on the Mats
Chronostratigraphy scale v.2018/08 | Cambrian |
stenian | The Stenian Period ( STEE-nee-ən, from Ancient Greek: στενός, romanized: stenós, meaning "narrow") is the final geologic period in the Mesoproterozoic Era and lasted from 1200 Mya to 1000 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically. The name derives from narrow polymetamorphic belts formed over this period.
Preceded by the Ectasian Period and followed by the Neoproterozoic Era.
The supercontinent Rodinia assembled during the Stenian. It would last into the Tonian Period.
This period includes the formation of the Keweenawan Rift at about 1100 Mya.Fossils of the oldest known sexually reproducing organism, Bangiomorpha pubescens, first appeared in the Stenian.
See also
Boring Billion – Earth history, 1.8 to 0.8 billion years ago
Riphean (stage) – stage in the geological timescale named after the UralsPages displaying wikidata descriptions as a fallback
Notes
References
"Stenian Period". GeoWhen Database. Archived from the original on May 12, 2006. Retrieved January 5, 2006.
James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492. |
devonian | The Devonian ( də-VOH-nee-ən, deh-) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, 419.2 million years ago (Ma), to the beginning of the Carboniferous, 358.9 Ma. It is named after Devon, England, where rocks from this period were first studied.
The first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. The arthropod groups of myriapods, arachnids and hexapods also became well-established early in this period, after starting their expansion to land at least from the Ordovician period.
Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fishes. The placoderms began dominating almost every known aquatic environment. The ancestors of all four-limbed vertebrates (tetrapods) began adapting to walk on land, as their strong pectoral and pelvic fins gradually evolved into legs, though they were not fully established until the Late Carboniferous. In the oceans, primitive sharks became more numerous than in the Silurian and Late Ordovician.
The first ammonites, a subclass of molluscs, appeared. Trilobites, the mollusc-like brachiopods, and the great coral reefs were still common. The Late Devonian extinction which started about 375 million years ago severely affected marine life, killing off all placodermi, and all trilobites, save for a few species of the order Proetida.
Devonian palaeogeography was dominated by the supercontinent of Gondwana to the south, the small continent of Siberia to the north, and the medium-sized continent of Laurussia to the east. Major tectonic events include the closure of the Rheic Ocean, the separation of South China from Gondwana, and the resulting expansion of the Paleo-Tethys Ocean. The Devonian experienced several major mountain-building events as Laurussia and Gondwana approached; these include the Acadian Orogeny in North America and the beginning of the Variscan Orogeny in Europe. These early collisions preceded the formation of Pangaea in the Late Paleozoic.
History of definition
The period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was eventually resolved by the definition of the Devonian Period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough. Murchison and Sedgwick won the debate and named the period they proposed as the Devonian System.While the rock beds that define the start and end of the Devonian Period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Ma, to the beginning of the Carboniferous 358.9 Ma – in North America, at the beginning of the Mississippian subperiod of the Carboniferous.
In 19th-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian, Breconian, and Farlovian stages, the latter three of which are placed in the Devonian.The Devonian has also erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid. In fact the climate in the Devonian differed greatly during its epochs and between geographic regions. For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, Australia, North America, and China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common.
Subdivisions
The Devonian Period is formally broken into Early, Middle and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System.
Early DevonianThe Early Devonian lasted from 419.2 to 393.3 Ma. It began with the Lochkovian Stage 419.2 to 410.8 Ma, which was followed by the Pragian from 410.8 to 407.6 Ma and then by the Emsian, which lasted until the Middle Devonian began, 393.3 Ma.
During this time, the first ammonoids appeared, descending from bactritoid nautiloids. Ammonoids during this time period were simple and differed little from their nautiloid counterparts. These ammonoids belong to the order Agoniatitida, which in later epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida. This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic Era.
Middle DevonianThe Middle Devonian comprised two subdivisions: first the Eifelian, which then gave way to the Givetian 387.7 Ma. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments partly due to drastic environmental changes and partly due to the increasing competition, predation, and diversity of jawed fishes. The shallow, warm, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, and the ability to crawl out of the water and onto the land for short periods of time.
Late DevonianFinally, the Late Devonian started with the Frasnian, 382.7 to 372.2 Ma, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivision, the beginning and end of which are marked with extinction events. This lasted until the end of the Devonian, 358.9 Ma.
Climate
The Devonian was a relatively warm period, although significant glaciers may have existed during the Early and Middle Devonian. The temperature gradient from the equator to the poles was not as large as it is today. The weather was also very arid, mostly along the equator where it was the driest. Reconstruction of tropical sea surface temperature from conodont apatite implies an average value of 30 °C (86 °F) in the Early Devonian. CO2 levels dropped steeply throughout the Devonian Period. The newly evolved forests drew carbon out of the atmosphere, which were then buried into sediments. This may be reflected by a Mid-Devonian cooling of around 5 °C (9 °F). The Late Devonian warmed to levels equivalent to the Early Devonian; while there is no corresponding increase in CO2 concentrations, continental weathering increases (as predicted by warmer temperatures); further, a range of evidence, such as plant distribution, points to a Late Devonian warming. The climate would have affected the dominant organisms in reefs; microbes would have been the main reef-forming organisms in warm periods, with corals and stromatoporoid sponges taking the dominant role in cooler times. The warming at the end of the Devonian may even have contributed to the extinction of the stromatoporoids. At the terminus of the Devonian, Earth rapidly cooled into an icehouse, marking the beginning of the Late Palaeozoic Ice Age.
Paleogeography
The Devonian world involved many continents and ocean basins of various sizes. The largest continent, Gondwana, was located entirely within the Southern Hemisphere. It corresponds to modern day South America, Africa, Australia, Antarctica, and India, as well as minor components of North America and Asia. The second-largest continent, Laurussia, was northwest of Gondwana, and corresponds to much of modern-day North America and Europe. Various smaller continents, microcontinents, and terranes were present east of Laurussia and north of Gondwana, corresponding to parts of Europe and Asia. The Devonian Period was a time of great tectonic activity, as the major continents of Laurussia and Gondwana drew closer together.Sea levels were high worldwide, and much of the land lay under shallow seas, where tropical reef organisms lived. The enormous "world ocean", Panthalassa, occupied much of the Northern Hemisphere as well as wide swathes east of Gondwana and west of Laurussia. Other minor oceans were the Paleo-Tethys Ocean and Rheic Ocean.
Laurussia
By the early Devonian, the continent Laurussia (also known as Euramerica) was fully formed through the collision of the continents Laurentia (modern day North America) and Baltica (modern day northern and eastern Europe). The tectonic effects of this collision continued into the Devonian, producing a string of mountain ranges along the southeastern coast of the continent. In present-day eastern North America, the Acadian Orogeny continued to raise the Appalachian Mountains. Further east, the collision also extended the rise of the Caledonian Mountains of Great Britain and Scandinavia. As the Caledonian Orogeny wound down in the later part of the period, orogenic collapse facilitated a cluster of granite intrusions in Scotland.Most of Laurussia was located south of the equator, but in the Devonian it moved northwards and began to rotate counterclockwise towards its modern position. While the most northern parts of the continent (such as Greenland and Ellesmere Island) established tropical conditions, most of the continent was located within the natural dry zone along the Tropic of Capricorn, which (as nowadays) is a result of the convergence of two great air-masses, the Hadley cell and the Ferrel cell. In these near-deserts, the Old Red Sandstone sedimentary beds formed, made red by the oxidised iron (hematite) characteristic of drought conditions. The abundance of red sandstone on continental land also lends Laurussia the name "the Old Red Continent". For much of the Devonian, the majority of western Laurussia (North America) was covered by subtropical inland seas which hosted a diverse ecosystem of reefs and marine life. Devonian marine deposits are particularly prevalent in the midwestern and northeastern United States. Devonian reefs also extended along the southeast edge of Laurussia, a coastline now corresponding to southern England, Belgium, and other mid-latitude areas of Europe.In the Early and Middle Devonian, the west coast of Laurussia was a passive margin with broad coastal waters, deep silty embayments, river deltas and estuaries, found today in Idaho and Nevada. In the Late Devonian, an approaching volcanic island arc reached the steep slope of the continental shelf and began to uplift deep water deposits. This minor collision sparked the start of a mountain-building episode called the Antler orogeny, which extended into the Carboniferous. Mountain building could also be found in the far northeastern extent of the continent, as minor tropical island arcs and detached Baltic terranes re-join the continent. Deformed remnants of these mountains can still be found on Ellesmere Island and Svalbard. Many of the Devonian collisions in Laurussia produce both mountain chains and foreland basins, which are frequently fossiliferous.
Gondwana
Gondwana was by far the largest continent on the planet. It was completely south of the equator, although the northeastern sector (now Australia) did reach tropical latitudes. The southwestern sector (now South America) was located to the far south, with Brazil situated near the South Pole. The northwestern edge of Gondwana was an active margin for much of the Devonian, and saw the accretion of many smaller land masses and island arcs. These include Chilenia, Cuyania, and Chaitenia, which now form much of Chile and Patagonia. These collisions were associated with volcanic activity and plutons, but by the Late Devonian the tectonic situation had relaxed and much of South America was covered by shallow seas. These south polar seas hosted a distinctive brachiopod fauna, the Malvinokaffric Realm, which extended eastward to marginal areas now equivalent to South Africa and Antarctica. Malvinokaffric faunas even managed to approach the South Pole via a tongue of Panthalassa which extended into the Paraná Basin.The northern rim of Gondwana was mostly a passive margin, hosting extensive marine deposits in areas such as northwest Africa and Tibet. The eastern margin, though warmer than the west, was equally active. Numerous mountain building events and granite and kimberlite intrusions affected areas equivalent to modern day eastern Australia, Tasmania, and Antarctica.
Asian terranes
Several island microcontinents (which would later coalesce into modern day Asia) stretched over a low-latitude archipelago to the north of Gondwana. They were separated from the southern continent by an oceanic basin: the Paleo-Tethys. Although the western Paleo-Tethys Ocean had existed since the Cambrian, the eastern part only began to rift apart as late as the Silurian. This process accelerated in the Devonian. The eastern branch of the Paleo-Tethys was fully opened when South China and Annamia (a terrane equivalent to most of Indochina), together as a unified continent, detached from the northeastern sector of Gondwana. Nevertheless, they remained close enough to Gondwana that their Devonian fossils were more closely related to Australian species than to north Asian species. Other Asian terranes remained attached to Gondwana, including Sibumasu (western Indochina), Tibet, and the rest of the Cimmerian blocks.While the South China-Annamia continent was the newest addition to the Asian microcontinents, it was not the first. North China and the Tarim Block (now northwesternmost China) were located westward and continued to drift northwards, powering over older oceanic crust in the process. Further west was a small ocean (the Turkestan Ocean), followed by the larger microcontinents of Kazakhstania, Siberia, and Amuria. Kazakhstania was a volcanically active region during the Devonian, as it continued to assimilate smaller island arcs. The island arcs of the region, such as the Balkhash-West Junggar Arc, exhibited biological endemism as a consequence of their location.Siberia was located just north of the equator as the largest landmass in the Northern Hemisphere. At the beginning of the Devonian, Siberia was inverted (upside down) relative to its modern orientation. Later in the period it moved northwards and began to twist clockwise, though it was not near its modern location. Siberia approached the eastern edge of Laurussia as the Devonian progressed, but it was still separated by a seaway, the Ural Ocean. Although Siberia's margins were generally tectonically stable and ecologically productive, rifting and deep mantle plumes impacted the continent with flood basalts during the Late Devonian. The Altai-Sayan region was shaken by volcanism in the Early and Middle Devonian, while Late Devonian magmatism was magnified further to produce the Vilyuy Traps, flood basalts which may have contributed to the Late Devonian Mass Extinction. The last major round of volcanism, the Yakutsk Large Igneous Province, continued into the Carboniferous to produce extensive kimberlite deposits.Similar volcanic activity also affected the nearby microcontinent of Amuria (now Manchuria, Mongolia and their vicinities). Though certainly close to Siberia in the Devonian, the precise location of Amuria is uncertain due to contradictory paleomagnetic data.
Closure of the Rheic Ocean
The Rheic Ocean, which separated Laurussia from Gondwana, was wide at the start of the Devonian, having formed after the drift of Avalonia away from Gondwana. It steadily shrunk as the period continued, as the two major continents approached near the equator in the early stages of the assembly of Pangaea. The closure of the Rheic Ocean began in the Devonian and continued into the Carboniferous. As the ocean narrowed, endemic marine faunas of Gondwana and Laurussia combined into a single tropical fauna. The history of the western Rheic Ocean is a subject of debate, but there is good evidence that Rheic oceanic crust experienced intense subduction and metamorphism under Mexico and Central America.The closure of the eastern part of the Rheic Ocean is associated with the assemblage of central and southern Europe. In the early Paleozoic, much of Europe was still attached to Gondwana, including the terranes of Iberia, Armorica (France), Palaeo-Adria (the western Mediterranean area), Bohemia, Franconia, and Saxothuringia. These continental blocks, collectively known as the Armorican Terrane Assemblage, split away from Gondwana in the Silurian and drifted towards Laurussia through the Devonian. Their collision with Laurussia leads to the beginning of the Variscan Orogeny, a major mountain-building event which would escalate further in the Late Paleozoic. Franconia and Saxothuringia collided with Laurussia near the end of the Early Devonian, pinching out the easternmost Rheic Ocean. The rest of the Armorican terranes followed, and by the end of the Devonian they were fully connected with Laurussia. This sequence of rifting and collision events led to the successive creation and destruction of several small seaways, including the Rheno-Hercynian, Saxo-Thuringian, and Galicia-Moldanubian oceans. Their sediments were eventually compressed and completely buried as Gondwana fully collided with Laurussia in the Carboniferous.
Life
Marine biota
Sea levels in the Devonian were generally high. Marine faunas continued to be dominated by conodonts, bryozoans, diverse and abundant brachiopods, the enigmatic hederellids, microconchids, and corals. Lily-like crinoids (animals, their resemblance to flowers notwithstanding) were abundant, and trilobites were still fairly common. Bivalves became commonplace in deep water and outer shelf environments. The first ammonites also appeared during or slightly before the early Devonian Period around 400 Ma. Bactritoids make their first appearance in the Early Devonian as well; their radiation, along with that of ammonoids, has been attributed by some authors to increased environmental stress resulting from decreasing oxygen levels in the deeper parts of the water column. Among vertebrates, jawless armored fish (ostracoderms) declined in diversity, while the jawed fish (gnathostomes) simultaneously increased in both the sea and fresh water. Armored placoderms were numerous during the lower stages of the Devonian Period and became extinct in the Late Devonian, perhaps because of competition for food against the other fish species. Early cartilaginous (Chondrichthyes) and bony fishes (Osteichthyes) also become diverse and played a large role within the Devonian seas. The first abundant genus of cartilaginous fish, Cladoselache, appeared in the oceans during the Devonian Period. The great diversity of fish around at the time has led to the Devonian being given the name "The Age of Fish" in popular culture.The Devonian saw significant expansion in the diversity of nektonic marine life driven by the abundance of planktonic microorganisms in the free water column as well as high ecological competition in benthic habitats, which were extremely saturated; this diversification has been labeled the Devonian Nekton Revolution by many researchers. However, other researchers have questioned whether this revolution existed at all; a 2018 study found that although the proportion of biodiversity constituted by nekton increased across the boundary between the Silurian and Devonian, it decreased across the span of the Devonian, particularly during the Pragian, and that the overall diversity of nektonic taxa did not increase significantly during the Devonian compared to during other geologic periods, and was in fact higher during the intervals spanning from the Wenlock to the Lochkovian and from the Carboniferous to the Permian. The study's authors instead attribute the increased overall diversity of nekton in the Devonian to a broader, gradual trend of nektonic diversification across the entire Palaeozoic.
Reefs
A now-dry barrier reef, located in present-day Kimberley Basin of northwest Australia, once extended 350 km (220 mi), fringing a Devonian continent. Reefs are generally built by various carbonate-secreting organisms that can erect wave-resistant structures near sea level. Although modern reefs are constructed mainly by corals and calcareous algae, Devonian reefs were either microbial reefs built up mostly by autotrophic cyanobacteria or coral-stromatoporoid reefs built up by coral-like stromatoporoids and tabulate and rugose corals. Microbial reefs dominated under the warmer conditions of the early and late Devonian, while coral-stromatoporoid reefs dominated during the cooler middle Devonian.
Terrestrial biota
By the Devonian Period, life was well underway in its colonization of the land. The moss forests and bacterial and algal mats of the Silurian were joined early in the period by primitive rooted plants that created the first stable soils and harbored arthropods like mites, scorpions, trigonotarbids and myriapods (although arthropods appeared on land much earlier than in the Early Devonian and the existence of fossils such as Protichnites suggest that amphibious arthropods may have appeared as early as the Cambrian). By far the largest land organism at the beginning of this period was the enigmatic Prototaxites, which was possibly the fruiting body of an enormous fungus, rolled liverwort mat, or another organism of uncertain affinities that stood more than 8 metres (26 ft) tall, and towered over the low, carpet-like vegetation during the early part of the Devonian. Also, the first possible fossils of insects appeared around 416 Ma, in the Early Devonian. Evidence for the earliest tetrapods takes the form of trace fossils in shallow lagoon environments within a marine carbonate platform/shelf during the Middle Devonian, although these traces have been questioned and an interpretation as fish feeding traces (Piscichnus) has been advanced.
The greening of land
Many Early Devonian plants did not have true roots or leaves like extant plants, although vascular tissue is observed in many of those plants. Some of the early land plants such as Drepanophycus likely spread by vegetative growth and spores. The earliest land plants such as Cooksonia consisted of leafless, dichotomous axes with terminal sporangia and were generally very short-statured, and grew hardly more than a few centimetres tall. Fossils of Armoricaphyton chateaupannense, about 400 million years old, represent the oldest known plants with woody tissue. By the Middle Devonian, shrub-like forests of primitive plants existed: lycophytes, horsetails, ferns, and progymnosperms evolved. Most of these plants had true roots and leaves, and many were quite tall. The earliest-known trees appeared in the Middle Devonian. These included a lineage of lycopods and another arborescent, woody vascular plant, the cladoxylopsids and progymnosperm Archaeopteris. These tracheophytes were able to grow to large size on dry land because they had evolved the ability to biosynthesize lignin, which gave them physical rigidity and improved the effectiveness of their vascular system while giving them resistance to pathogens and herbivores. These are the oldest-known trees of the world's first forests. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of many plant groups and growth forms has been referred to as the Devonian Explosion or the Silurian-Devonian Terrestrial Revolution.The 'greening' of the continents acted as a carbon sink, and atmospheric concentrations of carbon dioxide may have dropped. This may have cooled the climate and led to a massive extinction event. (See Late Devonian extinction).
Animals and the first soils
Primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed plants that characterized a recognizably modern world had its genesis in the Late Devonian Epoch. The development of soils and plant root systems probably led to changes in the speed and pattern of erosion and sediment deposition. The rapid evolution of a terrestrial ecosystem that contained copious animals opened the way for the first vertebrates to seek terrestrial living. By the end of the Devonian, arthropods were solidly established on the land.
Gallery
Late Devonian extinction
The Late Devonian extinction is not a single event, but rather is a series of pulsed extinctions at the Givetian-Frasnian boundary, the Frasnian-Famennian boundary, and the Devonian-Carboniferous boundary. Together, these are considered one of the "Big Five" mass extinctions in Earth's history. The Devonian extinction crisis primarily affected the marine community, and selectively affected shallow warm-water organisms rather than cool-water organisms. The most important group to be affected by this extinction event were the reef-builders of the great Devonian reef systems.Amongst the severely affected marine groups were the brachiopods, trilobites, ammonites, and acritarchs, and the world saw the disappearance of an estimated 96% of vertebrates like conodonts and bony fishes, and all of the ostracoderms and placoderms. Land plants as well as freshwater species, such as our tetrapod ancestors, were relatively unaffected by the Late Devonian extinction event (there is a counterargument that the Devonian extinctions nearly wiped out the tetrapods).
The reasons for the Late Devonian extinctions are still unknown, and all explanations remain speculative. Canadian paleontologist Digby McLaren suggested in 1969 that the Devonian extinction events were caused by an asteroid impact. However, while there were Late Devonian collision events (see the Alamo bolide impact), little evidence supports the existence of a large enough Devonian crater.
See also
Falls of the Ohio State Park – State park in Indiana, United States. One of the largest exposed Devonian fossil beds in the world.
Geologic time scale – System that relates geologic strata to time
List of Early Devonian land plants
List of fossil sites (with link directory)
Phacops rana – Extinct species of trilobitePages displaying short descriptions of redirect targets, a Devonian trilobiteCategories
Category:Devonian plants
Notes
References
External links
"Devonian". Devonian Times. Archived from the original on 11 February 2010.
"Devonian life". UC Berkeley. – site introduces the Devonian
"Geologic Time Scale". International Commission on Stratigraphy (ICS). 2004. Retrieved 19 September 2005.
"Examples of Devonian Fossils".
"Devonian chronostratigraphy scale".
"Devonian". Palaeos. Archived from the original on 28 October 2007.
"Museum". Age of Fishes. |
rhyacian | The Rhyacian Period ( ; Ancient Greek: ῥύαξ, romanized: rhýax, meaning "stream of lava") is the second geologic period in the Paleoproterozoic Era and lasted from 2300 Mya to 2050 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.The Bushveld Igneous Complex and some other similar intrusions formed during this period.The Huronian (Makganyene) global glaciation began at the start of the Rhyacian and lasted 100 million years. It lasted about 80% of this period.For the time interval from 2250 Ma to 2060 Ma, an alternative period based on stratigraphy rather than chronometry, named either the Jatulian or the Eukaryian, was suggested in the geological timescale review 2012 edited by Gradstein et al., but as of March 2020, this has not yet been officially adopted by the IUGS. The term Jatulian is, however, used in the regional stratigraphy of the Paleoproterozoic rocks of Fennoscandia.This is when the eukaryotes are thought to have originated from the symbiosis between asgardarchaea and alphaproteobacteria, as well as the sexual reproduction found within the eukaryotes only, thus the alternative name Eukaryian.
== References == |
statherian | The Statherian Period ( ; Ancient Greek: σταθερός, romanized: statherós, meaning "stable, firm") is the final geologic period in the Paleoproterozoic Era and lasted from 1800 Mya to 1600 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.The period was characterized on most continents by either new platforms or final cratonization of fold belts. Oxygen levels were 10% to 20% of current values.Rafatazmia, controversially claimed to be present in Statherian beds in India, may be the oldest known confirmably eukaryotic fossil organism.By the beginning of the Statherian, the supercontinent Columbia had assembled.Approximately 1.7 billion years ago, a series of natural nuclear fission reactors was operational in what is now Oklo, Gabon.
See also
Boring Billion – Earth history, 1.8 to 0.8 billion years ago
== References == |
ectasian | The Ectasian Period (from Ancient Greek: ἔκτασις, romanized: éktasis, meaning "extension") is the second geologic period in the Mesoproterozoic Era and lasted from 1400 Mya ago to 1200 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
Geologically the name refers to the continued expansion of platform covers during this period.
This period is interesting for the first evidence of sexual reproduction. The 1.2 billion years old Hunting Formation on Somerset Island, Canada, dates from the end of the Ectasian. It contains the microfossils of the multicellular filaments of Bangiomorpha pubescens (type of red algae), the first taxonomically resolved eukaryote. This was the first organism that exhibited sexual reproduction, which is an essential feature for complex multicellularity. Complex multicellularity is different from "simple" multicellularity, such as colonies of organisms living together. True multicellular organisms contain cells that are specialized for different functions. This is, in fact, an essential feature of sexual reproduction as well, since the male and female gametes are specialized cells. Organisms that reproduce sexually must solve the problem of generating an entire organism from just the germ cells.
Sexual reproduction and the ability of gametes to develop into an organism are the necessary antecedents to true multicellularity. In fact, we tend to think of sexual reproduction and true multicellularity as occurring at the same time, and true multicellularity is often taken as a marker for sexual reproduction.
See also
Boring Billion – Earth history, 1.8 to 0.8 billion years ago
Jotnian – Oldest known sediments in the Baltic area that have not been subject to metamorphism
Riphean (stage) – stage in the geological timescale named after the UralsPages displaying wikidata descriptions as a fallback
References
"Mesoproterozoic Era". essayweb.net. Archived from the original on 29 August 2011. Retrieved 13 September 2011.
James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492. |
paleogene | The Paleogene (IPA: PAY-lee-ə-jeen, -lee-oh-, PAL-ee-; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago (Mya) to the beginning of the Neogene Period 23.03 Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon. The earlier term Tertiary Period was used to define the span of time now covered by the Paleogene Period and subsequent Neogene Period; despite no longer being recognized as a formal stratigraphic term, "Tertiary" still sometimes remains in informal use. Paleogene is often abbreviated "Pg" (but the United States Geological Survey uses the abbreviation Pe for the Paleogene on the Survey's geologic maps).During the Paleogene, mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period.This period consists of the Paleocene, Eocene, and Oligocene epochs. The end of the Paleocene (56 Mya) was marked by the Paleocene–Eocene Thermal Maximum, one of the most significant periods of global change during the Cenozoic, which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals. The term "Paleogene System" is applied to the rocks deposited during the Paleogene Period.
Climate
The global climate of the Palaeogene began with the brief but intense impact winter brought by the Chicxulub impact. This intense impact winter was terminated by an abrupt warming. After temperatures stabilised, the steady cooling and drying of the Late Cretaceous-Early Palaeogene Cool Interval (LKEPCI) that had spanned the last two stages of the Late Cretaceous continued. About 62.2 Ma, the Latest Danian Event, a hyperthermal event, took place. Around 59 Ma, the LKEPCI was brought to an end by the Thanetian Thermal Event, which ushered in a departure from the relative cool of the Early and Middle Palaeocene and the dawn of an intense supergreenhouse.From about 56 to 48 Ma, annual air temperatures over land and at mid-latitude averaged about 23–29 °C (± 4.7 °C), which is 5–10 °C higher than most previous estimates. For comparison, this was 10 to 15 °C higher than the current annual mean temperatures in these areas. At the Palaeocene-Eocene boundary occurred the Paleocene–Eocene Thermal Maximum (PETM), one of the hottest times of the Phanerozoic eon, during which global mean surface temperatures rose to 31.6. It was followed by the less severe Eocene Thermal Maximum 2 (ETM2) about 53.69 Ma. Eocene Thermal Maximum 3 (ETM3) occurred about 53 Ma. The Early Eocene Climatic Optimum was brought to an end by the Azolla event about 48.5 Ma, when large amounts of carbon dioxide were sequestered by Azolla. From this point until about 34 Ma, there was a slow cooling trend known as the Middle-Late Eocene Cooling (MLEC). Approximately 41.5 Ma, this cooling was interrupted temporarily by the Middle Eocene Climatic Optimum (MECO). Then, about 39.4 Ma, a temperature drop called the Late Eocene Cool Event (LECE) is detected in the oxygen isotope record. A breakneck drop in global temperatures and formation of continental glaciers on Antarctica marked the end of the Eocene. This sharp cooling was partly caused by the formation of the Antarctic Circumpolar Current, which significantly lowered oceanic water temperatures.In the earliest Oligocene occurred the Early Oligocene Glacial Maximum (Oi1), which lasted for about 200 kyr. After Oi1, global mean surface temperature continued to slowly decline over the Early Oligocene. Another major cooling event transpired at the end of the Rupelian; its most likely cause was extreme biological productivity in the Southern Ocean fostered by tectonic reorganisation of ocean currents and an influx of nutrients from Antarctica. In the Late Oligocene, global temperatures began to warm slightly, though they continued to be significantly lower than during the previous epochs of the Palaeogene and polar ice remained.
Palaeogeography
During the Paleogene, the continents continued to drift closer to their current positions. India was in the process of colliding with Asia, forming the Himalayas. The Atlantic Ocean continued to widen by a few centimeters each year. Africa was moving north to collide with Europe and form the Mediterranean Sea, while South America was moving closer to North America (they would later connect via the Isthmus of Panama). Inland seas retreated from North America early in the period. Australia had also separated from Antarctica and was drifting toward Southeast Asia. The 1.2 Myr cycle of obliquity amplitude modulation governed eustatic sea level changes on shorter timescales, with periods of low amplitude coinciding with intervals of low sea levels and vice versa.
Flora and fauna
Tropical taxa diversified faster than those at higher latitudes following the Cretaceous–Paleogene extinction event, leading to the development of a significant latitudinal diversity gradient. Mammals began a rapid diversification during this period. After the Cretaceous–Paleogene extinction event, which saw the demise of the non-avian dinosaurs, mammals began to evolve from a few small and generalized forms into most of the modern varieties we see today. Some of these mammals evolved into large forms that dominated the land, while others became capable of living in marine, specialized terrestrial, and airborne environments. Those that took to the oceans became modern cetaceans, while those that took to the trees became primates, the group to which humans belong. Birds, extant dinosaurs which were already well established by the end of the Cretaceous, also experienced adaptive radiation as they took over the skies left empty by the now extinct pterosaurs. Some flightless birds such as penguins, ratites, and terror birds also filled niches left by the hesperornithes and other extinct dinosaurs.
Pronounced cooling in the Oligocene led to a massive floral shift, and many extant modern plants arose during this time. Grasses and herbs, such as Artemisia, began to proliferate, at the expense of tropical plants, which began to decline. Conifer forests developed in mountainous areas. This cooling trend continued, with major fluctuation, until the end of the Pleistocene. This evidence for this floral shift is found in the palynological record.
See also
Cretaceous–Paleogene boundary – Geological formation between time periods
References
External links
Paleogene Microfossils: 180+ images of Foraminifera
Paleogene (chronostratigraphy scale) |
cretaceous | The Cretaceous (IPA: krih-TAY-shəs) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites, and rudists, while dinosaurs continued to dominate on land. The world was ice-free, and forests extended to the poles. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras.
Etymology and history
The Cretaceous as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822 as the Terrain Crétacé, using strata in the Paris Basin and named for the extensive beds of chalk (calcium carbonate deposited by the shells of marine invertebrates, principally coccoliths), found in the upper Cretaceous of Western Europe. The name Cretaceous was derived from the Latin creta, meaning chalk. The twofold division of the Cretaceous was implemented by Conybeare and Phillips in 1822. Alcide d'Orbigny in 1840 divided the French Cretaceous into five étages (stages): the Neocomian, Aptian, Albian, Turonian, and Senonian, later adding the Urgonian between Neocomian and Aptian and the Cenomanian between the Albian and Turonian.
Geology
Subdivisions
The Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series. In older literature, the Cretaceous is sometimes divided into three series: Neocomian (lower/early), Gallic (middle) and Senonian (upper/late). A subdivision into 12 stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use.
From youngest to oldest, the subdivisions of the Cretaceous period are:
Boundaries
The lower boundary of the Cretaceous is currently undefined, and the Jurassic–Cretaceous boundary is currently the only system boundary to lack a defined Global Boundary Stratotype Section and Point (GSSP). Placing a GSSP for this boundary has been difficult because of the strong regionality of most biostratigraphic markers, and the lack of any chemostratigraphic events, such as isotope excursions (large sudden changes in ratios of isotopes) that could be used to define or correlate a boundary. Calpionellids, an enigmatic group of planktonic protists with urn-shaped calcitic tests briefly abundant during the latest Jurassic to earliest Cretaceous, have been suggested as the most promising candidates for fixing the Jurassic–Cretaceous boundary. In particular, the first appearance Calpionella alpina, coinciding with the base of the eponymous Alpina subzone, has been proposed as the definition of the base of the Cretaceous. The working definition for the boundary has often been placed as the first appearance of the ammonite Strambergella jacobi, formerly placed in the genus Berriasella, but its use as a stratigraphic indicator has been questioned, as its first appearance does not correlate with that of C. alpina. The boundary is officially considered by the International Commission on Stratigraphy to be approximately 145 million years ago, but other estimates have been proposed based on U-Pb geochronology, ranging as young as 140 million years ago.The upper boundary of the Cretaceous is sharply defined, being placed at an iridium-rich layer found worldwide that is believed to be associated with the Chicxulub impact crater, with its boundaries circumscribing parts of the Yucatán Peninsula and extending into the Gulf of Mexico. This layer has been dated at 66.043 Mya.At the end of the Cretaceous, the impact of a large body with the Earth may have been the punctuation mark at the end of a progressive decline in biodiversity during the Maastrichtian age. The result was the extinction of three-quarters of Earth's plant and animal species. The impact created the sharp break known as the K–Pg boundary (formerly known as the K–T boundary). Earth's biodiversity required substantial time to recover from this event, despite the probable existence of an abundance of vacant ecological niches.Despite the severity of the K-Pg extinction event, there were significant variations in the rate of extinction between and within different clades. Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked solar energy. As is the case today, photosynthesizing organisms, such as phytoplankton and land plants, formed the primary part of the food chain in the late Cretaceous, and all else that depended on them suffered, as well. Herbivorous animals, which depended on plants and plankton as their food, died out as their food sources became scarce; consequently, the top predators, such as Tyrannosaurus rex, also perished. Yet only three major groups of tetrapods disappeared completely; the nonavian dinosaurs, the plesiosaurs and the pterosaurs. The other Cretaceous groups that did not survive into the Cenozoic Era — the ichthyosaurs, last remaining temnospondyls (Koolasuchus), and nonmammalian cynodonts (Tritylodontidae) — were already extinct millions of years before the event occurred.Coccolithophorids and molluscs, including ammonites, rudists, freshwater snails, and mussels, as well as organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, ammonites are thought to have been the principal food of mosasaurs, a group of giant marine lizards related to snakes that became extinct at the boundary.Omnivores, insectivores, and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources. At the end of the Cretaceous, there seem to have been no purely herbivorous or carnivorous mammals. Mammals and birds that survived the extinction fed on insects, larvae, worms, and snails, which in turn fed on dead plant and animal matter. Scientists theorise that these organisms survived the collapse of plant-based food chains because they fed on detritus.In stream communities, few groups of animals became extinct. Stream communities rely less on food from living plants and more on detritus that washes in from land. This particular ecological niche buffered them from extinction. Similar, but more complex patterns have been found in the oceans. Extinction was more severe among animals living in the water column than among animals living on or in the seafloor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton, while animals living on or in the ocean floor feed on detritus or can switch to detritus feeding.The largest air-breathing survivors of the event, crocodilians and champsosaurs, were semiaquatic and had access to detritus. Modern crocodilians can live as scavengers and can survive for months without food and go into hibernation when conditions are unfavorable, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms or fragments of organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous.
Geologic formations
The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms. The Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone, a rock type that is formed under warm, shallow marine conditions. Due to the high sea level, there was extensive space for such sedimentation. Because of the relatively young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide.
Chalk is a rock type characteristic for (but not restricted to) the Cretaceous. It consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous seas.
Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half of the world's petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and the Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval, such as the Mancos Shale of western North America. These shales are an important source rock for oil and gas, for example in the subsurface of the North Sea.
Europe
In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group, which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast. The group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not easily consolidated and the Chalk Group still consists of loose sediments in many places. The group also has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites, ammonites and sea reptiles such as Mosasaurus.
In southern Europe, the Cretaceous is usually a marine system consisting of competent limestone beds or incompetent marls. Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf, at the margin of the Tethys Ocean.
North America
During the Cretaceous, the present North American continent was isolated from the other continents. In the Jurassic, the North Atlantic already opened, leaving a proto-ocean between Europe and North America. From north to south across the continent, the Western Interior Seaway started forming. This inland sea separated the elevated areas of Laramidia in the west and Appalachia in the east. Three dinosaur clades found in Laramidia (troodontids, therizinosaurids and oviraptorosaurs) are absent from Appalachia from the Coniacian through the Maastrichtian.
Paleogeography
During the Cretaceous, the late-Paleozoic-to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into the present-day continents, although their positions were substantially different at the time. As the Atlantic Ocean widened, the convergent-margin mountain building (orogenies) that had begun during the Jurassic continued in the North American Cordillera, as the Nevadan orogeny was followed by the Sevier and Laramide orogenies.
Gondwana had begun to break up during the Jurassic Period, but its fragmentation accelerated during the Cretaceous and was largely complete by the end of the period. South America, Antarctica, and Australia rifted away from Africa (though India and Madagascar remained attached to each other until around 80 million years ago); thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. During the most of the Late Cretaceous, North America would be divided in two by the Western Interior Seaway, a large interior sea, separating Laramidia to the west and Appalachia to the east, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. Bivalve palaeobiogeography also indicates that Africa was split in half by a shallow sea during the Coniacian and Santonian, connecting the Tethys with the South Atlantic by way of the central Sahara and Central Africa, which were then underwater. Yet another shallow seaway ran between what is now Norway and Greenland, connecting the Tethys to the Arctic Ocean and enabling biotic exchange between the two oceans. At the peak of the Cretaceous transgression, one-third of Earth's present land area was submerged.The Cretaceous is justly famous for its chalk; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic. Mid-ocean ridge activity—or rather, the circulation of seawater through the enlarged ridges—enriched the oceans in calcium; this made the oceans more saturated, as well as increased the bioavailability of the element for calcareous nanoplankton. These widespread carbonates and other sedimentary deposits make the Cretaceous rock record especially fine. Famous formations from North America include the rich marine fossils of Kansas's Smoky Hill Chalk Member and the terrestrial fauna of the late Cretaceous Hell Creek Formation. Other important Cretaceous exposures occur in Europe (e.g., the Weald) and China (the Yixian Formation). In the area that is now India, massive lava beds called the Deccan Traps were erupted in the very late Cretaceous and early Paleocene.
Climate
Palynological evidence indicates the Cretaceous climate had three broad phases: a Berriasian–Barremian warm-dry phase, a Aptian–Santonian warm-wet phase, and a Campanian–Maastrichtian cool-dry phase. As in the Cenozoic, the 400,000 year eccentricity cycle was the dominant orbital cycle governing carbon flux between different reservoirs and influencing global climate. The location of the Intertropical Convergence Zone (ITCZ) was roughly the same as in the present.The cooling trend of the last epoch of the Jurassic, the Tithonian, continued into the Berriasian, the first age of the Cretaceous. The North Atlantic seaway opened and enabled the flow of cool water from the Boreal Ocean into the Tethys. There is evidence that snowfalls were common in the higher latitudes during this age, and the tropics became wetter than during the Triassic and Jurassic. Glaciation was restricted to high-latitude mountains, though seasonal snow may have existed farther from the poles. After the end of the first age, however, temperatures began to increase again, with a number of thermal excursions, such as the middle Valanginian Weissert Thermal Excursion (WTX), which was caused by the Paraná-Etendeka Large Igneous Province's activity. It was followed by the middle Hauterivian Faraoni Thermal Excursion (FTX) and the early Barremian Hauptblatterton Thermal Event (HTE). The HTE marked the ultimate end of the Tithonian-early Barremian Cool Interval (TEBCI). The TEBCI was followed by the Barremian-Aptian Warm Interval (BAWI). This hot climatic interval coincides with Manihiki and Ontong Java Plateau volcanism and with the Selli Event. Early Aptian tropical sea surface temperatures (SSTs) were 27–32 °C, based on TEX86 measurements from the equatorial Pacific. During the Aptian, Milankovitch cycles governed the occurrence of anoxic events by modulating the intensity of the hydrological cycle and terrestrial runoff. The BAWI itself was followed by the Aptian-Albian Cold Snap (AACS) that began about 118 Ma. A short, relatively minor ice age may have occurred during this so-called "cold snap", as evidenced by glacial dropstones in the western parts of the Tethys Ocean and the expansion of calcareous nannofossils that dwelt in cold water into lower latitudes. The AACS is associated with an arid period in the Iberian Peninsula.Temperatures increased drastically after the end of the AACS, which ended around 111 Ma with the Paquier/Urbino Thermal Maximum, giving way to the Mid-Cretaceous Hothouse (MKH), which lasted from the early Albian until the early Campanian. Faster rates of seafloor spreading and entry of carbon dioxide into the atmosphere are believed to have initiated this period of extreme warmth. The MKH was punctuated by multiple thermal maxima of extreme warmth. The Leenhardt Thermal Event (LTE) occurred around 110 Ma, followed shortly by the l’Arboudeyesse Thermal Event (ATE) a million years later. Following these two hyperthermals was the Amadeus Thermal Maximum around 106 Ma, during the middle Albian. Then, around a million years after that, occurred the Petite Verol Thermal Event (PVTE). Afterwards, around 102.5 Ma, the Event 6 Thermal Event (EV6) took place; this event was itself followed by the Breistroffer Thermal Maximum around 101 Ma, during the latest Albian. Approximately 94 Ma, the Cenomanian-Turonian Thermal Maximum occurred, with this hyperthermal being the most extreme hothouse interval of the Cretaceous. Temperatures cooled down slightly over the next few million years, but then another thermal maximum, the Coniacian Thermal Maximum, happened, with this thermal event being dated to around 87 Ma. Atmospheric CO2 levels may have varied by thousands of ppm throughout the MKH. Mean annual temperatures at the poles during the MKH exceeded 14 °C. Such hot temperatures during the MKH resulted in a very gentle temperature gradient from the equator to the poles; the latitudinal temperature gradient during the Cenomanian-Turonian Thermal Maximum was 0.54 °C per ° latitude for the Southern Hemisphere and 0.49 °C per ° latitude for the Northern Hemisphere, in contrast to present day values of 1.07 and 0.69 °C per ° latitude for the Southern and Northern hemispheres, respectively. This meant weaker global winds, which drive the ocean currents, and resulted in less upwelling and more stagnant oceans than today. This is evidenced by widespread black shale deposition and frequent anoxic events. Tropical SSTs during the late Albian most likely averaged around 30 °C. Despite this high SST, seawater was not hypersaline at this time, as this would have required significantly higher temperatures still. On land, arid zones in the Albian regularly expanded northward in tandem with expansions of subtropical high pressure belts. Tropical SSTs during the Cenomanian-Turonian Thermal Maximum were at least 30 °C, though one study estimated them as high as between 33 and 42 °C. An intermediate estimate of ~33-34 °C has also been given. Meanwhile, deep ocean temperatures were as much as 15 to 20 °C (27 to 36 °F) warmer than today's; one study estimated that deep ocean temperatures were between 12 and 20 °C during the MKH. The poles were so warm that ectothermic reptiles were able to inhabit them.Beginning in the Santonian, near the end of the MKH, the global climate began to cool, with this cooling trend continuing across the Campanian. This period of cooling, driven by falling levels of atmospheric carbon dioxide, caused the end of the MKH and the transition into a cooler climatic interval, known formally as the Late Cretaceous-Early Palaeogene Cool Interval (LKEPCI). Tropical SSTs declined from around 35 °C in the early Campanian to around 28 °C in the Maastrichtian. Deep ocean temperatures declined to 9 to 12 °C, though the shallow temperature gradient between tropical and polar seas remained. Regional conditions in the Western Interior Seaway changed little between the MKH and the LKEPCI. During this period of relatively cool temperatures, the ITCZ became narrower, while the strength of both summer and winter monsoons in East Asia was directly correlated to atmospheric CO2 concentrations. The Maastrichtian was a time of chaotic, highly variable climate. Two upticks in global temperatures are known to have occurred during the Maastrichtian, bucking the trend of overall cooler temperatures during the LKEPCI. Between 70 and 69 Ma and 66–65 Ma, isotopic ratios indicate elevated atmospheric CO2 pressures with levels of 1000–1400 ppmV and mean annual temperatures in west Texas between 21 and 23 °C (70 and 73 °F). Atmospheric CO2 and temperature relations indicate a doubling of pCO2 was accompanied by a ~0.6 °C increase in temperature. The latter warming interval, occurring at the very end of the Cretaceous, was triggered by the activity of the Deccan Traps. The LKEPCI lasted into the Late Palaeocene, when it gave way to another supergreenhouse interval.
The production of large quantities of magma, variously attributed to mantle plumes or to extensional tectonics, further pushed sea levels up, so that large areas of the continental crust were covered with shallow seas. The Tethys Sea connecting the tropical oceans east to west also helped to warm the global climate. Warm-adapted plant fossils are known from localities as far north as Alaska and Greenland, while dinosaur fossils have been found within 15 degrees of the Cretaceous south pole. It was suggested that there was Antarctic marine glaciation in the Turonian Age, based on isotopic evidence. However, this has subsequently been suggested to be the result of inconsistent isotopic proxies, with evidence of polar rainforests during this time interval at 82° S. Rafting by ice of stones into marine environments occurred during much of the Cretaceous, but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia.
Flora
Flowering plants (angiosperms) make up around 90% of living plant species today. Prior to the rise of angiosperms, during the Jurassic and the Early Cretaceous, the higher flora was dominated by gymnosperm groups, including cycads, conifers, ginkgophytes, gnetophytes and close relatives, as well as the extinct Bennettitales. Other groups of plants included pteridosperms or "seed ferns", a collective term that refers to disparate groups of extinct seed plants with fern-like foliage, including groups such as Corystospermaceae and Caytoniales. The exact origins of angiosperms are uncertain, although molecular evidence suggests that they are not closely related to any living group of gymnosperms.The earliest widely accepted evidence of flowering plants are monosulcate (single-grooved) pollen grains from the late Valanginian (~ 134 million years ago) found in Israel and Italy, initially at low abundance. Molecular clock estimates conflict with fossil estimates, suggesting the diversification of crown-group angiosperms during the Upper Triassic or Jurassic, but such estimates are difficult to reconcile with the heavily sampled pollen record and the distinctive tricolpate to tricolporoidate (triple grooved) pollen of eudicot angiosperms. Among the oldest records of Angiosperm macrofossils are Montsechia from the Barremian aged Las Hoyas beds of Spain and Archaefructus from the Barremian-Aptian boundary Yixian Formation in China. Tricolpate pollen distinctive of eudicots first appears in the Late Barremian, while the earliest remains of monocots are known from the Aptian. Flowering plants underwent a rapid radiation beginning during the middle Cretaceous, becoming the dominant group of land plants by the end of the period, coincident with the decline of previously dominant groups such as conifers. The oldest known fossils of grasses are from the Albian, with the family having diversified into modern groups by the end of the Cretaceous. The oldest large angiosperm trees are known from the Turonian (c. 90 Mya) of New Jersey, with the trunk having a preserved diameter of 1.8 metres (5.9 ft) and an estimated height of 50 metres (160 ft).During the Cretaceous, ferns in the order Polypodiales, which make up 80% of living fern species, would also begin to diversify.
Terrestrial fauna
On land, mammals were generally small sized, but a very relevant component of the fauna, with cimolodont multituberculates outnumbering dinosaurs in some sites. Neither true marsupials nor placentals existed until the very end, but a variety of non-marsupial metatherians and non-placental eutherians had already begun to diversify greatly, ranging as carnivores (Deltatheroida), aquatic foragers (Stagodontidae) and herbivores (Schowalteria, Zhelestidae). Various "archaic" groups like eutriconodonts were common in the Early Cretaceous, but by the Late Cretaceous northern mammalian faunas were dominated by multituberculates and therians, with dryolestoids dominating South America.
The apex predators were archosaurian reptiles, especially dinosaurs, which were at their most diverse stage. Avians such as the ancestors of modern-day birds also diversified. They inhabited every continent, and were even found in cold polar latitudes. Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded they declined for poorly understood reasons (once thought to be due to competition with early birds, but now it is understood avian adaptive radiation is not consistent with pterosaur decline). By the end of the period only three highly specialized families remained; Pteranodontidae, Nyctosauridae, and Azhdarchidae.The Liaoning lagerstätte (Yixian Formation) in China is an important site, full of preserved remains of numerous types of small dinosaurs, birds and mammals, that provides a glimpse of life in the Early Cretaceous. The coelurosaur dinosaurs found there represent types of the group Maniraptora, which includes modern birds and their closest non-avian relatives, such as dromaeosaurs, oviraptorosaurs, therizinosaurs, troodontids along with other avialans. Fossils of these dinosaurs from the Liaoning lagerstätte are notable for the presence of hair-like feathers.
Insects diversified during the Cretaceous, and the oldest known ants, termites and some lepidopterans, akin to butterflies and moths, appeared. Aphids, grasshoppers and gall wasps appeared.
Rhynchocephalians
Rhynchocephalians (which today only includes the Tuatara) disappeared from North America and Europe after the Early Cretaceous, and were absent from North Africa and northern South America by the early Late Cretaceous. The cause of the decline of Rhynchocephalia remains unclear, but has often been suggested to be due to competition with advanced lizards and mammals. They appear to have remained diverse in high-latitude southern South America during the Late Cretaceous, where lizards remained rare, with their remains outnumbering terrestrial lizards 200:1.
Choristodera
Choristoderes, a group of freshwater aquatic reptiles that first appeared during the preceding Jurassic, underwent a major evolutionary radiation in Asia during the Early Cretaceous, which represents the high point of choristoderan diversity, including long necked forms such as Hyphalosaurus and the first records of the gharial-like Neochoristodera, which appear to have evolved in the regional absence of aquatic neosuchian crocodyliformes. During the Late Cretaceous the neochoristodere Champsosaurus was widely distributed across western North America. Due to the extreme climatic warmth in the Arctic, choristoderans were able to colonise it too during the Late Cretaceous.
Marine fauna
In the seas, rays, modern sharks and teleosts became common. Marine reptiles included ichthyosaurs in the early and mid-Cretaceous (becoming extinct during the late Cretaceous Cenomanian-Turonian anoxic event), plesiosaurs throughout the entire period, and mosasaurs appearing in the Late Cretaceous. Sea turtles in the form of Cheloniidae and Panchelonioidea lived during the period and survived the extinction event. Panchelonioidea is today represented by a single species; the leatherback sea turtle. The Hesperornithiformes were flightless, marine diving birds that swam like grebes.
Baculites, an ammonite genus with a straight shell, flourished in the seas along with reef-building rudist clams. Predatory gastropods with drilling habits were widespread. Globotruncanid Foraminifera and echinoderms such as sea urchins and starfish (sea stars) thrived. Ostracods were abundant in Cretaceous marine settings; ostracod species characterised by high male sexual investment had the highest rates of extinction and turnover. Thylacocephala, a class of crustaceans, went extinct in the Late Cretaceous. The first radiation of the diatoms (generally siliceous shelled, rather than calcareous) in the oceans occurred during the Cretaceous; freshwater diatoms did not appear until the Miocene. The Cretaceous was also an important interval in the evolution of bioerosion, the production of borings and scrapings in rocks, hardgrounds and shells.
See also
Mesozoic Era
Cretaceous-Paleogene extinction
Chalk Group
Cretaceous Thermal Maximum
List of fossil sites (with link directory)
South Polar region of the Cretaceous
References
Citations
Bibliography
Yuichiro Kashiyama; Nanako O. Ogawa; Junichiro Kuroda; Motoo Shiro; Shinya Nomoto; Ryuji Tada; Hiroshi Kitazato; Naohiko Ohkouchi (May 2008). "Diazotrophic cyanobacteria as the major photoautotrophs during mid-Cretaceous oceanic anoxic events: Nitrogen and carbon isotopic evidence from sedimentary porphyrin". Organic Geochemistry. 39 (5): 532–549. Bibcode:2008OrGeo..39..532K. doi:10.1016/j.orggeochem.2007.11.010.
Larson, Neal L; Jorgensen, Steven D; Farrar, Robert A; Larson, Peter L (1997). Ammonites and the other Cephalopods of the Pierre Seaway. Geoscience Press.
Ogg, Jim (June 2004). "Overview of Global Boundary Stratotype Sections and Points (GSSP's)". Archived from the original on 16 July 2006.
Ovechkina, M.N.; Alekseev, A.S. (2005). "Quantitative changes of calcareous nannoflora in the Saratov region (Russian Platform) during the late Maastrichtian warming event" (PDF). Journal of Iberian Geology. 31 (1): 149–165. Archived from the original (PDF) on August 24, 2006.
Rasnitsyn, A.P.; Quicke, D.L.J. (2002). History of Insects. Kluwer Academic Publishers. ISBN 978-1-4020-0026-3.—detailed coverage of various aspects of the evolutionary history of the insects.
Skinner, Brian J.; Porter, Stephen C. (1995). The Dynamic Earth: An Introduction to Physical Geology (3rd ed.). New York: John Wiley & Sons. ISBN 0-471-60618-9.
Stanley, Steven M. (1999). Earth System History. New York: W.H. Freeman and Company. ISBN 0-7167-2882-6.
Taylor, P. D.; Wilson, M. A. (2003). "Palaeoecology and evolution of marine hard substrate communities" (PDF). Earth-Science Reviews. 62 (1): 1–103. Bibcode:2003ESRv...62....1T. doi:10.1016/S0012-8252(02)00131-9.
External links
UCMP Berkeley Cretaceous page
Cretaceous Microfossils: 180+ images of Foraminifera
Cretaceous (chronostratigraphy scale)
"Cretaceous System" . Encyclopædia Britannica. Vol. 7 (11th ed.). 1911. pp. 414–418. |
paleozoic | The Paleozoic (IPA: /ˌpæli.əˈzoʊ.ɪk,-i.oʊ-, ˌpeɪ-/ PAL-ee-ə-ZOH-ik, -ee-oh-, PAY-; or Palaeozoic) Era is the first of three geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma at the start of the Mesozoic Era. The Paleozoic is subdivided into six geologic periods (from oldest to youngest):
Some geological timescales divide the Paleozoic informally into early and late sub-eras: the Early Paleozoic consisting of the Cambrian, Ordovician and Silurian; the Late Paleozoic consisting of the Devonian, Carboniferous and Permian.The name Paleozoic was first used by Adam Sedgwick (1785-1873) in 1838 to describe the Cambrian and Ordovician periods. It was redefined by John Phillips (1800–1874) in 1840 to in cover the Cambrian to Permian periods. It is derived from the Greek palaiós (παλαιός, "old") and zōḗ (ζωή, "life") meaning "ancient life".The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earth's history, known as the Cambrian explosion, in which most modern phyla first appeared. Arthropods, molluscs, fish, amphibians, reptiles, and synapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated synapsids and diapsids were dominant and the first modern plants (conifers) appeared.
The Paleozoic Era ended with the largest extinction event of the Phanerozoic Eon, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover.
Recovery of life in the sea may have been much faster.
Boundaries
The base of the Paleozoic is one of the major divisions in geological time representing the divide between the Proterozoic and Phanerozoic eons, the Paleozoic and Neoproterozoic eras and the Ediacaran and Cambrian periods. When Adam Sedgwick named the Paleozoic in 1835, he defined the base as the first appearance of complex life in the rock record as shown by the presence of trilobite-dominated fauna. Since then evidence of complex life in older rock sequences has increased and by the second half of the 20th century, the first appearance of small shelly fauna (SSF), also known as early skeletal fossils, were considered markers for the base of the Paleozoic. However, whilst SSF are well preserved in carbonate sediments, the majority of Ediacaran to Cambrian rock sequences are composed of siliciclastic rocks where skeletal fossils are rarely preserved. This led the International Commission on Stratigraphy (ICS) to use trace fossils as an indicator of complex life. Unlike later in the fossil record, Cambrian trace fossils are preserved in a wide range of sediments and environments, which aids correlation between different sites around the world. Trace fossils reflect the complexity of the body plan of the organism that made them. Ediacaran trace fossils are simple, sub-horizontal feeding traces. As more complex organisms evolved, their more complex behaviour was reflected in greater diversity and complexity of the trace fossils they left behind. After two decades of deliberation, the ICS chose Fortune Head, Burin Peninsula, Newfoundland as the basal Cambrian Global Stratotype Section and Point (GSSP) at the base of the Treptichnus pedum assemblage of trace fossils and immediately above the last occurrence of the Ediacaran problematica fossils Harlaniella podolica and Palaeopsacichnus. The base of the Phanerozoic, Paleozoic and Cambrian is dated at 538.8+/-0.2 Ma and now lies below both the first appearance of trilobites and SSF.The boundary between the Paleozoic and Mesozoic eras and the Permian and Triassic periods is marked by the first occurrence of the conodont Hindeodus parvus. This is the first biostratigraphic event found worldwide that is associated with the beginning of the recovery following the end-Permian mass extinctions and environmental changes. In non-marine strata, the equivalent level is marked by the disappearance of the Permian Dicynodon tetrapods. This means events previously considered to mark the Permian-Triassic boundary, such as the eruption of the Siberian Traps flood basalts, the onset of greenhouse climate, ocean anoxia and acidification and the resulting mass extinction are now regarded as being of latest Permian in age. The GSSP is near Meishan, Zhejiang Province, southern China. Radiometric dating of volcanic clay layers just above and below the boundary confine its age to a narrow range of 251.902+/-0.024 Ma.
Geology
The beginning of the Paleozoic Era witnessed the breakup of the supercontinent of Pannotia
and ended while the supercontinent Pangaea was assembling.
The breakup of Pannotia began with the opening of the Iapetus Ocean and other Cambrian seas and coincided with a dramatic rise in sea level.Paleoclimatic studies and evidence of glaciers indicate that Central Africa was most likely in the polar regions during the early Paleozoic. The breakup of Pannotia was followed by the assembly of the huge continent Gondwana (510 million years ago). By mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. By the late Paleozoic, continental collisions formed the supercontinent of Pangaea and created great mountain chains, including the Appalachians, Ural Mountains, and mountains of Tasmania.
Cambrian Period
The Cambrian spanned from 539–485 million years ago and is the first period of the Paleozoic Era of the Phanerozoic. The Cambrian marked a boom in evolution in an event known as the Cambrian explosion in which the largest number of creatures evolved in any single period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, like trilobites. Almost all marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, most of which later became the supercontinent Gondwana.
Ordovician Period
The Ordovician spanned from 485–444 million years ago. The Ordovician was a time in Earth's history in which many of the biological classes still prevalent today evolved, such as primitive fish, cephalopods, and coral. The most common forms of life, however, were trilobites, snails and shellfish. The first arthropods went ashore to colonize the empty continent of Gondwana. By the end of the Ordovician, Gondwana was at the south pole, early North America had collided with Europe, closing the Atlantic Ocean. Glaciation of Africa resulted in a major drop in sea level, killing off all life that had established along coastal Gondwana. Glaciation may have caused the Ordovician–Silurian extinction events, in which 60% of marine invertebrates and 25% of families became extinct, and is considered the first Phanerozoic mass extinction event, and the second deadliest.
Silurian Period
The Silurian spanned from 444–419 million years ago. The Silurian saw the rejuvenation of life as the Earth recovered from the previous glaciation. This period saw the mass evolution of fish, as jawless fish became more numerous, jawed fish evolved, and the first freshwater fish evolved, though arthropods, such as sea scorpions, were still apex predators. Fully terrestrial life evolved, including early arachnids, fungi, and centipedes. The evolution of vascular plants (Cooksonia) allowed plants to gain a foothold on land. These early plants were the forerunners of all plant life on land. During this time, there were four continents: Gondwana (Africa, South America, Australia, Antarctica, Siberia), Laurentia (North America), Baltica (Northern Europe), and Avalonia (Western Europe). The recent rise in sea levels allowed many new species to thrive in water.
Devonian Period
The Devonian spanned from 419–359 million years ago. Also known as "The Age of the Fish", the Devonian featured a huge diversification of fish, including armored fish like Dunkleosteus and lobe-finned fish which eventually evolved into the first tetrapods. On land, plant groups diversified rapidly in an event known as the Devonian explosion when plants made lignin, leading to taller growth and vascular tissue; the first trees and seeds evolved. These new habitats led to greater arthropod diversification. The first amphibians appeared and fish occupied the top of the food chain. Earth's second Phanerozoic mass extinction event (a group of several smaller extinction events), the Late Devonian extinction, ended 70% of existing species.
Carboniferous Period
The Carboniferous spanned from 359–299 million years ago. During this time, average global temperatures were exceedingly high; the early Carboniferous averaged at about 20 degrees Celsius (but cooled to 10 °C during the Middle Carboniferous). Tropical swamps dominated the Earth, and the lignin stiffened trees grew to greater heights and number. As the bacteria and fungi capable of eating the lignin had not yet evolved, their remains were left buried, which created much of the carbon that became the coal deposits of today (hence the name "Carboniferous"). Perhaps the most important evolutionary development of the time was the evolution of amniotic eggs, which allowed amphibians to move farther inland and remain the dominant vertebrates for the duration of this period. Also, the first reptiles and synapsids evolved in the swamps. Throughout the Carboniferous, there was a cooling trend, which led to the Permo-Carboniferous glaciation or the Carboniferous Rainforest Collapse. Gondwana was glaciated as much of it was situated around the south pole.
Permian Period
The Permian spanned from 299–252 million years ago and was the last period of the Paleozoic Era. At the beginning of this period, all continents joined together to form the supercontinent Pangaea, which was encircled by one ocean called Panthalassa. The land mass was very dry during this time, with harsh seasons, as the climate of the interior of Pangaea was not regulated by large bodies of water. Diapsids and synapsids flourished in the new dry climate. Creatures such as Dimetrodon and Edaphosaurus ruled the new continent. The first conifers evolved, and dominated the terrestrial landscape. Near the end of the Permian, however, Pangaea grew drier. The interior was desert, and new taxa such as Scutosaurus and Gorgonopsids filled it. Eventually they disappeared, along with 95% of all life on Earth, in a cataclysm known as "The Great Dying", the third and most severe Phanerozoic mass extinction.
Climate
The early Cambrian climate was probably moderate at first, becoming warmer over the course of the Cambrian, as the second-greatest sustained sea level rise in the Phanerozoic got underway. However, as if to offset this trend, Gondwana moved south, so that, in Ordovician time, most of West Gondwana (Africa and South America) lay directly over the South Pole.
The early Paleozoic climate was strongly zonal, with the result that the "climate", in an abstract sense, became warmer, but the living space of most organisms of the time – the continental shelf marine environment – became steadily colder. However, Baltica (Northern Europe and Russia) and Laurentia (eastern North America and Greenland) remained in the tropical zone, while China and Australia lay in waters which were at least temperate. The early Paleozoic ended, rather abruptly, with the short, but apparently severe, late Ordovician ice age. This cold spell caused the second-greatest mass extinction of the Phanerozoic Eon. Over time, the warmer weather moved into the Paleozoic Era.
The Ordovician and Silurian were warm greenhouse periods, with the highest sea levels of the Paleozoic (200 m above today's); the warm climate was interrupted only by a 30 million year cool period, the Early Palaeozoic Icehouse, culminating in the Hirnantian glaciation, 445 million years ago at the end of the Ordovician.The middle Paleozoic was a time of considerable stability. Sea levels had dropped coincident with the ice age, but slowly recovered over the course of the Silurian and Devonian. The slow merger of Baltica and Laurentia, and the northward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow sea floor. As plants took hold on the continental margins, oxygen levels increased and carbon dioxide dropped, although much less dramatically. The north–south temperature gradient also seems to have moderated, or metazoan life simply became hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwana became increasingly less barren. The Devonian ended with a series of turnover pulses which killed off much of middle Paleozoic vertebrate life, without noticeably reducing species diversity overall.
There are many unanswered questions about the late Paleozoic. The Mississippian (early Carboniferous Period) began with a spike in atmospheric oxygen, while carbon dioxide plummeted to new lows. This destabilized the climate and led to one, and perhaps two, ice ages during the Carboniferous. These were far more severe than the brief Late Ordovician ice age; but, this time, the effects on world biota were inconsequential. By the Cisuralian Epoch, both oxygen and carbon dioxide had recovered to more normal levels. On the other hand, the assembly of Pangaea created huge arid inland areas subject to temperature extremes. The Lopingian Epoch is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, culminating in the devastation of the Permian extinction.
Flora
While macroscopic plant life appeared early in the Paleozoic Era and possibly late in the Neoproterozoic Era of the earlier eon, plants mostly remained aquatic until the Silurian Period, about 420 million years ago, when they began to transition onto dry land. Terrestrial flora reached its climax in the Carboniferous, when towering lycopsid rainforests dominated the tropical belt of Euramerica. Climate change caused the Carboniferous Rainforest Collapse which fragmented this habitat, diminishing the diversity of plant life in the late Carboniferous and Permian periods.
Fauna
A noteworthy feature of Paleozoic life is the sudden appearance of nearly all of the invertebrate animal phyla in great abundance at the beginning of the Cambrian. The first vertebrates appeared in the form of primitive fish, which greatly diversified in the Silurian and Devonian Periods. The first animals to venture onto dry land were the arthropods. Some fish had lungs, and powerful bony fins that in the late Devonian, 367.5 million years ago, allowed them to crawl onto land. The bones in their fins eventually evolved into legs and they became the first tetrapods, 390 million years ago, and began to develop lungs. Amphibians were the dominant tetrapods until the mid-Carboniferous, when climate change greatly reduced their diversity. Later, reptiles prospered and continued to increase in number and variety by the late Permian period.
Microbiota
Palaeozoic phytoplankton overall were both nutrient-poor themselves and adapted to nutrient-poor environmental conditions. This phytoplankton nutrient poverty has been cited as an explanation for the Palaeozoic's relatively low biodiversity.
See also
Geologic time scale – System that relates geologic strata to time
Precambrian – History of Earth 4600–539 million years ago
Cenozoic – Third era of the Phanerozoic Eon (66 million years ago to present)
Mesozoic – Second era of the Phanerozoic Eon: ~252–66 million years ago
Phanerozoic – Fourth and current eon of the geological timescale
Footnotes
References
Further reading
External links
60+ images of Paleozoic Foraminifera
Paleozoic (chronostratigraphy scale) |
tonian | The Tonian (from Ancient Greek: τόνος, romanized: tónos, meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from 1000 to 720 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry. The Tonian is preceded by the Stenian Period of the Mesoproterozoic Era and followed by the Cryogenian.
Rifting leading to the breakup of supercontinent Rodinia, which had formed in the mid-Stenian, occurred during this period, starting from 900 to 850 Mya.
Biology
The first putative metazoan (animal) fossils are dated to the middle to late Tonian (c. 890-800 Mya). The fossils of Otavia antiqua, which has been described as a sponge by its discoverers and numerous other scholars, date back to about 800 mya. Even earlier sponge-like fossils have been reported in reefs dating back to 890 million years before the present, but their identity is highly debated. This dating is consistent with molecular data recovered through genetic studies on modern metazoan species; more recent studies have concluded that the base of the animal phylogenetic tree is in the Tonian.The first large evolutionary radiation of acritarchs occurred during the Tonian.
See also
Boring Billion – Earth history, 1.8 to 0.8 billion years ago
References
Further reading
"Tonian Period". GeoWhen Database. Archived from the original on May 12, 2006. Retrieved January 5, 2006.
Ogg, James G. (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492. |
cryptic (geology) | The Cryptic era is an informal term for the earliest geologic evolution of the Earth and Moon. It is the oldest (informal) era of the Hadean eon, and it is commonly accepted to have begun close to about 4.533 billion years ago when the Earth and Moon formed, and lasted to about 4.15 billion years ago. No samples exist to date the transition between the Cryptic era and the following Basin Groups era for the Moon (see also Pre-Nectarian), though sometimes it is stated that this era ended 4150 million years ago for one or both of these bodies. Neither this time period, nor any other Hadean subdivision, has been officially recognized by the International Commission on Stratigraphy.
This time is cryptic because very little geological evidence has survived from this time. Most geological landforms and rocks were probably destroyed in the early bombardment phase, or by the continued effects of plate tectonics. The Earth accreted, its interior differentiated and its molten surface solidified during the Cryptic era. The proposed collision that led to the formation of the Moon occurred also at this time. The oldest known minerals are from the Cryptic era.
See also
Hadean eon-related topics
Geological time scale (Earth)
Lunar geologic time scale
References
External links
"Cryptic" Geowhen Database |
capitanian mass extinction event | The Capitanian mass extinction event, also known as the end-Guadalupian extinction event, the Guadalupian-Lopingian boundary mass extinction, the pre-Lopingian crisis, or the Middle Permian extinction, was an extinction event that predated the end-Permian extinction event. The mass extinction occurred during a period of decreased species richness and increased extinction rates near the end of the Middle Permian, also known as the Guadalupian epoch. It is often called the end-Guadalupian extinction event because of its initial recognition between the Guadalupian and Lopingian series; however, more refined stratigraphic study suggests that extinction peaks in many taxonomic groups occurred within the Guadalupian, in the latter half of the Capitanian age. The extinction event has been argued to have begun around 262 million years ago with the Late Guadalupian crisis, though its most intense pulse occurred 259 million years ago in what is known as the Guadalupian-Lopingian boundary event.Having historically been considered as part of the end-Permian extinction event, and only viewed as separate relatively recently, this mass extinction is believed to be the third largest of the Phanerozoic in terms of the percentage of species lost, after the end-Permian and Late Ordovician mass extinctions, respectively, while being the fifth worst in terms of ecological severity. The global nature of the Capitanian mass extinction has been called into question by some palaeontologists as a result of some analyses finding it to have affected only low-latitude taxa in the Northern Hemisphere.
Magnitude
In the aftermath of Olson's Extinction, global diversity rose during the Capitanian. This was probably the result of disaster taxa replacing extinct guilds. The Capitanian mass extinction greatly reduced disparity (the range of different guilds); eight guilds were lost. It impacted the diversity within individual communities more severely than the Permian–Triassic extinction event. Although faunas began recovery immediately after the Capitanian extinction event, rebuilding complex trophic structures and refilling guilds, diversity and disparity fell further until the Permian–Triassic boundary.
Marine ecosystems
The impact of the Capitanian extinction event on marine ecosystems is still heavily debated by palaeontologists. Early estimates indicated a loss of marine invertebrate genera between 35 and 47%, while an estimate published in 2016 suggested a loss of 33–35% of marine genera when corrected for background extinction, the Signor–Lipps effect and clustering of extinctions in certain taxa. The loss of marine invertebrates during the Capitanian mass extinction was comparable in magnitude to the Cretaceous–Paleogene extinction event. Some studies have considered it the third or fourth greatest mass extinction in terms of the proportion of marine invertebrate genera lost; a different study found the Capitanian extinction event to be only the ninth worst in terms of taxonomic severity (number of genera lost) but found it to be the fifth worst with regard to its ecological impact (i.e., the degree of taxonomic restructuring within ecosystems or the loss of ecological niches or even entire ecosystems themselves).
Terrestrial ecosystems
Few published estimates for the impact on terrestrial ecosystems exist for the Capitanian mass extinction. Among vertebrates, Day and colleagues suggested a 74–80% loss of generic richness in tetrapods of the Karoo Basin in South Africa, including the extinction of the dinocephalians. In land plants, Stevens and colleagues found an extinction of 56% of plant species recorded in the mid-Upper Shihhotse Formation in North China, which was approximately mid-Capitanian in age. 24% of plant species in South China went extinct.
Timing
Although it is known that the Capitanian mass extinction occurred after Olson's Extinction and before the Permian–Triassic extinction event, the exact age of the Capitanian mass extinction remains controversial. This is partly due to the somewhat circumstantial age of the Capitanian–Wuchiapingian boundary itself, which is currently estimated to be approximately 259.1 million years old, but is subject to change by the Subcommission on Permian Stratigraphy of the International Commission on Stratigraphy. Additionally, there is a dispute regarding the severity of the extinction and whether the extinction in China happened at the same time as the extinction in Spitsbergen. According to one study, the Capitanian mass extinction was not one discrete event but a continuous decline in diversity that began at the end of the Wordian. Another study examining fossiliferous facies in Svalbard found no evidence for a sudden mass extinction, instead attributing local biotic changes during the Capitanian to the southward migration of many taxa through the Zechstein Sea. Carbonate platform deposits in Hungary and Hydra show no sign of an extinction event at the end of the Capitanian; the extinction event there is recorded in the middle Capitanian.The volcanics of the Emeishan Traps, which are interbedded with tropical carbonate platforms of the Maokou Formation, are unique for preserving a mass extinction and the cause of that mass extinction. Large phreatomagmatic eruptions occurred when the Emeishan Traps first started to erupt, leading to the extinction of fusulinacean foraminifera and calcareous algae.In the absence of radiometric ages directly constraining the extinction horizons themselves in the marine sections, most recent studies refrain from placing a number on its age, but based on extrapolations from the Permian timescale an age of approximately 260–262 Ma has been estimated; this fits broadly with radiometric ages from the terrestrial realm, assuming the two events are contemporaneous. Plant losses occurred either at the same time as the marine extinction or after it.
Marine realm
The extinction of fusulinacean foraminifera in Southwest China was originally dated to the end of the Guadalupian, but studies published in 2009 and 2010 dated the extinction of these fusulinaceans to the mid-Capitanian. Brachiopod and coral losses occurred in the middle of the Capitanian stage. The extinction suffered by the ammonoids may have occurred in the early Wuchiapingian.
Terrestrial realm
The existence of change in tetrapod faunas in the mid-Permian has long been known in South Africa and Russia. In Russia, it corresponded to the boundary between what became known as the Titanophoneus Superzone and the Scutosaurus Superzone and later the Dinocephalian Superassemblage and the Theriodontian Superassemblage, respectively. In South Africa, this corresponded to the boundary between the variously named Pareiasaurus, Dinocephalian or Tapinocephalus Assemblage Zone and the overlying assemblages. In both Russia and South Africa, this transition was associated with the extinction of the previously dominant group of therapsid amniotes, the dinocephalians, which led to its later designation as the dinocephalian extinction. Post-extinction origination rates remained low through the Pristerognathus Assemblage Zone for at least 1 million years, which suggests that there was a delayed recovery of Karoo Basin ecosystems.After the recognition of a separate marine mass extinction at the end of the Guadalupian, the dinocephalian extinction was seen to represent its terrestrial correlate. Though it was subsequently suggested that because the Russian Ischeevo fauna, which was considered the youngest dinocephalian fauna in that region, was constrained to below the Illawarra magnetic reversal and therefore had to have occurred in the Wordian stage, well before the end of the Guadalupian, this constraint applied to the type locality only. The recognition of a younger dinocephalian fauna in Russia (the Sundyr Tetrapod Assemblage) and the retrieval of biostratigraphically well-constrained radiometric ages via uranium–lead dating of a tuff from the Tapinocephalus Assemblage Zone of the Karoo Basin demonstrated that the dinocephalian extinction did occur in the late Capitanian, around 260 million years ago.
Effects on life
Marine life
In the oceans, the Capitanian extinction event led to high extinction rates among ammonoids, corals and calcareous algal reef-building organisms, foraminifera, bryozoans, and brachiopods. It appears to have been particularly selective against shallow-water taxa that relied on photosynthesis or a photosymbiotic relationship; many species with poorly buffered respiratory physiologies also became extinct. The extinction event led to a collapse of the reef carbonate factory in the shallow seas surrounding South China.The ammonoids, which had been in a long-term decline for a 30 million year period since the Roadian, suffered a selective extinction pulse at the end of the Capitanian. 75.6% of coral families, 77.8% of coral genera and 82.2% of coral species that were in Permian China were lost during the Capitanian mass extinction. The Verbeekinidae, a family of large fusuline foraminifera, went extinct.87% of brachiopod species found at the Kapp Starostin Formation on Spitsbergen disappeared over a period of tens of thousands of years; though new brachiopod and bivalve species emerged after the extinction, the dominant position of the brachiopods was taken over by the bivalves. Approximately 70% of other species found at the Kapp Starostin Formation also vanished. The fossil record of East Greenland is similar to that of Spitsbergen; the faunal losses in Canada's Sverdrup Basin are comparable to the extinctions in Spitsbergen and East Greenland, but the post-extinction recovery that happened in Spitsbergen and East Greenland did not occur in the Sverdrup Basin. Whereas rhynchonelliform brachiopods made up 99.1% of the individuals found in tropical carbonates in the Western United States, South China and Greece prior to the extinction, molluscs made up 61.2% of the individuals found in similar environments after the extinction. 87% of brachiopod species and 82% of fusulinacean foraminifer species in South China were lost. Although severe for brachiopods, the Capitanian extinction's impact on their diversity was nowhere near as strong as that of the later end-Permian extinction.Biomarker evidence indicates red algae and photoautotrophic bacteria dominated marine microbial communities. Significant turnovers in microbial ecosystems occurred during the Capitanian mass extinction, though they were smaller in magnitude than those associated with the end-Permian extinction.Most of the marine victims of the extinction were either endemic species of epicontinental seas around Pangaea that died when the seas closed, or were dominant species of the Paleotethys Ocean. Evidence from marine deposits in Japan and Primorye suggests that mid-latitude marine life became affected earlier by the extinction event than marine organisms of the tropics.Whether and to what degree latitude affected the likelihood of taxa to go extinct remains disputed amongst palaeontologists. Whereas some studies conclude that the extinction event was a regional one limited to tropical areas, others suggest that there was little latitudinal variation in extinction patterns. A study examining foraminiferal extinctions in particular found that the Central and Western Palaeotethys experienced taxonomic losses of a lower magnitude than the Northern and Eastern Palaeotethys, which had the highest extinction magnitude. The same study found that Panthalassa's overall extinction magnitude was similar to that of the Central and Western Palaeotethys, but that it had a high magnitude of extinction of endemic taxa.This mass extinction marked the beginning of the transition between the Palaeozoic and Modern evolutionary faunas. The brachiopod-mollusc transition that characterised the broader shift from the Palaeozoic to Modern evolutionary faunas has been suggested to have had its roots in the Capitanian mass extinction event, although other research has concluded that this may be an illusion created by taphonomic bias in silicified fossil assemblages, with the transition beginning only in the aftermath of the more cataclysmic end-Permian extinction. After the Capitanian mass extinction, disaster taxa such as Earlandia and Diplosphaerina became abundant in what is now South China. The initial recovery of reefs consisted of non-metazoan reefs: algal bioherms and algal-sponge reef buildups. This initial recovery interval was followed by an interval of Tubiphytes-dominated reefs, which in turn was followed by a return of metazoan, sponge-dominated reefs. Overall, reef recovery took approximately 2.5 million years.
Terrestrial life
Among terrestrial vertebrates, the main victims were dinocephalian therapsids, which were one of the most common elements of tetrapod fauna of the Guadalupian; only one dinocephalian genus survived the Capitanian extinction event. The diversity of the anomodonts that lived during the late Guadalupian was cut in half by the Capitanian mass extinction. Terrestrial survivors of the Capitanian extinction event were generally 20 kg (44 lb) to 50 kg (110 lb) and commonly found in burrows.
Causes
Emeishan Traps
Volcanic emissions
It is believed that the extinction, which coincided with the beginning of a major negative δ13C excursion signifying a severe disturbance of the carbon cycle, was triggered by eruptions of the Emeishan Traps large igneous province, basalt piles from which currently cover an area of 250,000 to 500,000 km2, although the original volume of the basalts may have been anywhere from 500,000 km3 to over 1,000,000 km3. The age of the extinction event and the deposition of the Emeishan basalts are in good alignment. Reefs and other marine sediments interbedded among basalt piles indicate Emeishan volcanism initially developed underwater; terrestrial outflows of lava occurred only later in the large igneous province's period of activity. These eruptions would have released high doses of toxic mercury; increased mercury concentrations are coincident with the negative carbon isotope excursion, indicating a common volcanic cause. Coronene enrichment at the Guadalupian-Lopingian boundary further confirms the existence of massive volcanic activity; coronene can only form at extremely high temperatures created either by extraterrestrial impacts or massive volcanism, with the former being ruled out because of an absence of iridium anomalies coeval with mercury and coronene anomalies. A large amount of carbon dioxide and sulphur dioxide is believed to have been discharged into the stratosphere of the Northern and Southern Hemispheres due to the equatorial location of the Emeishan Traps, leading to sudden global cooling and long-term global warming. The Emeishan Traps discharged between 130 and 188 teratonnes of carbon dioxide in total, doing so at a rate of between 0.08 to 0.25 gigatonnes of carbon dioxide per year, making them responsible for an increase in atmospheric carbon dioxide that was both one of the largest and one of the most precipitous in the entire geological history of the Earth. The rate of carbon dioxide emissions during the Capitanian mass extinction, though extremely abrupt, was nonetheless significantly slower than that during the end-Permian extinction, during which carbon dioxide levels rose five times faster according to one study. Significant quantities of methane released by dikes and sills intruding into coal-rich deposits has been implicated as an additional driver of warming, though this idea has been challenged by studies that instead conclude that the extinction was precipitated directly by the Emeishan Traps or by their interaction with platform carbonates.
Anoxia and euxinia
Global warming resulting from the large igneous province's activity has been implicated as a cause of marine anoxia. Two anoxic events, the middle Capitanian OAE-C1 and the end-Capitanian OAE-C2, occurred thanks to Emeishan volcanic activity. Volcanic greenhouse gas release and global warming increased continental weathering and mineral erosion, which in turn has been propounded as a factor enhancing oceanic euxinia. Euxinia may have been exacerbated even further by the increasing sluggishness of ocean circulation resulting from volcanically driven warming. The initial hydrothermal nature of the Emeishan Traps meant that local marine life around South China would have been especially jeopardised by anoxia due to hyaloclastite development in restricted, fault-bounded basins. Expansion of oceanic anoxia has been posited to have occurred slightly before the Capitanian extinction event itself by some studies, though it is probable that upwelling of anoxic waters prior to the mass extinction was a local phenomenon specific to South China.
Hypercapnia and acidification
Because the ocean acts as a carbon sink absorbing atmospheric carbon dioxide, it is likely that the excessive volcanic emissions of carbon dioxide resulted in marine hypercapnia, which would have acted in conjunction with other killing mechanisms to further increase the severity of the biotic crisis. The dissolution of volcanically emitted carbon dioxide in the oceans triggered ocean acidification, which probably contributed to the demise of various calcareous marine organisms, particularly giant alatoconchid bivalves. By virtue of the greater solubility of carbon dioxide in colder waters, ocean acidification was especially lethal in high latitude waters. Furthermore, acid rain would have arisen as yet another biocidal consequence of the intense sulphur emissions produced by Emeishan Traps volcanism. This resulted in soil acidification and a decline of terrestrial infaunal invertebrates. Some researchers have cast doubt on whether significant acidification took place globally, concluding that the carbon cycle perturbation was too small to have caused a major worldwide drop in pH.
Criticism of the volcanic cause hypothesis
Not all studies, however, have supported the volcanic warming hypothesis; analysis of δ13C and δ18O values from the tooth apatite of Diictodon feliceps specimens from the Karoo Supergroup shows a positive δ13C excursion and concludes that the end of the Capitanian was marked by massive aridification in the region, although the temperature remained largely the same, suggesting that global climate change did not account for the extinction event. Analysis of vertebrate extinction rates in the Karoo Basin, specifically the upper Abrahamskraal Formation and lower Teekloof Formation, show that the large scale decrease in terrestrial vertebrate diversity coincided with volcanism in the Emeishan Traps, although robust evidence for a causal relationship between these two events remains elusive. A 2015 study called into question whether the Capitanian mass extinction event was global in nature at all or merely a regional biotic crisis limited to South China and a few other areas, finding no evidence for terrestrial or marine extinctions in eastern Australia linked to the Emeishan Traps or to any proposed extinction triggers invoked to explain the biodiversity drop in low-latitudes of the Northern Hemisphere.
Sea level fall
The Capitanian mass extinction has been attributed to sea level fall, with the widespread demise of reefs in particular being linked to this marine regression. The Guadalupian-Lopingian boundary coincided with one of the most prominent first-order marine regressions of the Phanerozoic. Evidence for abrupt sea level fall at the terminus of the Guadalupian comes from evaporites and terrestrial facies overlying marine carbonate deposits across the Guadalupian-Lopingian transition. Additionally, a tremendous unconformity is associated with the Guadalupian-Lopingian boundary in many strata across the world. The closure of the Sino-Mongolian Seaway at the end of the Capitanian has been invoked as a potential driver of Palaeotethyan biodiversity loss.
Other hypotheses
Global drying, plate tectonics, and biological competition may have also played a role in the extinction. Potential drivers of extinction proposed as causes of end-Guadalupian reef decline include fluctuations in salinity and tectonic collisions of microcontinents.
== References == |
boring billion | The Boring Billion, otherwise known as the Mid Proterozoic and Earth's Middle Ages, is the time period between 1.8 and 0.8 billion years ago (Ga) spanning the middle Proterozoic eon, characterized by more or less tectonic stability, climatic stasis, and slow biological evolution. It is bordered by two different oxygenation and glacial events, but the Boring Billion itself had very low oxygen levels and no evidence of glaciation.
The oceans may have been oxygen- and nutrient-poor and sulfidic (euxinia), populated by mainly anoxygenic purple bacteria, a type of chlorophyll-based photosynthetic bacteria which uses hydrogen sulfide (H2S) instead of water and produces sulfur instead of oxygen. This is known as a Canfield ocean. Such composition may have caused the oceans to be black- and milky-turquoise instead of blue. (By contrast, during the much earlier Purple Earth phase the photosynthesis was retinal-based.)
Despite such adverse conditions, eukaryotes may have evolved around the beginning of the Boring Billion, and adopted several novel adaptations, such as various organelles, multicellularity, and possibly sexual reproduction, and diversified into plants, animals, and fungi at the end of this time interval. Such advances may have been important precursors to the evolution of large, complex life later in the Ediacaran and Phanerozoic. Nonetheless, prokaryotic cyanobacteria were the dominant lifeforms during this time, and likely supported an energy-poor food-web with a small number of protists at the apex level. The land was likely inhabited by prokaryotic cyanobacteria and eukaryotic proto-lichens, the latter more successful here probably due to the greater availability of nutrients than in offshore ocean waters.
Description
In 1995, geologists Roger Buick, Davis Des Marais, and Andrew Knoll reviewed the apparent lack of major biological, geological, and climatic events during the Mesoproterozoic era 1.6 to 1 billion years ago (Ga), and, thus, described it as "the dullest time in Earth's history". The term "Boring Billion" was coined by paleontologist Martin Brasier to refer to the time between about 2 and 1 Ga, which was characterized by geochemical stasis and glacial stagnation. In 2013, geochemist Grant Young used the term "Barren Billion" to refer to a period of apparent glacial stagnation and lack of carbon isotope excursions from 1.8 to 0.8 Ga. In 2014, geologists Peter Cawood and Chris Hawkesworth called the time between 1.7 and 0.75 Ga "Earth's Middle Ages" due to a lack of evidence of tectonic movement.The Boring Billion is now largely cited as spanning about 1.8 to 0.8 Ga, contained within the Proterozoic eon, mainly the Mesoproterozoic. The Boring Billion is characterized by geological, climatic, and by-and-large evolutionary stasis, with low nutrient abundance.In the time leading up to the Boring Billion, Earth experienced the Great Oxygenation Event due to the evolution of oxygenic photosynthetic cyanobacteria, and the resultant Huronian glaciation (Snowball Earth), formation of the UV-blocking ozone layer, and oxidation of several metals. Oxygen levels during the Boring Billion are thought to have been markedly lower than during the Great Oxidation Event, perhaps 0.1% to 10% of modern levels. It was ended by the breakup of the supercontinent Rodinia during the Tonian (1000–720 Ma) period, a second oxygenation event, and another Snowball Earth in the Cryogenian period.
Tectonic stasis
The evolution of Earth's biosphere, atmosphere, and hydrosphere has long been linked to the supercontinent cycle, where the continents aggregate and then drift apart. The Boring Billion saw the evolution of two supercontinents: Columbia (or Nuna) and Rodinia.The supercontinent Columbia formed between 2.0 and 1.7 Ga and remained intact until at least 1.3 Ga. Geological and paleomagnetic evidence suggest that Columbia underwent only minor changes to form the supercontinent Rodinia from 1.1 to 0.9 Ga. Paleogeographic reconstructions suggest that the supercontinent assemblage was located in equatorial and temperate climate zones, and there is little or no evidence for continental fragments in polar regions.Due to the lack of evidence of sediment build-up (on passive margins) which would occur as a result of rifting, the supercontinent probably did not break up, and rather was simply an assemblage of juxtaposed proto-continents and cratons. There is no evidence of rifting until the formation of Rodinia, 1.25 Ga in North Laurentia, and 1 Ga in East Baltica and South Siberia. Breakup did not occur until 0.75 Ga, marking the end of the Boring Billion. This tectonic stasis may have been related in ocean and atmospheric chemistry.It is possible the asthenosphere—the molten layer of Earth's mantle that tectonic plates essentially float and move around upon—was too hot to sustain modern plate tectonics at this time. Instead of vigorous plate recycling at subduction zones, plates were linked together for billions of years until the mantle cooled off sufficiently. The onset of this component of plate tectonics may have been aided by the cooling and thickening of the crust that, once initiated, made plate subduction anomalously strong, occurring at the end of the Boring Billion.Nonetheless, major magmatic events still occurred, such as the formation (via magma plume) of the 220,000 km2 (85,000 sq mi) central Australian Musgrave Province from 1.22 to 1.12 Ga, and the 2,700,000 km2 (1,000,000 sq mi) Canadian Mackenzie Large Igneous Province 1.27 Ga. Plate tectonics were still active enough to build mountains, with several orogenies, including the Grenville orogeny, occurring at the time.
Climatic stability
There is little evidence of significant climatic variability during this time period. Climate was likely not primarily dictated by solar luminosity because the Sun was 5–18% less luminous than it is today, but there is no evidence that Earth's climate was significantly cooler. In fact, the Boring Billion seems to lack any evidence of prolonged glaciations, which can be observed at regular periodicity in other parts of Earth's geologic history. High CO2 could not have been a main driver for warming because levels would have needed to be 30 to 100 times greater than pre-industrial levels and produced substantial ocean acidification to prevent ice formation, which also did not occur. Mesoproterozoic CO2 levels may have been comparable to those of the Phanerozoic eon, perhaps 7 to 10 times higher than modern levels. The first record of ice from this time period was reported in 2020 from the 1 Ga Scottish Diabaig Formation in the Torridon Group, where dropstone formations were likely formed by debris from ice rafting; the area, then situated between 35–50°S, was a (possibly upland) lake which is thought to have frozen over in the winter and melted in the summer, rafting occurring in the spring melt.A higher abundance of other greenhouse gases, namely methane produced by prokaryotes, may have compensated for the low CO2 levels; a largely ice-free world achieved by an atmospheric methane concentration of 140 parts per million (ppm). Methanogenic prokaryotes could not have produced so much methane, implying some other greenhouse gas, probably nitrous oxide, was elevated, perhaps to 3 ppm (10 times today's levels). Based on presumed greenhouse gas concentrations, equatorial temperatures during the Mesoproterozoic may have been about 295–300 K (22–27 °C; 71–80 °F), in the tropics 290 K (17 °C; 62 °F), at 60° 265–280 K (−8–7 °C; 17–44 °F), and the poles 250–275 K (−23–2 °C; −10–35 °F); and the global average temperature about 19 °C (66 °F), which is 4 °C (7.2 °F) warmer than today. Temperatures at the poles dropped below freezing in winter, allowing for temporary sea ice formation and snowfall, but there were likely no permanent ice sheets.It has also been proposed that, because the intensity of cosmic rays has been shown to be positively correlated to cloud cover, and cloud cover reflects light into space and reduces global temperatures, lower rates of bombardment during this time due to reduced star formation in the galaxy caused less cloud cover and prevented glaciation events, maintaining a warm climate. Also, some combination of weathering intensity which would have reduced CO2 levels by oxidation of exposed metals, cooling of the mantle and reduced geothermal heat and volcanism, and increasing solar intensity and solar heat may have reached an equilibrium, barring ice formation.Conversely, glacial movements over a billion years ago may not have left many remnants today, and an apparent lack of evidence could be due to the incompleteness of the fossil record rather than absence. Further, the low oxygen and solar intensity levels may have prevented the formation of the ozone layer, preventing greenhouse gasses from being trapped in the atmosphere and heating the Earth via the greenhouse effect, which would have caused glaciation. Though not much oxygen is necessary to sustain the ozone layer, and levels during the Boring Billion may have been high enough for it, the Earth may have been more heavily bombarded by UV radiation than today.
Oceanic composition
The oceans seem to have had low concentrations of key nutrients thought to be necessary for complex life, namely molybdenum, iron, nitrogen, and phosphorus, in large part due to a lack of oxygen and resultant oxidation necessary for these geochemical cycles. Nutrients could have been more abundant in terrestrial environments, such as lakes or nearshore environments closer to continental runoff.In general, the oceans may have had an oxygenated surface layer, a sulfidic middle layer, and suboxic bottom layer. The predominantly sulfidic composition may have caused the oceans to be a black- and milky-turquoise color instead of blue.
Oxygen
Earth's geologic record indicates two events associated with significant increases in oxygen levels on Earth, with one occurring between 2.4 and 2.1 Ga, known as the Great Oxidation Event (GOE), and the second occurring an approximate 0.8 Ga, known as the Neoproterozoic Oxygenation Event (NOE). The intermediary period, during the Boring Billion, is thought have had low oxygen levels (with minor fluctuations), leading to widespread anoxic waters.The oceans may have been distinctly stratified, with surface water being oxygenated and deep water being suboxic (less than 1 μM oxygen), the latter possibly maintained by lower levels of hydrogen (H2) and H2S output by deep sea hydrothermal vents which otherwise would have been chemically reduced by the oxygen. Even in the shallowest waters, significant quantities of oxygen may have been restricted mainly to areas near the coast. The decomposition of sinking organic matter would have also leached oxygen from deep waters.The sudden drop in O2 after the Great Oxygenation Event—indicated by δ13C levels to have been a loss of 10 to 20 times the current volume of atmospheric oxygen—is known as the Lomagundi-Jatuli Event, and is the most prominent carbon isotope event in Earth's history. Oxygen levels may have been less than 0.1 to 1% of modern-day levels, which would have effectively stalled the evolution of complex life during the Boring Billion. However, a Mesoproterozoic Oxygenation Event (MOE), during which oxygen rose transiently to about 4% PAL at various points in time, is proposed to have occurred from 1.59 to 1.36 Ga. In particular, some evidence from the Gaoyuzhuang Formation suggests a rise in oxygen around 1.57 Ga, while the Velkerri Formation in the Roper Group of the Northern Territory of Australia, the Kaltasy Formation of the Volga-Ural region of Russia, and the Xiamaling Formation in the northern North China Craton indicate noticeable oxygenation around 1.4 Ga, although the degree to which this represents global oxygen levels is unclear. Oxic conditions would have become dominant at the NOE causing the proliferation of aerobic activity over anaerobic, but widespread suboxic and anoxic conditions likely lasted until about 0.55 Ga corresponding with Ediacaran biota and the Cambrian explosion.
Sulfur
In 1998, geologist Donald Canfield proposed what is now known as the Canfield ocean hypothesis. Canfield claimed that increasing levels of oxygen in the atmosphere at the Great Oxygenation Event would have reacted with and oxidized continental iron pyrite (FeS2) deposits, with sulfate (SO42−) as a byproduct, which was transported into the sea. Sulfate-reducing microorganisms converted this to hydrogen sulfide (H2S), dividing the ocean into a somewhat oxic surface layer, and a sulfidic layer beneath, with anoxygenic bacteria living at the border, metabolizing the H2S and creating sulfur as a waste product. This created widespread euxinic conditions in middle-waters, an anoxic state with a high sulfur concentration, which was maintained by the bacteria. However, more systematic geochemical study of the Mid-Proterozoic indicates that the oceans were largely ferruginous with a thin surface layer of weakly oxygenated waters, and euxinia may have occurred over relatively small areas, perhaps less than 7% of the seafloor.
Iron
Among rocks dating to the Boring Billion, there is a conspicuous lack of banded iron formations, which form from iron in the upper water column (sourced from the deep ocean) reacting with oxygen and precipitating out of the water. They seemingly cease around the world after 1.85 Ga. Canfield argued that oceanic SO42− reduced all the iron in the anoxic deep sea. Iron could have been metabolized by anoxygenic bacteria. It has also been proposed that the 1.85 Ga Sudbury meteor impact mixed the previously stratified ocean via tsunamis, interaction between vaporized seawater and the oxygenated atmosphere, oceanic cavitation, and massive runoff of destroyed continental margins into the sea. Resultant suboxic deep waters (due to oxygenated surface water mixing with previously anoxic deep water) would have oxidized deep-water iron, preventing it from being transported and deposited on continental margins.Nonetheless, iron-rich waters did exist, such as the 1.4 Ga Xiamaling Formation of Northern China, which perhaps was fed by deep water hydrothermal vents. Iron-rich conditions also indicate anoxic bottom water in this area, as oxic conditions would have oxidized all the iron.
Lifeforms
Low nutrient abundance may have facilitated photosymbiosis—where one organism is capable of photosynthesis and the other metabolizes the waste product—among prokaryotes (bacteria and archaea), and the emergence of eukaryotes. Bacteria, Archaea, and Eukaryota are the three domains, the highest taxonomic ranking. Eukaryotes are distinguished from prokaryotes by a nucleus and membrane-bound organelles, and almost all multicellular organisms are eukaryotes.
Prokaryotes
Prokaryotes were the dominant lifeforms throughout the Boring Billion. Microfossils indicate the presence of cyanobacteria, green and purple sulfur bacteria, methane-producing archaea, sulfate-metabolizing bacteria, methane-metabolizing archaea or bacteria, iron-metabolizing bacteria, nitrogen-metabolizing bacteria, and anoxygenic photosynthetic bacteria.Anoxygenic cyanobacteria are thought to have been the dominant photosynthesizers, metabolizing the abundant H2S in the oceans. In iron-rich waters, cyanobacteria may have suffered from iron poisoning, especially in offshore waters where iron-rich deep water mixed with surface waters, and thus were outcompeted by other bacteria which could metabolize both iron and H2S. However, iron poisoning could have been abated by silica-rich waters or biomineralization of iron within the cell.Unicellular planktonic lineages of cyanobacteria evolved in freshwater during the middle of the Mesoproterozoic, and during the Neoproterozoic both benthic marine and some freshwater ancestors gave rise to marine planktonic cyanobacteria (both nitrogen-fixing and non-nitrogen fixing), contributing to the oxygenation of the Pre-Cambrian oceans.Research on cyanobacteria in the laboratory has shown that the enzyme nitrogenase, which is used to fix atmospheric nitrogen, stops working when the oxygen levels is higher than 10% of current atmospheric levels. The absence of nitrogen due to an increased amount of oxygen would have created a negative feedback loop where atmospheric oxygen levels stabilised at 2%. Which began to change about 600 million years ago when landplants started releasing oxygen. By 408 million years ago, nitrogen fixating cyanobacteria had evolved heterocysts to protect their nitrogenase from oxygen.
Eukaryotes
Eukaryotes may have arisen around the beginning of the Boring Billion, coinciding with the accretion of Columbia, which could have somehow increased oceanic oxygen levels. Although there have been claimed records of eukaryotes as early as 2.1 billion years ago, these have been considered questionable, with the oldest unambiguous eukaryote remains dating to around 1.8-1.6 billion years ago in China. Following this, eukaryotic evolution was rather slow, possibly due to the euxinic conditions of the Canfield ocean and a lack of key nutrients and metals which prevented large, complex life with high energy requirements from evolving. Euxinic conditions would have also decreased the solubility of iron and molybdenum, essential metals in nitrogen fixation. A lack of dissolved nitrogen would have favored prokaryotes over eukaryotes, as the former can metabolize gaseous nitrogen. An alternative hypothesis for the lack of diversification among eukaryotes implicates high temperatures during the Boring Billion rather than low oxygen levels, positing that the fact that oxygenation events prior to the Late Neoproterozoic did not kickstart eukaryotic evolution suggests it was not the main limiting factor inhibiting it.
Nonetheless, the diversification of crown group eukaryotic macroorganisms seems to have started about 1.6–1 Ga, seemingly coinciding with an increase in key nutrient concentrations. According to molecular clock analysis, plants diverged from animals and fungi about 1.6 Ga; animals and fungi about 1.5 Ga; Bilaterians and cnidarians (animals respectively with and without bilateral symmetry) about 1.3 Ga; sponges 1.35 Ga; and Ascomycota and Basidiomycota (the two divisions of the fungus subkingdom Dikarya) 0.97 Ga. The paper's authors state that their time estimates disagree with the scientific consensus.
Fossils from the late Palaeoproterozoic and early Mesoproterozoic of the Vindhyan sedimentary basin of India, the Ruyang Group of China, and the Kotuikan Formation of the Anabar Shield of Siberia indicate high rates (by pre-Ediacaran standards) of eukaryotic diversification between 1.7 and 1.4 Ga, although much of this diversity is represented by previously unknown, no longer existing clades of eukaryotes. The earliest known red algae mats date to 1.6 Ga. The earliest known fungus dates to 1.01–0.89 Ga from Northern Canada. Multicellular eukaryotes, thought to be the descendants of colonial unicellular aggregates, had probably evolved about 2–1.4 Ga. Likewise, early multicellular eukaryotes likely mainly aggregated into stromatolite mats.The red alga Bangiomorpha is the earliest known sexually reproducing and meiotic lifeform, and evolved by 1.047 Ga. Based on this, these adaptations evolved between ca. 2–1.4 Ga. Alternatively, these may have evolved well before the last common ancestor of eukaryotes given that meiosis is performed using the same proteins in all eukaryotes, perhaps stretching to as far back as the hypothesized RNA world.Cell organelles probably originated from free-living cyanobacteria (symbiogenesis) possibly after the evolution of phagocytosis (engulfing other cells) with the removal of the rigid cell wall which was only necessary for asexual reproduction. Mitochondria had already evolved in the Great Oxygenation Event, but plastids used in primoplants for photosynthesis are thought to have appeared about 1.6–1.5 Ga. Histones likely appeared during the Boring Billion to help organize and package the increasing amount of DNA in eukaryotic cells into nucleosomes. Hydrogenosomes used in anaerobic activity may have originated in this time from an archaeon.Given the evolutionary landmarks achieved by eukaryotes, this time period could be considered an important precursor to the Cambrian explosion about 0.54 Ga, and the evolution of relatively large, complex life.
Ecology
Due to the marginalization of large food particles, such as algae, in favor of cyanobacteria and prokaryotes which do not transmit as much energy to higher trophic levels, a complex food web likely did not form, and large lifeforms with high energy demands could not evolve. Such a food web probably only sustained a small number of protists as, in a sense, apex predators.The presumably oxygenic photosynthetic eukaryotic acritarchs, perhaps a type of microalga, inhabited the Mesoproterozoic surface waters. Their population may have been largely limited by nutrient availability rather than predation because species have been reported to have survived for hundreds of millions of years, but after 1 Ga, species duration dropped to about 100 Ma, perhaps due to increased herbivory by early protists. This is consistent with species survival dropping to 10 Ma just after the Cambrian explosion and the expansion of herbivorous animals.The relatively low concentrations of molybdenum in the ocean throughout the Boring Billion have been suggested as a major limiting factor that kept populations of open ocean nitrogen fixing microorganisms, which require molybdenum to produce nitrogenases, low, although freshwater and coastal environments close to riverine sources of dissolved molybdenum may have still hosted significant communities of nitrogen fixers. The low rate of nitrogen fixation, which only ended during the Cryogenian with the evolution of planktonic nitrogen fixers, meant that free ammonium was in short supply across this time interval, severely constraining the evolution and diversification of multicellular biota.
Life on land
Some of the earliest evidence of the prokaryotic colonization of land dates to before 3 Ga, possibly as early as 3.5 Ga. During the Boring Billion, land may have been inhabited mainly by cyanobacterial mats. Dust would have supplied an abundance of nutrients and a means of dispersal for surface-dwelling microbes, though microbial communities could have also formed in caves and freshwater lakes and rivers. By 1.2 Ga, microbial communities may have been abundant enough to have affected weathering, erosion, sedimentation, and various geochemical cycles, and expansive microbial mats could indicate biological soil crust was abundant.The earliest terrestrial eukaryotes may have been lichen fungi about 1.3 Ga, which grazed on the microbial mats. Abundant eukaryotic microfossils from the freshwater Scottish Torridon Group seems to indicate eukaryotic dominance in non-marine habitats by 1 Ga, probably due to increased nutrient availability in areas closer to the continents and continental runoff. These lichen may have later facilitated plant colonization 0.75 Ga in some manner. A massive increase in terrestrial photosynthetic biomass seems to have occurred about 0.85 Ga, indicated by a flux in terrestrially-sourced carbon, which may have increased oxygen levels enough to support an expansion of multicellular eukaryotes.
See also
Precambrian – History of Earth 4600–539 million years ago
Ediacaran biota – All organisms of the Ediacaran Period (c. 635–538.8 million years ago)
Francevillian biota – Possible Palaeoproterozoic multicellular fossils from Gabon
L'Atalante basin – Anoxic hypersaline brine basin at the bottom of the Mediterranean Sea
Snowball Earth – Worldwide glaciation episodes during the Proterozoic eon
The natural nuclear fission reactors at what is now Oklo, Gabon were active in this era
External links
Earth’s 'boring billion' years of stagnant, stinking oceans might actually have been rather dynamic
== References == |
limestone | Limestone (calcium carbonate CaCO3) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO3. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life.About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite, a closely related rock, which contains a high percentage of the mineral dolomite, CaMg(CO3)2. Magnesian limestone is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite (dolomitic limestone), or for any other limestone containing a significant percentage of magnesium. Most limestone was formed in shallow marine environments, such as continental shelves or platforms, though smaller amounts were formed in many other environments. Much dolomite is secondary dolomite, formed by chemical alteration of limestone. Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly soluble in rainwater, these exposures often are eroded to become karst landscapes. Most cave systems are found in limestone bedrock.
Limestone has numerous uses: as a chemical feedstock for the production of lime used for cement (an essential component of concrete), as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a soil conditioner, and as a popular decorative addition to rock gardens. Limestone formations contain about 30% of the world's petroleum reservoirs.
Description
Limestone is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3). Dolomite, CaMg(CO3)2, is an uncommon mineral in limestone, and siderite or other carbonate minerals are rare. However, the calcite in limestone often contains a few percent of magnesium. Calcite in limestone is divided into low-magnesium and high-magnesium calcite, with the dividing line placed at a composition of 4% magnesium. High-magnesium calcite retains the calcite mineral structure, which is distinct from dolomite. Aragonite does not usually contain significant magnesium. Most limestone is otherwise chemically fairly pure, with clastic sediments (mainly fine-grained quartz and clay minerals) making up less than 5% to 10% of the composition. Organic matter typically makes up around 0.2% of a limestone and rarely exceeds 1%.Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragments (such as sponge spicules, diatoms, or radiolarians). Fossils are also common in limestone.Limestone is commonly white to gray in color. Limestone that is unusually rich in organic matter can be almost black in color, while traces of iron or manganese can give limestone an off-white to yellow to red color. The density of limestone depends on its porosity, which varies from 0.1% for the densest limestone to 40% for chalk. The density correspondingly ranges from 1.5 to 2.7 g/cm3. Although relatively soft, with a Mohs hardness of 2 to 4, dense limestone can have a crushing strength of up to 180 MPa. For comparison, concrete typically has a crushing strength of about 40 MPa.Although limestones show little variability in mineral composition, they show great diversity in texture. However, most limestone consists of sand-sized grains in a carbonate mud matrix. Because limestones are often of biological origin and are usually composed of sediment that is deposited close to where it formed, classification of limestone is usually based on its grain type and mud content.
Grains
Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera. These organisms secrete structures made of aragonite or calcite, and leave these structures behind when they die. Other carbonate grains composing limestones are ooids, peloids, and limeclasts (intraclasts and extraclasts).Skeletal grains have a composition reflecting the organisms that produced them and the environment in which they were produced. Low-magnesium calcite skeletal grains are typical of articulate brachiopods, planktonic (free-floating) foraminifera, and coccoliths. High-magnesium calcite skeletal grains are typical of benthic (bottom-dwelling) foraminifera, echinoderms, and coralline algae. Aragonite skeletal grains are typical of molluscs, calcareous green algae, stromatoporoids, corals, and tube worms. The skeletal grains also reflect specific geological periods and environments. For example, coral grains are more common in high-energy environments (characterized by strong currents and turbulence) while bryozoan grains are more common in low-energy environments (characterized by quiet water).Ooids (sometimes called ooliths) are sand-sized grains (less than 2mm in diameter) consisting of one or more layers of calcite or aragonite around a central quartz grain or carbonate mineral fragment. These likely form by direct precipitation of calcium carbonate onto the ooid. Pisoliths are similar to ooids, but they are larger than 2 mm in diameter and tend to be more irregular in shape. Limestone composed mostly of ooids is called an oolite or sometimes an oolitic limestone. Ooids form in high-energy environments, such as the Bahama platform, and oolites typically show crossbedding and other features associated with deposition in strong currents.Oncoliths resemble ooids but show a radial rather than layered internal structure, indicating that they were formed by algae in a normal marine environment.Peloids are structureless grains of microcrystalline carbonate likely produced by a variety of processes. Many are thought to be fecal pellets produced by marine organisms. Others may be produced by endolithic (boring) algae or other microorganisms or through breakdown of mollusc shells. They are difficult to see in a limestone sample except in thin section and are less common in ancient limestones, possibly because compaction of carbonate sediments disrupts them.Limeclasts are fragments of existing limestone or partially lithified carbonate sediments. Intraclasts are limeclasts that originate close to where they are deposited in limestone, while extraclasts come from outside the depositional area. Intraclasts include grapestone, which is clusters of peloids cemented together by organic material or mineral cement. Extraclasts are uncommon, are usually accompanied by other clastic sediments, and indicate deposition in a tectonically active area or as part of a turbidity current.
Mud
The grains of most limestones are embedded in a matrix of carbonate mud. This is typically the largest fraction of an ancient carbonate rock. Mud consisting of individual crystals less than 5 μm (0.20 mils) in length is described as micrite. In fresh carbonate mud, micrite is mostly small aragonite needles, which may precipitate directly from seawater, be secreted by algae, or be produced by abrasion of carbonate grains in a high-energy environment. This is converted to calcite within a few million years of deposition. Further recrystallization of micrite produces microspar, with grains from 5 to 15 μm (0.20 to 0.59 mils) in diameter.Limestone often contains larger crystals of calcite, ranging in size from 0.02 to 0.1 mm (0.79 to 3.94 mils), that are described as sparry calcite or sparite. Sparite is distinguished from micrite by a grain size of over 20 μm (0.79 mils) and because sparite stands out under a hand lens or in thin section as white or transparent crystals. Sparite is distinguished from carbonate grains by its lack of internal structure and its characteristic crystal shapes. Geologists are careful to distinguish between sparite deposited as cement and sparite formed by recrystallization of micrite or carbonate grains. Sparite cement was likely deposited in pore space between grains, suggesting a high-energy depositional environment that removed carbonate mud. Recrystallized sparite is not diagnostic of depositional environment.
Other characteristics
Limestone outcrops are recognized in the field by their softness (calcite and aragonite both have a Mohs hardness of less than 4, well below common silicate minerals) and because limestone bubbles vigorously when a drop of dilute hydrochloric acid is dropped on it. Dolomite is also soft but reacts only feebly with dilute hydrochloric acid, and it usually weathers to a characteristic dull yellow-brown color due to the presence of ferrous iron. This is released and oxidized as the dolomite weathers. Impurities (such as clay, sand, organic remains, iron oxide, and other materials) will cause limestones to exhibit different colors, especially with weathered surfaces.
The makeup of a carbonate rock outcrop can be estimated in the field by etching the surface with dilute hydrochloric acid. This etches away the calcite and aragonite, leaving behind any silica or dolomite grains. The latter can be identified by their rhombohedral shape.Crystals of calcite, quartz, dolomite or barite may line small cavities (vugs) in the rock. Vugs are a form of secondary porosity, formed in existing limestone by a change in environment that increases the solubility of calcite.Dense, massive limestone is sometimes described as "marble". For example, the famous Portoro "marble" of Italy is actually a dense black limestone. True marble is produced by recrystallization of limestone during regional metamorphism that accompanies the mountain building process (orogeny). It is distinguished from dense limestone by its coarse crystalline texture and the formation of distinctive minerals from the silica and clay present in the original limestone.
Classification
Two major classification schemes, the Folk and Dunham, are used for identifying the types of carbonate rocks collectively known as limestone.
Folk classification
Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks. Based on composition, there are three main components: allochems (grains), matrix (mostly micrite), and cement (sparite). The Folk system uses two-part names; the first refers to the grains and the second to the cement. For example, a limestone consisting mainly of ooids, with a crystalline matrix, would be termed an oosparite. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample.
Dunham classification
Robert J. Dunham published his system for limestone in 1962. It focuses on the depositional fabric of carbonate rocks. Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles, based on criteria such as whether the grains were originally in mutual contact, and therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock. The Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample.A revised classification was proposed by Wright (1992). It adds some diagenetic patterns to the classification scheme.
Other descriptive terms
Travertine is a term applied to calcium carbonate deposits formed in freshwater environments, particularly waterfalls, cascades and hot springs. Such deposits are typically massive, dense, and banded. When the deposits are highly porous, so that they have a spongelike texture, they are typically described as tufa. Secondary calcite deposited by supersaturated meteoric waters (groundwater) in caves is also sometimes described as travertine. This produces speleothems, such as stalagmites and stalactites.Coquina is a poorly consolidated limestone composed of abraded pieces of coral, shells, or other fossil debris. When better consolidated, it is described as coquinite.Chalk is a soft, earthy, fine-textured limestone composed of the tests of planktonic microorganisms such as foraminifera, while
marl is an earthy mixture of carbonates and silicate sediments.
Formation
Limestone forms when calcite or aragonite precipitate out of water containing dissolved calcium, which can take place through both biological and nonbiological processes. The solubility of calcium carbonate (CaCO3) is controlled largely by the amount of dissolved carbon dioxide (CO2) in the water. This is summarized in the reaction:
CaCO3 + H2O + CO2 → Ca2+ + 2HCO−3Increases in temperature or decreases in pressure tend to reduce the amount of dissolved CO2 and precipitate CaCO3. Reduction in salinity also reduces the solubility of CaCO3, by several orders of magnitude for fresh water versus seawater.
Near-surface water of the earth's oceans are oversaturated with CaCO3 by a factor of more than six. The failure of CaCO3 to rapidly precipitate out of these waters is likely due to interference by dissolved magnesium ions with nucleation of calcite crystals, the necessary first step in precipitation. Precipitation of aragonite may be suppressed by the presence of naturally occurring organic phosphates in the water. Although ooids likely form through purely inorganic processes, the bulk of CaCO3 precipitation in the oceans is the result of biological activity. Much of this takes place on carbonate platforms.
The origin of carbonate mud, and the processes by which it is converted to micrite, continue to be a subject of research. Modern carbonate mud is composed mostly of aragonite needles around 5 μm (0.20 mils) in length. Needles of this shape and composition are produced by calcareous algae such as Penicillus, making this a plausible source of mud. Another possibility is direct precipitation from the water. A phenomenon known as whitings occurs in shallow waters, in which white streaks containing dispersed micrite appear on the surface of the water. It is uncertain whether this is freshly precipitated aragonite or simply material stirred up from the bottom, but there is some evidence that whitings are caused by biological precipitation of aragonite as part of a bloom of cyanobacteria or microalgae. However, stable isotope ratios in modern carbonate mud appear to be inconsistent with either of these mechanisms, and abrasion of carbonate grains in high-energy environments has been put forward as a third possibility.Formation of limestone has likely been dominated by biological processes throughout the Phanerozoic, the last 540 million years of the Earth's history. Limestone may have been deposited by microorganisms in the Precambrian, prior to 540 million years ago, but inorganic processes were probably more important and likely took place in an ocean more highly oversaturated in calcium carbonate than the modern ocean.
Diagenesis
Diagenesis is the process in which sediments are compacted and turned into solid rock. During diagenesis of carbonate sediments, significant chemical and textural changes take place. For example, aragonite is converted to low-magnesium calcite. Diagenesis is the likely origin of pisoliths, concentrically layered particles ranging from 1 to 10 mm (0.039 to 0.394 inches) in diameter found in some limestones. Pisoliths superficially resemble ooids but have no nucleus of foreign matter, fit together tightly, and show other signs that they formed after the original deposition of the sediments.
Silicification occurs early in diagenesis, at low pH and temperature, and contributes to fossil preservation. Silicification takes place through the reaction:
CaCO
3
+
H
2
O
+
CO
2
+
H
4
SiO
4
⟶
SiO
2
+
Ca
2
+
+
2
HCO
3
−
+
2
H
2
O
{\displaystyle {\ce {CaCO3 + H2O + CO2 + H4SiO4 -> SiO2 + Ca^2+ + 2HCO3- + 2 H2O}}}
Fossils are often preserved in exquisite detail as chert.Cementing takes place rapidly in carbonate sediments, typically within less than a million years of deposition. Some cementing occurs while the sediments are still under water, forming hardgrounds. Cementing accelerates after the retreat of the sea from the depositional environment, as rainwater infiltrates the sediment beds, often within just a few thousand years. As rainwater mixes with groundwater, aragonite and high-magnesium calcite are converted to low-calcium calcite. Cementing of thick carbonate deposits by rainwater may commence even before the retreat of the sea, as rainwater can infiltrate over 100 km (60 miles) into sediments beneath the continental shelf.As carbonate sediments are increasingly deeply buried under younger sediments, chemical and mechanical compaction of the sediments increases. Chemical compaction takes place by pressure solution of the sediments. This process dissolves minerals from points of contact between grains and redeposits it in pore space, reducing the porosity of the limestone from an initial high value of 40% to 80% to less than 10%. Pressure solution produces distinctive stylolites, irregular surfaces within the limestone at which silica-rich sediments accumulate. These may reflect dissolution and loss of a considerable fraction of the limestone bed. At depths greater than 1 km (0.62 miles), burial cementation completes the lithification process. Burial cementation does not produce stylolites.When overlying beds are eroded, bringing limestone closer to the surface, the final stage of diagenesis takes place. This produces secondary porosity as some of the cement is dissolved by rainwater infiltrating the beds. This may include the formation of vugs, which are crystal-lined cavities within the limestone.Diagenesis may include conversion of limestone to dolomite by magnesium-rich fluids. There is considerable evidence of replacement of limestone by dolomite, including sharp replacement boundaries that cut across bedding. The process of dolomitization remains an area of active research, but possible mechanisms include exposure to concentrated brines in hot environments (evaporative reflux) or exposure to diluted seawater in delta or estuary environments (Dorag dolomitization). However, Dorag dolomitization has fallen into disfavor as a mechanism for dolomitization, with one 2004 review paper describing it bluntly as "a myth". Ordinary seawater is capable of converting calcite to dolomite, if the seawater is regularly flushed through the rock, as by the ebb and flow of tides (tidal pumping). Once dolomitization begins, it proceeds rapidly, so that there is very little carbonate rock containing mixed calcite and dolomite. Carbonate rock tends to be either almost all calcite/aragonite or almost all dolomite.
Occurrence
About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. Limestone is found in sedimentary sequences as old as 2.7 billion years. However, the compositions of carbonate rocks show an uneven distribution in time in the geologic record. About 95% of modern carbonates are composed of high-magnesium calcite and aragonite. The aragonite needles in carbonate mud are converted to low-magnesium calcite within a few million years, as this is the most stable form of calcium carbonate. Ancient carbonate formations of the Precambrian and Paleozoic contain abundant dolomite, but limestone dominates the carbonate beds of the Mesozoic and Cenozoic. Modern dolomite is quite rare. There is evidence that, while the modern ocean favors precipitation of aragonite, the oceans of the Paleozoic and middle to late Cenozoic favored precipitation of calcite. This may indicate a lower Mg/Ca ratio in the ocean water of those times. This magnesium depletion may be a consequence of more rapid sea floor spreading, which removes magnesium from ocean water. The modern ocean and the ocean of the Mesozoic have been described as "aragonite seas".Most limestone was formed in shallow marine environments, such as continental shelves or platforms. Such environments form only about 5% of the ocean basins, but limestone is rarely preserved in continental slope and deep sea environments. The best environments for deposition are warm waters, which have both a high organic productivity and increased saturation of calcium carbonate due to lower concentrations of dissolved carbon dioxide. Modern limestone deposits are almost always in areas with very little silica-rich sedimentation, reflected in the relative purity of most limestones. Reef organisms are destroyed by muddy, brackish river water, and carbonate grains are ground down by much harder silicate grains. Unlike clastic sedimentary rock, limestone is produced almost entirely from sediments originating at or near the place of deposition.
Limestone formations tend to show abrupt changes in thickness. Large moundlike features in a limestone formation are interpreted as ancient reefs, which when they appear in the geologic record are called bioherms. Many are rich in fossils, but most lack any connected organic framework like that seen in modern reefs. The fossil remains are present as separate fragments embedded in ample mud matrix. Much of the sedimentation shows indications of occurring in the intertidal or supratidal zones, suggesting sediments rapidly fill available accommodation space in the shelf or platform. Deposition is also favored on the seaward margin of shelves and platforms, where there is upwelling deep ocean water rich in nutrients that increase organic productivity. Reefs are common here, but when lacking, ooid shoals are found instead. Finer sediments are deposited close to shore.The lack of deep sea limestones is due in part to rapid subduction of oceanic crust, but is more a result of dissolution of calcium carbonate at depth. The solubility of calcium carbonate increases with pressure and even more with higher concentrations of carbon dioxide, which is produced by decaying organic matter settling into the deep ocean that is not removed by photosynthesis in the dark depths. As a result, there is a fairly sharp transition from water saturated with calcium carbonate to water unsaturated with calcium carbonate, the lysocline, which occurs at the calcite compensation depth of 4,000 to 7,000 m (13,000 to 23,000 feet). Below this depth, foraminifera tests and other skeletal particles rapidly dissolve, and the sediments of the ocean floor abruptly transition from carbonate ooze rich in foraminifera and coccolith remains (Globigerina ooze) to silicic mud lacking carbonates.
In rare cases, turbidites or other silica-rich sediments bury and preserve benthic (deep ocean) carbonate deposits. Ancient benthic limestones are microcrystalline and are identified by their tectonic setting. Fossils typically are foraminifera and coccoliths. No pre-Jurassic benthic limestones are known, probably because carbonate-shelled plankton had not yet evolved.Limestones also form in freshwater environments. These limestones are not unlike marine limestone, but have a lower diversity of organisms and a greater fraction of silica and clay minerals characteristic of marls. The Green River Formation is an example of a prominent freshwater sedimentary formation containing numerous limestone beds. Freshwater limestone is typically micritic. Fossils of charophyte (stonewort), a form of freshwater green algae, are characteristic of these environments, where the charophytes produce and trap carbonates.Limestones may also form in evaporite depositional environments. Calcite is one of the first minerals to precipitate in marine evaporites.
Limestone and living organisms
Most limestone is formed by the activities of living organisms near reefs, but the organisms responsible for reef formation have changed over geologic time. For example, stromatolites are mound-shaped structures in ancient limestones, interpreted as colonies of cyanobacteria that accumulated carbonate sediments, but stromatolites are rare in younger limestones. Organisms precipitate limestone both directly as part of their skeletons, and indirectly by removing carbon dioxide from the water by photosynthesis and thereby decreasing the solubility of calcium carbonate.Limestone shows the same range of sedimentary structures found in other sedimentary rocks. However, finer structures, such as lamination, are often destroyed by the burrowing activities of organisms (bioturbation). Fine lamination is characteristic of limestone formed in playa lakes, which lack the burrowing organisms. Limestones also show distinctive features such as geopetal structures, which form when curved shells settle to the bottom with the concave face downwards. This traps a void space that can later be filled by sparite. Geologists use geopetal structures to determine which direction was up at the time of deposition, which is not always obvious with highly deformed limestone formations.The cyanobacterium Hyella balani can bore through limestone; as can the green alga Eugamantia sacculata and the fungus Ostracolaba implexa.
Micritic mud mounds
Micricitic mud mounds are subcircular domes of micritic calcite that lacks internal structure. Modern examples are up to several hundred meters thick and a kilometer across, and have steep slopes (with slope angles of around 50 degrees). They may be composed of peloids swept together by currents and stabilized by Thalassia grass or mangroves. Bryozoa may also contribute to mound formation by helping to trap sediments.Mud mounds are found throughout the geologic record, and prior to the early Ordovician, they were the dominant reef type in both deep and shallow water. These mud mounds likely are microbial in origin. Following the appearance of frame-building reef organisms, mud mounds were restricted mainly to deeper water.
Organic reefs
Organic reefs form at low latitudes in shallow water, not more than a few meters deep. They are complex, diverse structures found throughout the fossil record. The frame-building organisms responsible for organic reef formation are characteristic of different geologic time periods: Archaeocyathids appeared in the early Cambrian; these gave way to sponges by the late Cambrian; later successions included stromatoporoids, corals, algae, bryozoa, and rudists (a form of bivalve mollusc). The extent of organic reefs has varied over geologic time, and they were likely most extensive in the middle Devonian, when they covered an area estimated at 5,000,000 km2 (1,900,000 sq mi). This is roughly ten times the extent of modern reefs. The Devonian reefs were constructed largely by stromatoporoids and tabulate corals, which were devastated by the late Devonian extinction.Organic reefs typically have a complex internal structure. Whole body fossils are usually abundant, but ooids and interclasts are rare within the reef. The core of a reef is typically massive and unbedded, and is surrounded by a talus that is greater in volume than the core. The talus contains abundant intraclasts and is usually either floatstone, with 10% or more of grains over 2mm in size embedded in abundant matrix, or rudstone, which is mostly large grains with sparse matrix. The talus grades to planktonic fine-grained carbonate mud, then noncarbonate mud away from the reef.
Limestone landscape
Limestone is partially soluble, especially in acid, and therefore forms many erosional landforms. These include limestone pavements, pot holes, cenotes, caves and gorges. Such erosion landscapes are known as karsts. Limestone is less resistant to erosion than most igneous rocks, but more resistant than most other sedimentary rocks. It is therefore usually associated with hills and downland, and occurs in regions with other sedimentary rocks, typically clays.Karst regions overlying limestone bedrock tend to have fewer visible above-ground sources (ponds and streams), as surface water easily drains downward through joints in the limestone. While draining, water and organic acid from the soil slowly (over thousands or millions of years) enlarges these cracks, dissolving the calcium carbonate and carrying it away in solution. Most cave systems are through limestone bedrock. Cooling groundwater or mixing of different groundwaters will also create conditions suitable for cave formation.Coastal limestones are often eroded by organisms which bore into the rock by various means. This process is known as bioerosion. It is most common in the tropics, and it is known throughout the fossil record.Bands of limestone emerge from the Earth's surface in often spectacular rocky outcrops and islands. Examples include the Rock of Gibraltar, the Burren in County Clare, Ireland; Malham Cove in North Yorkshire and the Isle of Wight, England; the Great Orme in Wales; on Fårö near the Swedish island of Gotland, the Niagara Escarpment in Canada/United States; Notch Peak in Utah; the Ha Long Bay National Park in Vietnam; and the hills around the Lijiang River and Guilin city in China.The Florida Keys, islands off the south coast of Florida, are composed mainly of oolitic limestone (the Lower Keys) and the carbonate skeletons of coral reefs (the Upper Keys), which thrived in the area during interglacial periods when sea level was higher than at present.Unique habitats are found on alvars, extremely level expanses of limestone with thin soil mantles. The largest such expanse in Europe is the Stora Alvaret on the island of Öland, Sweden. Another area with large quantities of limestone is the island of Gotland, Sweden. Huge quarries in northwestern Europe, such as those of Mount Saint Peter (Belgium/Netherlands), extend for more than a hundred kilometers.
Uses
Limestone is a raw material that is used globally in a variety of different ways including construction, agriculture and as industrial materials. Limestone is very common in architecture, especially in Europe and North America. Many landmarks across the world, including the Great Pyramid and its associated complex in Giza, Egypt, were made of limestone. So many buildings in Kingston, Ontario, Canada were, and continue to be, constructed from it that it is nicknamed the 'Limestone City'. Limestone, metamorphosed by heat and pressure produces marble, which has been used for many statues, buildings and stone tabletops. On the island of Malta, a variety of limestone called Globigerina limestone was, for a long time, the only building material available, and is still very frequently used on all types of buildings and sculptures.Limestone can be processed into many various forms such as brick, cement, powdered/crushed, or as a filler. Limestone is readily available and relatively easy to cut into blocks or more elaborate carving. Ancient American sculptors valued limestone because it was easy to work and good for fine detail. Going back to the Late Preclassic period (by 200–100 BCE), the Maya civilization (Ancient Mexico) created refined sculpture using limestone because of these excellent carving properties. The Maya would decorate the ceilings of their sacred buildings (known as lintels) and cover the walls with carved limestone panels. Carved on these sculptures were political and social stories, and this helped communicate messages of the king to his people. Limestone is long-lasting and stands up well to exposure, which explains why many limestone ruins survive. However, it is very heavy (density 2.6), making it impractical for tall buildings, and relatively expensive as a building material.
Limestone was most popular in the late 19th and early 20th centuries. Railway stations, banks and other structures from that era were made of limestone in some areas. It is used as a façade on some skyscrapers, but only in thin plates for covering, rather than solid blocks. In the United States, Indiana, most notably the Bloomington area, has long been a source of high-quality quarried limestone, called Indiana limestone. Many famous buildings in London are built from Portland limestone. Houses built in Odesa in Ukraine in the 19th century were mostly constructed from limestone and the extensive remains of the mines now form the Odesa Catacombs.Limestone was also a very popular building block in the Middle Ages in the areas where it occurred, since it is hard, durable, and commonly occurs in easily accessible surface exposures. Many medieval churches and castles in Europe are made of limestone. Beer stone was a popular kind of limestone for medieval buildings in southern England.
Limestone is the raw material for production of lime, primarily known for treating soils, purifying water and smelting copper. Lime is an important ingredient used in chemical industries. Limestone and (to a lesser extent) marble are reactive to acid solutions, making acid rain a significant problem to the preservation of artifacts made from this stone. Many limestone statues and building surfaces have suffered severe damage due to acid rain. Likewise limestone gravel has been used to protect lakes vulnerable to acid rain, acting as a pH buffering agent. Acid-based cleaning chemicals can also etch limestone, which should only be cleaned with a neutral or mild alkali-based cleaner.
Other uses include:
It is the raw material for the manufacture of quicklime (calcium oxide), slaked lime (calcium hydroxide), cement and mortar.
Pulverized limestone is used as a soil conditioner to neutralize acidic soils (agricultural lime).
Is crushed for use as aggregate—the solid base for many roads as well as in asphalt concrete.
As a reagent in flue-gas desulfurization, where it reacts with sulfur dioxide for air pollution control.
In glass making, particularly in the manufacture of soda–lime glass.
As an additive toothpaste, paper, plastics, paint, tiles, and other materials as both white pigment and a cheap filler.
As rock dust, to suppress methane explosions in underground coal mines.
Purified, it is added to bread and cereals as a source of calcium.
As a calcium supplement in livestock feed, such as for poultry (when ground up).
For remineralizing and increasing the alkalinity of purified water to prevent pipe corrosion and to restore essential nutrient levels.
In blast furnaces, limestone binds with silica and other impurities to remove them from the iron.
It can aid in the removal of toxic components created from coal burning plants and layers of polluted molten metals.Many limestone formations are porous and permeable, which makes them important petroleum reservoirs. About 20% of North American hydrocarbon reserves are found in carbonate rock. Carbonate reservoirs are very common in the petroleum-rich Middle East, and carbonate reservoirs hold about a third of all petroleum reserves worldwide. Limestone formations are also common sources of metal ores, because their porosity and permeability, together with their chemical activity, promotes ore deposition in the limestone. The lead-zinc deposits of Missouri and the Northwest Territories are examples of ore deposits hosted in limestone.
Scarcity
Limestone is a major industrial raw material that is in constant demand. This raw material has been essential in the iron and steel industry since the nineteenth century. Companies have never had a shortage of limestone; however, it has become a concern as the demand continues to increase and it remains in high demand today. The major potential threats to supply in the nineteenth century were regional availability and accessibility. The two main accessibility issues were transportation and property rights. Other problems were high capital costs on plants and facilities due to environmental regulations and the requirement of zoning and mining permits. These two dominant factors led to the adaptation and selection of other materials that were created and formed to design alternatives for limestone that suited economic demands.Limestone was classified as a critical raw material, and with the potential risk of shortages, it drove industries to find new alternative materials and technological systems. This allowed limestone to no longer be classified as critical as replacement substances increased in production; minette ore is a common substitute, for example.
Occupational safety and health
Powdered limestone as a food additive is generally recognized as safe and limestone is not regarded as a hazardous material. However, limestone dust can be a mild respiratory and skin irritant, and dust that gets into the eyes can cause corneal abrasions. Because limestone contains small amounts of silica, inhalation of limestone dust could potentially lead to silicosis or cancer.
United States
The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for limestone exposure in the workplace as 15 mg/m3 (0.0066 gr/cu ft) total exposure and 5 mg/m3 (0.0022 gr/cu ft) respiratory exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 10 mg/m3 (0.0044 gr/cu ft) total exposure and 5 mg/m3 (0.0022 gr/cu ft) respiratory exposure over an 8-hour workday.
Graffiti
Removing graffiti from weathered limestone is difficult because it is a porous and permeable material. The surface is fragile so usual abrasion methods run the risk of severe surface loss. Because it is an acid-sensitive stone some cleaning agents cannot be used due to adverse effects.
Gallery
See also
Coral sand
Charmant Som
In Praise of Limestone – Poem by W. H. Auden
Kurkar – Regional name for an aeolian quartz calcrete on the Levantine coast
Limepit – Old method of calcining limestone
Sandstone – Type of sedimentary rock
Agricultural lime – Soil additive containing calcium carbonate and other ingredients
Liming (soil) – Application of minerals to soil
References
== Further reading == |
silurian | The Silurian ( sih-LURE-ee-ən, sy-) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.
One important event in this period was the initial establishment of terrestrial life in what is known as the Silurian-Devonian Terrestrial Revolution: vascular plants emerged from more primitive land plants, dikaryan fungi started expanding and diversifying along with glomeromycotan fungi, and three groups of arthropods (myriapods, arachnids and hexapods) became fully terrestrialized.A significant evolutionary milestone during the Silurian was the diversification of jawed fish and bony fish.
History of study
The Silurian system was first identified by the Scottish geologist Roderick Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s. He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick, who had named the period of his study the Cambrian, from the Latin name for Wales. This naming does not indicate any correlation between the occurrence of the Silurian rocks and the land inhabited by the Silures (cf. Geologic map of Wales, Map of pre-Roman tribes of Wales). In 1835 the two men presented a joint paper, under the title On the Silurian and Cambrian Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales, which was the germ of the modern geological time scale. As it was first identified, the "Silurian" series when traced farther afield quickly came to overlap Sedgwick's "Cambrian" sequence, however, provoking furious disagreements that ended the friendship.
The English geologist Charles Lapworth resolved the conflict by defining a new Ordovician system including the contested beds. An alternative name for the Silurian was "Gotlandian" after the strata of the Baltic island of Gotland.The French geologist Joachim Barrande, building on Murchison's work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge. He divided the Silurian rocks of Bohemia into eight stages. His interpretation was questioned in 1854 by Edward Forbes, and the later stages of Barrande; F, G and H have since been shown to be Devonian. Despite these modifications in the original groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest Silurian fossils.
Subdivisions
Paleogeography
With the supercontinent Gondwana covering the equator and much of the southern hemisphere, a large ocean occupied most of the northern half of the globe. The high sea levels of the Silurian and the relatively flat land (with few significant mountain belts) resulted in a number of island chains, and thus a rich diversity of environmental settings.During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of the late-Ordovician glaciation. The southern continents remained united during this period. The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. The continents of Avalonia, Baltica, and Laurentia drifted together near the equator, starting the formation of a second supercontinent known as Euramerica.
When the proto-Europe collided with North America, the collision folded coastal sediments that had been accumulating since the Cambrian off the east coast of North America and the west coast of Europe. This event is the Caledonian orogeny, a spate of mountain building that stretched from New York State through conjoined Europe and Greenland to Norway. At the end of the Silurian, sea levels dropped again, leaving telltale basins of evaporites extending from Michigan to West Virginia, and the new mountain ranges were rapidly eroded. The Teays River, flowing into the shallow mid-continental sea, eroded Ordovician Period strata, forming deposits of Silurian strata in northern Ohio and Indiana.
The vast ocean of Panthalassa covered most of the northern hemisphere. Other minor oceans include two phases of the Tethys, the Proto-Tethys and Paleo-Tethys, the Rheic Ocean, the Iapetus Ocean (a narrow seaway between Avalonia and Laurentia), and the newly formed Ural Ocean.
Climate and sea level
The Silurian period was once believed to have enjoyed relatively stable and warm temperatures, in contrast with the extreme glaciations of the Ordovician before it and the extreme heat of the ensuing Devonian; however, it is now known that the global climate underwent many drastic fluctuations throughout the Silurian, evidenced by numerous major carbon and oxygen isotope excursions during this geologic period. Sea levels rose from their Hirnantian low throughout the first half of the Silurian; they subsequently fell throughout the rest of the period, although smaller scale patterns are superimposed on this general trend; fifteen high-stands (periods when sea levels were above the edge of the continental shelf) can be identified, and the highest Silurian sea level was probably around 140 metres (459 ft) higher than the lowest level reached.During this period, the Earth entered a warm greenhouse phase, supported by high CO2 levels of 4500 ppm, and warm shallow seas covered much of the equatorial land masses. Early in the Silurian, glaciers retreated back into the South Pole until they almost disappeared in the middle of Silurian. Layers of broken shells (called coquina) provide strong evidence of a climate dominated by violent storms generated then as now by warm sea surfaces.
Perturbations
The climate and carbon cycle appear to be rather unsettled during the Silurian, which had a higher frequency of isotopic excursions (indicative of climate fluctuations) than any other period. The Ireviken event, Mulde event and Lau event each represent isotopic excursions following a minor mass extinction and associated with rapid sea-level change. Each one leaves a similar signature in the geological record, both geochemically and biologically; pelagic (free-swimming) organisms were particularly hard hit, as were brachiopods, corals and trilobites, and extinctions rarely occur in a rapid series of fast bursts. The climate fluctuations are best explained by a sequence of glaciations, but the lack of tillites in the middle to late Silurian make this explanation problematic.
Flora and fauna
The Silurian period has been viewed by some palaeontologists as an extended recovery interval following the Late Ordovician mass extinction (LOME), which interrupted the cascading increase in biodiversity that had continuously gone on throughout the Cambrian and most of the Ordovician.The Silurian was the first period to see megafossils of extensive terrestrial biota in the form of moss-like miniature forests along lakes and streams and networks of large, mycorrhizal nematophytes, heralding the beginning of the Silurian-Devonian Terrestrial Revolution. However, the land fauna did not have a major impact on the Earth until it diversified in the Devonian.The first fossil records of vascular plants, that is, land plants with tissues that carry water and food, appeared in the second half of the Silurian Period. The earliest-known representatives of this group are Cooksonia. Most of the sediments containing Cooksonia are marine in nature. Preferred habitats were likely along rivers and streams. Baragwanathia appears to be almost as old, dating to the early Ludlow (420 million years) and has branching stems and needle-like leaves of 10–20 centimetres (3.9–7.9 in). The plant shows a high degree of development in relation to the age of its fossil remains. Fossils of this plant have been recorded in Australia, Canada, and China. Eohostimella heathana is an early, probably terrestrial, "plant" known from compression fossils of Early Silurian (Llandovery) age. The chemistry of its fossils is similar to that of fossilised vascular plants, rather than algae.Fossils that are considered as terrestrial animals are also known from the Silurian. The definitive oldest record of millipede ever known is Kampecaris obanensis and Archidesmus sp. from the late Silurian (425 million years ago) of Kerrera. There are also millipedes, centipedes and trigonotarbid arachnoids known from Ludlow (420 millions years ago). Predatory invertebrates would indicate that simple food webs were in place that included non-predatory prey animals. Extrapolating back from Early Devonian biota, Andrew Jeram et al. in 1990 suggested a food web based on as-yet-undiscovered detritivores and grazers on micro-organisms. Millipedes from Cowie Formation such as Cowiedesmus and Pneumodesmus were considered as the oldest millipede from the middle Silurian at 428 millions years ago. Though the age of this formation is later reinterpreted to be from the early Devonian instead by some researchers, a more subsequent study in 2023 has reconfirmed its age to be the late Wenlock epoch of the middle Silurian. Regardless, Pneumodesmus is still an important fossil as the oldest definitive evidence of spiracles to breath in the air.The first bony fish, the Osteichthyes, appeared, represented by the Acanthodians covered with bony scales. Fish reached considerable diversity and developed movable jaws, adapted from the supports of the front two or three gill arches. A diverse fauna of eurypterids (sea scorpions)—some of them several meters in length—prowled the shallow Silurian seas and lakes of North America; many of their fossils have been found in New York state. Leeches also made their appearance during the Silurian Period. Brachiopods were abundant and diverse, with the taxonomic composition, ecology, and biodiversity of Silurian brachiopods mirroring Ordovician ones. Brachiopods that survived the LOME developed novel adaptations for environmental stress, and they tended to be endemic to a single palaeoplate in the mass extinction's aftermath, but expanded their range afterwards. The most abundant brachiopods were atrypids and pentamerides; atrypids were the first to recover and rediversify in the Rhuddanian after LOME, while pentameride recovery was delayed until the Aeronian. Bryozoans exhibited significant degrees of endemism to a particular shelf. They also developed symbiotic relationships with cnidarians and stromatolites. Many bivalve fossils have also been found in Silurian deposits, and the first deep-boring bivalves are known from this period. Chitons saw a peak in diversity during the middle of the Silurian. Hederelloids enjoyed significant success in the Silurian, with some developing symbioses with the colonial rugose coral Entelophyllum. The Silurian was a heyday for tentaculitoids, which experienced an evolutionary radiation focused mainly in Baltoscandia, along with an expansion of their geographic range in the Llandovery and Wenlock. Trilobites started to recover in the Rhuddanian, and they continued to enjoy success in the Silurian as they had in the Ordovician despite their reduction in clade diversity as a result of LOME. The Early Silurian was a chaotic time of turnover for crinoids as they rediversified after LOME. Members of Flexibilia, which were minimally impacted by LOME, took on an increasing ecological prominence in Silurian seas. Monobathrid camerates, like flexibles, diversified in the Llandovery, whereas cyathocrinids and dendrocrinids diversified later in the Silurian. Scyphocrinoid loboliths suddenly appeared in the terminal Silurian, shortly before the Silurian-Devonian boundary, and disappeared as abruptly as they appeared very shortly after their first appearance. Endobiotic symbionts were common in the corals and stromatoporoids. Rugose corals especially were colonised and encrusted by a diverse range of epibionts, including certain hederelloids as aforementioned.Reef abundance was patchy; sometimes, fossils are frequent, but at other points, are virtually absent from the rock record.
Notes
References
Emiliani, Cesare. (1992). Planet Earth : Cosmology, Geology, & the Evolution of Life & the Environment. Cambridge University Press. (Paperback Edition ISBN 0-521-40949-7)
Mikulic, DG, DEG Briggs, and J Kluessendorf. 1985. A new exceptionally preserved biota from the Lower Silurian of Wisconsin, USA. Philosophical Transactions of the Royal Society of London, 311B:75-86.
Moore, RA; Briggs, DEG; Braddy, SJ; Anderson, LI; Mikulic, DG; Kluessendorf, J (2005). "A new synziphosurine (Chelicerata: Xiphosura) from the Late Llandovery (Silurian) Waukesha Lagerstatte, Wisconsin, USA". Journal of Paleontology. 79 (2): 242–250. doi:10.1666/0022-3360(2005)079<0242:anscxf>2.0.co;2. S2CID 56570105.
External links
Ogg, Jim (June 2004), Overview of Global Boundary Stratotype Sections and Points (GSSP's)
Palaeos: Silurian
UCMP Berkeley: The Silurian
Paleoportal: Silurian strata in U.S., state by state
USGS:Silurian and Devonian Rocks (U.S.)
"International Commission on Stratigraphy (ICS)". Geologic Time Scale 2004. Retrieved September 19, 2005.
Examples of Silurian Fossils
GeoWhen Database for the Silurian
Silurian (Chronostratography scale) |
plecoptera | Plecoptera is an order of insects, commonly known as stoneflies. Some 3,500 species are described worldwide, with new species still being discovered. Stoneflies are found worldwide, except Antarctica. Stoneflies are believed to be one of the most primitive groups of Neoptera, with close relatives identified from the Carboniferous and Lower Permian geological periods, while true stoneflies are known from fossils only a bit younger. Their modern diversity, however, apparently is of Mesozoic origin.Plecoptera are found in both the Southern and Northern Hemispheres, and the populations are quite distinct, although the evolutionary evidence suggests species may have crossed the equator on a number of occasions before once again becoming geographically isolated.All species of Plecoptera are intolerant of water pollution, and their presence in a stream or still water is usually an indicator of good or excellent water quality.
Description and ecology
Stoneflies have a generalized anatomy, with few specialized features compared to other insects. They have simple mouthparts with chewing mandibles, long, multiple-segmented antennae, large compound eyes, and two or three ocelli. The legs are robust, with each ending in two claws. The abdomen is relatively soft, and may include remnants of the nymphal gills even in the adult. Both nymphs and adults have long, paired cerci projecting from the tip of their abdomens.The name "Plecoptera" literally means "braided-wings", from the Ancient Greek plekein (πλέκειν, "to braid") and pteryx (πτέρυξ, "wing"). This refers to the complex venation of their two pairs of wings, which are membranous and fold flat over their backs. Stoneflies are generally not strong fliers, and some species are entirely wingless.
A few wingless species, such as the Lake Tahoe benthic stonefly ("Capnia" lacustra) or Baikaloperla, are the only known insects, perhaps with the exception of Halobates, that are exclusively aquatic from birth to death. Some true water bugs (Nepomorpha) may also be fully aquatic for their entire lives, but can leave the water to travel.
The nymphs (technically, "naiads") are aquatic and live in the benthic zone of well-oxygenated lakes and streams. A few species found in New Zealand and nearby islands have terrestrial nymphs, but even these inhabit only very moist environments. The nymphs physically resemble wingless adults, but often have external gills, which may be present on almost any part of the body. Nymphs can acquire oxygen via diffusing through the exoskeleton, or through gills located on behind the head, on the thorax, or around the anus. Due to their nymph's requirement for well oxygenated water, the species is very sensitive to water pollution. This makes them important indicators for water quality. Most species are herbivorous as nymphs, feeding on submerged leaves and benthic algae, but many are hunters of other aquatic arthropods.
Life cycle
The female can lay up to one thousand eggs. It will fly over the water and drop the eggs in the water. It also may hang on a rock or branch. Eggs are covered in a sticky coating which allows them to adhere to rocks without being swept away by swift currents. The eggs typically take two to three weeks to hatch, but some species undergo diapause, with the eggs remaining dormant throughout a dry season, and hatching only when conditions are suitable.The insects remain in the nymphal form for one to four years, depending on species, and undergo from 12 to 36 molts before emerging and becoming terrestrial as adults. Before becoming adults, nymphs will leave the water, attach to a fixed surface and molt one last time.
The adults generally only survive for a few weeks, and emerge only during specific times of the year when resources are optimal. Some do not feed at all, but those that do are herbivorous. Adults are not strong fliers and generally stay near the stream or lake they hatched from.
Systematics
Traditionally, the stoneflies were divided into two suborders, the "Antarctoperlaria" (or "Archiperlaria") and the Arctoperlaria. However, the former simply consists of the two most basal superfamilies of stoneflies, which do not seem to be each other's closest relatives. Thus, the "Antarctoperlaria" are not considered a natural group (despite some claims to the contrary).The Arctoperlaria, though, have been divided into two infraorders, the Euholognatha (or Filipalpia) and the Systellognatha (also called Setipalpia or Subulipalpia). This corresponds to the phylogeny with one exception: the Scopuridae must be considered a basal family in the Arctoperlaria, not assignable to any of the infraorders. Alternatively, the Scopuridae were placed in an unranked clade "Holognatha" together with the Euholognatha (meaning roughly "advanced Holognatha"), but the Scopuridae do not appear significantly closer to the Euholognatha than to the Systellognatha.
In addition, not adopting the clades Antarctoperlaria and Holognatha allows for a systematic layout of the Plecoptera that adequately reproduces phylogeny, while retaining the traditional ranked taxa.
Basal lineages ("Antarctoperlaria")
Superfamily Eusthenioidea
Family Diamphipnoidae
Family Eustheniidae
Superfamily Leptoperloidea
Family Austroperlidae
Family GripopterygidaeSuborder Arctoperlaria
Basal family Scopuridae
Infraorder Euholognatha
Family Capniidae (about 300 species) – small winter stoneflies
Family Leuctridae (390+ species) – rolled-winged stoneflies
Family Nemouridae (over 700 species) – spring stoneflies
Family Notonemouridae
Family Taeniopterygidae (about 110 species) – winter stoneflies
Infraorder Systellognatha
Family Chloroperlidae (over 180 species) – green stoneflies
Family Perlidae (about 400 species) – common stoneflies
Family Perlodidae (350+ species)
Family Peltoperlidae (about 68 species) – roachlike stoneflies
Family Styloperlidae (about 10 species)
Family Pteronarcyidae (about 12 species) – salmonflies, giant stoneflies
Notes
References
External links
Media related to Plecoptera at Wikimedia Commons
Data related to Plecoptera at Wikispecies
Plecoptera Species File: order Plecoptera (Version 5.0/5.0) |
ediacaran | The Ediacaran Period ( EE-dee-AK-ər-ən, ED-ee-) is a geological period of the Neoproterozoic Era that spans 96 million years from the end of the Cryogenian Period at 635 Mya, to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic Eon as well as the so-called Precambrian "supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common.
The Ediacaran Period is named after the Ediacara Hills of South Australia, where trace fossils of a diverse community of previously unrecognized lifeforms (later named the Ediacaran biota) were first discovered by geologist Reg Sprigg in 1946. Its status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years. Although the period took namesake from the Ediacara Hills of the Nilpena Ediacara National Park, the type section is actually located in the bed of the Enorama Creek within the Brachina Gorge of the Ikara-Flinders Ranges National Park, at 31°19′53.8″S 138°38′0.1″E, approximately 55 km (34 mi) southeast of the Ediacara Hills fossil site.
The Ediacaran marks the first widespread appearance of complex multicellular fauna following the end of the Snowball Earth glacial age, known as the Avalon Explosion, which is represented by now-extinct, relatively simple animal phyla such as Proarticulata (bilaterians with simple articulation, e.g. Dickinsonia and Spriggina), Petalonamae (sea pen-like animals, e.g. Charnia), Aspidella (radial-shaped animals, e.g. Cyclomedusa) and Trilobozoa (animals with tri-radial symmetry, e.g. Tribrachidium). Most of those organisms appeared during or after the Avalon explosion event 575 million years ago and died out during an End-Ediacaran extinction event 539 million years ago. Forerunners of some modern phyla of animals also appeared during this period, including cnidarians and early bilaterians such as Xenacoelomorpha, as well as Mollusc-like Kimberella. Fossilized organisms with shells or endoskeletons were yet to evolve, and would not appear until the superseding Cambrian Period of the Phanerozoic Eon.
The supercontinent Pannotia formed and broke apart by the end of the period. The Ediacaran also witnessed several glaciation events, such as the Gaskiers and Baykonurian glaciations. The Shuram excursion also occurred during this period, but its glacial origin is unlikely.
Ediacaran and Vendian
The Ediacaran Period overlaps but is shorter than the Vendian Period (650 to 543 million years ago), a name that was earlier, in 1952, proposed by Russian geologist and paleontologist Boris Sokolov. The Vendian concept was formed stratigraphically top-down, and the lower boundary of the Cambrian became the upper boundary of the Vendian.Paleontological substantiation of this boundary was worked out separately for the siliciclastic basin (base of the Baltic Stage of the Eastern European Platform) and for the carbonate basin (base of the Tommotian stage of the Siberian Platform).
The lower boundary of the Vendian was suggested to be defined at the base of the Varanger (Laplandian) tillites.The Vendian in its type area consists of large subdivisions such as Laplandian, Redkino, Kotlin and Rovno regional stages with the globally traceable subdivisions and their boundaries, including its lower one.
The Redkino, Kotlin and Rovno regional stages have been substantiated in the type area of the Vendian on the basis of the abundant organic-walled microfossils, megascopic algae, metazoan body fossils and ichnofossils.The lower boundary of the Vendian could have a biostratigraphic substantiation as well taking into consideration the worldwide occurrence of the Pertatataka assemblage of giant acanthomorph acritarchs.
Upper and lower boundaries
The Ediacaran Period (c. 635–538.8 Mya) represents the time from the end of global Marinoan glaciation to the first appearance worldwide of somewhat complicated trace fossils (Treptichnus pedum (Seilacher, 1955)).Although the Ediacaran Period does contain soft-bodied fossils, it is unusual in comparison to later periods because its beginning is not defined by a change in the fossil record. Rather, the beginning is defined at the base of a chemically distinctive carbonate layer that is referred to as a "cap carbonate", because it caps glacial deposits.
This bed is characterized by an unusual depletion of 13C that indicates a sudden climatic change at the end of the Marinoan ice age. The lower global boundary stratotype section (GSSP) of the Ediacaran is at the base of the cap carbonate (Nuccaleena Formation), immediately above the Elatina diamictite in the Enorama Creek section, Brachina Gorge, Flinders Ranges, South Australia.
The GSSP of the upper boundary of the Ediacaran is the lower boundary of the Cambrian on the SE coast of Newfoundland approved by the International Commission on Stratigraphy as a preferred alternative to the base of the Tommotian Stage in Siberia which was selected on the basis of the ichnofossil Treptichnus pedum (Seilacher, 1955). In the history of stratigraphy it was the first case of usage of bioturbations for the System boundary definition.
Nevertheless, the definitions of the lower and upper boundaries of the Ediacaran on the basis of chemostratigraphy and ichnofossils are disputable.Cap carbonates generally have a restricted geographic distribution (due to specific conditions of their precipitation) and usually siliciclastic sediments laterally replace the cap carbonates in a rather short distance but cap carbonates do not occur above every tillite elsewhere in the world.
The C-isotope chemostratigraphic characteristics obtained for contemporaneous cap carbonates in different parts of the world may be variable in a wide range owing to different degrees of secondary alteration of carbonates, dissimilar criteria used for selection of the least altered samples, and, as far as the C-isotope data are concerned, due to primary lateral variations of δ l3Ccarb in the upper layer of the ocean.Furthermore, Oman presents in its stratigraphic record a large negative carbon isotope excursion, within the Shuram Formation that is clearly away from any glacial evidence strongly questioning systematic association of negative δ l3Ccarb excursion and glacial events. Also, the Shuram excursion is prolonged and is estimated to last for ~9.0 Myrs.As to the Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, its usage for the stratigraphic detection of this boundary is always risky, because of the occurrence of very similar trace fossils belonging to the Treptichnids group well below the level of T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western United States. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.
Subdivisions
The Ediacaran Period is not yet formally subdivided, but a proposed scheme recognises an Upper Ediacaran whose base corresponds with the Gaskiers glaciation, a Terminal Ediacaran Stage starting around 550 million years ago, a preceding stage beginning around 575 Ma with the earliest widespread Ediacaran biota fossils; two proposed schemes differ on whether the lower strata should be divided into an Early and Middle Ediacaran or not, because it is not clear whether the Shuram excursion (which would divide the Early and Middle) is a separate event from the Gaskiers, or whether the two events are correlated.
Absolute dating
The dating of the rock type section of the Ediacaran Period in South Australia has proven uncertain due to lack of overlying igneous material. Therefore, the age range of 635 to 538.8 million years is based on correlations to other countries where dating has been possible. The base age of approximately 635 million years is based on U–Pb (uranium–lead) and Re–Os (rhenium–osmium) dating from Africa, China, North America, and Tasmania.
Biota
The fossil record from the Ediacaran Period is sparse, as more easily fossilized hard-shelled animals had yet to evolve. The Ediacaran biota include the oldest definite multicellular organisms (with specialized tissues), the most common types of which resemble segmented worms, fronds, disks, or immobile bags. Auroralumina was a cnidarian.Most members of the Ediacaran biota bear little resemblance to modern lifeforms, and their relationship even with the immediately following lifeforms of the Cambrian explosion is rather difficult to interpret. More than 100 genera have been described, and well known forms include Arkarua, Charnia, Dickinsonia, Ediacaria, Marywadea, Cephalonega, Pteridinium, and Yorgia. However, despite the overall enigmaticness of most Ediacaran organisms, some fossils identifiable as hard-shelled agglutinated foraminifera (which are not classified as animals) are known from latest Ediacaran sediments of western Siberia.Four different biotic intervals are known in the Ediacaran, each being characterised by the prominence of a unique ecology and faunal assemblage. The first spanned from 635 to around 575 Ma and was dominated by acritarchs known as large ornamented Ediacaran microfossils. The second spanned from around 575 to 560 Ma and was characterised by the Avalon biota. The third spanned from 560 to 550 Ma; its biota has been dubbed the White Sea biota due to many fossils from this time being found along the coasts of the White Sea. The fourth lasted from 550 to 539 Ma and is known as the interval of the Nama biotic assemblage.There is evidence for a mass extinction during this period from early animals changing the environment, dating to the same time as the transition between the White Sea and the Nama-type biotas. Alternatively, this mass extinction has also been theorised to have been the result of an anoxic event.
Astronomical factors
The relative proximity of the Moon at this time meant that tides were stronger and more rapid than they are now. The day was 21.9 ± 0.4 hours, and there were 13.1 ± 0.1 synodic months/year and 400 ± 7 solar days/year.
Documentaries
A few English language documentaries have featured the Ediacaran Period and biota:
The Time Traveller's Guide To Australia (2012, ABC Science; Part 1 of 4).
The Geological History of Canada, as part of The Nature of Things series, CBC-SRC; 2011; Eastern Canada.
The first episode of a BBC documentary titled Life on Earth, with David Attenborough as narrator.
Another documentary narrated by David Attenborough titled First Life featuring Charnia, Dickinsonia, Spriggina, Funisia, and Kimberella animated in CGI.
In our time - Ediacara Biota, BBC, 9 July 2009
See also
List of fossil sites (with link directory)
Avalon explosion
End-Ediacaran extinction
References
External links
"Geological time gets a new period: Geologists have added a new period to their official calendar of Earth's history—the first in 120 years". London: BBC. 17 May 2004.
"Ediacaran Period". GeoWhen Database. Retrieved 5 January 2006.
Introduction to the Vendian Period
Introduction to the Ediacaran Fauna
transcript – Catalyst (Australian Broadcasting Corporation)
Mistaken Point Fauna: The Discovery
Earth's oldest animal ecosystem held in fossils at Nilpena Station in SA outback ABC News, 5 August 2013. Accessed 6 August 2013. |
resource | Resource refers to all the materials available in our environment which are technologically accessible, economically feasible and culturally sustainable and help us to satisfy our needs and wants. Resources can broadly be classified upon their availability — they are classified into renewable and non-renewable resources. They can also be classified as actual and potential on the basis of the level of development and use, on the basis of origin they can be classified as biotic and abiotic, and on the basis of their distribution, as ubiquitous and localised (private, community-owned, national and international resources). An item becomes a resource with time and developing technology. The benefits of resource utilization may include increased wealth, proper functioning of a system, or enhanced well-being. From a human perspective, a natural resource is anything obtained from the environment to satisfy human needs and wants. From a broader biological or ecological perspective, a resource satisfies the needs of a living organism (see biological resource).The concept of resources has been developed across many established areas of work, in economics, biology and ecology, computer science, management, and human resources for example - linked to the concepts of competition, sustainability, conservation, and stewardship. In application within human society, commercial or non-commercial factors require resource allocation through resource management.
The concept of a resource can also be tied to the direction of leadership over resources, this can include the things leaders have responsibility for over the human resources, with management, help, support or direction such as in charge of a professional group, technical experts, innovative leaders, archiving expertise, academic management, association management, business management, healthcare management, military management, public administration, spiritual leadership and social networking administrator.
individuals exploit the same amount of resource per unit biomass) to absolutely size-asymmetric (the largest individuals exploit all the available resource). The degree of size asymmetry has major effects on the structure and diversity of ecological communities, e.g. in plant communities size-asymmetric competition for light has stronger effects on diversity compared with competition for soil resources. The degree of size asymmetry has major effects on the structure and diversity of ecological communities.
Economic versus biological
There are three fundamental differences between economic versus ecological views: 1) the economic resource definition is human-centered (anthropocentric) and the biological or ecological resource definition is nature-centered (biocentric or ecocentric); 2) the economic view includes desire along with necessity, whereas the biological view is about basic biological needs; and 3) economic systems are based on markets of currency exchanged for goods and services, whereas biological systems are based on natural processes of growth, maintenance, and reproduction.
Computer resources
A computer resource is any physical or virtual component of limited availability within a computer or information management system. Computer resources include means for input, processing, output, communication, and storage.
Natural
Natural resources are derived from the environment. Many natural resources are essential for human survival, while others are used for satisfying human desire. Conservation is management of natural resources with the goal of sustainability. Natural resources may be further classified in different ways.Resources can be categorized on the basis of origin:
Abiotic resources comprise non-living things (e.g., land, water, air and minerals such as gold, iron, copper, silver).
Biotic resources are obtained from the biosphere. Forests and their products, animals, birds and their products, fish and other marine organisms are important examples. Minerals such as coal and petroleum are sometimes included in this category because they were formed from fossilized organic matter, though over long periods of time.Natural resources are also categorized based on the stage of development:
Potential resources are known to exist and may be used in the future. For example, petroleum may exist in many parts of India and Kuwait that have sedimentary rocks, but until the time it is actually drilled out and put into use, it remains a potential resource.
Actual resources are those that have been surveyed, their quantity and quality determined, and are being used in present times. For example, petroleum and natural gas is actively being obtained from the Mumbai High Fields. The development of an actual resource, such as wood processing depends upon the technology available and the cost involved. That part of the actual resource that can be developed profitably with available technology is known as a reserve resource, while that part that can not be developed profitably because of lack of technology is known as a stock resource.Natural resources can be categorized on the basis of renewability:
Non-renewable resources are formed over very long geological periods. Minerals and fossils are included in this category. Since their rate of formation is extremely slow, they cannot be replenished, once they are depleted. Even though metals can be recycled and reused, whereas petroleum and gas cannot, they are still considered non-renewable resources.
Renewable resources, such as forests and fisheries, can be replenished or reproduced relatively quickly. The highest rate at which a resource can be used sustainably is the sustainable yield. Some resources, such as sunlight, air, and wind, are called perpetual resources because they are available continuously, though at a limited rate. Their quantity is not affected by human consumption. Many renewable resources can be depleted by human use, but may also be replenished, thus maintaining a flow. Some of these, such as agricultural crops, take a short time for renewal; others, such as water, take a comparatively longer time, while still others, such as forests, take even longer.Dependent upon the speed and quantity of consumption, overconsumption can lead to depletion or total and everlasting destruction of a resource. Important examples are agricultural areas, fish and other animals, forests, healthy water and soil, cultivated and natural landscapes. Such conditionally renewable resources are sometimes classified as a third kind of resource, or as a subtype of renewable resources. Conditionally renewable resources are presently subject to excess human consumption and the only sustainable long term use of such resources is within the so-called zero ecological footprint, where in human use less than the Earth's ecological capacity to regenerate.
Natural resources are also categorized based on distribution:
Ubiquitous resources are found everywhere (for example air, light, and water).
Localized resources are found only in certain parts of the world (for example metal ores and geothermal power).Actual vs. potential natural resources are distinguished as follows:
Actual resources are those resources whose location and quantity are known and we have the technology to exploit and use them.
Potential resources are the ones of which we have insufficient knowledge or we do not have the technology to exploit them at present.On the basis of ownership, resources can be classified as individual, community, national, and international.
Labour or human resources
In economics, labor or human resources refers to the human effort in the production of goods and rendering of services. Human resources can be defined in terms of skills, energy, talent, abilities, or knowledge.In a project management context, human resources are those employees responsible for undertaking the activities defined in the project plan.
Capital or infrastructure
In social studies, capital refers to already-produced durable goods used in production of goods or services. In essence, capital refers to human-made resources created using knowledge and expertise based on utility or perceived value. Common examples of capital include buildings, machinery, railways, roads, and ships. As resources, capital goods may or may not be significantly consumed, though they may depreciate in the production process and they are typically of limited capacity or unavailable for use by others.
Tangible versus intangible
Whereas, tangible resources such as equipment have an actual physical existence, intangible resources such as corporate images, brands and patents, and other intellectual properties exist in abstraction.
Use and sustainable development
Typically resources cannot be consumed in their original form, but rather through resource development they must be processed into more usable commodities and usable things. The demand for resources is increasing as economies develop. There are marked differences in resource distribution and associated economic inequality between regions or countries, with developed countries using more natural resources than developing countries. Sustainable development is a pattern of resource use, that aims to meet human needs while preserving the environment. Sustainable development means that we should exploit our resources carefully to meet our present requirement without compromising the ability of future generations to meet their own needs. The practice of the three R's – reduce, reuse and recycle must be followed in order to save and extend the availability of resources.
Various problems relate to the usage of resources:
Environmental degradation
Over-consumption
Resource curse
Resource depletion
Tragedy of the commons
Myth of superabundanceVarious benefits can result from the wise usage of resources:
Economic growth
Ethical consumerism
Prosperity
Quality of life
Sustainability
Wealth
See also
Natural resource management
Resource-based view
Waste management
References
Further reading
Elizabeth Kolbert, "Needful Things: The raw materials for the world we've built come at a cost" (largely based on Ed Conway, Material World: The Six Raw Materials That Shape Modern Civilization, Knopf, 2023; Vince Beiser, The World in a Grain; and Chip Colwell, So Much Stuff: How Humans Discovered Tools, Invented Meaning, and Made More of Everything, Chicago), The New Yorker, 30 October 2023, pp. 20–23. Kolbert mainly discusses the importance to modern civilization, and the finite sources of, six raw materials: high-purity quartz (needed to produce silicon chips), sand, iron, copper, petroleum (which Conway lumps together with another fossil fuel, natural gas), and lithium. Kolbert summarizes archeologist Colwell's review of the evolution of technology, which has ended up giving the Global North a superabundance of "stuff," at an unsustainable cost to the world's environment and reserves of raw materials.
External links
The dictionary definition of resource at Wiktionary |
conodont | Conodonts (Greek kōnos, "cone", + odont, "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which are usually found in isolation and are now called conodont elements. Knowledge about soft tissues remains limited. They existed in the world's oceans for over 300 million years, from the Cambrian to the beginning of the Jurassic. Conodont elements are widely used as index fossils, fossils used to define and identify geological periods. The animals are also called Conodontophora (conodont bearers) to avoid ambiguity.
Discovery and understanding of conodonts
The teeth-like fossils of the conodont were first discovered by Heinz Christian Pander and the results published in Saint Petersburg, Russia, in 1856. The name pander is commonly used in scientific names of conodonts.It was only in the early 1980s that the first fossil evidence of the rest of the animal was found (see below). In the 1990s exquisite fossils were found in South Africa in which the soft tissue had been converted to clay, preserving even muscle fibres. The presence of muscles for rotating the eyes showed definitively that the animals were primitive vertebrates.
Description
Elements
Conodont elements consist of mineralised teeth-like structures of varying morphology and complexity. The evolution of mineralized tissues has been puzzling for more than a century. It has been hypothesized that the first mechanism of chordate tissue mineralization began either in the oral skeleton of conodonts or the dermal skeleton of early agnathans.
The element array constituted a feeding apparatus that is radically different from the jaws of modern animals. They are now termed "conodont elements" to avoid confusion. The three forms of teeth, i.e., coniform cones, ramiform bars, and pectiniform platforms, probably performed different functions.
For many years, conodonts were known only from enigmatic tooth-like microfossils (200 micrometers to 5 millimeters in length), which occur commonly, but not always, in isolation and were not associated with any other fossil. Until the early 1980s, conodont teeth had not been found in association with fossils of the host organism, in a konservat lagerstätte. This is because the conodont animal was soft-bodied, thus everything but the teeth was unsuited for preservation under normal circumstances.
These microfossils are made of hydroxylapatite (a phosphatic mineral). The conodont elements can be extracted from rock using adequate solvents.They are widely used in biostratigraphy. Conodont elements are also used as paleothermometers, a proxy for thermal alteration in the host rock, because under higher temperatures, the phosphate undergoes predictable and permanent color changes, measured with the conodont alteration index. This has made them useful for petroleum exploration where they are known, in rocks dating from the Cambrian to the Late Triassic.
Multielement conodonts
The conodont apparatus may comprise a number of discrete elements, including the spathognathiform, ozarkodiniform, trichonodelliform, neoprioniodiform, and other forms.In the 1930s, the concept of conodont assemblages was described by Hermann Schmidt and by Harold W. Scott in 1934.
Elements of ozarkodinids
The feeding apparatus of ozarkodinids is composed of an axial Sa element at the front, flanked by two groups of four close-set elongate Sb and Sc elements which were inclined obliquely inwards and forwards. Above these elements lay a pair of arched and inward pointing (makellate) M elements. Behind the S-M array lay transversely oriented and bilaterally opposed (pectiniform, i.e. comb-shaped) Pb and Pa elements.
Soft tissues
Although conodont elements are abundant in the fossil record, fossils preserving soft tissues of conodont animals are known from only a few deposits in the world. One of the first possible body fossils of a conodont were those of Typhloesus, an enigmatic animal known from the Bear Gulch limestone in Montana. This possible identification was based on the presence of conodont elements with the fossils of Typhloesus. This claim was disproved, however, as the conodont elements were actually in the creature's digestive area. That animal is now regarded as a possible mollusk related to gastropods. As of 2023, there are only three described species of conodonts that have preserved trunk fossils: Clydagnathus windsorensis from the Carboniferous aged Granton Shrimp Bed in Scotland, Promissum pulshrum from the Ordovician aged Soom Shale in South Africa, and Panderodus unicostatus from the Silurian aged Waukesha Biota in Wisconsin. There are other examples of conodont animals that only preserve the head region, including eyes, of the animals known from the Silurian aged Eramosa site in Ontario and Triassic aged Akkamori section in Japan.According to these fossils, conodonts had large eyes, fins with fin rays, chevron-shaped muscles and axial line, which were interpreted as notochord or the dorsal nerve cord. While Clydagnathus and Panderodus had lengths only reaching 4–5 cm (1.6–2.0 in), Promissum is estimated to reach 40 cm (16 in) in length, if it had the same proportions as Clydagnathus.
Ecology
The "teeth" of some conodonts have been interpreted as filter-feeding apparatuses, filtering plankton from the water and passing it down the throat. Others have been interpreted as a "grasping and crushing array". Wear on some conodont elements suggests that they functioned like teeth, with both wear marks likely created by food as well as by occlusion with other elements. Studies have concluded that conodonts taxa occupied both pelagic (open ocean) and nektobenthic (swimming above the sediment surface) niches. The preserved musculature suggests that some conodonts (Promissum at least) were efficient cruisers, but incapable of bursts of speed. Based on isotopic evidence, some Devonian conodonts have been proposed to have been low-level consumers that fed on zooplankton.A study on the population dynamics of Alternognathus has been published. Among other things, it demonstrates that at least this taxon had short lifespans lasting around a month. A study Sr/Ca and Ba/Ca ratios of a population of conodonts from a carbonate platform from the Silurian of Sweden found that the different conodont species and genera likely occupied different trophic niches.Some species of the genus Panderodus have been speculated to be venomous, based on grooves found on some elements.
Classification and phylogeny
As of 2012, scientists classify the conodonts in the phylum Chordata on the basis of their fins with fin rays, chevron-shaped muscles and notochord.Milsom and Rigby envision them as vertebrates similar in appearance to modern hagfish and lampreys,
and phylogenetic analysis suggests they are more derived than either of these groups.
However, this analysis comes with one caveat: early forms of conodonts, the protoconodonts, appear to form a distinct clade from the later paraconodonts and euconodonts. Protoconodonts likely represent a stem group to the phylum that includes chaetognath worms; this conclusion suggests that chaetognaths are not close relatives of true conodonts.
Moreover, some analyses do not regard conodonts as either vertebrates or craniates, because they lack the main characteristics of these groups. More recently it has been proposed that conodonts may be stem-cyclostomes, more closely related to hagfish and lampreys than other living vertebrates.
Evolutionary history
The earliest fossils of conodonts are known from the Cambrian period. Conodonts extensively diversified during the early Ordovician, reaching their apex of diversity during the middle part of the period, and experienced a sharp decline during the late Ordovician and Silurian, before reaching another peak of diversity during the mid-late Devonian. Conodont diversity declined during the Carboniferous, with an extinction event at the end of the middle Tournaisian and a prolonged period of significant loss of diversity during the Pennsylvanian. Only a handful of conodont genera were present during the Permian, though diversity increased after the P-T extinction during the Early Triassic. Diversity continued to decline during the Middle and Late Triassic, culminating in their extinction soon after the Triassic-Jurassic boundary. Much of their diversity during the Paleozoic was likely controlled by sea levels and temperature, with the major declines during the Late Ordovician and Late Carboniferous due to cooler temperatures, especially glacial events and associated marine regressions which reduced continental shelf area. However, their final demise is more likely related to biotic interactions, perhaps competition with new Mesozoic taxa.
Taxonomy
Conodonta taxonomy based on Sweet & Donoghue, Mikko's Phylogeny Archive and Fish classification 2017.Conodonta Pander, 1856 non Eichenberg, 1930 sensu Sweet & Donoghue, 2001 [Conodontia; Conodontophorida Eichenberg, 1930; Conodontochordata]
Paraconodonta Müller, 1962 [Paraconodontida]
Amphigeisiniformes
Amphigeisinidae Miller, 1981
Westergaardodiniformes Lindström, 1970
Westergaardodinidae Müller, 1959 [Chosonodinidae]
Furnishinidae Müller & Nogami, 1971
Conodontophora Eichenberg, 1930
Cavidonti Sweet, 1988
Proconodontiformes Sweet, 1988
Pseudooneotodidae Wang & Aldridge, 2010
Proconodontidae Lindström, 1981
Cordylodontidae Lindström, 1970 [Cyrtoniodontinae Hass, 1959]
Fryxellodontina
Fryxellodontidae Miller, 1981
Pygodontidae Bergstrom, 1981
Belodellina Sweet, 1988
Ansellidae Faohraeus & Hunter, 1985
Dapsilodontidae Sweet, 1988
Belodellidae Khodalevich & Tschernich, 1973 [Cambropustulidae]
Conodonti Pander, 1856 non Branson, 1938
Oneotodontidae Miller, 1981 [Teridontidae Miller, 1981]
Protopanderodontida Sweet, 1988 [Panderodontida]
?Pronodontidae Lindström, 1970
?Cornuodontidae Faohraeus, 1966
?Protopanderodontidae Lindström, 1970 [Juanognathidae Bergström, 1981]
?Strachanognathidae Bergström, 1981
?Pseudooneotodidae
Clavohamulidae Lindström, 1970
Drepanoistodontidae Faohraeus, 1978
Acanthodontidae Lindström, 1970
Scolopodontidae Bergström, 1981
Panderodontidae Lindström, 1970
Prioniodontida Dzik, 1976 [Distacodontida] (paraphyletic)
?Acodontidae Dzik, 1993 [Tripodontinae Sweet, 1988]
?Cahabagnathidae Stouge & Bagnoli 1999
?Distacodontidae Bassler, 1925 emend. Ulrich & Bassler, 1926 [Drepanodontinae Fahraeus & Nowlan, 1978; Lonchodininae Hass, 1959]
?Gamachignathidae Wang & Aldridge, 2010
?Jablonnodontidae Dzik, 2006
?Nurrellidae Pomešano-Cherchi, 1967
?Paracordylodontidae Bergström, 1981
?Playfordiidae Dzik, 2002
?Ulrichodinidae Bergström, 1981
Rossodus Repetski & Ethington, 1983
Multioistodontidae Harris, 1964 [Dischidognathidae]
Oistodontidae Lindström, 1970
Periodontidae Lindström, 1970
Rhipidognathidae Lindström, 1970 sensu Sweet, 1988
Prioniodontidae Bassler, 1925
Phragmodontidae Bergström, 1981
Plectodinidae Sweet, 1988
Icriodontacea
Balognathidae (Hass, 1959)
Polyplacognathidae Bergström, 1981
Distomodontidae Klapper, 1981
Icriodellidae Sweet, 1988
Icriodontidae Müller & Müller, 1957
Prioniodinida Sweet, 1988
?Oepikodontidae Bergström, 1981
?Xaniognathidae Sweet, 1981
Chirognathidae Branson & Mehl, 1944
Prioniodinidae Bassler, 1925 [Hibbardellidae Mueller, 1956]
Bactrognathidae Lindström, 1970
Ellisoniidae Clark, 1972
Gondolellidae Lindström, 1970
Ozarkodinida Dzik, 1976 [Polygnathida]
?Anchignathodontidae Clark, 1972
?Archeognathidae Miller, 1969
?Belodontidae Huddle, 1934
?Coleodontidae Branson & Mehl, 1944 [Hibbardellidae Müller, 1956; Loxodontidae]
?Eognathodontidae Bardashev, Weddige & Ziegler, 2002
?Francodinidae Dzik, 2006
?Gladigondolellidae (Hirsch, 1994) [Sephardiellinae Plasencia, Hirsch & Márquez-Aliaga, 2007; Neogondolellinae Hirsch, 1994; Cornudininae Orchard, 2005; Epigondolellinae Orchard, 2005; Marquezellinae Plasencia et al., 2018; Paragondolellinae Orchard, 2005; Pseudofurnishiidae Ramovs, 1977]
?Iowagnathidae Liu et al., 2017
?Novispathodontidae (Orchard, 2005)
?Trucherognathidae Branson & Mehl, 1944
?Vjalovognathidae Shen, Yuan & Henderson, 2015
?Wapitiodontidae Orchard, 2005
Cryptotaxidae Klapper & Philip, 1971
Spathognathodontidae Hass, 1959 [Ozarkodinidae Dzik, 1976]
Pterospathodontidae Cooper, 1977 [Carniodontidae]
Kockelellidae Klapper, 1981 [Caenodontontidae]
Polygnathidae Bassler, 1925 [?Eopolygnathidae Bardashev, Weddige & Ziegler, 2002]
Palmatolepidae Sweet, 1988
Hindeodontidae (Hass, 1959)
Elictognathidae Austin & Rhodes, 1981
Gnathodontidae Sweet, 1988
Idiognathodontidae Harris & Hollingsworth, 1933
Mestognathidae Austin & Rhodes, 1981
Cavusgnathidae Austin & Rhodes, 1981
Sweetognathidae Ritter, 1986
See also
Timeline of the evolutionary history of life
Micropaleontology
List of conodont genera
Conodont biostratigraphy
Conodont alteration index
References
Further reading
Aldridge, R. J.; Briggs, D. E. G.; Smith, M. Paul; Clarkson, E. N. K.; Clark, N. D. L. (1993). "The anatomy of conodonts". Philosophical Transactions of the Royal Society of London, Series B. 340 (1294): 405–421. doi:10.1098/rstb.1993.0082.
Aldridge, R. J.; Purnell, M. A. (1996). "The conodont controversies". Trends in Ecology and Evolution. 11 (11): 463–468. doi:10.1016/0169-5347(96)10048-3. PMID 21237922.
Donoghue, P. C. J.; Forey, P. L.; Aldridge, R. J. (2000). "Conodont affinity and chordate phylogeny". Biological Reviews. 75 (2): 191–251. doi:10.1111/j.1469-185X.1999.tb00045.x. PMID 10881388. S2CID 22803015.
Gould, Stephen Jay (1985). "Reducing Riddles". In The Flamingo's Smile, 245-260. New York, W.W. Norton and Company. ISBN 0-393-30375-6.
Janvier, P (1997). "Euconodonta". The tree of life web project. Retrieved 2007-09-05.
Knell, Simon J. The Great Fossil Enigma: The Search for the Conodont Animal (Indiana University Press; 2012) 440 pages
Sweet, Walter (1988). The Conodonta: morphology, taxonomy, paleoecology, and evolutionary history of a long-extinct animal phylum. Oxford, Clarendon Press.
Sweet, W. C.; Donoghue, P. C. J. (2001). "Conodonts: past, present and future" (PDF). Journal of Paleontology. 75 (6): 1174–1184. doi:10.1666/0022-3360(2001)075<1174:CPPF>2.0.CO;2. ISSN 0022-3360. S2CID 53395896. Archived (PDF) from the original on 2022-10-30.
Lindström, Maurits (1970). "A suprageneric taxonomy of the conodonts". Lethaia. 3 (4): 427–445. doi:10.1111/j.1502-3931.1970.tb00834.x.
External links
Mark Purnell. "An oblique anterior view of a model of the apparatus of the Pennsylvanian conodont Idiognathodus".
"'The Jaws That Catch': an Introduction to the Conodonta". Palæos. Retrieved 2013-07-01.
Jim Davison (2002-10-15). "Ordovician conodonts". Retrieved 2009-07-07. |
nectarian | The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris form the upper part of the densely cratered terrain found in lunar highlands.
Relationship to Earth's geologic time scale
Since little or no geological evidence on Earth exists from the time spanned by the Nectarian period of the Moon, the Nectarian has been used by at least one notable scientific work as an unofficial subdivision of the terrestrial Hadean eon.
See also
Hadean eon-related topics
== References == |
quaternary glaciation | The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describe this entire period up to the present as an "ice age", in popular culture this term usually refers to the most recent glacial period, or to the Pleistocene epoch in general. Since Earth still has polar ice sheets, geologists consider the Quaternary glaciation to be ongoing, though currently in an interglacial period.
During the Quaternary glaciation, ice sheets appeared, expanding during glacial periods and contracting during interglacial periods. Since the end of the last glacial period, only the Antarctic and Greenland ice sheets have survived, while other sheets formed during glacial periods, such as the Laurentide Ice Sheet, have completely melted.
The major effects of the Quaternary glaciation have been the continental erosion of land and the deposition of material; the modification of river systems; the formation of millions of lakes, including the development of pluvial lakes far from the ice margins; changes in sea level; the isostatic adjustment of the Earth's crust; flooding; and abnormal winds. The ice sheets, by raising the albedo (the ratio of solar radiant energy reflected from Earth back into space), generated significant feedback to further cool the climate. These effects have shaped land and ocean environments and biological communities.
Long before the Quaternary glaciation, land-based ice appeared and then disappeared during at least four other ice ages. The Quaternary glaciation can be considered a part of a Late Cenozoic Ice Age that began 33.9 Ma and is ongoing.
Discovery
Evidence for the Quaternary glaciation was first understood in the 18th and 19th centuries as part of the scientific revolution. Over the last century, extensive field observations have provided evidence that continental glaciers covered large parts of Europe, North America, and Siberia. Maps of glacial features were compiled after many years of fieldwork by hundreds of geologists who mapped the location and orientation of drumlins, eskers, moraines, striations, and glacial stream channels to reveal the extent of the ice sheets, the direction of their flow, and the systems of meltwater channels. They also allowed scientists to decipher a history of multiple advances and retreats of the ice. Even before the theory of worldwide glaciation was generally accepted, many observers recognized that more than a single advance and retreat of the ice had occurred.
Description
To geologists, an ice age is defined by the presence of large amounts of land-based ice. Prior to the Quaternary glaciation, land-based ice formed during at least four earlier geologic periods: the Karoo (360–260 Ma), Andean-Saharan (450–420 Ma), Cryogenian (720–635 Ma) and Huronian (2,400–2,100 Ma).Within the Quaternary ice age, there were also periodic fluctuations of the total volume of land ice, the sea level, and global temperatures. During the colder episodes (referred to as glacial periods or glacials) large ice sheets at least 4 km (2.5 mi) thick at their maximum covered parts of Europe, North America, and Siberia. The shorter warm intervals between glacials, when continental glaciers retreated, are referred to as interglacials. These are evidenced by buried soil profiles, peat beds, and lake and stream deposits separating the unsorted, unstratified deposits of glacial debris.
Initially the glacial/interglacial cycle length was about 41,000 years, but following the Mid-Pleistocene Transition about 1 Ma, it slowed to about 100,000 years, as evidenced most clearly by ice cores for the past 800,000 years and marine sediment cores for the earlier period. Over the past 740,000 years there have been eight glacial cycles.The entire Quaternary period, starting 2.58 Ma, is referred to as an ice age because at least one permanent large ice sheet—the Antarctic ice sheet—has existed continuously. There is uncertainty over how much of Greenland was covered by ice during each interglacial. Currently, Earth is in an interglacial period, the Holocene epoch beginning 15,000 to 10,000 years ago; this has caused the ice sheets from the Last Glacial Period to slowly melt. The remaining glaciers, now occupying about 10% of the world's land surface, cover Greenland, Antarctica and some mountainous regions. During the glacial periods, the present (i.e. interglacial) hydrologic system was completely interrupted throughout large areas of the world and was considerably modified in others. The volume of ice on land resulted in a sea level about 120 metres (394 ft) lower than present.
Causes
Earth's history of glaciation is a product of the internal variability of Earth's climate system (e.g., ocean currents, carbon cycle), interacting with external forcing by phenomena outside the climate system (e.g., changes in Earth's orbit, volcanism, and changes in solar output).
Astronomical cycles
The role of Earth's orbital changes in controlling climate was first advanced by James Croll in the late 19th century. Later, the Serbian geophysicist Milutin Milanković elaborated on the theory and calculated that these irregularities in Earth's orbit could cause the climatic cycles now known as Milankovitch cycles. They are the result of the additive behavior of several types of cyclical changes in Earth's orbital properties.
Firstly, changes in the orbital eccentricity of Earth occur on a cycle of about 100,000 years. Secondly, the inclination or tilt of Earth's axis varies between 22° and 24.5° in a cycle 41,000 years long. The tilt of Earth's axis is responsible for the seasons; the greater the tilt, the greater the contrast between summer and winter temperatures. Thirdly, precession of the equinoxes, or wobbles in the Earth's rotation axis, have a periodicity of 26,000 years. According to the Milankovitch theory, these factors cause a periodic cooling of Earth, with the coldest part in the cycle occurring about every 40,000 years. The main effect of the Milankovitch cycles is to change the contrast between the seasons, not the annual amount of solar heat Earth receives. The result is less ice melting than accumulating, and glaciers build up.
Milankovitch worked out the ideas of climatic cycles in the 1920s and 1930s, but it was not until the 1970s that a sufficiently long and detailed chronology of the Quaternary temperature changes was worked out to test the theory adequately. Studies of deep-sea cores and their fossils indicate that the fluctuation of climate during the last few hundred thousand years is remarkably close to that predicted by Milankovitch.
Atmospheric composition
One theory holds that decreases in atmospheric CO2, an important greenhouse gas, started the long-term cooling trend that eventually led to the formation of continental ice sheets in the Arctic. Geological evidence indicates a decrease of more than 90% in atmospheric CO2 since the middle of the Mesozoic Era. An analysis of CO2 reconstructions from alkenone records shows that CO2 in the atmosphere declined before and during Antarctic glaciation, and supports a substantial CO2 decrease as the primary cause of Antarctic glaciation.CO2 levels also play an important role in the transitions between interglacials and glacials. High CO2 contents correspond to warm interglacial periods, and low CO2 to glacial periods. However, studies indicate that CO2 may not be the primary cause of the interglacial-glacial transitions, but instead acts as a feedback. The explanation for this observed CO2 variation "remains a difficult attribution problem".
Plate tectonics and ocean currents
An important component in the development of long-term ice ages is the positions of the continents. These can control the circulation of the oceans and the atmosphere, affecting how ocean currents carry heat to high latitudes. Throughout most of geologic time, the North Pole appears to have been in a broad, open ocean that allowed major ocean currents to move unabated. Equatorial waters flowed into the polar regions, warming them. This produced mild, uniform climates that persisted throughout most of geologic time.
But during the Cenozoic Era, the large North American and South American continental plates drifted westward from the Eurasian Plate. This interlocked with the development of the Atlantic Ocean, running north–south, with the North Pole in the small, nearly landlocked basin of the Arctic Ocean. The Drake Passage opened 33.9 million years ago (the Eocene-Oligocene transition), severing Antarctica from South America. The Antarctic Circumpolar Current could then flow through it, isolating Antarctica from warm waters and triggering the formation of its huge ice sheets. The weakening of the North Atlantic Current around 3.65 to 3.5 million years ago resulted in cooling and freshening of the Arctic Ocean, nurturing the development of Arctic sea ice and preconditioning the formation of continental glaciers later in the Pliocene. The Isthmus of Panama developed at a convergent plate margin about 2.6 million years ago and further separated oceanic circulation, closing the last strait, outside the polar regions, that had connected the Pacific and Atlantic Oceans. This increased poleward salt and heat transport, strengthening the North Atlantic thermohaline circulation, which supplied enough moisture to arctic latitudes to initiate the northern glaciation.
Rise of mountains
The elevation of continental surface, often as mountain formation, is thought to have contributed to cause the Quaternary glaciation. The gradual movement of the bulk of Earth's landmasses away from the tropics in addition to increased mountain formation in the Late Cenozoic meant more land at high altitude and high latitude, favouring the formation of glaciers. For example, the Greenland ice sheet formed in connection to the uplift of the west Greenland and east Greenland uplands in two phases, 10 and 5 Ma, respectively. These mountains constitute passive continental margins. Computer models show that the uplift would have enabled glaciation through increased orographic precipitation and cooling of surface temperatures. For the Andes it is known that the Principal Cordillera had risen to heights that allowed for the development of valley glaciers about 1 Ma.
Effects
The presence of so much ice upon the continents had a profound effect upon almost every aspect of Earth's hydrologic system. Most obvious are the spectacular mountain scenery and other continental landscapes fashioned both by glacial erosion and deposition instead of running water. Entirely new landscapes covering millions of square kilometers were formed in a relatively short period of geologic time. In addition, the vast bodies of glacial ice affected Earth well beyond the glacier margins. Directly or indirectly, the effects of glaciation were felt in every part of the world.
Lakes
The Quaternary glaciation produced more lakes than all other geologic processes combined. The reason is that a continental glacier completely disrupts the preglacial drainage system. The surface over which the glacier moved was scoured and eroded by the ice, leaving many closed, undrained depressions in the bedrock. These depressions filled with water and became lakes.
Very large lakes were formed along the glacial margins. The ice on both North America and Europe was about 3,000 m (10,000 ft) thick near the centers of maximum accumulation, but it tapered toward the glacier margins. Ice weight caused crustal subsidence, which was greatest beneath the thickest accumulation of ice. As the ice melted, rebound of the crust lagged behind, producing a regional slope toward the ice. This slope formed basins that have lasted for thousands of years. These basins became lakes or were invaded by the ocean. The Baltic Sea and the Great Lakes of North America were formed primarily in this way.The numerous lakes of the Canadian Shield, Sweden, and Finland are thought to have originated at least partly from glaciers' selective erosion of weathered bedrock.
Pluvial lakes
The climatic conditions that cause glaciation had an indirect effect on arid and semiarid regions far removed from the large ice sheets. The increased precipitation that fed the glaciers also increased the runoff of major rivers and intermittent streams, resulting in the growth and development of large pluvial lakes. Most pluvial lakes developed in relatively arid regions where there typically was insufficient rain to establish a drainage system leading to the sea. Instead, stream runoff flowed into closed basins and formed playa lakes. With increased rainfall, the playa lakes enlarged and overflowed. Pluvial lakes were most extensive during glacial periods. During interglacial stages, with less rain, the pluvial lakes shrank to form small salt flats.
Isostatic adjustment
Major isostatic adjustments of the lithosphere during the Quaternary glaciation were caused by the weight of the ice, which depressed the continents. In Canada, a large area around Hudson Bay was depressed below (modern) sea level, as was the area in Europe around the Baltic Sea. The land has been rebounding from these depressions since the ice melted. Some of these isostatic movements triggered large earthquakes in Scandinavia about 9,000 years ago. These earthquakes are unique in that they are not associated with plate tectonics.
Studies have shown that the uplift has taken place in two distinct stages. The initial uplift following deglaciation was rapid (called "elastic"), and took place as the ice was being unloaded. After this "elastic" phase, uplift proceed by "slow viscous flow" so the rate decreased exponentially after that. Today, typical uplift rates are of the order of 1 cm per year or less, except in areas of North America, especially Alaska, where the rate of uplift is 2.54 cm per year (1 inch or more). In northern Europe, this is clearly shown by the GPS data obtained by the BIFROST GPS network. Studies suggest that rebound will continue for at least another 10,000 years. The total uplift from the end of deglaciation depends on the local ice load and could be several hundred meters near the center of rebound.
Winds
The presence of ice over so much of the continents greatly modified patterns of atmospheric circulation. Winds near the glacial margins were strong and persistent because of the abundance of dense, cold air coming off the glacier fields. These winds picked up and transported large quantities of loose, fine-grained sediment brought down by the glaciers. This dust accumulated as loess (wind-blown silt), forming irregular blankets over much of the Missouri River valley, central Europe, and northern China.
Sand dunes were much more widespread and active in many areas during the early Quaternary period. A good example is the Sand Hills region in Nebraska which covers an area of about 60,000 km2 (23,166 sq mi). This region was a large, active dune field during the Pleistocene epoch but today is largely stabilized by grass cover.
Ocean currents
Thick glaciers were heavy enough to reach the sea bottom in several important areas, which blocked the passage of ocean water and affected ocean currents. In addition to these direct effects, it also caused feedback effects, as ocean currents contribute to global heat transfer.
Gold deposits
Moraines and till deposited by Quaternary glaciers have contributed to the formation of valuable placer deposits of gold. This is the case of southernmost Chile where reworking of Quaternary moraines have concentrated gold offshore.
Records of prior glaciation
Glaciation has been a rare event in Earth's history, but there is evidence of widespread glaciation during the late Paleozoic Era (300 to 200 Ma) and the late Precambrian (i.e. the Neoproterozoic Era, 800 to 600 Ma). Before the current ice age, which began 2 to 3 Ma, Earth's climate was typically mild and uniform for long periods of time. This climatic history is implied by the types of fossil plants and animals and by the characteristics of sediments preserved in the stratigraphic record. There are, however, widespread glacial deposits, recording several major periods of ancient glaciation in various parts of the geologic record. Such evidence suggests major periods of glaciation prior to the current Quaternary glaciation.
One of the best documented records of pre-Quaternary glaciation, called the Karoo Ice Age, is found in the late Paleozoic rocks in South Africa, India, South America, Antarctica, and Australia. Exposures of ancient glacial deposits are numerous in these areas. Deposits of even older glacial sediment exist on every continent except South America. These indicate that two other periods of widespread glaciation occurred during the late Precambrian, producing the Snowball Earth during the Cryogenian period.
Next glacial period
The warming trend following the Last Glacial Maximum, since about 20,000 years ago, has resulted in a sea level rise by about 130 metres (427 ft). This warming trend subsided about 6,000 years ago, and sea level has been comparatively stable since the Neolithic. The present interglacial period (the Holocene climatic optimum) has been stable and warm compared to the preceding ones, which were interrupted by numerous cold spells lasting hundreds of years. This stability might have allowed the Neolithic Revolution and by extension human civilization.Based on orbital models, the cooling trend initiated about 6,000 years ago will continue for another 23,000 years. Slight changes in the Earth's orbital parameters may, however, indicate that, even without any human contribution, there will not be another glacial period for the next 50,000 years.
It is possible that the current cooling trend might be interrupted by an interstadial phase (a warmer period) in about 60,000 years, with the next glacial maximum reached only in about 100,000 years.Based on past estimates for interglacial durations of about 10,000 years, in the 1970s there was some concern that the next glacial period would be imminent. However, slight changes in the eccentricity of Earth's orbit around the Sun suggest a lengthy interglacial period lasting about another 50,000 years. Other models, based on periodic variations in solar output, give a different projection of the start of the next glacial period at around 10,000 years from now. Additionally, human impact is now seen as possibly extending what would already be an unusually long warm period. Projection of the timeline for the next glacial maximum depend crucially on the amount of CO2 in the atmosphere. Models assuming increased CO2 levels at 750 parts per million (ppm; current levels are at 417 ppm) have estimated the persistence of the current interglacial period for another 50,000 years. However, more recent studies concluded that the amount of heat trapping gases emitted into Earth's oceans and atmosphere will prevent the next glacial (ice age), which otherwise would begin in around 50,000 years, and likely more glacial cycles.
References
External links
The dictionary definition of glaciation at Wiktionary
Glaciers and Glaciation
Pleistocene Glaciation and Diversion of the Missouri River in Northern Montana Archived 2012-04-15 at the Wayback Machine
Clark, Peter U.; Bartlein, Patrick J. (1995). "Correlation of late Pleistocene glaciation in the western United States with North Atlantic Heinrich events". Geology. 23 (4): 483–6. Bibcode:1995Geo....23..483C. doi:10.1130/0091-7613(1995)023<0483:COLPGI>2.3.CO;2.
Pielou, E.C. (2008). After the Ice Age: The Return of Life to Glaciated North America. University of Chicago Press. ISBN 978-0-226-66809-3.
Alaska's Glacier and Icefields
Pleistocene glaciations at the Wayback Machine (archived 7 February 2012) (the last 2 million years)
IPCC's Palaeoclimate(pdf) Archived 2013-03-19 at the Wayback MachineCausesAstronomical Theory of Climate Change
Milutin Milankovitch and Milankovitch cycles |
mind over matter | "Mind over matter" is a phrase that has been used in several contexts, such as mind-centric spiritual doctrines, parapsychology, and philosophy.
Merriam Webster Dictionary defines mind as "the element or complex of elements in an individual that feels, perceives, thinks, wills, and especially reasons" and mind over matter as able to; "a situation in which someone is able to control a physical condition, problem, etc., by using the mind".
Origin
The phrase "mind over matter" first appeared in 1863 in The Geological Evidence of the Antiquity of Man by Sir Charles Lyell (1797–1875) and was first used to refer to the increasing status and evolutionary growth of the minds of animals and man throughout Earth history. It may be said that, so far from having a materialistic tendency, the supposed introduction into the earth at successive geological periods of life — sensation, instinct, the intelligence of the higher mammalia bordering on reason, and lastly, the improvable reason of Man himself — presents us with a picture of the ever-increasing dominion of mind over matter.
Another related saying, "the mind drives the mass", was coined almost two millennia earlier, in 19 B.C. by the poet Virgil in his work Aeneid, book 6, line 727.
Parapsychology
In the field of parapsychology, the phrase has been used to describe paranormal phenomena such as psychokinesis.
Mind over matter can be often attributed to survival. "it's a case of mind over matter."
Mao Zedong
"Mind over matter" was also Mao Zedong's idea that rural peasants could be "proletarianized" so they could lead the revolution and China could move from feudalism to socialism through New Democracy. According to some, it departs from Leninism in that the revolutionaries are peasants, instead of the urban proletariat.
Controlling pain
The phrase also relates to the ability to control the perception of pain that one may or may not be experiencing.
== References == |
global standard stratigraphic age | In the stratigraphy sub-discipline of geology, a Global Standard Stratigraphic Age, abbreviated GSSA, is a chronological reference point and criterion in the geologic record used to define the boundaries (an internationally sanctioned benchmark point) between different geological periods, epochs or ages on the overall geologic time scale in a chronostratigraphically useful rock layer. A worldwide multidisciplinary effort has been ongoing since 1974 to define such important metrics. The points and strata need be widespread and contain an identifiable sequence of layers or other unambiguous marker (identifiable or quantifiable) attributes.
GSSAs are defined by the International Commission on Stratigraphy (ICS) under the auspices of their parent organization, the International Union of Geological Sciences (IUGS), and are used primarily for time dating of rock layers older than 630 million years ago, lacking a good fossil record.
The geologic record becomes spotty prior to about 539 million years ago. This is because the Earth's crust in geological time scales is constantly being recycled by tectonic and weathering forces, and older rocks and especially readily accessible exposed strata that can act as a time calibration are rare.
For more recent periods, a Global Boundary Stratotype Section and Point (GSSP), largely based on paleontology and improved methods of fossil dating, is used to define such boundaries. In contrast to GSSAs, GSSPs are based on important events and transitions within a particular stratigraphic section. In older sections, there is insufficient fossil record or well preserved sections to identify the key events necessary for a GSSP, so GSSAs are defined based on fixed dates and selected criteria.
The ICS first attempts to meet the standards of the GSSPs (see below) and if those fail, usually have enough information to make a preliminary selection of several competing GSSA prospects or proposals.
See also
European Mammal Neogene
North American Land Mammal Age
Type locality
List of GSSPs
References
External links
The Global Boundary Stratotype Section and Point (GSSP): overview
Chart of The Global Boundary Stratotype Sections and Points (GSSP): chart
Geotime chart displaying geologic time periods compared to the fossil record - Deals with chronology and classifications for laymen (not GSSA/GSSPs) |
mesozoic | The Mesozoic Era is the second-to-last era of Earth's geological history, lasting from about 252 to 66 million years ago, comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of archosaurian reptiles, such as the dinosaurs; an abundance of gymnosperms, (such as ginkgoales, bennettitales) and ferns; a hot greenhouse climate; and the tectonic break-up of Pangaea. The Mesozoic is the middle of the three eras since complex life evolved: the Paleozoic, the Mesozoic, and the Cenozoic.
The era began in the wake of the Permian–Triassic extinction event, the largest well-documented mass extinction in Earth's history, and ended with the Cretaceous–Paleogene extinction event, another mass extinction whose victims included the non-avian dinosaurs, pterosaurs, mosasaurs, and plesiosaurs. The Mesozoic was a time of significant tectonic, climatic, and evolutionary activity. The era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would move into their current positions during the next era. The climate of the Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was hotter than it is today. Dinosaurs first appeared in the Mid-Triassic, and became the dominant terrestrial vertebrates in the Late Triassic or Early Jurassic, occupying this position for about 150 or 135 million years until their demise at the end of the Cretaceous. Archaic birds appeared in the Jurassic, having evolved from a branch of theropod dinosaurs, then true toothless birds appeared in the Cretaceous. The first mammals also appeared during the Mesozoic, but would remain small—less than 15 kg (33 lb)—until the Cenozoic. The flowering plants appeared in the early Cretaceous Period and would rapidly diversify throughout the end of the era, replacing conifers and other gymnosperms as the dominant group of plants.
Naming
The phrase "Age of Reptiles" was introduced by the 19th century paleontologist Gideon Mantell who viewed it as dominated by diapsids such as Iguanodon, Megalosaurus, Plesiosaurus, and Pterodactylus.
The current name was proposed in 1840 by the British geologist John Phillips (1800–1874). "Mesozoic" literally means 'middle life', deriving from the Greek prefix meso- (μεσο- 'between') and zōon (ζῷον 'animal, living being'). In this way, the Mesozoic is comparable to the Cenozoic (lit. 'new life') and Paleozoic ('old life') Eras as well as the Proterozoic ('earlier life') Eon.
The Mesozoic Era was originally described as the "secondary" era, following the "primary" (Paleozoic), and preceding the Tertiary.
Geologic periods
Following the Paleozoic, the Mesozoic extended roughly 186 million years, from 251.902 to 66 million years ago when the Cenozoic Era began. This time frame is separated into three geologic periods. From oldest to youngest:
Triassic (251.902 to 201.4 million years ago)
Jurassic (201.4 to 145 million years ago)
Cretaceous (145 to 66 million years ago)The lower boundary of the Mesozoic is set by the Permian–Triassic extinction event, during which it has been estimated that up to 90-96% of marine species became extinct although those approximations have been brought into question with some paleontologists estimating the actual numbers as low as 81%. It is also known as the "Great Dying" because it is considered the largest mass extinction in the Earth's history. The upper boundary of the Mesozoic is set at the Cretaceous–Paleogene extinction event (or K–Pg extinction event), which may have been caused by an asteroid impactor that created Chicxulub Crater on the Yucatán Peninsula. Towards the Late Cretaceous, large volcanic eruptions are also believed to have contributed to the Cretaceous–Paleogene extinction event. Approximately 50% of all genera became extinct, including all of the non-avian dinosaurs.
Triassic
The Triassic ranges roughly from 252 million to 201 million years ago, preceding the Jurassic Period. The period is bracketed between the Permian–Triassic extinction event and the Triassic–Jurassic extinction event, two of the "big five", and it is divided into three major epochs: Early, Middle, and Late Triassic.
The Early Triassic, about 252 to 247 million years ago, was dominated by deserts in the interior of the Pangaea supercontinent. The Earth had just witnessed a massive die-off in which 95% of all life became extinct, and the most common vertebrate life on land were Lystrosaurus, labyrinthodonts, and Euparkeria along with many other creatures that managed to survive the Permian extinction. Temnospondyls reached peak diversity during the early Triassic. The Middle Triassic, from 247 to 237 million years ago, featured the beginnings of the breakup of Pangaea and the opening of the Tethys Ocean. Ecosystems had recovered from the Permian extinction. Algae, sponge, corals, and crustaceans all had recovered, and new aquatic reptiles evolved, such as ichthyosaurs and nothosaurs. On land, pine forests flourished, as did groups of insects like mosquitoes and fruit flies. Reptiles began to get bigger and bigger, and the first crocodilians and dinosaurs evolved, which sparked competition with the large amphibians that had previously ruled the freshwater world, respectively mammal-like reptiles on land.Following the bloom of the Middle Triassic, the Late Triassic, from 237 to 201 million years ago, featured frequent heat spells and moderate precipitation (10–20 inches per year). The recent warming led to a boom of dinosaurian evolution on land as the continents began to separate from each other (Nyasasaurus from 243 to 210 million years ago, approximately 235–30 ma, some of them separated into Sauropodomorphs, Theropods and Herrerasaurids), as well as the first pterosaurs. During the Late Triassic, some advanced cynodonts gave rise to the first Mammaliaformes. All this climatic change, however, resulted in a large die-out known as the Triassic–Jurassic extinction event, in which many archosaurs (excluding pterosaurs, dinosaurs and crocodylomorphs), most synapsids, and almost all large amphibians became extinct, as well as 34% of marine life, in the Earth's fourth mass extinction event. The cause is debatable; flood basalt eruptions at the Central Atlantic magmatic province is cited as one possible cause.
Jurassic
The Jurassic ranges from 200 million years to 145 million years ago and features three major epochs: The Early Jurassic, the Middle Jurassic, and the Late Jurassic.The Early Jurassic spans from 200 to 175 million years ago. The climate was tropical and much more humid than the Triassic, as a result of the large seas appearing between the land masses. In the oceans, plesiosaurs, ichthyosaurs and ammonites were abundant. On land, dinosaurs and other archosaurs staked their claim as the dominant race, with theropods such as Dilophosaurus at the top of the food chain. The first true crocodiles evolved, pushing the large amphibians to near extinction. All-in-all, archosaurs rose to rule the world. Meanwhile, the first true mammals evolved, remaining relatively small but spreading widely; the Jurassic Castorocauda, for example, had adaptations for swimming, digging and catching fish. Fruitafossor, from the late Jurassic Period about 150 million years ago, was about the size of a chipmunk, and its teeth, forelimbs and back suggest that it dug open the nests of social insects (probably termites, as ants had not yet appeared) ; Volaticotherium was able to glide for short distances, like modern flying squirrels. The first multituberculates like Rugosodon evolved.
The Middle Jurassic spans from 175 to 163 million years ago. During this epoch, dinosaurs flourished as huge herds of sauropods, such as Brachiosaurus and Diplodocus, filled the fern prairies, chased by many new predators such as Allosaurus. Conifer forests made up a large portion of the forests. In the oceans, plesiosaurs were quite common, and ichthyosaurs flourished. This epoch was the peak of the reptiles. The Late Jurassic spans from 163 to 145 million years ago. During this epoch, the first avialans, like Archaeopteryx, evolved from small coelurosaurian dinosaurs. The increase in sea levels opened up the Atlantic seaway, which has grown continually larger until today. The further separation of the continents gave opportunity for the diversification of new dinosaurs.
Cretaceous
The Cretaceous is the longest period of the Mesozoic, but has only two epochs: Early and Late Cretaceous. The Early Cretaceous spans from 145 to 100 million years ago. The Early Cretaceous saw the expansion of seaways and a decline in diversity of sauropods, stegosaurs, and other high-browsing groups, with sauropods particularly scarce in North America. Some island-hopping dinosaurs, like Eustreptospondylus, evolved to cope with the coastal shallows and small islands of ancient Europe. Other dinosaurs rose up to fill the empty space that the Jurassic-Cretaceous extinction left behind, such as Carcharodontosaurus and Spinosaurus. Seasons came back into effect and the poles got seasonally colder, but some dinosaurs still inhabited the polar forests year round, such as Leaellynasaura and Muttaburrasaurus. The poles were too cold for crocodiles, and became the last stronghold for large amphibians like Koolasuchus. Pterosaurs got larger as genera like Tapejara and Ornithocheirus evolved. Mammals continued to expand their range: eutriconodonts produced fairly large, wolverine-like predators like Repenomamus and Gobiconodon, early therians began to expand into metatherians and eutherians, and cimolodont multituberculates went on to become common in the fossil record.
The Late Cretaceous spans from 100 to 66 million years ago. The Late Cretaceous featured a cooling trend that would continue in the Cenozoic Era. Eventually, tropics were restricted to the equator and areas beyond the tropic lines experienced extreme seasonal changes in weather. Dinosaurs still thrived, as new taxa such as Tyrannosaurus, Ankylosaurus, Triceratops and hadrosaurs dominated the food web. In the oceans, mosasaurs ruled, filling the role of the ichthyosaurs, which, after declining, had disappeared in the Cenomanian-Turonian boundary event. Though pliosaurs had gone extinct in the same event, long-necked plesiosaurs such as Elasmosaurus continued to thrive. Flowering plants, possibly appearing as far back as the Triassic, became truly dominant for the first time. Pterosaurs in the Late Cretaceous declined for poorly understood reasons, though this might be due to tendencies of the fossil record, as their diversity seems to be much higher than previously thought. Birds became increasingly common and diversified into a variety of enantiornithe and ornithurine forms. Though mostly small, marine hesperornithes became relatively large and flightless, adapted to life in the open sea. Metatherians and primitive eutherian also became common and even produced large and specialised genera like Didelphodon and Schowalteria. Still, the dominant mammals were multituberculates, cimolodonts in the north and gondwanatheres in the south. At the end of the Cretaceous, the Deccan traps and other volcanic eruptions were poisoning the atmosphere. As this continued, it is thought that a large meteor smashed into earth 66 million years ago, creating the Chicxulub Crater in an event known as the K-Pg Extinction (formerly K-T), the fifth and most recent mass extinction event, in which 75% of life became extinct, including all non-avian dinosaurs.
Paleogeography and tectonics
Compared to the vigorous convergent plate mountain-building of the late Paleozoic, Mesozoic tectonic deformation was comparatively mild. The sole major Mesozoic orogeny occurred in what is now the Arctic, creating the Innuitian orogeny, the Brooks Range, the Verkhoyansk and Cherskiy Ranges in Siberia, and the Khingan Mountains in Manchuria.
This orogeny was related to the opening of the Arctic Ocean and suturing of the North China and Siberian cratons to Asia. In contrast, the era featured the dramatic rifting of the supercontinent Pangaea, which gradually split into a northern continent, Laurasia, and a southern continent, Gondwana. This created the passive continental margin that characterizes most of the Atlantic coastline (such as along the U.S. East Coast) today.By the end of the era, the continents had rifted into nearly their present forms, though not their present positions. Laurasia became North America and Eurasia, while Gondwana split into South America, Africa, Australia, Antarctica and the Indian subcontinent, which collided with the Asian plate during the Cenozoic, giving rise to the Himalayas.
Climate
The Triassic was generally dry, a trend that began in the late Carboniferous, and highly seasonal, especially in the interior of Pangaea. Low sea levels may have also exacerbated temperature extremes. With its high specific heat capacity, water acts as a temperature-stabilizing heat reservoir, and land areas near large bodies of water—especially oceans—experience less variation in temperature. Because much of Pangaea's land was distant from its shores, temperatures fluctuated greatly, and the interior probably included expansive deserts. Abundant red beds and evaporites such as halite support these conclusions, but some evidence suggests the generally dry climate of was punctuated by episodes of increased rainfall. The most important humid episodes were the Carnian Pluvial Event and one in the Rhaetian, a few million years before the Triassic–Jurassic extinction event.
Sea levels began to rise during the Jurassic, probably caused by an increase in seafloor spreading. The formation of new crust beneath the surface displaced ocean waters by as much as 200 m (656 ft) above today's sea level, flooding coastal areas. Furthermore, Pangaea began to rift into smaller divisions, creating new shoreline around the Tethys Ocean. Temperatures continued to increase, then began to stabilize. Humidity also increased with the proximity of water, and deserts retreated.
The climate of the Cretaceous is less certain and more widely disputed. Probably, higher levels of carbon dioxide in the atmosphere are thought to have almost eliminated the north–south temperature gradient: temperatures were about the same across the planet, and about 10°C higher than today. The circulation of oxygen to the deep ocean may also have been disrupted, preventing the decomposition of large volumes of organic matter, which was eventually deposited as "black shale".Different studies have come to different conclusions about the amount of oxygen in the atmosphere during different parts of the Mesozoic, with some concluding oxygen levels were lower than the current level (about 21%) throughout the Mesozoic, some concluding they were lower in the Triassic and part of the Jurassic but higher in the Cretaceous, and some concluding they were higher throughout most or all of the Triassic, Jurassic and Cretaceous.
Life
Flora
The dominant land plant species of the time were gymnosperms, which are vascular, cone-bearing, non-flowering plants such as conifers that produce seeds without a coating. This contrasts with the earth's current flora, in which the dominant land plants in terms of number of species are angiosperms. The earliest members of the genus Ginkgo first appeared during the Middle Jurassic. This genus is represented today by a single species, Ginkgo biloba. Modern conifer groups began to radiate during the Jurassic. Bennettitales, an extinct group of gymnosperms with foliage superficially resembling that of cycads gained a global distribution during the Late Triassic, and represented one of the most common groups of Mesozoic seed plants.Flowering plants radiated during the early Cretaceous, first in the tropics, but the even temperature gradient allowed them to spread toward the poles throughout the period. By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that biomass was still dominated by cycads and ferns until after the Cretaceous–Paleogene extinction. Some plant species had distributions that were markedly different from succeeding periods; for example, the Schizeales, a fern order, were skewed to the Northern Hemisphere in the Mesozoic, but are now better represented in the Southern Hemisphere.
Fauna
The extinction of nearly all animal species at the end of the Permian Period allowed for the radiation of many new lifeforms. In particular, the extinction of the large herbivorous pareiasaurs and carnivorous gorgonopsians left those ecological niches empty. Some were filled by the surviving cynodonts and dicynodonts, the latter of which subsequently became extinct.
Recent research indicates that it took much longer for the reestablishment of complex ecosystems with high biodiversity, complex food webs, and specialized animals in a variety of niches, beginning in the mid-Triassic 4 million to 6 million years after the extinction, and not fully proliferated until 30 million years after the extinction. Animal life was then dominated by various archosaurs: dinosaurs, pterosaurs, and aquatic reptiles such as ichthyosaurs, plesiosaurs, and mosasaurs.
The climatic changes of the late Jurassic and Cretaceous favored further adaptive radiation. The Jurassic was the height of archosaur diversity, and the first birds and eutherian mammals also appeared. Some have argued that insects diversified in symbiosis with angiosperms, because insect anatomy, especially the mouth parts, seems particularly well-suited for flowering plants. However, all major insect mouth parts preceded angiosperms, and insect diversification actually slowed when they arrived, so their anatomy originally must have been suited for some other purpose.
Microbiota
At the dawn of the Mesozoic, ocean plankton communities transitioned from ones dominated by green archaeplastidans to ones dominated by endosymbiotic algae with red-algal-derived plastids. This transition is speculated to have been caused by an increasing paucity of many trace metals in the Mesozoic.
See also
Mesozoic portal
References
External links
Mesozoic (chronostratigraphy scale) |
geochronology | Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is provided by tools such as paleomagnetism and stable isotope ratios. By combining multiple geochronological (and biostratigraphic) indicators the precision of the recovered age can be improved.
Geochronology is different in application from biostratigraphy, which is the science of assigning sedimentary rocks to a known geological period via describing, cataloging and comparing fossil floral and faunal assemblages. Biostratigraphy does not directly provide an absolute age determination of a rock, but merely places it within an interval of time at which that fossil assemblage is known to have coexisted. Both disciplines work together hand in hand, however, to the point where they share the same system of naming strata (rock layers) and the time spans utilized to classify sublayers within a stratum.
The science of geochronology is the prime tool used in the discipline of chronostratigraphy, which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies.
Dating methods
Radiometric dating
By measuring the amount of radioactive decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material. A number of radioactive isotopes are used for this purpose, and depending on the rate of decay, are used for dating different geological periods. More slowly decaying isotopes are useful for longer periods of time, but less accurate in absolute years. With the exception of the radiocarbon method, most of these techniques are actually based on measuring an increase in the abundance of a radiogenic isotope, which is the decay-product of the radioactive parent isotope. Two or more radiometric methods can be used in concert to achieve more robust results. Most radiometric methods are suitable for geological time only, but some such as the radiocarbon method and the 40Ar/39Ar dating method can be extended into the time of early human life and into recorded history.Some of the commonly used techniques are:
Radiocarbon dating. This technique measures the decay of carbon-14 in organic material and can be best applied to samples younger than about 60,000 years.
Uranium–lead dating. This technique measures the ratio of two lead isotopes (lead-206 and lead-207) to the amount of uranium in a mineral or rock. Often applied to the trace mineral zircon in igneous rocks, this method is one of the two most commonly used (along with argon–argon dating) for geologic dating. Monazite geochronology is another example of U–Pb dating, employed for dating metamorphism in particular. Uranium–lead dating is applied to samples older than about 1 million years.
Uranium–thorium dating. This technique is used to date speleothems, corals, carbonates, and fossil bones. Its range is from a few years to about 700,000 years.
Potassium–argon dating and argon–argon dating. These techniques date metamorphic, igneous and volcanic rocks. They are also used to date volcanic ash layers within or overlying paleoanthropologic sites. The younger limit of the argon–argon method is a few thousand years.
Electron spin resonance (ESR) dating
Fission-track dating
Cosmogenic nuclide geochronology
A series of related techniques for determining the age at which a geomorphic surface was created (exposure dating), or at which formerly surficial materials were buried (burial dating). Exposure dating uses the concentration of exotic nuclides (e.g. 10Be, 26Al, 36Cl) produced by cosmic rays interacting with Earth materials as a proxy for the age at which a surface, such as an alluvial fan, was created. Burial dating uses the differential radioactive decay of 2 cosmogenic elements as a proxy for the age at which a sediment was screened by burial from further cosmic rays exposure.
Luminescence dating
Luminescence dating techniques observe 'light' emitted from materials such as quartz, diamond, feldspar, and calcite. Many types of luminescence techniques are utilized in geology, including optically stimulated luminescence (OSL), cathodoluminescence (CL), and thermoluminescence (TL). Thermoluminescence and optically stimulated luminescence are used in archaeology to date 'fired' objects such as pottery or cooking stones and can be used to observe sand migration.
Incremental dating
Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be fixed (i.e. linked to the present day and thus calendar or sidereal time) or floating.
Dendrochronology
Ice cores
Lichenometry
Varves
Paleomagnetic dating
A sequence of paleomagnetic poles (usually called virtual geomagnetic poles), which are already well defined in age, constitutes an apparent polar wander path (APWP). Such a path is constructed for a large continental block. APWPs for different continents can be used as a reference for newly obtained poles for the rocks with unknown age. For paleomagnetic dating, it is suggested to use the APWP in order to date a pole obtained from rocks or sediments of unknown age by linking the paleopole to the nearest point on the APWP. Two methods of paleomagnetic dating have been suggested: (1) the angular method and (2) the rotation method. The first method is used for paleomagnetic dating of rocks inside of the same continental block. The second method is used for the folded areas where tectonic rotations are possible.
Magnetostratigraphy
Magnetostratigraphy determines age from the pattern of magnetic polarity zones in a series of bedded sedimentary and/or volcanic rocks by comparison to the magnetic polarity timescale. The polarity timescale has been previously determined by dating of seafloor magnetic anomalies, radiometrically dating volcanic rocks within magnetostratigraphic sections, and astronomically dating magnetostratigraphic sections.
Chemostratigraphy
Global trends in isotope compositions, particularly carbon-13 and strontium isotopes, can be used to correlate strata.
Correlation of marker horizons
Marker horizons are stratigraphic units of the same age and of such distinctive composition and appearance that, despite their presence in different geographic sites, there is certainty about their age-equivalence. Fossil faunal and floral assemblages, both marine and terrestrial, make for distinctive marker horizons. Tephrochronology is a method for geochemical correlation of unknown volcanic ash (tephra) to geochemically fingerprinted, dated tephra. Tephra is also often used as a dating tool in archaeology, since the dates of some eruptions are well-established.
Geological hierarchy of chronological periodization
Geochronology, from largest to smallest:
Supereon
Eon
Era
Period
Epoch
Age
Chron
Differences from chronostratigraphy
It is important not to confuse geochronologic and chronostratigraphic units. Geochronological units are periods of time, thus it is correct to say that Tyrannosaurus rex lived during the Late Cretaceous Epoch. Chronostratigraphic units are geological material, so it is also correct to say that fossils of the genus Tyrannosaurus have been found in the Upper Cretaceous Series. In the same way, it is entirely possible to go and visit an Upper Cretaceous Series deposit – such as the Hell Creek deposit where the Tyrannosaurus fossils were found – but it is naturally impossible to visit the Late Cretaceous Epoch as that is a period of time.
See also
Astronomical chronology
Age of Earth
Age of the universe
Chronological dating, archaeological chronology
Absolute dating
Relative dating
Phase (archaeology)
Archaeological association
Geochronology
Closure temperature
Geologic time scale
Geological history of Earth
Thermochronology
List of geochronologic names
General
Consilience, evidence from independent, unrelated sources can "converge" on strong conclusions
References
Further reading
Smart, P.L., and Frances, P.D. (1991), Quaternary dating methods - a user's guide. Quaternary Research Association Technical Guide No.4 ISBN 0-907780-08-3
Lowe, J.J., and Walker, M.J.C. (1997), Reconstructing Quaternary Environments (2nd edition). Longman publishing ISBN 0-582-10166-2
Mattinson, J. M. (2013), Revolution and evolution: 100 years of U-Pb geochronology. Elements 9, 53–57.
Geochronology bibliography Talk:Origins Archive
External links
Geochronology and Isotopes Data Portal
International Commission on Stratigraphy
BGS Open Data Geochronological Ontologies |
earth | Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is enabled by Earth being a water world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its global ocean, covering 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is land, most of which is located in the form of continental landmasses within one hemisphere, Earth's land hemisphere. Most of Earth's land is somewhat humid and covered by vegetation, while large sheets of ice at Earth's polar deserts retain more water than Earth's groundwater, lakes, rivers and atmospheric water combined. Earth's crust consists of slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth has a liquid outer core that generates a magnetosphere capable of deflecting most of the destructive solar winds and cosmic radiation.
Earth has a dynamic atmosphere, which sustains Earth's surface conditions and protects it from most meteoroids and UV-light at entry. It has a composition of primarily nitrogen and oxygen. Water vapor is widely present in the atmosphere, forming clouds that cover most of the planet. The water vapor acts as a greenhouse gas and, together with other greenhouse gases in the atmosphere, particularly carbon dioxide (CO2), creates the conditions for both liquid surface water and water vapor to persist via the capturing of energy from the Sun's light. This process maintains the current average surface temperature of 14.76 °C, at which water is liquid under atmospheric pressure. Differences in the amount of captured energy between geographic regions (as with the equatorial region receiving more sunlight than the polar regions) drive atmospheric and ocean currents, producing a global climate system with different climate regions, and a range of weather phenomena such as precipitation, allowing components such as nitrogen to cycle.
Earth is rounded into an ellipsoid with a circumference of about 40,000 km. It is the densest planet in the Solar System. Of the four rocky planets, it is the largest and most massive. Earth is about eight light-minutes away from the Sun and orbits it, taking a year (about 365.25 days) to complete one revolution. Earth rotates around its own axis in slightly less than a day (in about 23 hours and 56 minutes). Earth's axis of rotation is tilted with respect to the perpendicular to its orbital plane around the Sun, producing seasons. Earth is orbited by one permanent natural satellite, the Moon, which orbits Earth at 384,400 km (1.28 light seconds) and is roughly a quarter as wide as Earth. Through tidal locking, the Moon always faces Earth with the same side, which causes tides, stabilizes Earth's axis, and gradually slows its rotation.
Earth, like most other bodies in the Solar System, formed 4.5 billion years ago from gas in the early Solar System. During the first billion years of Earth's history, the ocean formed and then life developed within it. Life spread globally and has been altering Earth's atmosphere and surface, leading to the Great Oxidation Event two billion years ago. Humans emerged 300,000 years ago in Africa and have spread across every continent on Earth with the exception of Antarctica. Humans depend on Earth's biosphere and natural resources for their survival, but have increasingly impacted the planet's environment. Humanity's current impact on Earth's climate and biosphere is unsustainable, threatening the livelihood of humans and many other forms of life, and causing widespread extinctions.
Etymology
The Modern English word Earth developed, via Middle English, from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their ancestral root has been reconstructed as *erþō. In its earliest attestation, the word eorðe was used to translate the many senses of Latin terra and Greek γῆ gē: the ground, its soil, dry land, the human world, the surface of the world (including the sea), and the globe itself. As with Roman Terra/Tellūs and Greek Gaia, Earth may have been a personified goddess in Germanic paganism: late Norse mythology included Jörð ("Earth"), a giantess often given as the mother of Thor.Historically, "earth" has been written in lowercase. Beginning with the use of Early Middle English, its definite sense as "the globe" was expressed as "the earth". By the era of Early Modern English, capitalization of nouns began to prevail, and the earth was also written the Earth, particularly when referenced along with other heavenly bodies. More recently, the name is sometimes simply given as Earth, by analogy with the names of the other planets, though "earth" and forms with "the earth" remain common. House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name, such as a description of the "Earth's atmosphere", but employs the lowercase when it is preceded by "the", such as "the atmosphere of the earth"). It almost always appears in lowercase in colloquial expressions such as "what on earth are you doing?"The name Terra occasionally is used in scientific writing and especially in science fiction to distinguish humanity's inhabited planet from others, while in poetry Tellus has been used to denote personification of the Earth. Terra is also the name of the planet in some Romance languages, languages that evolved from Latin, like Italian and Portuguese, while in other Romance languages the word gave rise to names with slightly altered spellings, like the Spanish Tierra and the French Terre. The Latinate form Gæa or Gaea (English: ) of the Greek poetic name Gaia (Γαῖα; Ancient Greek: [ɡâi̯.a] or [ɡâj.ja]) is rare, though the alternative spelling Gaia has become common due to the Gaia hypothesis, in which case its pronunciation is rather than the more classical English .There are a number of adjectives for the planet Earth. The word "earthly" is derived from "Earth". The word "Terra" is derived from the Latin word "terran" . The word "terrestrial" , is derived from the French word "terrene" . The world "tellurian" is derived from the Latin word "Tellus" and "telluric".
Natural history
Formation
The oldest material found in the Solar System is dated to 4.5682+0.0002−0.0004 Ga (billion years) ago. By 4.54±0.04 Ga the primordial Earth had formed. The bodies in the Solar System formed and evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, and dust (including primordial nuclides). According to nebular theory, planetesimals formed by accretion, with the primordial Earth being estimated as likely taking anywhere from 70 to 100 million years to form.Estimates of the age of the Moon range from 4.5 Ga to significantly younger. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object with about 10% of Earth's mass, named Theia, collided with Earth. It hit Earth with a glancing blow and some of its mass merged with Earth. Between approximately 4.1 and 3.8 Ga, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth.
After formation
Earth's atmosphere and oceans were formed by volcanic activity and outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids, protoplanets, and comets. Sufficient water to fill the oceans may have been on Earth since it formed. In this model, atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Ga, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.As the molten outer layer of Earth cooled it formed the first solid crust, which is thought to have been mafic in composition. The first continental crust, which was more felsic in composition, formed by the partial melting of this mafic crust. The presence of grains of the mineral zircon of Hadean age in Eoarchean sedimentary rocks suggests that at least some felsic crust existed as early as 4.4 Ga, only 140 Ma after Earth's formation. There are two main models of how this initial small volume of continental crust evolved to reach its current abundance: (1) a relatively steady growth up to the present day, which is supported by the radiometric dating of continental crust globally and (2) an initial rapid growth in the volume of continental crust during the Archean, forming the bulk of the continental crust that now exists, which is supported by isotopic evidence from hafnium in zircons and neodymium in sedimentary rocks. The two models and the data that support them can be reconciled by large-scale recycling of the continental crust, particularly during the early stages of Earth's history.New continental crust forms as a result of plate tectonics, a process ultimately driven by the continuous loss of heat from Earth's interior. Over the period of hundreds of millions of years, tectonic forces have caused areas of continental crust to group together to form supercontinents that have subsequently broken apart. At approximately 750 Ma, one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia at 600–540 Ma, then finally Pangaea, which also began to break apart at 180 Ma.The most recent pattern of ice ages began about 40 Ma, and then intensified during the Pleistocene about 3 Ma. High- and middle-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating about every 21,000, 41,000 and 100,000 years. The Last Glacial Period, colloquially called the "last ice age", covered large parts of the continents, to the middle latitudes, in ice and ended about 11,700 years ago.
Origin of life and evolution
Chemical reactions led to the first self-replicating molecules about four billion years ago. A half billion years later, the last common ancestor of all current life arose. The evolution of photosynthesis allowed the Sun's energy to be harvested directly by life forms. The resultant molecular oxygen (O2) accumulated in the atmosphere and due to interaction with ultraviolet solar radiation, formed a protective ozone layer (O3) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes. True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized Earth's surface. Among the earliest fossil evidence for life is microbial mat fossils found in 3.48 billion-year-old sandstone in Western Australia, biogenic graphite found in 3.7 billion-year-old metasedimentary rocks in Western Greenland, and remains of biotic material found in 4.1 billion-year-old rocks in Western Australia. The earliest direct evidence of life on Earth is contained in 3.45 billion-year-old Australian rocks showing fossils of microorganisms.During the Neoproterozoic, 1000 to 539 Ma, much of Earth might have been covered in ice. This hypothesis has been termed "Snowball Earth", and it is of particular interest because it preceded the Cambrian explosion, when multicellular life forms significantly increased in complexity. Following the Cambrian explosion, 535 Ma, there have been at least five major mass extinctions and many minor ones. Apart from the proposed current Holocene extinction event, the most recent was 66 Ma, when an asteroid impact triggered the extinction of the non-avian dinosaurs and other large reptiles, but largely spared small animals such as insects, mammals, lizards and birds. Mammalian life has diversified over the past 66 Mys, and several million years ago an African ape species gained the ability to stand upright. This facilitated tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which led to the evolution of humans. The development of agriculture, and then civilization, led to humans having an influence on Earth and the nature and quantity of other life forms that continues to this day.
Future
Earth's expected long-term future is tied to that of the Sun. Over the next 1.1 billion years, solar luminosity will increase by 10%, and over the next 3.5 billion years by 40%. Earth's increasing surface temperature will accelerate the inorganic carbon cycle, reducing CO2 concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in approximately 100–900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, making animal life impossible. Due to the increased luminosity, Earth's mean temperature may reach 100 °C (212 °F) in 1.5 billion years, and all ocean water will evaporate and be lost to space, which may trigger a runaway greenhouse effect, within an estimated 1.6 to 3 billion years. Even if the Sun were stable, a fraction of the water in the modern oceans will descend to the mantle, due to reduced steam venting from mid-ocean ridges.The Sun will evolve to become a red giant in about 5 billion years. Models predict that the Sun will expand to roughly 1 AU (150 million km; 93 million mi), about 250 times its present radius. Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, Earth will move to an orbit 1.7 AU (250 million km; 160 million mi) from the Sun when the star reaches its maximum radius, otherwise, with tidal effects, it may enter the Sun's atmosphere and be vaporized.
Physical characteristics
Size and shape
Earth has a rounded shape, through hydrostatic equilibrium, with an average diameter of 12,742 kilometers (7,918 mi), making it the fifth largest planetary sized and largest terrestrial object of the Solar System.
Due to Earth's rotation it has the shape of an ellipsoid, bulging at its Equator; its diameter is 43 kilometers (27 mi) longer there than at its poles.
Earth's shape furthermore has local topographic variations. Though the largest local variations, like the Mariana Trench (10,925 meters or 35,843 feet below local sea level), only shortens Earth's average radius by 0.17% and Mount Everest (8,848 meters or 29,029 feet above local sea level) lengthens it by only 0.14%. Since Earth's surface is farthest out from Earth's center of mass at its equatorial bulge, the summit of the volcano Chimborazo in Ecuador (6,384.4 km or 3,967.1 mi) is its farthest point out.
Parallel to the rigid land topography the Ocean exhibits a more dynamic topography.To measure the local variation of Earth's topography, geodesy employs an idealized Earth producing a shape called a geoid. Such a geoid shape is gained if the ocean is idealized, covering Earth completely and without any perturbations such as tides and winds. The result is a smooth but gravitational irregular geoid surface, providing a mean sea level (MSL) as a reference level for topographic measurements.
Surface
Earth's surface is the boundary between the atmosphere, and the solid Earth and oceans. Defined in this way, Earth's shape is an idealized spheroid – a squashed sphere – with a surface area of about 510 million km2 (197 million sq mi). Earth can be divided into two hemispheres: by latitude into the polar Northern and Southern hemispheres; or by longitude into the continental Eastern and Western hemispheres.
Most of Earth's surface is ocean water: 70.8% or 361 million km2 (139 million sq mi). This vast pool of salty water is often called the world ocean, and makes Earth with its dynamic hydrosphere a water world or ocean world. Indeed, in Earth's early history the ocean may have covered Earth completely. The world ocean is commonly divided into the Pacific Ocean, Atlantic Ocean, Indian Ocean, Antarctic or Southern Ocean, and Arctic Ocean, from largest to smallest. The ocean covers Earth's oceanic crust, but to a lesser extent with shelf seas also shelves of the continental crust. The oceanic crust forms large oceanic basins with features like abyssal plains, seamounts, submarine volcanoes, oceanic trenches, submarine canyons, oceanic plateaus, and a globe-spanning mid-ocean ridge system.
At Earth's polar regions, the ocean surface is covered by seasonally variable amounts of sea ice that often connects with polar land, permafrost and ice sheets, forming polar ice caps.
Earth's land covers 29.2%, or 149 million km2 (58 million sq mi) of Earth's surface. The land surface includes many islands around the globe, but most of the land surface is taken by the four continental landmasses, which are (in descending order): Africa-Eurasia, America (landmass), Antarctica, and Australia (landmass). These landmasses are further broken down and grouped into the continents. The terrain of the land surface varies greatly and consists of mountains, deserts, plains, plateaus, and other landforms. The elevation of the land surface varies from a low point of −418 m (−1,371 ft) at the Dead Sea, to a maximum altitude of 8,848 m (29,029 ft) at the top of Mount Everest. The mean height of land above sea level is about 797 m (2,615 ft).Land can be covered by surface water, snow, ice, artificial structures or vegetation. Most of Earth's land hosts vegetation, but ice sheets (10%, not including the equally large land under permafrost) or cold as well as hot deserts (33%) occupy also considerable amounts of it.
The pedosphere is the outermost layer of Earth's land surface and is composed of soil and subject to soil formation processes. Soil is crucial for land to be arable. Earth's total arable land is 10.7% of the land surface, with 1.3% being permanent cropland. Earth has an estimated 16.7 million km2 (6.4 million sq mi) of cropland and 33.5 million km2 (12.9 million sq mi) of pastureland.The land surface and the ocean floor form the top of Earth's crust, which together with parts of the upper mantle form Earth's lithosphere. Earth's crust may be divided into oceanic and continental crust. Beneath the ocean-floor sediments, the oceanic crust is predominantly basaltic, while the continental crust may include lower density materials such as granite, sediments and metamorphic rocks. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form about 5% of the mass of the crust.Earth's surface topography comprises both the topography of the ocean surface, and the shape of Earth's land surface. The submarine terrain of the ocean floor has an average bathymetric depth of 4 km, and is as varied as the terrain above sea level.
Earth's surface is continually being shaped by internal plate tectonic processes including earthquakes and volcanism; by weathering and erosion driven by ice, water, wind and temperature; and by biological processes including the growth and decomposition of biomass into soil.
Tectonic plates
Earth's mechanically rigid outer layer of Earth's crust and upper mantle, the lithosphere, is divided into tectonic plates. These plates are rigid segments that move relative to each other at one of three boundaries types: at convergent boundaries, two plates come together; at divergent boundaries, two plates are pulled apart; and at transform boundaries, two plates slide past one another laterally. Along these plate boundaries, earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur. The tectonic plates ride on top of the asthenosphere, the solid but less-viscous part of the upper mantle that can flow and move along with the plates.As the tectonic plates migrate, oceanic crust is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes recycles the oceanic crust back into the mantle. Due to this recycling, most of the ocean floor is less than 100 Ma old. The oldest oceanic crust is located in the Western Pacific and is estimated to be 200 Ma old. By comparison, the oldest dated continental crust is 4,030 Ma, although zircons have been found preserved as clasts within Eoarchean sedimentary rocks that give ages up to 4,400 Ma, indicating that at least some continental crust existed at that time.The seven major plates are the Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, and South American. Other notable plates include the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. The Australian Plate fused with the Indian Plate between 50 and 55 Ma. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/a (3.0 in/year) and the Pacific Plate moving 52–69 mm/a (2.0–2.7 in/year). At the other extreme, the slowest-moving plate is the South American Plate, progressing at a typical rate of 10.6 mm/a (0.42 in/year).
Internal structure
Earth's interior, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties. The outer layer is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity. The thickness of the crust varies from about 6 kilometers (3.7 mi) under the oceans to 30–50 km (19–31 mi) for the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, which is divided into independently moving tectonic plates.Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 km (250 and 410 mi) below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core. Earth's inner core may be rotating at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year, although both somewhat higher and much lower rates have also been proposed. The radius of the inner core is about one-fifth of that of Earth.
Density increases with depth, as described in the table on the right.
Among the Solar System's planetary-sized objects Earth is the object with the highest density.
Chemical composition
Earth's mass is approximately 5.97×1024 kg (5,970 Yg). It is composed mostly of iron (32.1% by mass), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminum (1.4%), with the remaining 1.2% consisting of trace amounts of other elements. Due to gravitational separation, the core is primarily composed of the denser elements: iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements. The most common rock constituents of the crust are oxides. Over 99% of the crust is composed of various oxides of eleven elements, principally oxides containing silicon (the silicate minerals), aluminum, iron, calcium, magnesium, potassium, or sodium.
Internal heat
The major heat-producing isotopes within Earth are potassium-40, uranium-238, and thorium-232. At the center, the temperature may be up to 6,000 °C (10,830 °F), and the pressure could reach 360 GPa (52 million psi). Because much of the heat is provided by radioactive decay, scientists postulate that early in Earth's history, before isotopes with short half-lives were depleted, Earth's heat production was much higher. At approximately 3 Gyr, twice the present-day heat would have been produced, increasing the rates of mantle convection and plate tectonics, and allowing the production of uncommon igneous rocks such as komatiites that are rarely formed today.The mean heat loss from Earth is 87 mW m−2, for a global heat loss of 4.42×1013 W. A portion of the core's thermal energy is transported toward the crust by mantle plumes, a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts. More of the heat in Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs under the oceans because the crust there is much thinner than that of the continents.
Gravitational field
The gravity of Earth is the acceleration that is imparted to objects due to the distribution of mass within Earth. Near Earth's surface, gravitational acceleration is approximately 9.8 m/s2 (32 ft/s2). Local differences in topography, geology, and deeper tectonic structure cause local and broad regional differences in Earth's gravitational field, known as gravity anomalies.
Magnetic field
The main part of Earth's magnetic field is generated in the core, the site of a dynamo process that converts the kinetic energy of thermally and compositionally driven convection into electrical and magnetic field energy. The field extends outwards from the core, through the mantle, and up to Earth's surface, where it is, approximately, a dipole. The poles of the dipole are located close to Earth's geographic poles. At the equator of the magnetic field, the magnetic-field strength at the surface is 3.05×10−5 T, with a magnetic dipole moment of 7.79×1022 Am2 at epoch 2000, decreasing nearly 6% per century (although it still remains stronger than its long time average). The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes secular variation of the main field and field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.The extent of Earth's magnetic field in space defines the magnetosphere. Ions and electrons of the solar wind are deflected by the magnetosphere; solar wind pressure compresses the dayside of the magnetosphere, to about 10 Earth radii, and extends the nightside magnetosphere into a long tail. Because the velocity of the solar wind is greater than the speed at which waves propagate through the solar wind, a supersonic bow shock precedes the dayside magnetosphere within the solar wind. Charged particles are contained within the magnetosphere; the plasmasphere is defined by low-energy particles that essentially follow magnetic field lines as Earth rotates. The ring current is defined by medium-energy particles that drift relative to the geomagnetic field, but with paths that are still dominated by the magnetic field, and the Van Allen radiation belts are formed by high-energy particles whose motion is essentially random, but contained in the magnetosphere.During magnetic storms and substorms, charged particles can be deflected from the outer magnetosphere and especially the magnetotail, directed along field lines into Earth's ionosphere, where atmospheric atoms can be excited and ionized, causing the aurora.
Orbit and rotation
Rotation
Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time (86,400.0025 SI seconds). Because Earth's solar day is now slightly longer than it was during the 19th century due to tidal deceleration, each day varies between 0 and 2 ms longer than the mean solar day.Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86,164.0989 seconds of mean solar time (UT1), or 23h 56m 4.0989s. Earth's rotation period relative to the precessing or moving mean March equinox (when the Sun is at 90° on the equator), is 86,164.0905 seconds of mean solar time (UT1) (23h 56m 4.0905s). Thus the sidereal day is shorter than the stellar day by about 8.4 ms.Apart from meteors within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in Earth's sky is to the west at a rate of 15°/h = 15'/min. For bodies near the celestial equator, this is equivalent to an apparent diameter of the Sun or the Moon every two minutes; from Earth's surface, the apparent sizes of the Sun and the Moon are approximately the same.
Orbit
Earth orbits the Sun, making Earth the third-closest planet to the Sun and part of the inner Solar System. Earth's average orbital distance is about 150 million km (93 million mi), which is the basis for the Astronomical Unit and is equal to roughly 8.3 light minutes or 380 times Earth's distance to the Moon.
Earth orbits the Sun every 365.2564 mean solar days, or one sidereal year. With an apparent movement of the Sun in Earth's sky at a rate of about 1°/day eastward, which is one apparent Sun or Moon diameter every 12 hours. Due to this motion, on average it takes 24 hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the meridian.
The orbital speed of Earth averages about 29.78 km/s (107,200 km/h; 66,600 mph), which is fast enough to travel a distance equal to Earth's diameter, about 12,742 km (7,918 mi), in seven minutes, and the distance to the Moon, 384,000 km (239,000 mi), in about 3.5 hours.The Moon and Earth orbit a common barycenter every 27.32 days relative to the background stars. When combined with the Earth–Moon system's common orbit around the Sun, the period of the synodic month, from new moon to new moon, is 29.53 days. Viewed from the celestial north pole, the motion of Earth, the Moon, and their axial rotations are all counterclockwise. Viewed from a vantage point above the Sun and Earth's north poles, Earth orbits in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.44 degrees from the perpendicular to the Earth–Sun plane (the ecliptic), and the Earth-Moon plane is tilted up to ±5.1 degrees against the Earth–Sun plane. Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses.The Hill sphere, or the sphere of gravitational influence, of Earth is about 1.5 million km (930,000 mi) in radius. This is the maximum distance at which Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun. Earth, along with the Solar System, is situated in the Milky Way and orbits about 28,000 light-years from its center. It is about 20 light-years above the galactic plane in the Orion Arm.
Axial tilt and seasons
The axial tilt of Earth is approximately 23.439281° with the axis of its orbit plane, always pointing towards the Celestial Poles. Due to Earth's axial tilt, the amount of sunlight reaching any given point on the surface varies over the course of the year. This causes the seasonal change in climate, with summer in the Northern Hemisphere occurring when the Tropic of Cancer is facing the Sun, and in the Southern Hemisphere when the Tropic of Capricorn faces the Sun. In each instance, winter occurs simultaneously in the opposite hemisphere.
During the summer, the day lasts longer, and the Sun climbs higher in the sky. In winter, the climate becomes cooler and the days shorter. Above the Arctic Circle and below the Antarctic Circle there is no daylight at all for part of the year, causing a polar night, and this night extends for several months at the poles themselves. These same latitudes also experience a midnight sun, where the sun remains visible all day.By astronomical convention, the four seasons can be determined by the solstices—the points in the orbit of maximum axial tilt toward or away from the Sun—and the equinoxes, when Earth's rotational axis is aligned with its orbital axis. In the Northern Hemisphere, winter solstice currently occurs around 21 December; summer solstice is near 21 June, spring equinox is around 20 March and autumnal equinox is about 22 or 23 September. In the Southern Hemisphere, the situation is reversed, with the summer and winter solstices exchanged and the spring and autumnal equinox dates swapped.The angle of Earth's axial tilt is relatively stable over long periods of time. Its axial tilt does undergo nutation; a slight, irregular motion with a main period of 18.6 years. The orientation (rather than the angle) of Earth's axis also changes over time, precessing around in a complete circle over each 25,800-year cycle; this precession is the reason for the difference between a sidereal year and a tropical year. Both of these motions are caused by the varying attraction of the Sun and the Moon on Earth's equatorial bulge. The poles also migrate a few meters across Earth's surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. Earth's rotational velocity also varies in a phenomenon known as length-of-day variation.In modern times, Earth's perihelion occurs around 3 January, and its aphelion around 4 July. These dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. The changing Earth–Sun distance causes an increase of about 6.8% in solar energy reaching Earth at perihelion relative to aphelion. Because the Southern Hemisphere is tilted toward the Sun at about the same time that Earth reaches the closest approach to the Sun, the Southern Hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. This effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of water in the Southern Hemisphere.
Earth–Moon system
Moon
The Moon is a relatively large, terrestrial, planet-like natural satellite, with a diameter about one-quarter of Earth's. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger relative to the dwarf planet Pluto. The natural satellites of other planets are also referred to as "moons", after Earth's. The most widely accepted theory of the Moon's origin, the giant-impact hypothesis, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. This hypothesis explains the Moon's relative lack of iron and volatile elements and the fact that its composition is nearly identical to that of Earth's crust.The gravitational attraction between Earth and the Moon causes tides on Earth. The same effect on the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit Earth. As a result, it always presents the same face to the planet. As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases. Due to their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm/a (1.5 in/year). Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23 µs/yr—add up to significant changes. During the Ediacaran period, for example, (approximately 620 Ma) there were 400±7 days in a year, with each day lasting 21.9±0.4 hours.The Moon may have dramatically affected the development of life by moderating the planet's climate. Paleontological evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon. Some theorists think that without this stabilization against the torques applied by the Sun and planets to Earth's equatorial bulge, the rotational axis might be chaotically unstable, exhibiting large changes over millions of years, as is the case for Mars, though this is disputed.Viewed from Earth, the Moon is just far enough away to have almost the same apparent-sized disk as the Sun. The angular size (or solid angle) of these two bodies match because, although the Sun's diameter is about 400 times as large as the Moon's, it is also 400 times more distant. This allows total and annular solar eclipses to occur on Earth.On 1 November 2023, scientists reported that, according to computer simulations, remnants of a protoplanet, named Theia, could be inside the Earth, left over from a collision with the Earth in ancient times, and afterwards becoming the Moon.
Asteroids and artificial satellites
Earth's co-orbital asteroids population consists of quasi-satellites, objects with a horseshoe orbit and trojans. There are at least five quasi-satellites, including 469219 Kamoʻoalewa. A trojan asteroid companion, 2010 TK7, is librating around the leading Lagrange triangular point, L4, in Earth's orbit around the Sun. The tiny near-Earth asteroid 2006 RH120 makes close approaches to the Earth–Moon system roughly every twenty years. During these approaches, it can orbit Earth for brief periods of time.As of September 2021, there are 4,550 operational, human-made satellites orbiting Earth. There are also inoperative satellites, including Vanguard 1, the oldest satellite currently in orbit, and over 16,000 pieces of tracked space debris. Earth's largest artificial satellite is the International Space Station.
Hydrosphere
Earth's hydrosphere is the sum of Earth's water and its distribution. Most of Earth's hydrosphere consists of Earth's global ocean. Earth's hydrosphere also consists of water in the atmosphere and on land, including clouds, inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m (6,600 ft).
The mass of the oceans is approximately 1.35×1018 metric tons or about 1/4400 of Earth's total mass. The oceans cover an area of 361.8 million km2 (139.7 million sq mi) with a mean depth of 3,682 m (12,080 ft), resulting in an estimated volume of 1.332 billion km3 (320 million cu mi). If all of Earth's crustal surface were at the same elevation as a smooth sphere, the depth of the resulting world ocean would be 2.7 to 2.8 km (1.68 to 1.74 mi). About 97.5% of the water is saline; the remaining 2.5% is fresh water. Most fresh water, about 68.7%, is present as ice in ice caps and glaciers. The remaining 30% is ground water, 1% surface water (covering only 2.8% of Earth's land) and other small forms of fresh water deposits such as permafrost, water vapor in the atmosphere, biological binding, etc. .In Earth's coldest regions, snow survives over the summer and changes into ice. This accumulated snow and ice eventually forms into glaciers, bodies of ice that flow under the influence of their own gravity. Alpine glaciers form in mountainous areas, whereas vast ice sheets form over land in polar regions. The flow of glaciers erodes the surface changing it dramatically, with the formation of U-shaped valleys and other landforms. Sea ice in the Arctic covers an area about as big as the United States, although it is quickly retreating as a consequence of climate change.The average salinity of Earth's oceans is about 35 grams of salt per kilogram of seawater (3.5% salt). Most of this salt was released from volcanic activity or extracted from cool igneous rocks. The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms. Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir. Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño–Southern Oscillation.The abundance of water, particularly liquid water, on Earth's surface is a unique feature that distinguishes it from other planets in the Solar System. Solar System planets with considerable atmospheres do partly host atmospheric water vapor, but they lack surface conditions for stable surface water. Despite some moons showing signs of large reservoirs of extraterrestrial liquid water, with possibly even more volume than Earth's ocean, all of them are large bodies of water under a kilometers thick frozen surface layer.
Atmosphere
The atmospheric pressure at Earth's sea level averages 101.325 kPa (14.696 psi), with a scale height of about 8.5 km (5.3 mi). A dry atmosphere is composed of 78.084% nitrogen, 20.946% oxygen, 0.934% argon, and trace amounts of carbon dioxide and other gaseous molecules. Water vapor content varies between 0.01% and 4% but averages about 1%. Clouds cover around two thirds of Earth's surface, more so over oceans than land. The height of the troposphere varies with latitude, ranging between 8 km (5 mi) at the poles to 17 km (11 mi) at the equator, with some variation resulting from weather and seasonal factors.Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 Gya, forming the primarily nitrogen–oxygen atmosphere of today. This change enabled the proliferation of aerobic organisms and, indirectly, the formation of the ozone layer due to the subsequent conversion of atmospheric O2 into O3. The ozone layer blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature. This last phenomenon is the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the surface, thereby raising the average temperature. Water vapor, carbon dioxide, methane, nitrous oxide, and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C (0 °F), in contrast to the current +15 °C (59 °F), and life on Earth probably would not exist in its current form.
Weather and climate
Earth's atmosphere has no definite boundary, gradually becoming thinner and fading into outer space. Three-quarters of the atmosphere's mass is contained within the first 11 km (6.8 mi) of the surface; this lowest layer is called the troposphere. Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower-density air then rises and is replaced by cooler, higher-density air. The result is atmospheric circulation that drives the weather and climate through redistribution of thermal energy.The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°. Ocean heat content and currents are also important factors in determining climate, particularly the thermohaline circulation that distributes thermal energy from the equatorial oceans to the polar regions.Earth receives 1361 W/m2 of solar irradiance. The amount of solar energy that reaches Earth's surface decreases with increasing latitude. At higher latitudes, the sunlight reaches the surface at lower angles, and it must pass through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level decreases by about 0.4 °C (0.7 °F) per degree of latitude from the equator. Earth's surface can be subdivided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, temperate and polar climates.Further factors that affect a location's climates are its proximity to oceans, the oceanic and atmospheric circulation, and topology. Places close to oceans typically have colder summers and warmer winters, due to the fact that oceans can store large amounts of heat. The wind transports the cold or the heat of the ocean to the land. Atmospheric circulation also plays an important role: San Francisco and Washington DC are both coastal cities at about the same latitude. San Francisco's climate is significantly more moderate as the prevailing wind direction is from sea to land. Finally, temperatures decrease with height causing mountainous areas to be colder than low-lying areas.Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and falls to the surface as precipitation. Most of the water is then transported to lower elevations by river systems and usually returned to the oceans or deposited into lakes. This water cycle is a vital mechanism for supporting life on land and is a primary factor in the erosion of surface features over geological periods. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topographic features, and temperature differences determine the average precipitation that falls in each region.The commonly used Köppen climate classification system has five broad groups (humid tropics, arid, humid middle latitudes, continental and cold polar), which are further divided into more specific subtypes. The Köppen system rates regions based on observed temperature and precipitation. Surface air temperature can rise to around 55 °C (131 °F) in hot deserts, such as Death Valley, and can fall as low as −89 °C (−128 °F) in Antarctica.
Upper atmosphere
The upper atmosphere, the atmosphere above the troposphere, is usually divided into the stratosphere, mesosphere, and thermosphere. Each layer has a different lapse rate, defining the rate of change in temperature with height. Beyond these, the exosphere thins out into the magnetosphere, where the geomagnetic fields interact with the solar wind. Within the stratosphere is the ozone layer, a component that partially shields the surface from ultraviolet light and thus is important for life on Earth. The Kármán line, defined as 100 km (62 mi) above Earth's surface, is a working definition for the boundary between the atmosphere and outer space.Thermal energy causes some of the molecules at the outer edge of the atmosphere to increase their velocity to the point where they can escape from Earth's gravity. This causes a slow but steady loss of the atmosphere into space. Because unfixed hydrogen has a low molecular mass, it can achieve escape velocity more readily, and it leaks into outer space at a greater rate than other gases. The leakage of hydrogen into space contributes to the shifting of Earth's atmosphere and surface from an initially reducing state to its current oxidizing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is thought to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere. Hence the ability of hydrogen to escape from the atmosphere may have influenced the nature of life that developed on Earth. In the current, oxygen-rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.
Life on Earth
Earth is the only known place that has ever been habitable for life. Earth's life developed in Earth's early bodies of water some hundred million years after Earth formed.
Earth's life has been shaping and inhabiting many particular ecosystems on Earth and has eventually expanded globally forming an overarching biosphere. Therefore, life has impacted Earth, significantly altering Earth's atmosphere and surface over long periods of time, causing changes like the Great Oxidation Event.Earth's life has over time greatly diversified, allowing the biosphere to have different biomes, which are inhabited by comparatively similar plants and animals. The different biomes developed at distinct elevations or water depths, planetary temperature latitudes and on land also with different humidity. Earth's species diversity and biomass reaches a peak in shallow waters and with forests, particularly in equatorial, warm and humid conditions. While freezing polar regions and high altitudes, or extremely arid areas are relatively barren of plant and animal life.Earth provides liquid water—an environment where complex organic molecules can assemble and interact, and sufficient energy to sustain a metabolism. Plants and other organisms take up nutrients from water, soils and the atmosphere. These nutrients are constantly recycled between different species.Extreme weather, such as tropical cyclones (including hurricanes and typhoons), occurs over most of Earth's surface and has a large impact on life in those areas. From 1980 to 2000, these events caused an average of 11,800 human deaths per year. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, blizzards, floods, droughts, wildfires, and other calamities and disasters. Human impact is felt in many areas due to pollution of the air and water, acid rain, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion and erosion. Human activities release greenhouse gases into the atmosphere which cause global warming. This is driving changes such as the melting of glaciers and ice sheets, a global rise in average sea levels, increased risk of drought and wildfires, and migration of species to colder areas.
Human geography
Originating from earlier primates in Eastern Africa 300,000 years ago humans have since been migrating and with the advent of agriculture in the 10th millennium BC increasingly settling Earth's land. In the 20th century Antarctica had been the last continent to see a first and until today limited human presence.
Human population has since the 19th century grown exponentially to seven billion in the early 2010s, and is projected to peak at around ten billion in the second half of the 21st century. Most of the growth is expected to take place in sub-Saharan Africa.Distribution and density of human population varies greatly around the world with the majority living in south to eastern Asia and 90% inhabiting only the Northern Hemisphere of Earth, partly due to the hemispherical predominance of the world's land mass, with 68% of the world's land mass being in the Northern Hemisphere. Furthermore, since the 19th century humans have increasingly converged into urban areas with the majority living in urban areas by the 21st century.Beyond Earth's surface humans have lived on a temporary basis, with only special purpose deep underground and underwater presence, and a few space stations. Human population virtually completely remains on Earth's surface, fully depending on Earth and the environment it sustains. Since the second half of the 20th century, some hundreds of humans have temporarily stayed beyond Earth, a tiny fraction of whom have reached another celestial body, the Moon.Earth has been subject to extensive human settlement, and humans have developed diverse societies and cultures. Most of Earth's land has been territorially claimed since the 19th century by sovereign states (countries) separated by political borders, and more than 200 such states exist today, with only parts of Antarctica and few small regions remaining unclaimed. Most of these states together form the United Nations, the leading worldwide intergovernmental organization, which extends human governance over the ocean and Antarctica, and therefore all of Earth.
Natural resources and land use
Earth has resources that have been exploited by humans. Those termed non-renewable resources, such as fossil fuels, are only replenished over geological timescales. Large deposits of fossil fuels are obtained from Earth's crust, consisting of coal, petroleum, and natural gas. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed within the crust through a process of ore genesis, resulting from actions of magmatism, erosion, and plate tectonics. These metals and other elements are extracted by mining, a process which often brings environmental and health damage.Earth's biosphere produces many useful biological products for humans, including food, wood, pharmaceuticals, oxygen, and the recycling of organic waste. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends on dissolved nutrients washed down from the land. In 2019, 39 million km2 (15 million sq mi) of Earth's land surface consisted of forest and woodlands, 12 million km2 (4.6 million sq mi) was shrub and grassland, 40 million km2 (15 million sq mi) were used for animal feed production and grazing, and 11 million km2 (4.2 million sq mi) were cultivated as croplands. Of the 12–14% of ice-free land that is used for croplands, 2 percentage points were irrigated in 2015. Humans use building materials to construct shelters.
Humans and the environment
Human activities have impacted Earth's environments. Through activities such as the burning of fossil fuels, humans have been increasing the amount of greenhouse gases in the atmosphere, altering Earth's energy budget and climate. It is estimated that global temperatures in the year 2020 were 1.2 °C (2.2 °F) warmer than the preindustrial baseline. This increase in temperature, known as global warming, has contributed to the melting of glaciers, rising sea levels, increased risk of drought and wildfires, and migration of species to colder areas.The concept of planetary boundaries was introduced to quantify humanity's impact on Earth. Of the nine identified boundaries, five have been crossed: Biosphere integrity, climate change, chemical pollution, destruction of wild habitats and the nitrogen cycle are thought to have passed the safe threshold. As of 2018, no country meets the basic needs of its population without transgressing planetary boundaries. It is thought possible to provide all basic physical needs globally within sustainable levels of resource use.
Cultural and historical viewpoint
Human cultures have developed many views of the planet. The standard astronomical symbols of Earth are a quartered circle, , representing the four corners of the world, and a globus cruciger, . Earth is sometimes personified as a deity. In many cultures it is a mother goddess that is also the primary fertility deity. Creation myths in many religions involve the creation of Earth by a supernatural deity or deities. The Gaia hypothesis, developed in the mid-20th century, compared Earth's environments and life as a single self-regulating organism leading to broad stabilization of the conditions of habitability.Images of Earth taken from space, particularly during the Apollo program, have been credited with altering the way that people viewed the planet that they lived on, called the overview effect, emphasizing its beauty, uniqueness and apparent fragility. In particular, this caused a realization of the scope of effects from human activity on Earth's environment. Enabled by science, particularly Earth observation, humans have started to take action on environmental issues globally, acknowledging the impact of humans and the interconnectedness of Earth's environments.
Scientific investigation has resulted in several culturally transformative shifts in people's view of the planet. Initial belief in a flat Earth was gradually displaced in Ancient Greece by the idea of a spherical Earth, which was attributed to both the philosophers Pythagoras and Parmenides. Earth was generally believed to be the center of the universe until the 16th century, when scientists first concluded that it was a moving object, one of the planets of the Solar System.It was only during the 19th century that geologists realized Earth's age was at least many millions of years. Lord Kelvin used thermodynamics to estimate the age of Earth to be between 20 million and 400 million years in 1864, sparking a vigorous debate on the subject; it was only when radioactivity and radioactive dating were discovered in the late 19th and early 20th centuries that a reliable mechanism for determining Earth's age was established, proving the planet to be billions of years old.
See also
Notes
References
External links
Earth – Profile – Solar System Exploration – NASA
Earth Observatory – NASA
Earth – Videos – International Space Station:
Video (01:02) on YouTube – Earth (time-lapse)
Video (00:27) on YouTube – Earth and auroras (time-lapse)
Google Earth 3D, interactive map
Interactive 3D visualization of the Sun, Earth and Moon system
GPlates Portal (University of Sydney) |
historical geology | Historical geology or palaeogeology is a discipline that uses the principles and methods of geology to reconstruct the geological history of Earth. Historical geology examines the vastness of geologic time, measured in billions of years, and investigates changes in the Earth, gradual and sudden, over this deep time. It focuses on geological processes, such as plate tectonics, that have changed the Earth's surface and subsurface over time and the use of methods including stratigraphy, structural geology, paleontology, and sedimentology to tell the sequence of these events. It also focuses on the evolution of life during different time periods in the geologic time scale.
Historical development
During the 17th century, Nicolas Steno was the first to observe and propose a number of basic principles of historical geology, including three key stratigraphic principles: the law of superposition, the principle of original horizontality, and the principle of lateral continuity.18th-century geologist James Hutton contributed to an early understanding of the Earth's history by proposing the theory of uniformitarianism, which is now a basic principle in all branches of geology. Uniformitarianism describes an Earth formed by the same natural phenomena that are at work today, the product of slow and continuous geological changes. The theory can be summarized by the phrase "the present is the key to the past." Hutton also described the concept of deep time. The prevailing conceptualization of Earth history in 18th-century Europe, grounded in a literal interpretation of Christian scripture, was that of a young Earth shaped by catastrophic events. Hutton, however, depicted a very old Earth, shaped by slow, continuous change. Charles Lyell further developed the theory of uniformitarianism in the 19th century. Modern geologists have generally acknowledged that Earth's geological history is a product of both sudden, cataclysmic events (such as meteorite impacts and volcanic eruptions) and gradual processes (such as weathering, erosion, and deposition).
The discovery of radioactive decay in the late 19th century and the development of radiometric dating techniques in the 20th century provided a means of deriving absolute ages of events in geological history.
Use and importance
Geology is considered a historical science; accordingly, historical geology plays a prominent role in the field.Historical geology covers much of the same subject matter as physical geology, the study of geological processes and the ways in which they shape the Earth's structure and composition. Historical geology extends physical geology into the past.Economic geology, the search for and extraction of fuel and raw materials, is heavily dependent on an understanding of the geological history of an area. Environmental geology, which examines the impacts of natural hazards such as earthquakes and volcanism, must rely on a detailed knowledge of geological history.
Methods
Stratigraphy
Layers of rock, or strata, represent a geologic record of Earth's history. Stratigraphy is the study of strata: their order, position, and age.
Structural geology
Structural geology is concerned with rocks' deformational histories.
Paleontology
Fossils are organic traces of Earth's history. In a historical geology context, paleontological methods can be used to study fossils and their environments, including surrounding rocks, and place them within the geologic time scale.
Sedimentology
Sedimentology is the study of the formation, transport, deposition, and diagenesis of sediments. Sedimentary rocks, including limestone, sandstone, and shale, serve as a record of Earth's history: they contain fossils and are transformed by geological processes, such as weathering, erosion, and deposition, through deep time.
Relative dating
Historical geology makes use of relative dating in order to establish the sequence of geological events in relation to each another, without determining their specific numerical ages or ranges.
Absolute dating
Absolute dating allows geologists to determine a more precise chronology of geological events, based on numerical ages or ranges. Absolute dating includes the use of radiometric dating methods, such as radiocarbon dating, potassium–argon dating, and uranium–lead dating. Luminescence dating, dendrochronology, and amino acid dating are other methods of absolute dating.
Plate tectonics
The theory of plate tectonics explains how the movement of lithospheric plates has structured the Earth throughout its geological history.
Weathering, erosion, and deposition
Weathering, erosion, and deposition are examples of gradual geological processes, taking place over large sections of the geologic time scale. In the rock cycle, rocks are continually broken down, transported, and deposited, cycling through three main rock types: sedimentary, metamorphic, and igneous.
Paleoclimatology
Paleoclimatology is the study of past climates recorded in geological time.
Brief geological history
External links
Geology – Earth history | Encyclopedia Britannica
Historical Geology | OpenGeology.org
GEOL 102 Historical Geology | Lecture notes for course at the University of Maryland
== Notes == |
principle of faunal succession | The principle of faunal succession, also known as the law of faunal succession, is based on the observation that sedimentary rock strata contain fossilized flora and fauna, and that these fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances. A fossilized Neanderthal bone (less than 500,000 years old) will never be found in the same stratum as a fossilized Megalosaurus (about 160 million years old), for example, because neanderthals and megalosaurs lived during different geological periods, separated by millions of years. This allows for strata to be identified and dated by the fossils found within.
This principle, which received its name from the English geologist William Smith, is of great importance in determining the relative age of rocks and strata. The fossil content of rocks together with the law of superposition helps to determine the time sequence in which sedimentary rocks were laid down.
Evolution explains the observed faunal and floral succession preserved in rocks. Faunal succession was documented by Smith in England during the first decade of the 19th century, and concurrently in France by Cuvier (with the assistance of the mineralogist Alexandre Brongniart). Archaic biological features and organisms are succeeded in the fossil record by more modern versions. For instance, paleontologists investigating the evolution of birds predicted that feathers would first be seen in primitive forms on flightless predecessor organisms such as feathered dinosaurs. This is precisely what has been discovered in the fossil record: simple feathers, incapable of supporting flight, are succeeded by increasingly large and complex feathers.In practice, the most useful diagnostic species are those with the fastest rate of species turnover and the widest distribution; their study is termed biostratigraphy, the science of dating rocks by using the fossils contained within them. In Cenozoic strata, fossilized tests of foraminifera are often used to determine faunal succession on a refined scale, each biostratigraphic unit (biozone) being a geological stratum that is defined on the basis of its characteristic fossil taxa. An outline microfaunal zonal scheme based on both foraminifera and ostracoda was compiled by M. B. Hart (1972).
Earlier fossil life forms are simpler than more recent forms, and more recent fossil forms are more similar to living forms (principle of faunal succession).
See also
Index fossil
Law of superposition
Principle of cross-cutting relationships
Principle of lateral continuity
Principle of original horizontality
== References == |
trivia | Trivia is information and data that are considered to be of little value. The word is derived from the Latin word triviae, meaning a place where a road split into two (thus, creating a three-way intersection). It was introduced into English as the adjective trivial in the 15th and 16th centuries.
Modern usage of the term trivia dates back to the 1960s, when college students introduced question-and-answer contests to their universities. A board game, Trivial Pursuit, was released in 1982 in the same vein as these contests. Since the beginning of its modern usage, trivia contests have been established at various academic levels as well as casual venues such as bars and restaurants.
Latin etymology
The ancient Romans used the word triviae to describe where one road split or forked into two roads. Triviae was formed from tri (three) and viae (roads) – literally meaning "three roads", and in transferred use "a public place" and hence the meaning "commonplace."
The Latin adjective triviālis in Classical Latin besides its literal meaning could have the meaning "appropriate to the street corner, commonplace, vulgar." In late Latin, it could also simply mean "triple."
In medieval Latin, the trivia (singular trivium) came to refer to the lower division of the Artes Liberales: grammar, rhetoric, and logic. These were the topics of basic education, and were foundational to the quadrivia of higher education: arithmetic, geometry, music, and astronomy.
English usage
The adjective trivial introduced into English in the 15th to 16th century was influenced by all three meanings of the Latin adjective:
A 15th century English translation of Ranulf Higden mentions the arte trivialle, referring to the trivium of the Liberal Arts.
The same work also calls a triuialle distinccion a threefold division. This is due to an application of the term by Arnobius, and was never common either in Latin or English.
The meaning "trite, commonplace, unimportant, slight" occurs from the late 16th century, notably in the works of Shakespeare.Trivia was used as a title by Logan Pearsall Smith in 1902, followed by More Trivia and All Trivia in 1921 and 1933, respectively, collections of short "moral pieces" or aphorisms. Book II of the 1902 publication is headed with a quote from "Gay's Trivia, or New Art of Walking Streets of London.",
"Thou, Trivia, goddess, aid my song: Through spacious streets conduct thy bard along."
Modern usage
Trivialities, bits of information of little consequence was the title of a popular book by British aphorist Logan Pearsall Smith (1865–1946), first published in 1902 but popularized in 1918 (with More Trivia following in 1921 and a collected edition including both in 1933). It consisted of short essays often tied to observation of small things and commonplace moments. Trivia is the plural of trivium, "a public place." The adjectival form of this, trivialis, was hence translated by Smith as "commonplace."In the 1918 version of his book Trivia, Smith wrote:
I know too much; I have stuffed too many of the facts of History and Science into my intellectuals. My eyes have grown dim over books; believing in geological periods, cave dwellers, Chinese Dynasties, and the fixed stars has prematurely aged me.
In the 1960s, nostalgic college students and others began to informally trade questions and answers about the popular culture of their youth. The first known documented labeling of this casual parlor game as "Trivia" was in a Columbia Daily Spectator column published on February 5, 1965. The author, Ed Goodgold, then started the first organized "trivia contests" with the help of Dan Carlinsky. Ed and Dan wrote the book Trivia (Dell, 1966), which achieved a ranking on the New York Times best-seller list; the book was an extension of the pair's Columbia contests and was followed by other Goodgold and Carlinsky trivia titles. In their second book, More Trivial Trivia, the authors criticized practitioners who were "indiscriminate enough to confuse the flower of trivia with the weed of minutiae"; Trivia, they wrote, "is concerned with tugging at heartstrings," while minutiae deals with such unevocative questions as "Which state is the largest consumer of Jell-O?" The board game Trivial Pursuit was released in 1982 and was a craze in the U.S. for several years thereafter.
Organized competition
The largest current trivia contest is held in Stevens Point, Wisconsin, at the University of Wisconsin–Stevens Point's college radio station WWSP 89.9 FM. This is a student-run community station with 30,000 watts of power and about a 65-mile (105-kilometre) radius, and the contest serves as a fund raiser for the station. The contest is open to anyone, and it is played in April of each year spanning 54 hours over a weekend with eight questions each hour. There are usually 400 teams ranging from 1 to 150 players. The top ten teams are awarded trophies. As of 2022, the contest is in its 52nd year. The dates for Trivia 52: The Stacked Deck, are April 8-10, 2022.The two longest continuous trivia contests in the world are the Great Midwest Trivia Contest at Lawrence University and the Williams Trivia Contest, which both debuted in the spring of 1966. Lawrence hosts its contest annually. Unusually, Williams has a separate contest for each semester, and thus its 84th game took place in May 2008.
The University of Colorado Trivia Bowl was a mostly student contest featuring a single-elimination tournament based on the GE College Bowl. Many of the best trivia players in America trace participation through this tournament including many Jeopardy! and Who Wants to Be a Millionaire? contestants. In recent years, the event has been conducted in a round robin competition format and operated as a regional qualifier for T.R.A.S.H. (Testing Recall About Strange Happenings).
Today, many bars and restaurants host weekly trivia nights in an effort to draw in more patrons, especially during weeknights.
See also
Factoid
Pub quiz
Triviality (mathematics)
== References == |
copernican period | The Copernican Period in the lunar geologic timescale runs from approximately 1.1 billion years ago to the present day. The base of the Copernican period is defined by impact craters that possess bright optically immature ray systems. The crater Copernicus is a prominent example of rayed crater, but it does not mark the base of the Copernican period.
Copernican age deposits are mostly represented by crater ejecta, but a small area of mare basalt has covered part of (and is thus younger than) some of the rays of the Copernican crater Lichtenberg, and therefore the basalt is mapped as Copernican age.
Definition
The base of the Copernican period is defined based on the recognition that freshly excavated materials on the lunar surface are generally "bright" and that they become darker over time as a result of space weathering processes. Operationally, this period was originally defined as the time at which impact craters "lost" their bright ray systems. This definition, however, has recently been subjected to some criticism as some crater rays are bright for compositional reasons that are unrelated to the amount of space weathering they have incurred. In particular, if the ejecta from a crater formed in the highlands (which is composed of bright anorthositic materials) is deposited on the low albedo mare, it will remain bright even after being space weathered.
Examples
Other than Copernicus itself, there are many examples of Copernican craters. Large examples on the near side include Tycho, Aristillus, Autolycus, Stevinus, Kepler, Theophilus, Taruntius, Eudoxus, Bürg, Römer, Harpalus, Carpenter, Philolaus, Anaxagoras, Glushko, Hayn, Zucchius, and Rutherfurd. Examples on the far side include Ohm, Jackson, King, Necho, Giordano Bruno, O'Day, Crookes, Robertson, Vavilov, and Sharonov.
Many craters visited by the Apollo astronauts were of Copernican age. These include North Ray and South Ray on Apollo 16, which were dated by cosmic ray exposure to approximately 50 million and 2 million years age, respectively.
Relationship to Earth's geologic time scale
Its Earth equivalents are the Neoproterozoic era of the Proterozoic eon and the whole of the Phanerozoic eon. So, while animal life bloomed on Earth, the Moon's geologic activity was coming to an end.
References
Martel, Linda M. V. (2004-09-28). "Lunar Crater Rays Point to a New Lunar Time Scale". Hawai'i Institute of Geophysics and Planetology (HIGP). Planetary Science Research Discoveries (PSRD). |
dryas (plant) | Dryas is a genus of perennial cushion-forming evergreen dwarf shrubs in the family Rosaceae, native to the arctic and alpine regions of Europe, Asia and North America. The genus is named after the dryads, the tree nymphs of ancient Greek mythology. The classification of Dryas within the Rosaceae has been unclear. The genus was formerly placed in the subfamily Rosoideae, but is now placed in subfamily Dryadoideae.The species are superficially similar to Geum (with which they share the common name avens), Potentilla, and Fragaria (strawberry). However, Dryas are distinct in having flowers with eight petals (rarely seven or up to ten), instead of the five petals found in most other genera in the Rosaceae. The flowers are erect and white with a yellow centre (Dryas integrifolia, Dryas octopetala) or pendulous and all-yellow (Dryas drummondii), and held conspicuously above the small plants. This makes them very popular in rockeries and alpine gardens. The hybrid Dryas × suendermannii, with cream coloured flowers, has gained the Royal Horticultural Society’s Award of Garden Merit.Dryas tolerates a wide variety of unshaded habitats, including alpine situations with sand or gravel substrate, similar substrates in flat tundra lowlands, and also fen habitats upon organic substrate where some shading from adjacent sedges or shrubs may occur.
The Younger Dryas and Older Dryas stadials are geological periods of cold temperature that are named after Dryas octopetala, which flourished during that time and is used as a fossil indicator of those periods.
Gallery
Taxonomy
Species
Dryas comprises three species, but the genus is in need of taxonomic revision:
Dryas drummondii Richardson ex Hook. – Drummond's avens
var. drummondii Richardson ex Hook. – Yellow avens
var. tomentosa (Farr) L.O. Williams – Tomentose avens
Dryas integrifolia Vahl – Entire-leaved avens
subsp. chamissonis (Spreng.) Scoggan – White avens
subsp. crenulata (Juz.) J. Kozhevn – Crenulate avens
subsp. integrifolia Vahl – Entire-leaved avens
subsp. sylvatica (Hultén) Hultén – Forest avens
Dryas octopetala L. – Mountain avens
subsp. alaskensis (A.E. Porsild) Hultén – Alaskan avens
subsp. hookeriana (Juz.) Hultén – Hooker's avens
subsp. octopetala L. – Eight-petal avens
var. angustifolia C.L. Hitchc. – Narrow-leaved avens
var. argentea Blytt – Silvery avens
var. kamtschatica (Juz.) Hultén – Kamtschatca avens
var. octopetala L. – Eight-petal avens
subsp. punctata (Juz.) Hultén – Pointed avens
Species names with uncertain taxonomic status
The status of the following species is unresolved:
Hybrids
Two hybrids have been described:
Dryas × suendermannii Kellerer ex Sundermann—(D. drummondii × D. octopetala)
Dryas × wyssiana Beauverd—(D. drummondii × D. integrifolia)
Species names with uncertain taxonomic status
The status of the following hybrids is unresolved:
Dryas × chamissonis Jurtzev
Dryas × grandiformis Jurtzev
Dryas × intermedia Juz.
Dryas × lewinii Rouleau
Nitrogen Fixation
Some Dryas plants have root nodules that host the nitrogen-fixing bacterium Frankia.
Dryas drummondii forms root nodules and fixes nitrogen with Frankia.
Dryas integrifolia does not form root nodules or fix nitrogen with Frankia.
Dryas octopetala does not form root nodules or fix nitrogen with Frankia.
Dryas × suendermannii (D. drummondii × D. octopetala) does not form root nodules or fix nitrogen with Frankia.
References
== External links == |
meganeura | Meganeura is a genus of extinct insects from the Late Carboniferous (approximately 300 million years ago). They resembled and are related to the present-day dragonflies and damselflies, and were predatory, with their diet mainly consisting of other insects. The genus belongs to the Meganeuridae, a family including other similarly giant dragonfly-like insects ranging from the Late Carboniferous to Middle Permian. With a wingspan about 65–75 cm (2.13–2.46 ft), M. monyi is one of the largest-known flying insect species.
Fossils of Meganeura were first discovered in Late Carboniferous (Stephanian) Coal Measures of Commentry, France in 1880. In 1885, French paleontologist Charles Brongniart described and named the fossil "Meganeura" (large-nerved), which refers to the network of veins on the insect's wings. Another fine fossil specimen was found in 1979 at Bolsover in Derbyshire. The holotype is housed in the National Museum of Natural History, in Paris. Despite being the iconic "giant dragonfly", fossils of Meganeura are poorly preserved in comparison to other meganeurids.
Lifestyle
Research on close relatives Meganeurula and Meganeurites suggest that Meganeura was adapted to open habitats, and similar in behaviour to extant hawkers. The eyes of Meganeura were likely enlarged relative to body size. Meganeura had spines on the tibia and tarsi sections of the legs, which would have functioned as a "flying trap" to capture prey. An engineering examination estimated that the mass of the largest specimens with wingspans over 70 cm to be 100 to 150 grams. The analysis also suggested that Meganeura would be susceptible to overheating.
Size
There has been some controversy as to how insects of the Carboniferous period were able to grow so large.
Oxygen levels and atmospheric density. The way oxygen is diffused through the insect's body via its tracheal breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed by Harlé (1911) that Meganeura was able to fly only because the atmosphere of Earth at that time contained more oxygen than the present 20 percent. This hypothesis was initially dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability. If this hypothesis is correct, these insects would have been susceptible to falling oxygen levels and certainly could not survive in our modern atmosphere. Other research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion". Recent analysis of the flight energetics of modern insects and birds suggests that both the oxygen levels and air density provide an upper bound on size. The presence of very large Meganeuridae with wing spans rivaling those of Meganeura during the Permian, when the oxygen content of the atmosphere was already much lower than in the Carboniferous, presented a problem to the oxygen-related explanations in the case of the giant dragonflies. However, despite the fact that Meganeurids had the largest-known wingspans, their bodies were not very heavy, being less massive than those of several living Coleoptera; therefore, they were not true giant insects, only being giant in comparison with their living relatives.
Lack of predators. Other explanations for the large size of Meganeurids compared to living relatives are warranted. Bechly (2004) suggested that the lack of aerial vertebrate predators allowed pterygote insects to evolve to maximum sizes during the Carboniferous and Permian periods, perhaps accelerated by an evolutionary "arms race" for increase in body size between plant-feeding Palaeodictyoptera and Meganisoptera as their predators.
Aquatic larvae stadium. Another theory suggests that insects that developed in water before becoming terrestrial as adults grew bigger as a way to protect themselves against the high levels of oxygen.
See also
List of largest insects
References
Bibliography
Bechly, G (2004). "Evolution and systematics" (PDF). In Hutchins, M.; Evans, A.V.; Garrison, R.W. & Schlager, N. (eds.). Grzimek's Animal Life Encyclopedia. Vol. Insects (2nd ed.). Farmington Hills, MI: Gale. pp. 7–16.
Chapelle, Gauthier & Peck, Lloyd S. (May 1999). "Polar gigantism dictated by oxygen availability". Nature. 399 (6732): 114–115. Bibcode:1999Natur.399..114C. doi:10.1038/20099. S2CID 4308425.
Dudley, Robert (April 1998). "Atmospheric oxygen, giant Paleozoic insects and the evolution of aerial locomotion performance". The Journal of Experimental Biology. 201 (Pt8): 1043–1050. doi:10.1242/jeb.201.8.1043. PMID 9510518.
Harlé, Edouard (1911). "Le Vol de grands reptiles et insectes disparus semble indiquer une pression atmosphérique élevée". Extr. Du Bulletin de la Sté Géologique de France (in French). 4 (9): 118–121.
Nel, André; Fleck, Günther; Garrouste, Romain & Gand, Georges (2008). "The Odonatoptera of the Late Permian Lodève Basin (Insecta)". Journal of Iberian Geology. 34 (1): 115–122.
Rake, Matthew (2017). Prehistoric Ancestors of Modern Animals. Hungry Tomato. p. 20. ISBN 978-1512436099.
Taylor, Paul D.; Lewis, David N. (2007). Fossil Invertebrates (repeated ed.). Harvard University Press. p. 160. ISBN 978-0674025745.
Westneat, MW; Betz, O; Blob, RW; Fezzaa, K; Cooper, WJ & Lee, WK (January 2003). "Tracheal respiration in insects visualized with synchrotron x-ray imaging". Science. 299 (5606): 558–560. Bibcode:2003Sci...299..558W. doi:10.1126/science.1078008. PMID 12543973. S2CID 43634044.
External links
Media related to Meganeura at Wikimedia Commons
Picture of life sized model of Meganeura monyi made for Denver Museum of Natural History. |
welsh | Welsh may refer to:
Related to Wales
Welsh, of or about Wales
Welsh language, spoken in Wales
Welsh people, an ethnic group native to Wales
Places
Welsh, Arkansas, U.S.
Welsh, Louisiana, U.S.
Welsh, Ohio, U.S.
Welsh Basin, during the Cambrian, Ordovician and Silurian geological periods
Other uses
Welsh (surname), including a list of people with the name
Welsh pig, a breed of domestic pig
See also
All pages with titles beginning with Welsh
All pages with titles containing Welsh
Welch (disambiguation)
Welsch, a surname
Cambrian
Celtic Britons |
pliocene | The Pliocene ( PLY-ə-seen, PLY-oh-; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 million years ago. It is the second and most recent epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the four most recent major glaciations entirely within the Pleistocene, the Pliocene also included the Gelasian Stage, which lasted from 2.588 to 1.806 million years ago, and is now included in the Pleistocene.As with other older geologic periods, the geological strata that define the start and end are well-identified but the exact dates of the start and end of the epoch are slightly uncertain. The boundaries defining the Pliocene are not set at an easily identified worldwide event but rather at regional boundaries between the warmer Miocene and the relatively cooler Pleistocene. The upper boundary was set at the start of the Pleistocene glaciations.
Etymology
Charles Lyell (later Sir Charles) gave the Pliocene its name in Principles of Geology (volume 3, 1833).The word pliocene comes from the Greek words πλεῖον (pleion, "more") and καινός (kainos, "new" or "recent") and means roughly "continuation of the recent", referring to the essentially modern marine mollusc fauna.
Subdivisions
In the official timescale of the ICS, the Pliocene is subdivided into two stages. From youngest to oldest they are:
Piacenzian (3.600–2.58 Ma)
Zanclean (5.333–3.600 Ma)The Piacenzian is sometimes referred to as the Late Pliocene, whereas the Zanclean is referred to as the Early Pliocene.
In the system of
North American Land Mammal Ages (NALMA) include Hemphillian (9–4.75 Ma), and Blancan (4.75–1.6 Ma). The Blancan extends forward into the Pleistocene.
South American Land Mammal Ages (SALMA) include Montehermosan (6.8–4.0 Ma), Chapadmalalan (4.0–3.0 Ma) and Uquian (3.0–1.2 Ma).In the Paratethys area (central Europe and parts of western Asia) the Pliocene contains the Dacian (roughly equal to the Zanclean) and Romanian (roughly equal to the Piacenzian and Gelasian together) stages. As usual in stratigraphy, there are many other regional and local subdivisions in use.
In Britain, the Pliocene is divided into the following stages (old to young): Gedgravian, Waltonian, Pre-Ludhamian, Ludhamian, Thurnian, Bramertonian or Antian, Pre-Pastonian or Baventian, Pastonian and Beestonian. In the Netherlands the Pliocene is divided into these stages (old to young): Brunssumian C, Reuverian A, Reuverian B, Reuverian C, Praetiglian, Tiglian A, Tiglian B, Tiglian C1-4b, Tiglian C4c, Tiglian C5, Tiglian C6 and Eburonian. The exact correlations between these local stages and the International Commission on Stratigraphy (ICS) stages is still a matter of detail.
Climate
The beginning of the Pliocene was marked by an increase in global temperatures relative to the cooler Messinian related to the 1.2 million year obliquity amplitude modulation cycle. The global average temperature in the mid-Pliocene (3.3–3 mya) was 2–3 °C higher than today, carbon dioxide levels were the same as today, and global sea level was 25 m higher. The northern hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 Ma.
The formation of an Arctic ice cap is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific Ocean beds. Mid-latitude glaciation was probably underway before the end of the epoch. The global cooling that occurred during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas.
Paleogeography
Continents continued to drift, moving from positions possibly as far as 250 km from their present locations to positions only 70 km from their current locations. South America became linked to North America through the Isthmus of Panama during the Pliocene, making possible the Great American Interchange and bringing a nearly complete end to South America's distinctive native ungulate fauna, though other South American lineages like its predatory mammals were already extinct by this point and others like xenarthrans continued to do well afterwards. The formation of the Isthmus had major consequences on global temperatures, since warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters dropping temperatures in the now-isolated Atlantic Ocean.Africa's collision with Europe formed the Mediterranean Sea, cutting off the remnants of the Tethys Ocean. The border between the Miocene and the Pliocene is also the time of the Messinian salinity crisis.During the Late Pliocene, the Himalayas became less active in their uplift, as evidenced by sedimentation changes in the Bengal Fan.The land bridge between Alaska and Siberia (Beringia) was first flooded near the start of the Pliocene, allowing marine organisms to spread between the Arctic and Pacific Oceans. The bridge would continue to be periodically flooded and restored thereafter.Pliocene marine formations are exposed in northeast Spain, southern California, New Zealand, and Italy.During the Pliocene parts of southern Norway and southern Sweden that had been near sea level rose. In Norway this rise elevated the Hardangervidda plateau to 1200 m in the Early Pliocene. In Southern Sweden similar movements elevated the South Swedish highlands leading to a deflection of the ancient Eridanos river from its original path across south-central Sweden into a course south of Sweden.
Environment and evolution of human ancestors
The Pliocene is bookended by two significant events in the evolution of human ancestors. The first is the appearance of the hominin Australopithecus anamensis in the early Pliocene, around 4.2 million years ago. The second is the appearance of Homo, the genus that includes modern humans and their closest extinct relatives, near the end of the Pliocene at 2.6 million years ago. Key traits that evolved among hominins during the Pliocene include terrestrial bipedality and, by the end of the Pliocene, encephalized brains (brains with a large neocortex relative to body mass and stone tool manufacture.Improvements in dating methods and in the use of climate proxies have provided scientists with the means to test hypotheses of the evolution of human ancestors. Early hypotheses of the evolution of human traits emphasized the selective pressures produced by particular habitats. For example, many scientists have long favored the savannah hypothesis. This proposes that the evolution of terrestrial bipedality and other traits was an adaptive response to Pliocene climate change that transformed forests into more open savannah. This was championed by Grafton Elliot Smith in his 1924 book, The Evolution of Man, as "the unknown world beyond the trees", and was further elaborated by Raymond Dart as the killer ape theory. Other scientists, such as Sherwood L. Washburn, emphasized an intrinsic model of hominin evolution. According to this model, early evolutionary developments triggered later developments. The model placed little emphasis on the surrounding environment. Anthropologists tended to focus on intrinsic models while geologists and vertebrate paleontologists tended to put greater emphasis on habitats.Alternatives to the savanna hypothesis include the woodland/forest hypothesis, which emphasizes the evolution of hominins in closed habitats, or hypotheses emphasizing the influence of colder habitats at higher latitudes or the influence of seasonal variation. More recent research has emphasized the variability selection hypothesis, which proposes that variability in climate fostered development of hominin traits. Improved climate proxies show that the Pliocene climate of east Africa was highly variable, suggesting that adaptability to varying conditions was more important in driving hominin evolution than the steady pressure of a particular habitat.
Flora
The change to a cooler, drier, more seasonal climate had considerable impacts on Pliocene vegetation, reducing tropical species worldwide. Deciduous forests proliferated, coniferous forests and tundra covered much of the north, and grasslands spread on all continents (except Antarctica). Tropical forests were limited to a tight band around the equator, and in addition to dry savannahs, deserts appeared in Asia and Africa.
Fauna
Both marine and continental faunas were essentially modern, although continental faunas were a bit more primitive than today.
The land mass collisions meant great migration and mixing of previously isolated species, such as in the Great American Interchange. Herbivores got bigger, as did specialized predators.
Mammals
In North America, rodents, large mastodons and gomphotheres, and opossums continued successfully, while hoofed animals (ungulates) declined, with camel, deer and horse all seeing populations recede. Three-toed horses (Nannippus), oreodonts, protoceratids, and chalicotheres became extinct. Borophagine dogs and Agriotherium became extinct, but other carnivores including the weasel family diversified, and dogs and short-faced bears did well. Ground sloths, huge glyptodonts, and armadillos came north with the formation of the Isthmus of Panama.
In Eurasia rodents did well, while primate distribution declined. Elephants, gomphotheres and stegodonts were successful in Asia (the largest land mammals of the Pliocene were such proboscideans as Deinotherium, Anancus and Mammut borsoni), and hyraxes migrated north from Africa. Horse diversity declined, while tapirs and rhinos did fairly well. Bovines and antelopes were successful; some camel species crossed into Asia from North America. Hyenas and early saber-toothed cats appeared, joining other predators including dogs, bears and weasels.
Africa was dominated by hoofed animals, and primates continued their evolution, with australopithecines (some of the first hominins) and baboon-like monkeys such as the Dinopithecus appearing in the late Pliocene. Rodents were successful, and elephant populations increased. Cows and antelopes continued diversification and overtook pigs in numbers of species. Early giraffes appeared. Horses and modern rhinos came onto the scene. Bears, dogs and weasels (originally from North America) joined cats, hyenas and civets as the African predators, forcing hyenas to adapt as specialized scavengers. Most mustelids in Africa declined as a result of increased competition from the new predators, although Enhydriodon omoensis remained an unusually successful terrestrial predator.
South America was invaded by North American species for the first time since the Cretaceous, with North American rodents and primates mixing with southern forms. Litopterns and the notoungulates, South American natives, were mostly wiped out, except for the macrauchenids and toxodonts, which managed to survive. Small weasel-like carnivorous mustelids, coatis and short-faced bears migrated from the north. Grazing glyptodonts, browsing giant ground sloths and smaller caviomorph rodents, pampatheres, and armadillos did the opposite, migrating to the north and thriving there.
The marsupials remained the dominant Australian mammals, with herbivore forms including wombats and kangaroos, and the huge Diprotodon. Carnivorous marsupials continued hunting in the Pliocene, including dasyurids, the dog-like thylacine and cat-like Thylacoleo. The first rodents arrived in Australia. The modern platypus, a monotreme, appeared.
Birds
The predatory South American phorusrhacids were rare in this time; among the last was Titanis, a large phorusrhacid that migrated to North America and rivaled mammals as top predator. Other birds probably evolved at this time, some modern (such as the genera Cygnus, Bubo, Struthio and Corvus), some now extinct.
Reptiles and amphibians
Alligators and crocodiles died out in Europe as the climate cooled. Venomous snake genera continued to increase as more rodents and birds evolved. Rattlesnakes first appeared in the Pliocene. The modern species Alligator mississippiensis, having evolved in the Miocene, continued into the Pliocene, except with a more northern range; specimens have been found in very late Miocene deposits of Tennessee. Giant tortoises still thrived in North America, with genera like Hesperotestudo. Madtsoid snakes were still present in Australia. The amphibian order Allocaudata became extinct.
Corals
The Pliocene was a high water mark for species diversity among Caribbean corals. From 5 to 2 Ma, coral species origination rates were relatively high in the Caribbean, although a noticeable extinction event and drop in diversity occurred at the end of this interval.
Oceans
Oceans continued to be relatively warm during the Pliocene, though they continued cooling. The Arctic ice cap formed, drying the climate and increasing cool shallow currents in the North Atlantic. Deep cold currents flowed from the Antarctic.
The formation of the Isthmus of Panama about 3.5 million years ago cut off the final remnant of what was once essentially a circum-equatorial current that had existed since the Cretaceous and the early Cenozoic. This may have contributed to further cooling of the oceans worldwide.
The Pliocene seas were alive with sea cows, seals, sea lions and sharks.
See also
List of fossil sites (with link directory)
Notes
References
Further reading
Comins, Niel F.; William J. Kaufmann III (2005). Discovering the Universe (7th ed.). New York, NY: Susan Finnemore Brennan. ISBN 978-0-7167-7584-3.
Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
Ogg, Jim (June 2004). "Overview of Global Boundary Stratotype Sections and Points (GSSP's)". Archived from the original on 23 April 2006. Retrieved 30 April 2006.
Van Andel, Tjeerd H. (1994). New Views on an Old Planet: a History of Global Change (2nd ed.). Cambridge: Cambridge University Press. ISBN 978-0-521-44243-5.
External links
Mid-Pliocene Global Warming: NASA/GISS Climate Modeling
Palaeos Pliocene
PBS Change: Deep Time: Pliocene
Possible Pliocene supernova
"Supernova dealt deaths on Earth? Stellar blasts may have killed ancient marine life" Science News Online retrieved February 2, 2002
UCMP Berkeley Pliocene Epoch Page
Pliocene Microfossils: 100+ images of Pliocene Foraminifera
Human Timeline (Interactive) – Smithsonian, National Museum of Natural History (August 2016). |
geological history of earth | The geological history of the Earth follows the major geological events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System.
Initially, Earth was molten due to extreme volcanism and frequent collisions with other bodies. Eventually, the outer layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as a result of the impact of a planetoid with the Earth. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans. However, in 2020, researchers reported that sufficient water to fill the oceans may have always been on the Earth since the beginning of the planet's formation.As the surface continually reshaped itself over hundreds of millions of years, continents formed and broke apart. They migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago, the earliest-known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia, 600 to 540 million years ago, then finally Pangaea, which broke apart 200 million years ago.
The present pattern of ice ages began about 40 million years ago, then intensified at the end of the Pliocene. The polar regions have since undergone repeated cycles of glaciation and thawing, repeating every 40,000–100,000 years. The Last Glacial Period of the current ice age ended about 10,000 years ago.
Precambrian
The Precambrian includes approximately 90% of geologic time. It extends from 4.6 billion years ago to the beginning of the Cambrian Period (about 539 Ma). It includes the first three of the four eons of Earth's prehistory (the Hadean, Archean and Proterozoic) and precedes the Phanerozoic eon.Major volcanic events altering the Earth's environment and causing extinctions may have occurred 10 times in the past 3 billion years.
Hadean Eon
During Hadean time (4.6–4 Ga), the Solar System was forming, probably within a large cloud of gas and dust around the Sun, called an accretion disc from which Earth formed 4,500 million years ago.
The Hadean Eon is not formally recognized, but it essentially marks the era before we have adequate record of significant solid rocks. The oldest dated zircons date from about 4,400 million years ago.
Earth was initially molten due to extreme volcanism and frequent collisions with other bodies. Eventually, the outer layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as a result of the impact of a large planetoid with the Earth. More recent potassium isotopic studies suggest that the Moon was formed by a smaller, high-energy, high-angular-momentum giant impact cleaving off a significant portion of the Earth. Some of this object's mass merged with Earth, significantly altering its internal composition, and a portion was ejected into space. Some of the material survived to form the orbiting Moon. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans. However, in 2020, researchers reported that sufficient water to fill the oceans may have always been on the Earth since the beginning of the planet's formation.During the Hadean the Late Heavy Bombardment occurred (approximately 4,100 to 3,800 million years ago) during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus and Mars as well. However, some scientists argue against this hypothetical Late Heavy Bombardment, pointing out that the conclusion has been drawn from data which are not fully representative (only a few crater hotspots on the Moon have been analyzed).
Archean Eon
The Earth of the early Archean (4,031 to 2,500 million years ago) may have had a different tectonic style. During this time, the Earth's crust cooled enough that rocks and continental plates began to form. Some scientists think because the Earth was hotter, that plate tectonic activity was more vigorous than it is today, resulting in a much greater rate of recycling of crustal material. This may have prevented cratonization and continent formation until the mantle cooled and convection slowed down. Others argue that the subcontinental lithospheric mantle is too buoyant to subduct and that the lack of Archean rocks is a function of erosion and subsequent tectonic events. Some geologists view the sudden increase in aluminum content in zircons as an indicator of the beginning of plate tectonics.In contrast to the Proterozoic, Archean rocks are often heavily metamorphized deep-water sediments, such as graywackes, mudstones, volcanic sediments and banded iron formations. Greenstone belts are typical Archean formations, consisting of alternating high- and low-grade metamorphic rocks. The high-grade rocks were derived from volcanic island arcs, while the low-grade metamorphic rocks represent deep-sea sediments eroded from the neighboring island rocks and deposited in a forearc basin. In short, greenstone belts represent sutured protocontinents.The Earth's magnetic field was established 3.5 billion years ago. The solar wind flux was about 100 times the value of the modern Sun, so the presence of the magnetic field helped prevent the planet's atmosphere from being stripped away, which is what probably happened to the atmosphere of Mars. However, the field strength was lower than at present and the magnetosphere was about half the modern radius.
Proterozoic Eon
The geologic record of the Proterozoic (2,500 to 538.8 million years ago) is more complete than that for the preceding Archean. In contrast to the deep-water deposits of the Archean, the Proterozoic features many strata that were laid down in extensive shallow epicontinental seas; furthermore, many of these rocks are less metamorphosed than Archean-age ones, and plenty are unaltered. Study of these rocks shows that the eon featured massive, rapid continental accretion (unique to the Proterozoic), supercontinent cycles, and wholly modern orogenic activity. Roughly 750 million years ago, the earliest-known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 Ma.The first-known glaciations occurred during the Proterozoic, one that began shortly after the beginning of the eon, while there were at least four during the Neoproterozoic, climaxing with the Snowball Earth of the Varangian glaciation.
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale. It covers roughly 539 million years. During this period continents drifted apart, but eventually collected into a single landmass known as Pangea, before splitting again into the current continental landmasses.
The Phanerozoic is divided into three eras – the Paleozoic, the Mesozoic and the Cenozoic.
Most of the evolution of multicellular life occurred during this time period.
Paleozoic Era
The Paleozoic era spanned roughly 539 to 251 million years ago (Ma) and is subdivided into six geologic periods; from oldest to youngest, they are the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. Geologically, the Paleozoic starts shortly after the breakup of a supercontinent called Pannotia and at the end of a global ice age. Throughout the early Paleozoic, Earth's landmass was broken up into a substantial number of relatively small continents. Toward the end of the era, the continents gathered together into a supercontinent called Pangaea, which included most of Earth's land area.
Cambrian Period
The Cambrian is a major division of the geologic timescale that begins about 538.8 ± 0.2 Ma. Cambrian continents are thought to have resulted from the breakup of a Neoproterozoic supercontinent called Pannotia. The waters of the Cambrian period appear to have been widespread and shallow. Continental drift rates may have been anomalously high. Laurentia, Baltica and Siberia remained independent continents following the break-up of the supercontinent of Pannotia. Gondwana started to drift toward the South Pole. Panthalassa covered most of the southern hemisphere, and minor oceans included the Proto-Tethys Ocean, Iapetus Ocean and Khanty Ocean.
Ordovician period
The Ordovician period started at a major extinction event called the Cambrian–Ordovician extinction event some time about 485.4 ± 1.9 Ma. During the Ordovician the southern continents were collected into a single continent called Gondwana. Gondwana started the period in the equatorial latitudes and, as the period progressed, drifted toward the South Pole. Early in the Ordovician the continents Laurentia, Siberia and Baltica were still independent continents (since the break-up of the supercontinent Pannotia earlier), but Baltica began to move toward Laurentia later in the period, causing the Iapetus Ocean to shrink between them. Also, Avalonia broke free from Gondwana and began to head north toward Laurentia. The Rheic Ocean was formed as a result of this. By the end of the period, Gondwana had neared or approached the pole and was largely glaciated.
The Ordovician came to a close in a series of extinction events that, taken together, comprise the second-largest of the five major extinction events in Earth's history in terms of percentage of genera that became extinct. The only larger one was the Permian-Triassic extinction event. The extinctions occurred approximately 447 to 444 million years ago and mark the boundary between the Ordovician and the following Silurian Period.
The most-commonly accepted theory is that these events were triggered by the onset of an ice age, in the Hirnantian faunal stage that ended the long, stable greenhouse conditions typical of the Ordovician. The ice age was probably not as long-lasting as once thought; study of oxygen isotopes in fossil brachiopods shows that it was probably no longer than 0.5 to 1.5 million years. The event was preceded by a fall in atmospheric carbon dioxide (from 7000ppm to 4400ppm) which selectively affected the shallow seas where most organisms lived. As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it. Evidence of these ice caps has been detected in Upper Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time.
Silurian Period
The Silurian is a major division of the geologic timescale that started about 443.8 ± 1.5 Ma. During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian ice caps were less extensive than those of the late Ordovician glaciation. The melting of ice caps and glaciers contributed to a rise in sea levels, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. Other cratons and continent fragments drifted together near the equator, starting the formation of a second supercontinent known as Euramerica. The vast ocean of Panthalassa covered most of the northern hemisphere. Other minor oceans include Proto-Tethys, Paleo-Tethys, Rheic Ocean, a seaway of Iapetus Ocean (now in between Avalonia and Laurentia), and newly formed Ural Ocean.
Devonian Period
The Devonian spanned roughly from 419 to 359 Ma. The period was a time of great tectonic activity, as Laurasia and Gondwana drew closer together. The continent Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn. In these near-deserts, the Old Red Sandstone sedimentary beds formed, made red by the oxidized iron (hematite) characteristic of drought conditions. Near the equator Pangaea began to consolidate from the plates containing North America and Europe, further raising the northern Appalachian Mountains and forming the Caledonian Mountains in Great Britain and Scandinavia. The southern continents remained tied together in the supercontinent of Gondwana. The remainder of modern Eurasia lay in the Northern Hemisphere. Sea levels were high worldwide, and much of the land lay submerged under shallow seas. The deep, enormous Panthalassa (the "universal ocean") covered the rest of the planet. Other minor oceans were Paleo-Tethys, Proto-Tethys, Rheic Ocean and Ural Ocean (which was closed during the collision with Siberia and Baltica).
Carboniferous Period
The Carboniferous extends from about 358.9 ± 0.4 to about 298.9 ± 0.15 Ma.A global drop in sea level at the end of the Devonian reversed early in the Carboniferous; this created the widespread epicontinental seas and carbonate deposition of the Mississippian. There was also a drop in south polar temperatures; southern Gondwana was glaciated throughout the period, though it is uncertain if the ice sheets were a holdover from the Devonian or not. These conditions apparently had little effect in the deep tropics, where lush coal swamps flourished within 30 degrees of the northernmost glaciers. A mid-Carboniferous drop in sea-level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard. This sea-level drop and the associated unconformity in North America separate the Mississippian Period from the Pennsylvanian period.The Carboniferous was a time of active mountain building, as the supercontinent Pangea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America-Europe (Laurussia) along the present line of eastern North America. This continental collision resulted in the Hercynian orogeny in Europe, and the Alleghenian orogeny in North America; it also extended the newly uplifted Appalachians southwestward as the Ouachita Mountains. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural mountains. There were two major oceans in the Carboniferous: the Panthalassa and Paleo-Tethys. Other minor oceans were shrinking and eventually closed the Rheic Ocean (closed by the assembly of South and North America), the small, shallow Ural Ocean (which was closed by the collision of Baltica, and Siberia continents, creating the Ural Mountains) and Proto-Tethys Ocean.
Permian Period
The Permian extends from about 298.9 ± 0.15 to 252.17 ± 0.06 Ma.During the Permian all the Earth's major land masses, except portions of East Asia, were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean (Panthalassa, the universal sea), and the Paleo-Tethys Ocean, a large ocean that was between Asia and Gondwana. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink. A new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era. Large continental landmasses create climates with extreme variations of heat and cold ("continental climate") and monsoon conditions with highly seasonal rainfall patterns. Deserts seem to have been widespread on Pangaea.
Mesozoic Era
The Mesozoic extended roughly from 252 to 66 million years ago.After the vigorous convergent plate mountain-building of the late Paleozoic, Mesozoic tectonic deformation was comparatively mild. Nevertheless, the era featured the dramatic rifting of the supercontinent Pangaea. Pangaea gradually split into a northern continent, Laurasia, and a southern continent, Gondwana. This created the passive continental margin that characterizes most of the Atlantic coastline (such as along the U.S. East Coast) today.
Triassic Period
The Triassic Period extends from about 252.17 ± 0.06 to 201.3 ± 0.2 Ma. During the Triassic, almost all the Earth's land mass was concentrated into a single supercontinent centered more or less on the equator, called Pangaea ("all the land"). This took the form of a giant "Pac-Man" with an east-facing "mouth" constituting the Tethys sea, a vast gulf that opened farther westward in the mid-Triassic, at the expense of the shrinking Paleo-Tethys Ocean, an ocean that existed during the Paleozoic.
The remainder was the world-ocean known as Panthalassa ("all the sea"). All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates; thus, very little is known of the Triassic open ocean. The supercontinent Pangaea was rifting during the Triassic—especially late in the period—but had not yet separated. The first nonmarine sediments in the rift that marks the initial break-up of Pangea—which separated New Jersey from Morocco—are of Late Triassic age; in the U.S., these thick sediments comprise the Newark Supergroup.
Because of the limited shoreline of one super-continental mass, Triassic marine deposits are globally relatively rare; despite their prominence in Western Europe, where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the west. Thus Triassic stratigraphy is mostly based on organisms living in lagoons and hypersaline environments, such as Estheria crustaceans and terrestrial vertebrates.
Jurassic Period
The Jurassic Period extends from about 201.3 ± 0.2 to 145.0 Ma.
During the early Jurassic, the supercontinent Pangaea broke up into the northern supercontinent Laurasia and the southern supercontinent Gondwana; the Gulf of Mexico opened in the new rift between North America and what is now Mexico's Yucatan Peninsula. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous Period, when Gondwana itself rifted apart.
The Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation. As in the Triassic, there was apparently no land near either pole, and no extensive ice caps existed. The Jurassic geological record is good in western Europe, where extensive marine sequences indicate a time when much of the continent was submerged under shallow tropical seas; famous locales include the Jurassic Coast World Heritage Site and the renowned late Jurassic lagerstätten of Holzmaden and Solnhofen.
In contrast, the North American Jurassic record is the poorest of the Mesozoic, with few outcrops at the surface. Though the epicontinental Sundance Sea left marine deposits in parts of the northern plains of the United States and Canada during the late Jurassic, most exposed sediments from this period are continental, such as the alluvial deposits of the Morrison Formation. The first of several massive batholiths were emplaced in the northern Cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. Important Jurassic exposures are also found in Russia, India, South America, Japan, Australasia and the United Kingdom.
Cretaceous Period
The Cretaceous Period extends from circa 145 million years ago to 66 million years ago.During the Cretaceous, the late Paleozoic-early Mesozoic supercontinent of Pangaea completed its breakup into present day continents, although their positions were substantially different at the time. As the Atlantic Ocean widened, the convergent-margin orogenies that had begun during the Jurassic continued in the North American Cordillera, as the Nevadan orogeny was followed by the Sevier and Laramide orogenies. Though Gondwana was still intact in the beginning of the Cretaceous, Gondwana itself broke up as South America, Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached to each other); thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide.
To the north of Africa the Tethys Sea continued to narrow. Broad shallow seas advanced across central North America (the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. At the peak of the Cretaceous transgression, one-third of Earth's present land area was submerged. The Cretaceous is justly famous for its chalk; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic. Mid-ocean ridge activity—or rather, the circulation of seawater through the enlarged ridges—enriched the oceans in calcium; this made the oceans more saturated, as well as increased the bioavailability of the element for calcareous nanoplankton. These widespread carbonates and other sedimentary deposits make the Cretaceous rock record especially fine. Famous formations from North America include the rich marine fossils of Kansas's Smoky Hill Chalk Member and the terrestrial fauna of the late Cretaceous Hell Creek Formation. Other important Cretaceous exposures occur in Europe and China. In the area that is now India, massive lava beds called the Deccan Traps were laid down in the very late Cretaceous and early Paleocene.
Cenozoic Era
The Cenozoic Era covers the 66 million years since the Cretaceous–Paleogene extinction event up to and including the present day. By the end of the Mesozoic era, the continents had rifted into nearly their present form. Laurasia became North America and Eurasia, while Gondwana split into South America, Africa, Australia, Antarctica and the Indian subcontinent, which collided with the Asian plate. This impact gave rise to the Himalayas. The Tethys Sea, which had separated the northern continents from Africa and India, began to close up, forming the Mediterranean Sea.
Paleogene Period
The Paleogene (alternatively Palaeogene) Period is a unit of geologic time that began 66 and ended 23.03 Ma and comprises the first part of the Cenozoic Era. This period consists of the Paleocene, Eocene and Oligocene Epochs.
Paleocene Epoch
The Paleocene, lasted from 66 million years ago to 56 million years ago.In many ways, the Paleocene continued processes that had begun during the late Cretaceous Period. During the Paleocene, the continents continued to drift toward their present positions. Supercontinent Laurasia had not yet separated into three continents. Europe and Greenland were still connected. North America and Asia were still intermittently joined by a land bridge, while Greenland and North America were beginning to separate. The Laramide orogeny of the late Cretaceous continued to uplift the Rocky Mountains in the American west, which ended in the succeeding epoch. South and North America remained separated by equatorial seas (they joined during the Neogene); the components of the former southern supercontinent Gondwana continued to split apart, with Africa, South America, Antarctica and Australia pulling away from each other. Africa was heading north toward Europe, slowly closing the Tethys Ocean, and India began its migration to Asia that would lead to a tectonic collision and the formation of the Himalayas.
Eocene Epoch
During the Eocene (56 million years ago - 33.9 million years ago), the continents continued to drift toward their present positions. At the beginning of the period, Australia and Antarctica remained connected, and warm equatorial currents mixed with colder Antarctic waters, distributing the heat around the world and keeping global temperatures high. But when Australia split from the southern continent around 45 Ma, the warm equatorial currents were deflected away from Antarctica, and an isolated cold water channel developed between the two continents. The Antarctic region cooled down, and the ocean surrounding Antarctica began to freeze, sending cold water and ice floes north, reinforcing the cooling. The present pattern of ice ages began about 40 million years ago.The northern supercontinent of Laurasia began to break up, as Europe, Greenland and North America drifted apart. In western North America, mountain building started in the Eocene, and huge lakes formed in the high flat basins among uplifts. In Europe, the Tethys Sea finally vanished, while the uplift of the Alps isolated its final remnant, the Mediterranean, and created another shallow sea with island archipelagos to the north. Though the North Atlantic was opening, a land connection appears to have remained between North America and Europe since the faunas of the two regions are very similar. India continued its journey away from Africa and began its collision with Asia, creating the Himalayan orogeny.
Oligocene Epoch
The Oligocene Epoch extends from about 34 million years ago to 23 million years ago. During the Oligocene the continents continued to drift toward their present positions.
Antarctica continued to become more isolated and finally developed a permanent ice cap. Mountain building in western North America continued, and the Alps started to rise in Europe as the African plate continued to push north into the Eurasian plate, isolating the remnants of Tethys Sea. A brief marine incursion marks the early Oligocene in Europe. There appears to have been a land bridge in the early Oligocene between North America and Europe since the faunas of the two regions are very similar. During the Oligocene, South America was finally detached from Antarctica and drifted north toward North America. It also allowed the Antarctic Circumpolar Current to flow, rapidly cooling the continent.
Neogene Period
The Neogene Period is a unit of geologic time starting 23.03 Ma. and ends at 2.588 Ma. The Neogene Period follows the Paleogene Period. The Neogene consists of the Miocene and Pliocene and is followed by the Quaternary Period.
Miocene Epoch
The Miocene extends from about 23.03 to 5.333 Ma.During the Miocene continents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between South America and North America was absent, the subduction zone along the Pacific Ocean margin of South America caused the rise of the Andes and the southward extension of the Meso-American peninsula. India continued to collide with Asia. The Tethys Seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish-Arabian region between 19 and 12 Ma (ICS 2004). Subsequent uplift of mountains in the western Mediterranean region and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea resulting in the Messinian salinity crisis near the end of the Miocene.
Pliocene Epoch
The Pliocene extends from 5.333 million years ago to 2.588 million years ago. During the Pliocene continents continued to drift toward their present positions, moving from positions possibly as far as 250 kilometres (155 mi) from their present locations to positions only 70 km from their current locations.
South America became linked to North America through the Isthmus of Panama during the Pliocene, bringing a nearly complete end to South America's distinctive marsupial faunas. The formation of the Isthmus had major consequences on global temperatures, since warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters dropping temperatures in the now-isolated Atlantic Ocean. Africa's collision with Europe formed the Mediterranean Sea, cutting off the remnants of the Tethys Ocean. Sea level changes exposed the land-bridge between Alaska and Asia. Near the end of the Pliocene, about 2.58 million years ago (the start of the Quaternary Period), the current ice age began. The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40,000–100,000 years.
Quaternary Period
Pleistocene Epoch
The Pleistocene extends from 2.588 million years ago to 11,700 years before present. The modern continents were essentially at their present positions during the Pleistocene, the plates upon which they sit probably having moved no more than 100 kilometres (62 mi) relative to each other since the beginning of the period.
Holocene Epoch
The Holocene Epoch began approximately 11,700 calendar years before present and continues to the present. During the Holocene, continental motions have been less than a kilometer.
The last glacial period of the current ice age ended about 10,000 years ago. Ice melt caused world sea levels to rise about 35 metres (115 ft) in the early part of the Holocene. In addition, many areas above about 40 degrees north latitude had been depressed by the weight of the Pleistocene glaciers and rose as much as 180 metres (591 ft) over the late Pleistocene and Holocene, and are still rising today. The sea level rise and temporary land depression allowed temporary marine incursions into areas that are now far from the sea. Holocene marine fossils are known from Vermont, Quebec, Ontario and Michigan. Other than higher latitude temporary marine incursions associated with glacial depression, Holocene fossils are found primarily in lakebed, floodplain and cave deposits. Holocene marine deposits along low-latitude coastlines are rare because the rise in sea levels during the period exceeds any likely upthrusting of non-glacial origin. Post-glacial rebound in Scandinavia resulted in the emergence of coastal areas around the Baltic Sea, including much of Finland. The region continues to rise, still causing weak earthquakes across Northern Europe. The equivalent event in North America was the rebound of Hudson Bay, as it shrank from its larger, immediate post-glacial Tyrrell Sea phase, to near its present boundaries.
See also
Astronomical chronology
Age of Earth
Age of the universe
Chronological dating, archaeological chronology
Absolute dating
Relative dating
Phase (archaeology)
Archaeological association
Geochronology
Future of Earth
Geologic time scale
Plate reconstruction
Plate tectonics
Thermochronology
Timeline of natural history
List of geochronologic names
General
Consilience, evidence from independent, unrelated sources can "converge" on strong conclusions
References
Further reading
External links
Cosmic Evolution — a detailed look at events from the origin of the universe to the present
Valley, John W. "A Cool Early Earth?" Scientific American. 2005 Oct:58–65. – discusses the timing of the formation of the oceans and other major events in Earth's early history.
Davies, Paul. "Quantum leap of life". The Guardian. 2005 Dec 20. – discusses speculation into the role of quantum systems in the origin of life
Evolution timeline (requires Flash Player). Animated story of life since about 13,700,000,000 shows everything from the big bang to the formation of the Earth and the development of bacteria and other organisms to the ascent of man.
Theory of the Earth and Abstract of the Theory of the Earth
Paleomaps Since 600 Ma (Mollweide Projection, Longitude 0) Archived 2012-10-20 at the Wayback Machine
Paleomaps Since 600 Ma (Mollweide Projection, Longitude 180) Archived 2012-10-20 at the Wayback Machine
Ageing the Earth on In Our Time at the BBC |
interglacial | An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene interglacial began at the end of the Pleistocene, about 11,700 years ago.
Pleistocene
During the 2.5 million years of the Pleistocene, numerous glacials, or significant advances of continental ice sheets, in North America and Europe, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials.
During interglacials, such as the present one, the climate warms and the tundra recedes polewards following the ice sheets. Forests return to areas that once supported tundra vegetation. Interglacials are identified on land or in shallow epicontinental seas by their paleontology. Floral and faunal remains of species pointing to temperate climate and indicating a specific age are used to identify particular interglacials. Commonly used are mammalian and molluscan species, pollen and plant macro-remains (seeds and fruits). However, many other fossil remains may be helpful: insects, ostracods, foraminifera, diatoms, etc. Recently, ice cores and ocean sediment cores provide more quantitative and accurately-dated evidence for temperatures and total ice volumes.
Interglacials and glacials coincide with cyclic changes in Earth's orbit. Three orbital variations contribute to interglacials. The first is a change in Earth's orbit around the Sun, or eccentricity. The second is a shift in the tilt of Earth's axis, or obliquity. The third is the wobbling motion of Earth's axis, or precession.In the Southern Hemisphere, warmer summers occur when the lower-half of Earth is tilted toward the Sun and the planet is nearest the Sun in its elliptical orbit. Cooler summers occur when Earth is farthest from the Sun during the Southern Hemisphere summer. Such effects are more pronounced when the eccentricity of the orbit is large. When the obliquity is large, seasonal changes are more extreme.Interglacials are a useful tool for geological mapping and for anthropologists, as they can be used as a dating method for hominid fossils.Brief periods of milder climate that occurred during the last glacial are called interstadials. Most, but not all, interstadials are shorter than interglacials. Interstadial climates may have been relatively warm, but not necessarily. Because the colder periods (stadials) have often been very dry, wetter (not necessarily warmer) periods have been registered in the sedimentary record as interstadials as well.
The oxygen isotope ratio obtained from seabed sediment core samples, a proxy for the average global temperature, is an important source of information for changes in Earth's climate.
An interglacial optimum, or climatic optimum of an interglacial, is the period within an interglacial that experienced the most 'favourable' climate and often occurs during the middle of that interglacial. The climatic optimum of an interglacial both follows and is followed by phases within the same interglacial that experienced a less favourable climate (but still a 'better' climate than the one during the preceding or succeeding glacials). During an interglacial optimum, sea levels rise to their highest values, but not necessarily exactly at the same time as the climatic optimum.
Specific interglacials
The last six interglacials are:
Marine Isotope Stage 13 (524–474 thousand years ago).
Hoxnian / Holstein / Mindel-Riss / Marine Isotope Stage 11 (424–374 thousand years ago).
Purfleet Interglacial / Holstein / Mindel-Riss / Marine Isotope Stage 9 (337–300 thousand years ago).
La Bouchet Interglacial / Arousa Interglacial / Aveley Interglacial / Marine Isotope Stage 7e (242–230 thousand years ago). MIS 7a, MIS 7b and MIS 7c may or may not be included. MIS 7d was a cold period dividing the MIS 7 interglacial into two distinct periods. MIS 7e contained the climatic optimum.
Eemian / Marine Isotope Stage 5e (130–115 thousand years ago). The preceding interglacial optimum occurred during the Late Pleistocene Eemian Stage, 131–114 ka. During the Eemian the climatic optimum took place during pollen zone E4 in the type area (city of Amersfoort, Netherlands). Here this zone is characterized by the expansion of Quercus (oak), Corylus (hazel), Taxus (yew), Ulmus (elm), Fraxinus (ash), Carpinus (hornbeam), and Picea (spruce). During the Eemian Stage (from about 128,000 BCE until 113,000 BCE), sea level was between 5 and 9.4 meters higher than today and the water temperature of the North Sea was about 2 °C higher than at present.
Holocene (12,000 years ago to the present). During the present interglacial, the Holocene, the climatic optimum occurred during the Subboreal (5 to 2.5 ka BP, which corresponds to 3000 BC–500 BC) and Atlanticum (9 to 5 ka, which corresponds to roughly 7000 BC–3000 BC). The current climatic phase following this climatic optimum is still within the same interglacial (the Holocene). That warm period was followed by a gradual decline until about 2000 years ago, with another warm period until the Little Ice Age (1250–1850).
See also
Greenhouse and icehouse Earth
Milankovitch cycles
Snowball Earth
Interstadial periods
Last glacial maximum
Timeline of glaciation
== References == |
geology | Geology (from Ancient Greek γῆ (gê) 'earth', and λoγία (-logía) 'study of, discourse') is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth sciences, including hydrology. It is integrated with Earth system science and planetary science.
Geology describes the structure of the Earth on and beneath its surface and the processes that have shaped that structure. Geologists study the mineralogical composition of rocks in order to get insight into their history of formation. Geology determines the relative ages of rocks found at a given location; geochemistry (a branch of geology) determines their absolute ages. By combining various petrological, crystallographic, and paleontological tools, geologists are able to chronicle the geological history of the Earth as a whole. One aspect is to demonstrate the age of the Earth. Geology provides evidence for plate tectonics, the evolutionary history of life, and the Earth's past climates.
Geologists broadly study the properties and processes of Earth and other terrestrial planets. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including fieldwork, rock description, geophysical techniques, chemical analysis, physical experiments, and numerical modelling. In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding natural hazards, remediating environmental problems, and providing insights into past climate change. Geology is a major academic discipline, and it is central to geological engineering and plays an important role in geotechnical engineering.
Geological material
The majority of geological data comes from research on solid Earth materials. Meteorites and other extraterrestrial natural materials are also studied by geological methods.
Mineral
Minerals are naturally occurring elements and compounds with a definite homogeneous chemical composition and ordered atomic composition.
Each mineral has distinct physical properties, and there are many tests to determine each of them. Minerals are often identified through these tests. The specimens can be tested for:
Luster: Quality of light reflected from the surface of a mineral. Examples are metallic, pearly, waxy, dull.
Color: Minerals are grouped by their color. Mostly diagnostic but impurities can change a mineral's color.
Streak: Performed by scratching the sample on a porcelain plate. The color of the streak can help name the mineral.
Hardness: The resistance of a mineral to scratching.
Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces, and the latter a breakage along closely spaced parallel planes.
Specific gravity: the weight of a specific volume of a mineral.
Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing.
Magnetism: Involves using a magnet to test for magnetism.
Taste: Minerals can have a distinctive taste such as halite (which tastes like table salt).
Rock
A rock is any naturally occurring solid mass or aggregate of minerals or mineraloids. Most research in geology is associated with the study of rocks, as they provide the primary record of the majority of the geological history of the Earth. There are three major types of rock: igneous, sedimentary, and metamorphic. The rock cycle
illustrates the relationships among them (see diagram).
When a rock solidifies or crystallizes from melt (magma or lava), it is an igneous rock. This rock can be weathered and eroded, then redeposited and lithified into a sedimentary rock. It can then be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric. All three types may melt again, and when this happens, new magma is formed, from which an igneous rock may once again solidify.
Organic matter, such as coal, bitumen, oil, and natural gas, is linked mainly to organic-rich sedimentary rocks.
To study all three types of rock, geologists evaluate the minerals of which they are composed and their other physical properties, such as texture and fabric.
Unlithified material
Geologists also study unlithified materials (referred to as superficial deposits) that lie above the bedrock. This study is often known as Quaternary geology, after the Quaternary period of geologic history, which is the most recent period of geologic time.
Magma
Magma is the original unlithified source of all igneous rocks. The active flow of molten rock is closely studied in volcanology, and igneous petrology aims to determine the history of igneous rocks from their original molten source to their final crystallization.
Whole-Earth structure
Plate tectonics
In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, solid, upper mantle, which is called the asthenosphere. This theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle (that is, the heat transfer caused by the slow movement of ductile mantle rock). Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is actually the rigid upper thermal boundary layer of the convecting mantle. This coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics.
The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geological features are explained as plate boundaries.
For example:
Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent boundaries, where two plates move apart.
Arcs of volcanoes and earthquakes are theorized as convergent boundaries, where one plate subducts, or moves, under another.Transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes. Plate tectonics also has provided a mechanism for Alfred Wegener's theory of continental drift, in which the continents move across the surface of the Earth over geological time. They also provided a driving force for crustal deformation, and a new setting for the observations of structural geology. The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convecting mantle.
Earth structure
Advances in seismology, computer modeling, and mineralogy and crystallography at high temperatures and pressures give insights into the internal composition and structure of the Earth.
Seismologists can use the arrival times of seismic waves to image the interior of the Earth. Early advances in this field showed the existence of a liquid outer core (where shear waves were not able to propagate) and a dense solid inner core. These advances led to the development of a layered model of the Earth, with a crust and lithosphere on top, the mantle below (separated within itself by seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that. More recently, seismologists have been able to create detailed images of wave speeds inside the earth in the same way a doctor images a body in a CT scan. These images have led to a much more detailed view of the interior of the Earth, and have replaced the simplified layered model with a much more dynamic model.
Mineralogists have been able to use the pressure and temperature data from the seismic and modeling studies alongside knowledge of the elemental composition of the Earth to reproduce these conditions in experimental settings and measure changes within the crystal structure. These studies explain the chemical changes associated with the major seismic discontinuities in the mantle and show the crystallographic structures expected in the inner core of the Earth.
Geological time
The geological time scale encompasses the history of the Earth. It is bracketed at the earliest by the dates of the first Solar System material at 4.567 Ga (or 4.567 billion years ago) and the formation of the Earth at
4.54 Ga
(4.54 billion years), which is the beginning of the informally recognized Hadean eon – a division of geological time. At the later end of the scale, it is marked by the present day (in the Holocene epoch).
Timescale of the Earth
The following five timelines show the geologic time scale to scale. The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon. The second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in the third timeline, the most recent period is expanded in the fourth timeline, and the most recent epoch is expanded in the fifth timeline.
Important milestones on Earth
4.567 Ga (gigaannum: billion years ago): Solar system formation
4.54 Ga: Accretion, or formation, of Earth
c. 4 Ga: End of Late Heavy Bombardment, the first life
c. 3.5 Ga: Start of photosynthesis
c. 2.3 Ga: Oxygenated atmosphere, first snowball Earth
730–635 Ma (megaannum: million years ago): second snowball Earth
541 ± 0.3 Ma: Cambrian explosion – vast multiplication of hard-bodied life; first abundant fossils; start of the Paleozoic
c. 380 Ma: First vertebrate land animals
250 Ma: Permian-Triassic extinction – 90% of all land animals die; end of Paleozoic and beginning of Mesozoic
66 Ma: Cretaceous–Paleogene extinction – Dinosaurs die; end of Mesozoic and beginning of Cenozoic
c. 7 Ma: First hominins appear
3.9 Ma: First Australopithecus, direct ancestor to modern Homo sapiens, appear
200 ka (kiloannum: thousand years ago): First modern Homo sapiens appear in East Africa
Timescale of the Moon
Timescale of Mars
Dating methods
Relative dating
Methods for relative dating were developed when geology first emerged as a natural science. Geologists still use the following principles today as a means to provide information about geological history and the timing of geological events.
The principle of uniformitarianism states that the geological processes observed in operation that modify the Earth's crust at present have worked in much the same way over geological time. A fundamental principle of geology advanced by the 18th-century Scottish physician and geologist James Hutton is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now."The principle of intrusive relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock. Different types of intrusions include stocks, laccoliths, batholiths, sills and dikes.
The principle of cross-cutting relationships pertains to the formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether the fault is a normal fault or a thrust fault.The principle of inclusions and components states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix. As a result, xenoliths are older than the rock that contains them.
The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal).The principle of superposition states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. Logically a younger layer cannot slip beneath a layer previously deposited. This principle allows sedimentary layers to be viewed as a form of the vertical timeline, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed.The principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist during the same period throughout the world, their presence or (sometimes) absence provides a relative age of the formations where they appear. Based on principles that William Smith laid out almost a hundred years before the publication of Charles Darwin's theory of evolution, the principles of succession developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilization, localization of fossil types due to lateral changes in habitat (facies change in sedimentary strata), and that not all fossils formed globally at the same time.
Absolute dating
Geologists also use methods to determine the absolute age of rock samples and geological events. These dates are useful on their own and may also be used in conjunction with relative dating methods or to calibrate relative methods.At the beginning of the 20th century, advancement in geological science was facilitated by the ability to obtain accurate absolute dates to geological events using radioactive isotopes and other methods. This changed the understanding of geological time. Previously, geologists could only use fossils and stratigraphic correlation to date sections of rock relative to one another. With isotopic dates, it became possible to assign absolute ages to rock units, and these absolute dates could be applied to fossil sequences in which there was datable material, converting the old relative ages into new absolute ages.
For many geological applications, isotope ratios of radioactive elements are measured in minerals that give the amount of time that has passed since a rock passed through its particular closure temperature, the point at which different radiometric isotopes stop diffusing into and out of the crystal lattice. These are used in geochronologic and thermochronologic studies. Common methods include uranium–lead dating, potassium–argon dating, argon–argon dating and uranium–thorium dating. These methods are used for a variety of applications. Dating of lava and volcanic ash layers found within a stratigraphic sequence can provide absolute age data for sedimentary rock units that do not contain radioactive isotopes and calibrate relative dating techniques. These methods can also be used to determine ages of pluton emplacement.
Thermochemical techniques can be used to determine temperature profiles within the crust, the uplift of mountain ranges, and paleo-topography.
Fractionation of the lanthanide series elements is used to compute ages since rocks were removed from the mantle.
Other methods are used for more recent events. Optically stimulated luminescence and cosmogenic radionuclide dating are used to date surfaces and/or erosion rates. Dendrochronology can also be used for the dating of landscapes. Radiocarbon dating is used for geologically young materials containing organic carbon.
Geological development of an area
The geology of an area changes through time as rock units are deposited and inserted, and deformational processes alter their shapes and locations.
Rock units are first emplaced either by deposition onto the surface or intrusion into the overlying rock. Deposition can occur when sediments settle onto the surface of the Earth and later lithify into sedimentary rock, or when as volcanic material such as volcanic ash or lava flows blanket the surface. Igneous intrusions such as batholiths, laccoliths, dikes, and sills, push upwards into the overlying rock, and crystallize as they intrude.
After the initial sequence of rocks has been deposited, the rock units can be deformed and/or metamorphosed. Deformation typically occurs as a result of horizontal shortening, horizontal extension, or side-to-side (strike-slip) motion. These structural regimes broadly relate to convergent boundaries, divergent boundaries, and transform boundaries, respectively, between tectonic plates.
When rock units are placed under horizontal compression, they shorten and become thicker. Because rock units, other than muds, do not significantly change in volume, this is accomplished in two primary ways: through faulting and folding. In the shallow crust, where brittle deformation can occur, thrust faults form, which causes the deeper rock to move on top of the shallower rock. Because deeper rock is often older, as noted by the principle of superposition, this can result in older rocks moving on top of younger ones. Movement along faults can result in folding, either because the faults are not planar or because rock layers are dragged along, forming drag folds as slip occurs along the fault. Deeper in the Earth, rocks behave plastically and fold instead of faulting. These folds can either be those where the material in the center of the fold buckles upwards, creating "antiforms", or where it buckles downwards, creating "synforms". If the tops of the rock units within the folds remain pointing upwards, they are called anticlines and synclines, respectively. If some of the units in the fold are facing downward, the structure is called an overturned anticline or syncline, and if all of the rock units are overturned or the correct up-direction is unknown, they are simply called by the most general terms, antiforms, and synforms.
Even higher pressures and temperatures during horizontal shortening can cause both folding and metamorphism of the rocks. This metamorphism causes changes in the mineral composition of the rocks; creates a foliation, or planar surface, that is related to mineral growth under stress. This can remove signs of the original textures of the rocks, such as bedding in sedimentary rocks, flow features of lavas, and crystal patterns in crystalline rocks.
Extension causes the rock units as a whole to become longer and thinner. This is primarily accomplished through normal faulting and through the ductile stretching and thinning. Normal faults drop rock units that are higher below those that are lower. This typically results in younger units ending up below older units. Stretching of units can result in their thinning. In fact, at one location within the Maria Fold and Thrust Belt, the entire sedimentary sequence of the Grand Canyon appears over a length of less than a meter. Rocks at the depth to be ductilely stretched are often also metamorphosed. These stretched rocks can also pinch into lenses, known as boudins, after the French word for "sausage" because of their visual similarity.
Where rock units slide past one another, strike-slip faults develop in shallow regions, and become shear zones at deeper depths where the rocks deform ductilely.
The addition of new rock units, both depositionally and intrusively, often occurs during deformation. Faulting and other deformational processes result in the creation of topographic gradients, causing material on the rock unit that is increasing in elevation to be eroded by hillslopes and channels. These sediments are deposited on the rock unit that is going down. Continual motion along the fault maintains the topographic gradient in spite of the movement of sediment and continues to create accommodation space for the material to deposit. Deformational events are often also associated with volcanism and igneous activity. Volcanic ashes and lavas accumulate on the surface, and igneous intrusions enter from below. Dikes, long, planar igneous intrusions, enter along cracks, and therefore often form in large numbers in areas that are being actively deformed. This can result in the emplacement of dike swarms, such as those that are observable across the Canadian shield, or rings of dikes around the lava tube of a volcano.
All of these processes do not necessarily occur in a single environment and do not necessarily occur in a single order. The Hawaiian Islands, for example, consist almost entirely of layered basaltic lava flows. The sedimentary sequences of the mid-continental United States and the Grand Canyon in the southwestern United States contain almost-undeformed stacks of sedimentary rocks that have remained in place since Cambrian time. Other areas are much more geologically complex. In the southwestern United States, sedimentary, volcanic, and intrusive rocks have been metamorphosed, faulted, foliated, and folded. Even older rocks, such as the Acasta gneiss of the Slave craton in northwestern Canada, the oldest known rock in the world have been metamorphosed to the point where their origin is indiscernible without laboratory analysis. In addition, these processes can occur in stages. In many places, the Grand Canyon in the southwestern United States being a very visible example, the lower rock units were metamorphosed and deformed, and then deformation ended and the upper, undeformed units were deposited. Although any amount of rock emplacement and rock deformation can occur, and they can occur any number of times, these concepts provide a guide to understanding the geological history of an area.
Methods of geology
Geologists use a number of fields, laboratory, and numerical modeling methods to decipher Earth history and to understand the processes that occur on and inside the Earth. In typical geological investigations, geologists use primary information related to petrology (the study of rocks), stratigraphy (the study of sedimentary layers), and structural geology (the study of positions of rock units and their deformation). In many cases, geologists also study modern soils, rivers, landscapes, and glaciers; investigate past and current life and biogeochemical pathways, and use geophysical methods to investigate the subsurface. Sub-specialities of geology may distinguish endogenous and exogenous geology.
Field methods
Geological field work varies depending on the task at hand. Typical fieldwork could consist of:
Geological mappingStructural mapping: identifying the locations of major rock units and the faults and folds that led to their placement there.
Stratigraphic mapping: pinpointing the locations of sedimentary facies (lithofacies and biofacies) or the mapping of isopachs of equal thickness of sedimentary rock
Surficial mapping: recording the locations of soils and surficial deposits
Surveying of topographic features
compilation of topographic maps
Work to understand change across landscapes, including:
Patterns of erosion and deposition
River-channel change through migration and avulsion
Hillslope processes
Subsurface mapping through geophysical methodsThese methods include:
Shallow seismic surveys
Ground-penetrating radar
Aeromagnetic surveys
Electrical resistivity tomography
They aid in:
Hydrocarbon exploration
Finding groundwater
Locating buried archaeological artifacts
High-resolution stratigraphy
Measuring and describing stratigraphic sections on the surface
Well drilling and logging
Biogeochemistry and geomicrobiologyCollecting samples to:
determine biochemical pathways
identify new species of organisms
identify new chemical compounds
and to use these discoveries to:
understand early life on Earth and how it functioned and metabolized
find important compounds for use in pharmaceuticals
Paleontology: excavation of fossil material
For research into past life and evolution
For museums and education
Collection of samples for geochronology and thermochronology
Glaciology: measurement of characteristics of glaciers and their motion
Petrology
In addition to identifying rocks in the field (lithology), petrologists identify rock samples in the laboratory. Two of the primary methods for identifying rocks in the laboratory are through optical microscopy and by using an electron microprobe. In an optical mineralogy analysis, petrologists analyze thin sections of rock samples using a petrographic microscope, where the minerals can be identified through their different properties in plane-polarized and cross-polarized light, including their birefringence, pleochroism, twinning, and interference properties with a conoscopic lens. In the electron microprobe, individual locations are analyzed for their exact chemical compositions and variation in composition within individual crystals. Stable and radioactive isotope studies provide insight into the geochemical evolution of rock units.
Petrologists can also use fluid inclusion data and perform high temperature and pressure physical experiments to understand the temperatures and pressures at which different mineral phases appear, and how they change through igneous and metamorphic processes. This research can be extrapolated to the field to understand metamorphic processes and the conditions of crystallization of igneous rocks. This work can also help to explain processes that occur within the Earth, such as subduction and magma chamber evolution.
Structural geology
Structural geologists use microscopic analysis of oriented thin sections of geological samples to observe the fabric within the rocks, which gives information about strain within the crystalline structure of the rocks. They also plot and combine measurements of geological structures to better understand the orientations of faults and folds to reconstruct the history of rock deformation in the area. In addition, they perform analog and numerical experiments of rock deformation in large and small settings.
The analysis of structures is often accomplished by plotting the orientations of various features onto stereonets. A stereonet is a stereographic projection of a sphere onto a plane, in which planes are projected as lines and lines are projected as points. These can be used to find the locations of fold axes, relationships between faults, and relationships between other geological structures.
Among the most well-known experiments in structural geology are those involving orogenic wedges, which are zones in which mountains are built along convergent tectonic plate boundaries. In the analog versions of these experiments, horizontal layers of sand are pulled along a lower surface into a back stop, which results in realistic-looking patterns of faulting and the growth of a critically tapered (all angles remain the same) orogenic wedge. Numerical models work in the same way as these analog models, though they are often more sophisticated and can include patterns of erosion and uplift in the mountain belt. This helps to show the relationship between erosion and the shape of a mountain range. These studies can also give useful information about pathways for metamorphism through pressure, temperature, space, and time.
Stratigraphy
In the laboratory, stratigraphers analyze samples of stratigraphic sections that can be returned from the field, such as those from drill cores. Stratigraphers also analyze data from geophysical surveys that show the locations of stratigraphic units in the subsurface. Geophysical data and well logs can be combined to produce a better view of the subsurface, and stratigraphers often use computer programs to do this in three dimensions. Stratigraphers can then use these data to reconstruct ancient processes occurring on the surface of the Earth, interpret past environments, and locate areas for water, coal, and hydrocarbon extraction.
In the laboratory, biostratigraphers analyze rock samples from outcrop and drill cores for the fossils found in them. These fossils help scientists to date the core and to understand the depositional environment in which the rock units formed. Geochronologists precisely date rocks within the stratigraphic section to provide better absolute bounds on the timing and rates of deposition.
Magnetic stratigraphers look for signs of magnetic reversals in igneous rock units within the drill cores. Other scientists perform stable-isotope studies on the rocks to gain information about past climate.
Planetary geology
With the advent of space exploration in the twentieth century, geologists have begun to look at other planetary bodies in the same ways that have been developed to study the Earth. This new field of study is called planetary geology (sometimes known as astrogeology) and relies on known geological principles to study other bodies of the solar system. This is a major aspect of planetary science, and largely focuses on the terrestrial planets, icy moons, asteroids, comets, and meteorites. However, some planetary geophysicists study the giant planets and exoplanets.Although the Greek-language-origin prefix geo refers to Earth, "geology" is often used in conjunction with the names of other planetary bodies when describing their composition and internal processes: examples are "the geology of Mars" and "Lunar geology". Specialized terms such as selenology (studies of the Moon), areology (of Mars), etc., are also in use.
Although planetary geologists are interested in studying all aspects of other planets, a significant focus is to search for evidence of past or present life on other worlds. This has led to many missions whose primary or ancillary purpose is to examine planetary bodies for evidence of life. One of these is the Phoenix lander, which analyzed Martian polar soil for water, chemical, and mineralogical constituents related to biological processes.
Applied geology
Economic geology
Economic geology is a branch of geology that deals with aspects of economic minerals that humankind uses to fulfill various needs. Economic minerals are those extracted profitably for various practical uses. Economic geologists help locate and manage the Earth's natural resources, such as petroleum and coal, as well as mineral resources, which include metals such as iron, copper, and uranium.
Mining geology
Mining geology consists of the extractions of mineral resources from the Earth. Some resources of economic interests include gemstones, metals such as gold and copper, and many minerals such as asbestos, perlite, mica, phosphates, zeolites, clay, pumice, quartz, and silica, as well as elements such as sulfur, chlorine, and helium.
Petroleum geology
Petroleum geologists study the locations of the subsurface of the Earth that can contain extractable hydrocarbons, especially petroleum and natural gas. Because many of these reservoirs are found in sedimentary basins, they study the formation of these basins, as well as their sedimentary and tectonic evolution and the present-day positions of the rock units.
Engineering geology
Engineering geology is the application of geological principles to engineering practice for the purpose of assuring that the geological factors affecting the location, design, construction, operation, and maintenance of engineering works are properly addressed. Engineering geology is distinct from geological engineering, particularly in North America.
In the field of civil engineering, geological principles and analyses are used in order to ascertain the mechanical principles of the material on which structures are built. This allows tunnels to be built without collapsing, bridges and skyscrapers to be built with sturdy foundations, and buildings to be built that will not settle in clay and mud.
Hydrology
Geology and geological principles can be applied to various environmental problems such as stream restoration, the restoration of brownfields, and the understanding of the interaction between natural habitat and the geological environment. Groundwater hydrology, or hydrogeology, is used to locate groundwater, which can often provide a ready supply of uncontaminated water and is especially important in arid regions, and to monitor the spread of contaminants in groundwater wells.
Paleoclimatology
Geologists also obtain data through stratigraphy, boreholes, core samples, and ice cores. Ice cores and sediment cores are used for paleoclimate reconstructions, which tell geologists about past and present temperature, precipitation, and sea level across the globe. These datasets are our primary source of information on global climate change outside of instrumental data.
Natural hazards
Geologists and geophysicists study natural hazards in order to enact safe building codes and warning systems that are used to prevent loss of property and life. Examples of important natural hazards that are pertinent to geology (as opposed those that are mainly or only pertinent to meteorology) are:
History
The study of the physical material of the Earth dates back at least to ancient Greece when Theophrastus (372–287 BCE) wrote the work Peri Lithon (On Stones). During the Roman period, Pliny the Elder wrote in detail of the many minerals and metals, then in practical use – even correctly noting the origin of amber. Additionally, in the 4th century BCE Aristotle made critical observations of the slow rate of geological change. He observed the composition of the land and formulated a theory where the Earth changes at a slow rate and that these changes cannot be observed during one person's lifetime. Aristotle developed one of the first evidence-based concepts connected to the geological realm regarding the rate at which the Earth physically changes.Abu al-Rayhan al-Biruni (973–1048 CE) was one of the earliest Persian geologists, whose works included the earliest writings on the geology of India, hypothesizing that the Indian subcontinent was once a sea. Drawing from Greek and Indian scientific literature that were not destroyed by the Muslim conquests, the Persian scholar Ibn Sina (Avicenna, 981–1037) proposed detailed explanations for the formation of mountains, the origin of earthquakes, and other topics central to modern geology, which provided an essential foundation for the later development of the science. In China, the polymath Shen Kuo (1031–1095) formulated a hypothesis for the process of land formation: based on his observation of fossil animal shells in a geological stratum in a mountain hundreds of miles from the ocean, he inferred that the land was formed by the erosion of the mountains and by deposition of silt.Georgius Agricola (1494–1555) published his groundbreaking work De Natura Fossilium in 1546 and is seen as the founder of geology as a scientific discipline.Nicolas Steno (1638–1686) is credited with the law of superposition, the principle of original horizontality, and the principle of lateral continuity: three defining principles of stratigraphy.
The word geology was first used by Ulisse Aldrovandi in 1603, then by Jean-André Deluc in 1778 and introduced as a fixed term by Horace-Bénédict de Saussure in 1779. The word is derived from the Greek γῆ, gê, meaning "earth" and λόγος, logos, meaning "speech". But according to another source, the word "geology" comes from a Norwegian, Mikkel Pedersøn Escholt (1600–1669), who was a priest and scholar. Escholt first used the definition in his book titled, Geologia Norvegica (1657).William Smith (1769–1839) drew some of the first geological maps and began the process of ordering rock strata (layers) by examining the fossils contained in them.In 1763, Mikhail Lomonosov published his treatise On the Strata of Earth. His work was the first narrative of modern geology, based on the unity of processes in time and explanation of the Earth's past from the present.James Hutton (1726–1797) is often viewed as the first modern geologist. In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh. In his paper, he explained his theory that the Earth must be much older than had previously been supposed to allow enough time for mountains to be eroded and for sediments to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. Hutton published a two-volume version of his ideas in 1795.Followers of Hutton were known as Plutonists because they believed that some rocks were formed by vulcanism, which is the deposition of lava from volcanoes, as opposed to the Neptunists, led by Abraham Werner, who believed that all rocks had settled out of a large ocean whose level gradually dropped over time.
The first geological map of the U.S. was produced in 1809 by William Maclure. In 1807, Maclure commenced the self-imposed task of making a geological survey of the United States. Almost every state in the Union was traversed and mapped by him, the Allegheny Mountains being crossed and recrossed some 50 times. The results of his unaided labours were submitted to the American Philosophical Society in a memoir entitled Observations on the Geology of the United States explanatory of a Geological Map, and published in the Society's Transactions, together with the nation's first geological map. This antedates William Smith's geological map of England by six years, although it was constructed using a different classification of rocks.
Sir Charles Lyell (1797–1875) first published his famous book, Principles of Geology, in 1830. This book, which influenced the thought of Charles Darwin, successfully promoted the doctrine of uniformitarianism. This theory states that slow geological processes have occurred throughout the Earth's history and are still occurring today. In contrast, catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time.
Much of 19th-century geology revolved around the question of the Earth's exact age. Estimates varied from a few hundred thousand to billions of years. By the early 20th century, radiometric dating allowed the Earth's age to be estimated at two billion years. The awareness of this vast amount of time opened the door to new theories about the processes that shaped the planet.
Some of the most significant advances in 20th-century geology have been the development of the theory of plate tectonics in the 1960s and the refinement of estimates of the planet's age. Plate tectonics theory arose from two separate geological observations: seafloor spreading and continental drift. The theory revolutionized the Earth sciences. Today the Earth is known to be approximately 4.5 billion years old.
Fields or related disciplines
See also
References
External links
One Geology: This interactive geological map of the world is an international initiative of the geological surveys around the globe. This groundbreaking project was launched in 2007 and contributed to the 'International Year of Planet Earth', becoming one of their flagship projects.
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Chronostratigraphy benchmarks |
eocene | The Eocene (IPA: EE-ə-seen, EE-oh-) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name Eocene comes from the Ancient Greek ἠώς (ēṓs, "dawn") and καινός (kainós, "new") and refers to the "dawn" of modern ('new') fauna that appeared during the epoch.The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by a brief period in which the concentration of the carbon isotope 13C in the atmosphere was exceptionally low in comparison with the more common isotope 12C. The end is set at a major extinction event called the Grande Coupure (the "Great Break" in continuity) or the Eocene–Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay. As with other geologic periods, the strata that define the start and end of the epoch are well identified, though their exact dates are slightly uncertain.
Etymology
The term "Eocene" is derived from Ancient Greek ἠώς eos meaning "dawn", and καινός kainos meaning "new" or "recent", as the epoch saw the dawn of recent, or modern, life.
Scottish geologist Charles Lyell (ignoring the Quaternary) divided the Tertiary Epoch into the Eocene, Miocene, Pliocene, and New Pliocene (Holocene) Periods in 1833. British geologist John Phillips proposed the Cenozoic in 1840 in place of the Tertiary, and Austrian paleontologist Moritz Hörnes introduced the Paleogene for the Eocene and Neogene for the Miocene and Pliocene in 1853. After decades of inconsistent usage, the newly formed International Commission on Stratigraphy (ICS), in 1969, standardized stratigraphy based on the prevailing opinions in Europe: the Cenozoic Era subdivided into the Tertiary and Quaternary sub-eras, and the Tertiary subdivided into the Paleogene and Neogene periods. In 1978, the Paleogene was officially defined as the Paleocene, Eocene, and Oligocene epochs; and the Neogene as the Miocene and Pliocene epochs. In 1989, Tertiary and Quaternary were removed from the time scale due to the arbitrary nature of their boundary, but Quaternary was reinstated in 2009.
Geology
Boundaries
The Eocene is a dynamic epoch that represents global climatic transitions between two climatic extremes, transitioning from the hot house to the cold house. The beginning of the Eocene is marked by the Paleocene–Eocene Thermal Maximum, a short period of intense warming and ocean acidification brought about by the release of carbon en masse into the atmosphere and ocean systems, which led to a mass extinction of 30–50% of benthic foraminifera (single-celled species which are used as bioindicators of the health of a marine ecosystem)—one of the largest in the Cenozoic. This event happened around 55.8 Ma, and was one of the most significant periods of global change during the Cenozoic.The middle Eocene was characterized by the shift towards a cooler climate at the end of the EECO, around 47.8 Ma, which was briefly interrupted by another warming event called the middle Eocene climatic optimum (MECO). Lasting for about 400,000 years, the MECO was responsible for a globally uniform 4° to 6°C warming of both the surface and deep oceans, as inferred from foraminiferal stable oxygen isotope records. The resumption of a long-term gradual cooling trend resulted in a glacial maximum at the late Eocene/early Oligocene boundary.
The end of the Eocene was also marked by the Eocene–Oligocene extinction event, also known as the Grande Coupure.
Stratigraphy
The Eocene is conventionally divided into early (56–47.8 Ma), middle (47.8–38 Ma), and late (38–33.9 Ma) subdivisions. The corresponding rocks are referred to as lower, middle, and upper Eocene. The Ypresian Stage constitutes the lower, the Priabonian Stage the upper; and the Lutetian and Bartonian stages are united as the middle Eocene.
Palaeogeography and tectonics
During the Eocene, the continents continued to drift toward their present positions.
At the beginning of the period, Australia and Antarctica remained connected, and warm equatorial currents may have mixed with colder Antarctic waters, distributing the heat around the planet and keeping global temperatures high. When Australia split from the southern continent around 45 Ma, the warm equatorial currents were routed away from Antarctica. An isolated cold water channel developed between the two continents. However, modeling results call into question the thermal isolation model for late Eocene cooling, and decreasing carbon dioxide levels in the atmosphere may have been more important. Once the Antarctic region began to cool down, the ocean surrounding Antarctica began to freeze, sending cold water and icefloes north and reinforcing the cooling.The northern supercontinent of Laurasia began to fragment, as Europe, Greenland and North America drifted apart.In western North America, the Laramide Orogeny came to an end in the Eocene, and compression was replaced with crustal extension that ultimately gave rise to the Basin and Range Province. The Kishenehn Basin, around 1.5 km in elevation during the Lutetian, was uplifted to an altitude of 2.5 km by the Priabonian. Huge lakes formed in the high flat basins among uplifts, resulting in the deposition of the Green River Formation lagerstätte.At about 35 Ma, an asteroid impact on the eastern coast of North America formed the Chesapeake Bay impact crater.In Europe, the Tethys Sea finally disappeared, while the uplift of the Alps isolated its final remnant, the Mediterranean, and created another shallow sea with island archipelagos to the north. Planktonic foraminifera in the northwestern Peri-Tethys are very similar to those of the Tethys in the middle Lutetian but become completely disparate in the Bartonian, indicating biogeographic separation. Though the North Atlantic was opening, a land connection appears to have remained between North America and Europe since the faunas of the two regions are very similar.Eurasia was separated in three different landmasses 50 Ma; Western Europe, Balkanatolia and Asia. About 40 Ma, Balkanatolia and Asia were connected, while Europe was connected 34 Ma. The Fushun Basin contained large, suboxic lakes known as the paleo-Jijuntun Lakes.India collided with Asia, folding to initiate formation of the Himalayas. The incipient subcontinent collided with the Kohistan–Ladakh Arc around 50.2 Ma and with Karakoram around 40.4 Ma, with the final collision between Asia and India occurring ~40 Ma.
Climate
The Eocene Epoch contained a wide variety of different climate conditions that includes the warmest climate in the Cenozoic Era, and arguably the warmest time interval since the Permian-Triassic mass extinction and Early Triassic, and ends in an icehouse climate. The evolution of the Eocene climate began with warming after the end of the Paleocene–Eocene Thermal Maximum (PETM) at 56 Ma to a maximum during the Eocene Optimum at around 49 Ma. Recent study show elevation-dependent temperature changes during the Eocene hothouse. During this period of time, little to no ice was present on Earth with a smaller difference in temperature from the equator to the poles. Because of this the maximum sea level was 150 meters higher than current levels. Following the maximum was a descent into an icehouse climate from the Eocene Optimum to the Eocene–Oligocene transition at 34 Ma. During this decrease, ice began to reappear at the poles, and the Eocene–Oligocene transition is the period of time when the Antarctic ice sheet began to rapidly expand.
Early Eocene
Greenhouse gases, in particular carbon dioxide and methane, played a significant role during the Eocene in controlling the surface temperature. The end of the PETM was met with very large sequestration of carbon dioxide into the forms of methane clathrate, coal, and crude oil at the bottom of the Arctic Ocean, that reduced the atmospheric carbon dioxide. This event was similar in magnitude to the massive release of greenhouse gasses at the beginning of the PETM, and it is hypothesized that the sequestration was mainly due to organic carbon burial and weathering of silicates. For the early Eocene there is much discussion on how much carbon dioxide was in the atmosphere. This is due to numerous proxies representing different atmospheric carbon dioxide content. For example, diverse geochemical and paleontological proxies indicate that at the maximum of global warmth the atmospheric carbon dioxide values were at 700–900 ppm, while model simulations suggest a concentration of 1,680 ppm fits best with deep sea, sea surface, and near-surface air temperatures of the time. Other proxies such as pedogenic (soil building) carbonate and marine boron isotopes indicate large changes of carbon dioxide of over 2,000 ppm over periods of time of less than 1 million years. Sources for this large influx of carbon dioxide could be attributed to volcanic out-gassing due to North Atlantic rifting or oxidation of methane stored in large reservoirs deposited from the PETM event in the sea floor or wetland environments. For contrast, today the carbon dioxide levels are at 400 ppm or 0.04%. During the early Eocene, methane was another greenhouse gas that had a drastic effect on the climate. Methane has 30 times more of a warming effect than carbon dioxide on a 100-year scale (i.e., methane has a global warming potential of 29.8±11). Most of the methane released to the atmosphere during this period of time would have been from wetlands, swamps, and forests. The atmospheric methane concentration today is 0.000179% or 1.79 ppmv. As a result of the warmer climate and the sea level rise associated with the early Eocene, more wetlands, more forests, and more coal deposits would have been available for methane release. If we compare the early Eocene production of methane to current levels of atmospheric methane, the early Eocene would have produced triple the amount of methane. The warm temperatures during the early Eocene could have increased methane production rates, and methane that is released into the atmosphere would in turn warm the troposphere, cool the stratosphere, and produce water vapor and carbon dioxide through oxidation. Biogenic production of methane produces carbon dioxide and water vapor along with the methane, as well as yielding infrared radiation. The breakdown of methane in an atmosphere containing oxygen produces carbon monoxide, water vapor and infrared radiation. The carbon monoxide is not stable, so it eventually becomes carbon dioxide and in doing so releases yet more infrared radiation. Water vapor traps more infrared than does carbon dioxide. At about the beginning of the Eocene Epoch (55.8–33.9 Ma) the amount of oxygen in the Earth's atmosphere more or less doubled.During the warming in the early Eocene between 55 and 52 Ma, there were a series of short-term changes of carbon isotope composition in the ocean. These isotope changes occurred due to the release of carbon from the ocean into the atmosphere that led to a temperature increase of 4–8 °C (7.2–14.4 °F) at the surface of the ocean. Recent analysis of and research into these hyperthermals in the early Eocene has led to hypotheses that the hyperthermals are based on orbital parameters, in particular eccentricity and obliquity. The hyperthermals in the early Eocene, notably the Palaeocene–Eocene Thermal Maximum (PETM), the Eocene Thermal Maximum 2 (ETM2), and the Eocene Thermal Maximum 3 (ETM3), were analyzed and found that orbital control may have had a role in triggering the ETM2 and ETM3. An enhancement of the biological pump proved effective at sequestering excess carbon during the recovery phases of these hyperthermals. These hyperthermals led to increased perturbations in planktonic and benthic foraminifera, with a higher rate of fluvial sedimentation as a consequence of the warmer temperatures. Unlike the PETM, the lesser hyperthermals of the Early Eocene had negligible consequences for terrestrial mammals. These Early Eocene hyperthermals produced a sustained period of extremely hot climate known as the Early Eocene Climatic Optimum (EECO). During the early and middle EECO, the superabundance of the euryhaline dinocyst Homotryblium in New Zealand indicates elevated ocean salinity in the region.
Equable climate problem
One of the unique features of the Eocene's climate as mentioned before was the equable and homogeneous climate that existed in the early parts of the Eocene. A multitude of proxies support the presence of a warmer equable climate being present during this period of time. A few of these proxies include the presence of fossils native to warm climates, such as crocodiles, located in the higher latitudes, the presence in the high latitudes of frost-intolerant flora such as palm trees which cannot survive during sustained freezes, and fossils of snakes found in the tropics that would require much higher average temperatures to sustain them. TEX86 BAYSPAR measurements indicate extremely high sea surface temperatures of 40 °C (104 °F) to 45 °C (113 °F) at low latitudes, although clumped isotope analyses point to a maximum low latitude sea surface temperature of 36.3 °C (97.3 °F) ± 1.9 °C (35.4 °F) during the EECO. Relative to present-day values, bottom water temperatures are 10 °C (18 °F) higher according to isotope proxies. With these bottom water temperatures, temperatures in areas where deep water forms near the poles are unable to be much cooler than the bottom water temperatures.An issue arises, however, when trying to model the Eocene and reproduce the results that are found with the proxy data. Using all different ranges of greenhouse gasses that occurred during the early Eocene, models were unable to produce the warming that was found at the poles and the reduced seasonality that occurs with winters at the poles being substantially warmer. The models, while accurately predicting the tropics, tend to produce significantly cooler temperatures of up to 20 °C (36 °F) colder than the actual determined temperature at the poles. This error has been classified as the "equable climate problem". To solve this problem, the solution would involve finding a process to warm the poles without warming the tropics. Some hypotheses and tests which attempt to find the process are listed below.
Large lakes
Due to the nature of water as opposed to land, less temperature variability would be present if a large body of water is also present. In an attempt to try to mitigate the cooling polar temperatures, large lakes were proposed to mitigate seasonal climate changes. To replicate this case, a lake was inserted into North America and a climate model was run using varying carbon dioxide levels. The model runs concluded that while the lake did reduce the seasonality of the region greater than just an increase in carbon dioxide, the addition of a large lake was unable to reduce the seasonality to the levels shown by the floral and faunal data.
Ocean heat transport
The transport of heat from the tropics to the poles, much like how ocean heat transport functions in modern times, was considered a possibility for the increased temperature and reduced seasonality for the poles. With the increased sea surface temperatures and the increased temperature of the deep ocean water during the early Eocene, one common hypothesis was that due to these increases there would be a greater transport of heat from the tropics to the poles. Simulating these differences, the models produced lower heat transport due to the lower temperature gradients and were unsuccessful in producing an equable climate from only ocean heat transport.
Orbital parameters
While typically seen as a control on ice growth and seasonality, the orbital parameters were theorized as a possible control on continental temperatures and seasonality. Simulating the Eocene by using an ice free planet, eccentricity, obliquity, and precession were modified in different model runs to determine all the possible different scenarios that could occur and their effects on temperature. One particular case led to warmer winters and cooler summer by up to 30% in the North American continent, and it reduced the seasonal variation of temperature by up to 75%. While orbital parameters did not produce the warming at the poles, the parameters did show a great effect on seasonality and needed to be considered.
Polar stratospheric clouds
Another method considered for producing the warm polar temperatures were polar stratospheric clouds. Polar stratospheric clouds are clouds that occur in the lower stratosphere at very low temperatures. Polar stratospheric clouds have a great impact on radiative forcing. Due to their minimal albedo properties and their optical thickness, polar stratospheric clouds act similar to a greenhouse gas and traps outgoing longwave radiation. Different types of polar stratospheric clouds occur in the atmosphere: polar stratospheric clouds that are created due to interactions with nitric or sulfuric acid and water (Type I) or polar stratospheric clouds that are created with only water ice (Type II).Methane is an important factor in the creation of the primary Type II polar stratospheric clouds that were created in the early Eocene. Since water vapor is the only supporting substance used in Type II polar stratospheric clouds, the presence of water vapor in the lower stratosphere is necessary where in most situations the presence of water vapor in the lower stratosphere is rare. When methane is oxidized, a significant amount of water vapor is released. Another requirement for polar stratospheric clouds is cold temperatures to ensure condensation and cloud production. Polar stratospheric cloud production, since it requires the cold temperatures, is usually limited to nighttime and winter conditions. With this combination of wetter and colder conditions in the lower stratosphere, polar stratospheric clouds could have formed over wide areas in Polar Regions.To test the polar stratospheric clouds effects on the Eocene climate, models were run comparing the effects of polar stratospheric clouds at the poles to an increase in atmospheric carbon dioxide. The polar stratospheric clouds had a warming effect on the poles, increasing temperatures by up to 20 °C in the winter months. A multitude of feedbacks also occurred in the models due to the polar stratospheric clouds' presence. Any ice growth was slowed immensely and would lead to any present ice melting. Only the poles were affected with the change in temperature and the tropics were unaffected, which with an increase in atmospheric carbon dioxide would also cause the tropics to increase in temperature. Due to the warming of the troposphere from the increased greenhouse effect of the polar stratospheric clouds, the stratosphere would cool and would potentially increase the amount of polar stratospheric clouds.
While the polar stratospheric clouds could explain the reduction of the equator to pole temperature gradient and the increased temperatures at the poles during the early Eocene, there are a few drawbacks to maintaining polar stratospheric clouds for an extended period of time. Separate model runs were used to determine the sustainability of the polar stratospheric clouds. It was determined that in order to maintain the lower stratospheric water vapor, methane would need to be continually released and sustained. In addition, the amounts of ice and condensation nuclei would need to be high in order for the polar stratospheric cloud to sustain itself and eventually expand.
Middle Eocene
The Eocene is not only known for containing the warmest period during the Cenozoic; it also marked the decline into an icehouse climate and the rapid expansion of the Antarctic ice sheet. The transition from a warming climate into a cooling climate began at around 49 Ma. Isotopes of carbon and oxygen indicate a shift to a global cooling climate. The cause of the cooling has been attributed to a significant decrease of >2,000 ppm in atmospheric carbon dioxide concentrations. One proposed cause of the reduction in carbon dioxide during the warming to cooling transition was the azolla event. With the equable climate during the early Eocene, warm temperatures in the arctic allowed for the growth of azolla, which is a floating aquatic fern, on the Arctic Ocean. The significantly high amounts of carbon dioxide also acted to facilitate azolla blooms across the Arctic Ocean. Compared to current carbon dioxide levels, these azolla grew rapidly in the enhanced carbon dioxide levels found in the early Eocene. The isolation of the Arctic Ocean, evidenced by euxinia that occurred at this time, led to stagnant waters and as the azolla sank to the sea floor, they became part of the sediments on the seabed and effectively sequestered the carbon by locking it out of the atmosphere for good. The ability for the azolla to sequester carbon is exceptional, and the enhanced burial of azolla could have had a significant effect on the world atmospheric carbon content and may have been the event to begin the transition into an ice house climate. The azolla event could have led to a draw down of atmospheric carbon dioxide of up to 470 ppm. Assuming the carbon dioxide concentrations were at 900 ppmv prior to the Azolla Event they would have dropped to 430 ppmv, or 30 ppmv more than they are today, after the Azolla Event. This cooling trend at the end of the EECO has also been proposed to have been caused by increased siliceous plankton productivity and marine carbon burial, which also helped draw carbon dioxide out of the atmosphere. Cooling after this event, part of a trend known as the Middle-Late Eocene Cooling (MLEC), continued due to continual decrease in atmospheric carbon dioxide from organic productivity and weathering from mountain building. Many regions of the world became more arid and cold over the course of the stage, such as the Fushun Basin. In East Asia, lake level changes were in sync with global sea level changes over the course of the MLEC.Global cooling continued until there was a major reversal from cooling to warming in the Bartonian. This warming event, signifying a sudden and temporary reversal of the cooling conditions, is known as the Middle Eocene Climatic Optimum (MECO). At around 41.5 Ma, stable isotopic analysis of samples from Southern Ocean drilling sites indicated a warming event for 600,000 years. A similar shift in carbon isotopes is known from the Northern Hemisphere in the Scaglia Limestones of Italy. Oxygen isotope analysis showed a large negative change in the proportion of heavier oxygen isotopes to lighter oxygen isotopes, which indicates an increase in global temperatures. The warming is considered to be primarily due to carbon dioxide increases, because carbon isotope signatures rule out major methane release during this short-term warming. A sharp increase in atmospheric carbon dioxide was observed with a maximum of 4,000 ppm: the highest amount of atmospheric carbon dioxide detected during the Eocene. Other studies suggest a more modest rise in carbon dioxide levels. The increase in atmospheric carbon dioxide has also been hypothesised to have been driven by increased seafloor spreading rates and metamorphic decarbonation reactions between Australia and Antarctica and increased amounts of volcanism in the region. One possible cause of atmospheric carbon dioxide increase could have been a sudden increase due to metamorphic release due to continental drift and collision of India with Asia and the resulting formation of the Himalayas; however, data on the exact timing of metamorphic release of atmospheric carbon dioxide is not well resolved in the data. Recent studies have mentioned, however, that the removal of the ocean between Asia and India could have released significant amounts of carbon dioxide. Another hypothesis still implicates a diminished negative feedback of silicate weathering as a result of continental rocks having become less weatherable during the warm Early and Middle Eocene, allowing volcanically released carbon dioxide to persist in the atmosphere for longer. Yet another explanation hypothesises that MECO warming was caused by the simultaneous occurrence of minima in both the 400 kyr and 2.4 Myr eccentricity cycles. During the MECO, sea surface temperatures in the Tethys Ocean jumped to 32–36 °C, and Tethyan seawater became more dysoxic. A decline in carbonate accumulation at ocean depths of greater than three kilometres took place synchronously with the peak of the MECO, signifying ocean acidification took place in the deep ocean. On top of that, MECO warming caused an increase in the respiration rates of pelagic heterotrophs, leading to a decreased proportion of primary productivity making its way down to the seafloor and causing a corresponding decline in populations of benthic foraminifera. An abrupt decrease in lakewater salinity in western North America occurred during this warming interval. This warming is short lived, as benthic oxygen isotope records indicate a return to cooling at ~40 Ma.
Late Eocene
At the end of the MECO, the MLEC resumed. Cooling and the carbon dioxide drawdown continued through the late Eocene and into the Eocene–Oligocene transition around 34 Ma. The post-MECO cooling brought with it a major aridification trend in Asia. The cooling during the initial stages of the opening of the Drake Passage ~38.5 Ma was not global, as evidenced by an absence of cooling in the North Atlantic. During the cooling period, benthic oxygen isotopes show the possibility of ice creation and ice increase during this later cooling. The end of the Eocene and beginning of the Oligocene is marked with the massive expansion of area of the Antarctic ice sheet that was a major step into the icehouse climate. Multiple proxies, such as oxygen isotopes and alkenones, indicate that at the Eocene–Oligocene transition, the atmospheric carbon dioxide concentration had decreased to around 750–800 ppm, approximately twice that of present levels. Along with the decrease of atmospheric carbon dioxide reducing the global temperature, orbital factors in ice creation can be seen with 100,000-year and 400,000-year fluctuations in benthic oxygen isotope records. Another major contribution to the expansion of the ice sheet was the creation of the Antarctic Circumpolar Current. The creation of the Antarctic circumpolar current would isolate the cold water around the Antarctic, which would reduce heat transport to the Antarctic along with creating ocean gyres that result in the upwelling of colder bottom waters. The issue with this hypothesis of the consideration of this being a factor for the Eocene-Oligocene transition is the timing of the creation of the circulation is uncertain. For Drake Passage, sediments indicate the opening occurred ~41 Ma while tectonics indicate that this occurred ~32 Ma.
Flora
During the early-middle Eocene, forests covered most of the Earth including the poles. Tropical forests extended across much of modern Africa, South America, Central America, India, South-east Asia and China. Paratropical forests grew over North America, Europe and Russia, with broad-leafed evergreen and broad-leafed deciduous forests at higher latitudes.Polar forests were quite extensive. Fossils and even preserved remains of trees such as swamp cypress and dawn redwood from the Eocene have been found on Ellesmere Island in the Arctic. Even at that time, Ellesmere Island was only a few degrees in latitude further south than it is today. Fossils of subtropical and even tropical trees and plants from the Eocene also have been found in Greenland and Alaska. Tropical rainforests grew as far north as northern North America and Europe.Palm trees were growing as far north as Alaska and northern Europe during the early Eocene, although they became less abundant as the climate cooled. Dawn redwoods were far more extensive as well.The earliest definitive Eucalyptus fossils were dated from 51.9 Ma, and were found in the Laguna del Hunco deposit in Chubut province in Argentina.Cooling began mid-period, and by the end of the Eocene continental interiors had begun to dry, with forests thinning considerably in some areas. The newly evolved grasses were still confined to river banks and lake shores, and had not yet expanded into plains and savannas.The cooling also brought seasonal changes. Deciduous trees, better able to cope with large temperature changes, began to overtake evergreen tropical species. By the end of the period, deciduous forests covered large parts of the northern continents, including North America, Eurasia and the Arctic, and rainforests held on only in equatorial South America, Africa, India and Australia.Antarctica began the Eocene fringed with a warm temperate to sub-tropical rainforest. Pollen found in Prydz Bay from the Eocene suggest taiga forest existed there. It became much colder as the period progressed; the heat-loving tropical flora was wiped out, and by the beginning of the Oligocene, the continent hosted deciduous forests and vast stretches of tundra.
Fauna
During the Eocene, plants and marine faunas became quite modern. Many modern bird orders first appeared in the Eocene. The Eocene oceans were warm and teeming with fish and other sea life.
Mammals
The oldest known fossils of most of the modern mammal orders appear within a brief period during the early Eocene. At the beginning of the Eocene, several new mammal groups arrived in North America. These modern mammals, like artiodactyls, perissodactyls, and primates, had features like long, thin legs, feet, and hands capable of grasping, as well as differentiated teeth adapted for chewing. Dwarf forms reigned. All the members of the new mammal orders were small, under 10 kg; based on comparisons of tooth size, Eocene mammals were only 60% of the size of the primitive Palaeocene mammals that preceded them. They were also smaller than the mammals that followed them. It is assumed that the hot Eocene temperatures favored smaller animals that were better able to manage the heat.Both groups of modern ungulates (hoofed animals) became prevalent because of a major radiation between Europe and North America, along with carnivorous ungulates like Mesonyx. Early forms of many other modern mammalian orders appeared, including horses (most notably the Eohippus), bats, proboscidians (elephants), primates, rodents, and marsupials. Older primitive forms of mammals declined in variety and importance. Important Eocene land fauna fossil remains have been found in western North America, Europe, Patagonia, Egypt, and southeast Asia. Marine fauna are best known from South Asia and the southeast United States.Established megafauna of the Eocene include the Uintatherium, Arsinoitherium, and brontotheres, in which the former two, unlike the latter, did not belong to ungulates but groups that became extinct shortly after their establishments.
Large terrestrial mammalian predators began to take form as the terrestrial carnivores like the Hyaenodon and Daphoenus (the earliest lineage of a once-successful predatory family known as bear dogs). Entelodonts meanwhile established themselves as some of the largest omnivores. The first nimravids, including Dinictis, established themselves as amongst the first feliforms to appear. Their groups became highly successful and continued to live past the Eocene.
Basilosaurus is a very well-known Eocene whale, but whales as a group had become very diverse during the Eocene, which is when the major transitions from being terrestrial to fully aquatic in cetaceans occurred. The first sirenians were evolving at this time, and would eventually evolve into the extant manatees and dugongs.
It is thought that millions of years after the Cretaceous-Paleogene extinction event, brain sizes of mammals now started to increase, "likely driven by a need for greater cognition in increasingly complex environments".
Birds
Eocene birds include some enigmatic groups with resemblances to modern forms, some of which continued from the Paleocene. Bird taxa of the Eocene include carnivorous psittaciforms, such as Messelasturidae, Halcyornithidae, large flightless forms such as Gastornis and Eleutherornis, long legged falcon Masillaraptor, ancient galliforms such as Gallinuloides, putative rail relatives of the family Songziidae, various pseudotooth birds such as Gigantornis, the ibis relative Rhynchaeites, primitive swifts of the genus Aegialornis, and primitive penguins such as Archaeospheniscus and Inkayacu.
Reptiles
Reptile fossils from this time, such as fossils of pythons and turtles, are abundant.
Insects and arachnids
Several rich fossil insect faunas are known from the Eocene, notably the Baltic amber found mainly along the south coast of the Baltic Sea, amber from the Paris Basin, France, the Fur Formation, Denmark, and the Bembridge Marls from the Isle of Wight, England. Insects found in Eocene deposits mostly belong to genera that exist today, though their range has often shifted since the Eocene. For instance the bibionid genus Plecia is common in fossil faunas from presently temperate areas, but only lives in the tropics and subtropics today.
Gallery
See also
Bolca in Italy
List of fossil sites (with link directory)
London Clay
Messel pit in Germany
Wadi El Hitan in Egypt
Notes
References
Further reading
Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) Global Stratotype Sections and Points Accessed April 30, 2006.
Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6
External links
PaleoMap Project
Paleos Eocene page
PBS Deep Time: Eocene
Eocene and Oligocene Fossils
The UPenn Fossil Forest Project, focusing on the Eocene polar forests in Ellesmere Island, Canada
Basilosaurus Primitive Eocene Whales
Basilosaurus - The plesiosaur that wasn't....
Detailed maps of Tertiary Western North America
Map of Eocene Earth
Eocene Microfossils: 60+ images of Foraminifera
Eocene Epoch. (2011). In Encyclopædia Britannica. Retrieved from Eocene Epoch | geochronology |
long-lived fission product | Long-lived fission products (LLFPs) are radioactive materials with a long half-life (more than 200,000 years) produced by nuclear fission of uranium and plutonium. Because of their persistent radiotoxicity, it is necessary to isolate them from humans and the biosphere and to confine them in nuclear waste repositories for geological periods of time.
Evolution of radioactivity in nuclear waste
Nuclear fission produces fission products, as well as actinides from nuclear fuel nuclei that capture neutrons but fail to fission, and activation products from neutron activation of reactor or environmental materials.
Short-term
The high short-term radioactivity of spent nuclear fuel is primarily from fission products with short half-life.
The radioactivity in the fission product mixture is mostly short-lived isotopes such as 131I and 140Ba, after about four months 141Ce, 95Zr/95Nb and 89Sr take the largest share, while after about two or three years the largest share is taken by 144Ce/144Pr, 106Ru/106Rh and 147Pm.
Note that in the case of a release of radioactivity from a power reactor or used fuel, only some elements are released. As a result, the isotopic signature of the radioactivity is very different from an open air nuclear detonation where all the fission products are dispersed.
Medium-lived fission products
After several years of cooling, most radioactivity is from the fission products caesium-137 and strontium-90, which are each produced in about 6% of fissions, and have half-lives of about 30 years. Other fission products with similar half-lives have much lower fission product yields, lower decay energy, and several (151Sm, 155Eu, 113mCd) are also quickly destroyed by neutron capture while still in the reactor, so are not responsible for more than a tiny fraction of the radiation production at any time. Therefore, in the period from several years to several hundred years after use, radioactivity of spent fuel can be modeled simply as exponential decay of the 137Cs and 90Sr. These are sometimes known as medium-lived fission products.Krypton-85, the 3rd most active MLFP, is a noble gas which is allowed to escape during current nuclear reprocessing; however, its inertness means that it does not concentrate in the environment, but diffuses to a uniform low concentration in the atmosphere. Spent fuel in the U.S. and some other countries is not likely to be reprocessed until decades after use, and by that time most of the 85Kr will have decayed.
Actinides
After 137Cs and 90Sr have decayed to low levels, the bulk of radioactivity from spent fuel come not from fission products but actinides, notably plutonium-239 (half-life 24 ka), plutonium-240 (6.56 ka), americium-241 (432 years), americium-243 (7.37 ka), curium-245 (8.50 ka), and curium-246 (4.73 ka). These can be recovered by nuclear reprocessing (either before or after most 137Cs and 90Sr decay) and fissioned, offering the possibility of greatly reducing waste radioactivity in the time scale of about 103 to 105 years. 239Pu is usable as fuel in existing thermal reactors, but some minor actinides like 241Am, as well as the non-fissile and less-fertile isotope plutonium-242, are better destroyed in fast reactors, accelerator-driven subcritical reactors, or fusion reactors. Americium-241 has some industrial applications and is used in smoke detectors and is thus often separated from waste as it fetches a price that makes such separation economic.
Long-lived fission products
On scales greater than 105 years, fission products, chiefly 99Tc, again represent a significant proportion of the remaining, though lower radioactivity, along with longer-lived actinides like neptunium-237 and plutonium-242, if those have not been destroyed.
The most abundant long-lived fission products have total decay energy around 100–300 keV, only part of which appears in the beta particle; the rest is lost to a neutrino that has no effect. In contrast, actinides undergo multiple alpha decays, each with decay energy around 4–5 MeV.
Only seven fission products have long half-lives, and these are much longer than 30 years, in the range of 200,000 to 16 million years. These are known as long-lived fission products (LLFP). Three have relatively high yields of about 6%, while the rest appear at much lower yields. (This list of seven excludes isotopes with very slow decay and half-lives longer than the age of the universe, which are effectively stable and already found in nature, as well as a few nuclides like technetium-98 and samarium-146 that are "shadowed" from beta decay and can only occur as direct fission products, not as beta decay products of more neutron-rich initial fission products. The shadowed fission products have yields on the order of one millionth as much as iodine-129.)
The 7 long-lived fission products
The first three have similar half-lives, between 200 thousand and 300 thousand years; the last four have longer half-lives, in the low millions of years.
Technetium-99 produces the largest amount of LLFP radioactivity. It emits beta particles of low to medium energy but no gamma rays, so has little hazard on external exposure, but only if ingested. However, technetium's chemistry allows it to form anions (pertechnetate, TcO4−) that are relatively mobile in the environment.
Tin-126 has a large decay energy (due to its following short half-life decay product) and is the only LLFP that emits energetic gamma radiation, which is an external exposure hazard. However, this isotope is produced in very small quantities in fission by thermal neutrons, so the energy per unit time from 126Sn is only about 5% as much as from 99Tc for U-235 fission, or 20% as much for 65% U-235+35% Pu-239. Fast fission may produce higher yields. Tin is an inert metal with little mobility in the environment, helping to limit health risks from its radiation.
Selenium-79 is produced at low yields and emits only weak radiation. Its decay energy per unit time should be only about 0.2% that of Tc-99.
Zirconium-93 is produced at a relatively high yield of about 6%, but its decay is 7.5 times slower than Tc-99, and its decay energy is only 30% as great; therefore its energy production is initially only 4% as great as Tc-99, though this fraction will increase as the Tc-99 decays. 93Zr does produce gamma radiation, but of a very low energy, and zirconium is relatively inert in the environment.
Caesium-135's predecessor xenon-135 is produced at a high rate of over 6% of fissions, but is an extremely potent absorber of thermal neutrons (neutron poison), so that most of it is transmuted to almost-stable xenon-136 before it can decay to caesium-135. If 90% of 135Xe is destroyed, then the remaining 135Cs's decay energy per unit time is initially only about 1% as great as that of the 99Tc. In a fast reactor, less of the Xe-135 may be destroyed.135Cs is the only alkaline or electropositive LLFP; in contrast, the main medium-lived fission products and the minor actinides other than neptunium are all alkaline and tend to stay together during reprocessing; with many reprocessing techniques such as salt solution or salt volatilization, 135Cs will also stay with this group, although some techniques such as high-temperature volatilization can separate it. Often the alkaline wastes are vitrified to form high level waste, which will include the 135Cs.Fission caesium contains not only 135Cs but also stable but neutron-absorbing 133Cs (which wastes neutrons and forms 134Cs which is radioactive with a half-life of 2 years) as well as the common fission product 137Cs which does not absorb neutrons but is highly radioactive, making handling more hazardous and complicated; for all these reasons, transmutation disposal of 135Cs would be more difficult.
Palladium-107 has a very long half-life, a low yield (though the yield for plutonium fission is higher than the yield from uranium-235 fission), and very weak radiation. Its initial contribution to LLFP radiation should be only about one part in 10000 for 235U fission, or 2000 for 65% 235U+35% 239Pu. Palladium is a noble metal and extremely inert.
Iodine-129 has the longest half-life, 15.7 million years, and due to its higher half life, lower fission fraction and decay energy it produces only about 1% the intensity of radioactivity as 99Tc. However, radioactive iodine is a disproportionate biohazard because the thyroid gland concentrates iodine. 129I has a half-life nearly a billion times as long as its more hazardous sister isotope 131I; therefore, with a shorter half-life and a higher decay energy, 131I is approximately a billion times more radioactive than the longer-lived 129I. (What relevance 131I has in this coverage of LLFPs is debatable.)
LLFP radioactivity compared
In total, the other six LLFPs, in thermal reactor spent fuel, initially release only a bit more than 10% as much energy per unit time as Tc-99 for U-235 fission, or 25% as much for 65% U-235+35% Pu-239. About 1000 years after fuel use, radioactivity from the medium-lived fission products Cs-137 and Sr-90 drops below the level of radioactivity from Tc-99 or LLFPs in general. (Actinides, if not removed, will be emitting more radioactivity than either at this point.) By about 1 million years, Tc-99 radioactivity will have declined below that of Zr-93, though immobility of the latter means it is probably still a lesser hazard. By about 3 million years, Zr-93 decay energy will have declined below that of I-129.
Nuclear transmutation is under consideration as a disposal method, primarily for Tc-99 and I-129 as these both represent the greatest biohazards and have the greatest neutron capture cross sections, although transmutation is still slow compared to fission of actinides in a reactor. Transmutation has also been considered for Cs-135, but is almost certainly not worthwhile for the other LLFPs. Given that stable Caesium-133 is also produced in nuclear fission and both it and its neutron activation product 134Cs are neutron poisons, transmutation of 135Cs might necessitate isotope separation. 99Tc is particularly attractive for transmutation not only due to the undesirable properties of the product to be destroyed and the relatively high neutron absorption cross section but also because 100Tc rapidly beta decays to stable 100Ru. Ruthenium has no radioactive isotopes with half lives much longer than a year and the price of ruthenium is relatively high, making the destruction of 99Tc into a potentially lucrative source of producing a precious metal from an undesirable feedstock.
== References == |
meganisoptera | Meganisoptera is an extinct order of very large to gigantic winged insects, informally known as griffenflies or (incorrectly) as giant dragonflies. The order was formerly named Protodonata, the "proto-Odonata", for their similar appearance and supposed relation to modern Odonata (damselflies and dragonflies). They range in Palaeozoic (Late Carboniferous to Late Permian) times. Though most were only slightly larger than modern dragonflies, the order includes the largest known insect species, such as the late Carboniferous Meganeura monyi and the even larger early Permian Meganeuropsis permiana, with wingspans of up to 71 centimetres (28 in).
The forewings and hindwings are similar in venation (a primitive feature) except for the larger anal (rearwards) area in the hindwing. The forewing is usually slenderer and slightly longer than the hindwing. Unlike the true dragonflies, the Odonata, they had no pterostigmata, and had a somewhat simpler pattern of veins in the wings.
Most specimens are known from wing fragments only; with only a few as complete wings, and even fewer (of the family Meganeuridae) with body impressions. These show a globose head with large dentate mandibles, strong spiny legs, a large thorax, and long and slender dragonfly-like abdomen. Like true dragonflies, they were presumably predators.
A few nymphs are also known, and show mouthparts similar to those of modern dragonfly nymphs, suggesting that they were also active aquatic predators.Although sometimes included under the dragonflies, the Meganisoptera lack certain distinctive wing features that characterise the Odonata. Grimaldi & Engel 2005 point out that the colloquial term "giant dragonfly" is therefore misleading, and suggest "griffenfly" instead.
Size
Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen is diffused through the insect's body via its tracheal breathing system (see Respiratory system of insects) puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed in Harlé (1911) that Meganeura was only able to fly because the atmosphere at that time contained more oxygen than the present 20%. This theory was dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability. If this theory is correct, these insects would have been susceptible to falling oxygen levels and certainly could not survive in modern atmosphere. Other research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion". Recent analysis of the flight energetics of modern insects and birds suggests that both the oxygen levels and air density provide a bound on size.A general problem with all oxygen related explanations of giant griffenflies is the circumstance that very large Meganeuridae with a wingspan of 45 cm also occurred in the Upper Permian of Lodève in France, when the oxygen content of the atmosphere was already much lower than in the Carboniferous and Lower Permian.Bechly 2004 suggested that the lack of aerial vertebrate predators allowed pterygote insects to evolve to maximum sizes during the Carboniferous and Permian periods, maybe accelerated by an "evolutionary arms race" for increase in body size between plant-feeding Palaeodictyoptera and meganeurids as their predators.
Families and genera
These families belong to the order Meganisoptera:
Aulertupidae Zessin & Brauckmann 2010
Kohlwaldiidae Guthörl 1962
Meganeuridae Handlirsch 1906
Namurotypidae Bechly 1996
Paralogidae Handlirsch 1906These genera belong to the order Meganisoptera, but have not been placed in families:
Alanympha Kukalova-Peck 2009
Asapheneura Pruvost 1919
Dragonympha Kukalova-Peck 2009
Palaeotherates Handlirsch 1906
Paralogopsis Handlirsch 1911
Schlechtendaliola Handlirsch, 1919
Typoides Zalessky 1948
Notes
References
Bibliography
Bechly, G (2004). "Evolution and systematics" (PDF). In Hutchins, M.; Evans, A.V.; Garrison, R.W. & Schlager, N. (eds.). Grzimek's Animal Life Encyclopedia. Vol. Insects (2nd ed.). Farmington Hills, MI: Gale. pp. 7–16.
Carpenter, F. M. (1992). "Superclass Hexapoda". Treatise on Invertebrate Paleontology. Vol. 3 of Part R, Arthropoda 4. Boulder, CO: Geological Society of America.
Dudley, Robert (April 1998). "Atmospheric oxygen, giant Paleozoic insects and the evolution of aerial locomotion performance". The Journal of Experimental Biology. 201 (Pt8): 1043–1050. doi:10.1242/jeb.201.8.1043. PMID 9510518.
Chapelle, Gauthier & Peck, Lloyd S. (May 1999). "Polar gigantism dictated by oxygen availability". Nature. 399 (6732): 114–115. Bibcode:1999Natur.399..114C. doi:10.1038/20099. S2CID 4308425.
Grimaldi, David & Engel, Michael S. (2005-05-16). Evolution of the Insects. Cambridge University Press. ISBN 978-0-521-82149-0.
Harlé, Edouard (1911). "Le Vol de grands reptiles et insectes disparus semble indiquer une pression atmosphérique élevée". Extr. Du Bulletin de la Sté Géologique de France (in French). 4 (9): 118–121.
Hoell, H.V.; Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity (2nd ed.). Oxford University Press. ISBN 978-0-19-510033-4.
Nel, André; Fleck, Günther; Garrouste, Romain; Gand, Georges; Lapeyrie, Jean; Bybee, Seth M & Prokop, Jakub (2009). "Revision of Permo-Carboniferous griffenflies (Insecta: Odonatoptera: Meganisoptera) based upon new species and redescription of selected poorly known taxa from Eurasia". Palaeontographica Abteilung A. 289 (4–6): 89–121. doi:10.1127/pala/289/2009/89.
Nel, André; Fleck, Günther; Garrouste, Romain & Gand, Georges (2008). "The Odonatoptera of the Late Permian Lodève Basin (Insecta)". Journal of Iberian Geology. 34 (1): 115–122.
Tasch, Paul (1980) [1973]. Paleobiology of the Invertebrates. John Wiley and Sons. p. 617.
Tillyard, R.J. (1917). The Biology of Dragonflies. Cambridge University Press. p. 324. GGKEY:0Z7A1R071DD.
Westneat, MW; Betz, O; Blob, RW; Fezzaa, K; Cooper, WJ & Lee, WK (January 2003). "Tracheal respiration in insects visualized with synchrotron x-ray imaging". Science. 299 (5606): 558–560. Bibcode:2003Sci...299..558W. doi:10.1126/science.1078008. PMID 12543973. S2CID 43634044.
External links
Phylogenetic Systematics of Odonata |
coral reef | A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
Coral belongs to the class Anthozoa in the animal phylum Cnidaria, which includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons that support and protect the coral. Most reefs grow best in warm, shallow, clear, sunny and agitated water. Coral reefs first appeared 485 million years ago, at the dawn of the Early Ordovician, displacing the microbial and sponge reefs of the Cambrian.Sometimes called rainforests of the sea, shallow coral reefs form some of Earth's most diverse ecosystems. They occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, mollusks, worms, crustaceans, echinoderms, sponges, tunicates and other cnidarians. Coral reefs flourish in ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas.
Coral reefs have declined by 50% since 1950, partly because they are sensitive to water conditions. They are under threat from excess nutrients (nitrogen and phosphorus), rising ocean heat content and acidification, overfishing (e.g., from blast fishing, cyanide fishing, spearfishing on scuba), sunscreen use, and harmful land-use practices, including runoff and seeps (e.g., from injection wells and cesspools).Coral reefs deliver ecosystem services for tourism, fisheries and shoreline protection. The annual global economic value of coral reefs has been estimated at anywhere from US$30–375 billion (1997 and 2003 estimates) to US$2.7 trillion (a 2020 estimate) to US$9.9 trillion (a 2014 estimate).
Formation
Most coral reefs were formed after the Last Glacial Period when melting ice caused sea level to rise and flood continental shelves. Most coral reefs are less than 10,000 years old. As communities established themselves, the reefs grew upwards, pacing rising sea levels. Reefs that rose too slowly could become drowned, without sufficient light. Coral reefs are also found in the deep sea away from continental shelves, around oceanic islands and atolls. The majority of these islands are volcanic in origin. Others have tectonic origins where plate movements lifted the deep ocean floor.
In The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the Beagle. He theorized that uplift and subsidence of Earth's crust under the oceans formed the atolls. Darwin set out a sequence of three stages in atoll formation. A fringing reef forms around an extinct volcanic island as the island and ocean floor subside. As the subsidence continues, the fringing reef becomes a barrier reef and ultimately an atoll reef.
Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast to form fringing reefs, and can eventually grow to become a barrier reef.
Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides slowly, the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land. A barrier reef can encircle an island, and once the island sinks below sea level a roughly circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not usually form complete circles but are broken in places by storms. Like sea level rise, a rapidly subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called coral drowning. Corals that rely on zooxanthellae can die when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure.The two main variables determining the geomorphology, or shape, of coral reefs are the nature of the substrate on which they rest, and the history of the change in sea level relative to that substrate.
The approximately 20,000-year-old Great Barrier Reef offers an example of how coral reefs formed on continental shelves. Sea level was then 120 m (390 ft) lower than in the 21st century. As sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain. By 13,000 years ago, sea level had risen to 60 m (200 ft) lower than at present, and many hills of the coastal plains had become continental islands. As sea level rise continued, water topped most of the continental islands. The corals could then overgrow the hills, forming cays and reefs. Sea level on the Great Barrier Reef has not changed significantly in the last 6,000 years. The age of living reef structure is estimated to be between 6,000 and 8,000 years. Although the Great Barrier Reef formed along a continental shelf, and not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, since Australia is not about to submerge. It formed the world's largest barrier reef, 300–1,000 m (980–3,280 ft) from shore, stretching for 2,000 km (1,200 mi).Healthy tropical coral reefs grow horizontally from 1 to 3 cm (0.39 to 1.18 in) per year, and grow vertically anywhere from 1 to 25 cm (0.39 to 9.84 in) per year; however, they grow only at depths shallower than 150 m (490 ft) because of their need for sunlight, and cannot grow above sea level.
Material
As the name implies, coral reefs are made up of coral skeletons from mostly intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, aragonite is formed. However, shell fragments and the remains of coralline algae such as the green-segmented genus Halimeda can add to the reef's ability to withstand damage from storms and other threats. Such mixtures are visible in structures such as Eniwetok Atoll.
In the geologic past
The times of maximum reef development were in the Middle Cambrian (513–501 Ma), Devonian (416–359 Ma) and Carboniferous (359–299 Ma), owing to order Rugosa extinct corals and Late Cretaceous (100–66 Ma) and all Neogene (23 Ma–present), owing to order Scleractinia corals.Not all reefs in the past were formed by corals: those in the Early Cambrian (542–513 Ma) resulted from calcareous algae and archaeocyathids (small animals with conical shape, probably related to sponges) and in the Late Cretaceous (100–66 Ma), when reefs formed by a group of bivalves called rudists existed; one of the valves formed the main conical structure and the other, much smaller valve acted as a cap.Measurements of the oxygen isotopic composition of the aragonitic skeleton of coral reefs, such as Porites, can indicate changes in sea surface temperature and sea surface salinity conditions during the growth of the coral. This technique is often used by climate scientists to infer a region's paleoclimate.
Types
Since Darwin's identification of the three classical reef formations – the fringing reef around a volcanic island becoming a barrier reef and then an atoll – scientists have identified further reef types. While some sources find only three, Thomas lists "Four major forms of large-scale coral reefs" – the fringing reef, barrier reef, atoll and table reef based on Stoddart, D.R. (1969). Spalding et al. list four main reef types that can be clearly illustrated – the fringing reef, barrier reef, atoll, and "bank or platform reef"—and notes that many other structures exist which do not conform easily to strict definitions, including the "patch reef".
Fringing reef
A fringing reef, also called a shore reef, is directly attached to a shore, or borders it with an intervening narrow, shallow channel or lagoon. It is the most common reef type. Fringing reefs follow coastlines and can extend for many kilometres. They are usually less than 100 metres wide, but some are hundreds of metres wide. Fringing reefs are initially formed on the shore at the low water level and expand seawards as they grow in size. The final width depends on where the sea bed begins to drop steeply. The surface of the fringe reef generally remains at the same height: just below the waterline. In older fringing reefs, whose outer regions pushed far out into the sea, the inner part is deepened by erosion and eventually forms a lagoon. Fringing reef lagoons can become over 100 metres wide and several metres deep. Like the fringing reef itself, they run parallel to the coast. The fringing reefs of the Red Sea are "some of the best developed in the world" and occur along all its shores except off sandy bays.
Barrier reef
Barrier reefs are separated from a mainland or island shore by a deep channel or lagoon. They resemble the later stages of a fringing reef with its lagoon but differ from the latter mainly in size and origin. Their lagoons can be several kilometres wide and 30 to 70 metres deep. Above all, the offshore outer reef edge formed in open water rather than next to a shoreline. Like an atoll, it is thought that these reefs are formed either as the seabed lowered or sea level rose. Formation takes considerably longer than for a fringing reef, thus barrier reefs are much rarer.
The best known and largest example of a barrier reef is the Australian Great Barrier Reef. Other major examples are the Belize Barrier Reef and the New Caledonian Barrier Reef. Barrier reefs are also found on the coasts of Providencia, Mayotte, the Gambier Islands, on the southeast coast of Kalimantan, on parts of the coast of Sulawesi, southeastern New Guinea and the south coast of the Louisiade Archipelago.
Platform reef
Platform reefs, variously called bank or table reefs, can form on the continental shelf, as well as in the open ocean, in fact anywhere where the seabed rises close enough to the surface of the ocean to enable the growth of zooxanthemic, reef-forming corals. Platform reefs are found in the southern Great Barrier Reef, the Swain and Capricorn Group on the continental shelf, about 100–200 km from the coast. Some platform reefs of the northern Mascarenes are several thousand kilometres from the mainland. Unlike fringing and barrier reefs which extend only seaward, platform reefs grow in all directions. They are variable in size, ranging from a few hundred metres to many kilometres across. Their usual shape is oval to elongated. Parts of these reefs can reach the surface and form sandbanks and small islands around which may form fringing reefs. A lagoon may form In the middle of a platform reef.
Platform reefs can be found within atolls. There they are called patch reefs and may reach only a few dozen metres in diameter. Where platform reefs form on an elongated structure, e. g. an old, eroded barrier reef, they can form a linear arrangement. This is the case, for example, on the east coast of the Red Sea near Jeddah. In old platform reefs, the inner part can be so heavily eroded that it forms a pseudo-atoll. These can be distinguished from real atolls only by detailed investigation, possibly including core drilling. Some platform reefs of the Laccadives are U-shaped, due to wind and water flow.
Atoll
Atolls or atoll reefs are a more or less circular or continuous barrier reef that extends all the way around a lagoon without a central island. They are usually formed from fringing reefs around volcanic islands. Over time, the island erodes away and sinks below sea level. Atolls may also be formed by the sinking of the seabed or rising of the sea level. A ring of reefs results, which enclose a lagoon. Atolls are numerous in the South Pacific, where they usually occur in mid-ocean, for example, in the Caroline Islands, the Cook Islands, French Polynesia, the Marshall Islands and Micronesia.Atolls are found in the Indian Ocean, for example, in the Maldives, the Chagos Islands, the Seychelles and around Cocos Island. The entire Maldives consist of 26 atolls.
Other reef types or variants
Apron reef – short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore. The initial stage of a fringing reef.
Bank reef – isolated, flat-topped reef larger than a patch reef and usually on mid-shelf regions and linear or semi-circular in shape; a type of platform reef.
Patch reef – common, isolated, comparatively small reef outcrop, usually within a lagoon or embayment, often circular and surrounded by sand or seagrass. Can be considered as a type of platform reef or as features of fringing reefs, atolls and barrier reefs. The patches may be surrounded by a ring of reduced seagrass cover referred to as a grazing halo.
Ribbon reef – long, narrow, possibly winding reef, usually associated with an atoll lagoon. Also called a shelf-edge reef or sill reef.
Drying reef – a part of a reef which is above water at low tide but submerged at high tide
Habili – reef specific to the Red Sea; does not reach near enough to the surface to cause visible surf; may be a hazard to ships (from the Arabic for "unborn")
Microatoll – community of species of corals; vertical growth limited by average tidal height; growth morphologies offer a low-resolution record of patterns of sea level change; fossilized remains can be dated using radioactive carbon dating and have been used to reconstruct Holocene sea levels
Cays – small, low-elevation, sandy islands formed on the surface of coral reefs from eroded material that piles up, forming an area above sea level; can be stabilized by plants to become habitable; occur in tropical environments throughout the Pacific, Atlantic and Indian Oceans (including the Caribbean and on the Great Barrier Reef and Belize Barrier Reef), where they provide habitable and agricultural land
Seamount or guyot – formed when a coral reef on a volcanic island subsides; tops of seamounts are rounded and guyots are flat; flat tops of guyots, or tablemounts, are due to erosion by waves, winds, and atmospheric processes
Zones
Coral reef ecosystems contain distinct zones that host different kinds of habitats. Usually, three major zones are recognized: the fore reef, reef crest, and the back reef (frequently referred to as the reef lagoon).
The three zones are physically and ecologically interconnected. Reef life and oceanic processes create opportunities for the exchange of seawater, sediments, nutrients and marine life.
Most coral reefs exist in waters less than 50 m deep. Some inhabit tropical continental shelves where cool, nutrient-rich upwelling does not occur, such as the Great Barrier Reef. Others are found in the deep ocean surrounding islands or as atolls, such as in the Maldives. The reefs surrounding islands form when islands subside into the ocean, and atolls form when an island subsides below the surface of the sea.
Alternatively, Moyle and Cech distinguish six zones, though most reefs possess only some of the zones.
The reef surface is the shallowest part of the reef. It is subject to surge and tides. When waves pass over shallow areas, they shoal, as shown in the adjacent diagram. This means the water is often agitated. These are the precise condition under which corals flourish. The light is sufficient for photosynthesis by the symbiotic zooxanthellae, and agitated water brings plankton to feed the coral.
The off-reef floor is the shallow sea floor surrounding a reef. This zone occurs next to reefs on continental shelves. Reefs around tropical islands and atolls drop abruptly to great depths and do not have such a floor. Usually sandy, the floor often supports seagrass meadows which are important foraging areas for reef fish.
The reef drop-off is, for its first 50 m, habitat for reef fish who find shelter on the cliff face and plankton in the water nearby. The drop-off zone applies mainly to the reefs surrounding oceanic islands and atolls.
The reef face is the zone above the reef floor or the reef drop-off. This zone is often the reef's most diverse area. Coral and calcareous algae provide complex habitats and areas that offer protection, such as cracks and crevices. Invertebrates and epiphytic algae provide much of the food for other organisms. A common feature on this forereef zone is spur and groove formations that serve to transport sediment downslope.
The reef flat is the sandy-bottomed flat, which can be behind the main reef, containing chunks of coral. This zone may border a lagoon and serve as a protective area, or it may lie between the reef and the shore, and in this case is a flat, rocky area. Fish tend to prefer it when it is present.The reef lagoon is an entirely enclosed region, which creates an area less affected by wave action and often contains small reef patches.However, the "topography of coral reefs is constantly changing. Each reef is made up of irregular patches of algae, sessile invertebrates, and bare rock and sand. The size, shape and relative abundance of these patches change from year to year in response to the various factors that favor one type of patch over another. Growing coral, for example, produces constant change in the fine structure of reefs. On a larger scale, tropical storms may knock out large sections of reef and cause boulders on sandy areas to move."
Locations
Coral reefs are estimated to cover 284,300 km2 (109,800 sq mi), just under 0.1% of the oceans' surface area. The Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs account for 7.6%.Although corals exist both in temperate and tropical waters, shallow-water reefs form only in a zone extending from approximately 30° N to 30° S of the equator. Tropical corals do not grow at depths of over 50 meters (160 ft). The optimum temperature for most coral reefs is 26–27 °C (79–81 °F), and few reefs exist in waters below 18 °C (64 °F). When the net production by reef building corals no longer keeps pace with relative sea level and the reef structure permanently drowns a Darwin Point is reached. One such point exists at the northwestern end of the Hawaiian Archipelago; see Evolution of Hawaiian volcanoes#Coral atoll stage.However, reefs in the Persian Gulf have adapted to temperatures of 13 °C (55 °F) in winter and 38 °C (100 °F) in summer. 37 species of scleractinian corals inhabit such an environment around Larak Island.Deep-water coral inhabits greater depths and colder temperatures at much higher latitudes, as far north as Norway. Although deep water corals can form reefs, little is known about them.
Coral reefs are rare along the west coasts of the Americas and Africa, due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas (the Peru, Benguela and Canary Currents respectively). Corals are seldom found along the coastline of South Asia—from the eastern tip of India (Chennai) to the Bangladesh and Myanmar borders—as well as along the coasts of northeastern South America and Bangladesh, due to the freshwater release from the Amazon and Ganges Rivers respectively.
Significant coral reefs include:
The Great Barrier Reef—largest, comprising over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometers (1,600 mi) off Queensland, Australia
The Mesoamerican Barrier Reef System—second largest, stretching 1,000 kilometers (620 mi) from Isla Contoy at the tip of the Yucatán Peninsula down to the Bay Islands of Honduras
The New Caledonia Barrier Reef—second longest double barrier reef, covering 1,500 kilometers (930 mi)
The Andros, Bahamas Barrier Reef—third largest, following the east coast of Andros Island, Bahamas, between Andros and Nassau
The Red Sea—includes 6,000-year-old fringing reefs located along a 2,000 km (1,240 mi) coastline
The Florida Reef Tract—largest continental US reef and the third-largest coral barrier reef, extends from Soldier Key, located in Biscayne Bay, to the Dry Tortugas in the Gulf of Mexico
Pulley Ridge—deepest photosynthetic coral reef, Florida
Numerous reefs around the Maldives
The Philippines coral reef area, the second-largest in Southeast Asia, is estimated at 26,000 square kilometers. 915 reef fish species and more than 400 scleractinian coral species, 12 of which are endemic are found there.
The Raja Ampat Islands in Indonesia's West Papua province offer the highest known marine diversity.
Bermuda is known for its northernmost coral reef system, located at 32.4°N 64.8°W / 32.4; -64.8. The presence of coral reefs at this high latitude is due to the proximity of the Gulf Stream. Bermuda coral species represent a subset of those found in the greater Caribbean.
The world's northernmost individual coral reef is located within a bay of Japan's Tsushima Island in the Korea Strait.
The world's southernmost coral reef is at Lord Howe Island, in the Pacific Ocean off the east coast of Australia.
Coral
When alive, corals are colonies of small animals embedded in calcium carbonate shells. Coral heads consist of accumulations of individual animals called polyps, arranged in diverse shapes. Polyps are usually tiny, but they can range in size from a pinhead to 12 inches (30 cm) across.
Reef-building or hermatypic corals live only in the photic zone (above 70 m), the depth to which sufficient sunlight penetrates the water.
Zooxanthellae
Coral polyps do not photosynthesize, but have a symbiotic relationship with microscopic algae (dinoflagellates) of the genus Symbiodinium, commonly referred to as zooxanthellae. These organisms live within the polyps' tissues and provide organic nutrients that nourish the polyp in the form of glucose, glycerol and amino acids. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Without their symbionts, coral growth would be too slow to form significant reef structures. Corals get up to 90% of their nutrients from their symbionts. In return, as an example of mutualism, the corals shelter the zooxanthellae, averaging one million for every cubic centimeter of coral, and provide a constant supply of the carbon dioxide they need for photosynthesis.
The varying pigments in different species of zooxanthellae give them an overall brown or golden-brown appearance and give brown corals their colors. Other pigments such as reds, blues, greens, etc. come from colored proteins made by the coral animals. Coral that loses a large fraction of its zooxanthellae becomes white (or sometimes pastel shades in corals that are pigmented with their own proteins) and is said to be bleached, a condition which, unless corrected, can kill the coral.
There are eight clades of Symbiodinium phylotypes. Most research has been conducted on clades A–D. Each clade contributes their own benefits as well as less compatible attributes to the survival of their coral hosts. Each photosynthetic organism has a specific level of sensitivity to photodamage to compounds needed for survival, such as proteins. Rates of regeneration and replication determine the organism's ability to survive. Phylotype A is found more in the shallow waters. It is able to produce mycosporine-like amino acids that are UV resistant, using a derivative of glycerin to absorb the UV radiation and allowing them to better adapt to warmer water temperatures. In the event of UV or thermal damage, if and when repair occurs, it will increase the likelihood of survival of the host and symbiont. This leads to the idea that, evolutionarily, clade A is more UV resistant and thermally resistant than the other clades.Clades B and C are found more frequently in deeper water, which may explain their higher vulnerability to increased temperatures. Terrestrial plants that receive less sunlight because they are found in the undergrowth are analogous to clades B, C, and D. Since clades B through D are found at deeper depths, they require an elevated light absorption rate to be able to synthesize as much energy. With elevated absorption rates at UV wavelengths, these phylotypes are more prone to coral bleaching versus the shallow clade A.
Clade D has been observed to be high temperature-tolerant, and has a higher rate of survival than clades B and C during modern bleaching events.
Skeleton
Reefs grow as polyps and other organisms deposit calcium carbonate, the basis of coral, as a skeletal structure beneath and around themselves, pushing the coral head's top upwards and outwards. Waves, grazing fish (such as parrotfish), sea urchins, sponges and other forces and organisms act as bioeroders, breaking down coral skeletons into fragments that settle into spaces in the reef structure or form sandy bottoms in associated reef lagoons.
Typical shapes for coral species are named by their resemblance to terrestrial objects such as wrinkled brains, cabbages, table tops, antlers, wire strands and pillars. These shapes can depend on the life history of the coral, like light exposure and wave action, and events such as breakages.
Reproduction
Corals reproduce both sexually and asexually. An individual polyp uses both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. The reproductive cells are found on the mesenteries, membranes that radiate inward from the layer of tissue that lines the stomach cavity. Some mature adult corals are hermaphroditic; others are exclusively male or female. A few species change sex as they grow.
Internally fertilized eggs develop in the polyp for a period ranging from days to weeks. Subsequent development produces a tiny larva, known as a planula. Externally fertilized eggs develop during synchronized spawning. Polyps across a reef simultaneously release eggs and sperm into the water en masse. Spawn disperse over a large area. The timing of spawning depends on time of year, water temperature, and tidal and lunar cycles. Spawning is most successful given little variation between high and low tide. The less water movement, the better the chance for fertilization. The release of eggs or planula usually occurs at night and is sometimes in phase with the lunar cycle (three to six days after a full moon).
The period from release to settlement lasts only a few days, but some planulae can survive afloat for several weeks. During this process, the larvae may use several different cues to find a suitable location for settlement. At long distances sounds from existing reefs are likely important, while at short distances chemical compounds become important. The larvae are vulnerable to predation and environmental conditions. The lucky few planulae that successfully attach to substrate then compete for food and space.
Gallery of reef-building corals
Other reef builders
Corals are the most prodigious reef-builders. However many other organisms living in the reef community contribute skeletal calcium carbonate in the same manner as corals. These include coralline algae, some sponges and bivalves. Reefs are always built by the combined efforts of these different phyla, with different organisms leading reef-building in different geological periods.
Coralline algae
Coralline algae are important contributors to reef structure. Although their mineral deposition rates are much slower than corals, they are more tolerant of rough wave-action, and so help to create a protective crust over those parts of the reef subjected to the greatest forces by waves, such as the reef front facing the open ocean. They also strengthen the reef structure by depositing limestone in sheets over the reef surface.
Sponges
"Sclerosponge" is the descriptive name for all Porifera that build reefs. In the early Cambrian period, Archaeocyatha sponges were the world's first reef-building organisms, and sponges were the only reef-builders until the Ordovician. Sclerosponges still assist corals building modern reefs, but like coralline algae are much slower-growing than corals and their contribution is (usually) minor.In the northern Pacific Ocean cloud sponges still create deep-water mineral-structures without corals, although the structures are not recognizable from the surface like tropical reefs. They are the only extant organisms known to build reef-like structures in cold water.
Bivalves
Oyster reefs are dense aggregations of oysters living in colonial communities. Other regionally-specific names for these structures include oyster beds and oyster banks. Oyster larvae require a hard substrate or surface to attach on, which includes the shells of old or dead oysters. Thus reefs can build up over time as new larvae settle on older individuals. Crassostrea virginica were once abundant in Chesapeake Bay and shorelines bordering the Atlantic coastal plain until the late nineteenth century. Ostrea angasi is a species of flat oyster that had also formed large reefs in South Australia.Hippuritida, an extinct order of bivalves known as rudists, were major reef-building organisms during the Cretaceous. By the mid-Cretaceous, rudists became the dominant tropical reef-builders, becoming more numerous than scleractinian corals. During this period, ocean temperatures and saline levels—which corals are sensitive to—were higher than it is today, which may have contributed to the success of rudist reefs.
Darwin's paradox
In The Structure and Distribution of Coral Reefs, published in 1842, Darwin described how coral reefs were found in some tropical areas but not others, with no obvious cause. The largest and strongest corals grew in parts of the reef exposed to the most violent surf and corals were weakened or absent where loose sediment accumulated.Tropical waters contain few nutrients yet a coral reef can flourish like an "oasis in the desert". This has given rise to the ecosystem conundrum, sometimes called "Darwin's paradox": "How can such high production flourish in such nutrient poor conditions?"Coral reefs support over one-quarter of all marine species. This diversity results in complex food webs, with large predator fish eating smaller forage fish that eat yet smaller zooplankton and so on. However, all food webs eventually depend on plants, which are the primary producers. Coral reefs typically produce 5–10 grams of carbon per square meter per day (gC·m−2·day−1) biomass.One reason for the unusual clarity of tropical waters is their nutrient deficiency and drifting plankton. Further, the sun shines year-round in the tropics, warming the surface layer, making it less dense than subsurface layers. The warmer water is separated from deeper, cooler water by a stable thermocline, where the temperature makes a rapid change. This keeps the warm surface waters floating above the cooler deeper waters. In most parts of the ocean, there is little exchange between these layers. Organisms that die in aquatic environments generally sink to the bottom, where they decompose, which releases nutrients in the form of nitrogen (N), phosphorus (P) and potassium (K). These nutrients are necessary for plant growth, but in the tropics, they do not directly return to the surface.Plants form the base of the food chain and need sunlight and nutrients to grow. In the ocean, these plants are mainly microscopic phytoplankton which drift in the water column. They need sunlight for photosynthesis, which powers carbon fixation, so they are found only relatively near the surface, but they also need nutrients. Phytoplankton rapidly use nutrients in the surface waters, and in the tropics, these nutrients are not usually replaced because of the thermocline.
Explanations
Around coral reefs, lagoons fill in with material eroded from the reef and the island. They become havens for marine life, providing protection from waves and storms.
Most importantly, reefs recycle nutrients, which happens much less in the open ocean. In coral reefs and lagoons, producers include phytoplankton, as well as seaweed and coralline algae, especially small types called turf algae, which pass nutrients to corals. The phytoplankton form the base of the food chain and are eaten by fish and crustaceans. Recycling reduces the nutrient inputs needed overall to support the community.Corals also absorb nutrients, including inorganic nitrogen and phosphorus, directly from water. Many corals extend their tentacles at night to catch zooplankton that pass near. Zooplankton provide the polyp with nitrogen, and the polyp shares some of the nitrogen with the zooxanthellae, which also require this element.
Sponges live in crevices in the reefs. They are efficient filter feeders, and in the Red Sea they consume about 60% of the phytoplankton that drifts by. Sponges eventually excrete nutrients in a form that corals can use.The roughness of coral surfaces is key to coral survival in agitated waters. Normally, a boundary layer of still water surrounds a submerged object, which acts as a barrier. Waves breaking on the extremely rough edges of corals disrupt the boundary layer, allowing the corals access to passing nutrients. Turbulent water thereby promotes reef growth. Without the access to nutrients brought by rough coral surfaces, even the most effective recycling would not suffice.Deep nutrient-rich water entering coral reefs through isolated events may have significant effects on temperature and nutrient systems. This water movement disrupts the relatively stable thermocline that usually exists between warm shallow water and deeper colder water. Temperature regimes on coral reefs in the Bahamas and Florida are highly variable with temporal scales of minutes to seasons and spatial scales across depths.
Water can pass through coral reefs in various ways, including current rings, surface waves, internal waves and tidal changes. Movement is generally created by tides and wind. As tides interact with varying bathymetry and wind mixes with surface water, internal waves are created. An internal wave is a gravity wave that moves along density stratification within the ocean. When a water parcel encounters a different density it oscillates and creates internal waves. While internal waves generally have a lower frequency than surface waves, they often form as a single wave that breaks into multiple waves as it hits a slope and moves upward. This vertical breakup of internal waves causes significant diapycnal mixing and turbulence. Internal waves can act as nutrient pumps, bringing plankton and cool nutrient-rich water to the surface.
The irregular structure characteristic of coral reef bathymetry may enhance mixing and produce pockets of cooler water and variable nutrient content. Arrival of cool, nutrient-rich water from depths due to internal waves and tidal bores has been linked to growth rates of suspension feeders and benthic algae as well as plankton and larval organisms. The seaweed Codium isthmocladum reacts to deep water nutrient sources because their tissues have different concentrations of nutrients dependent upon depth. Aggregations of eggs, larval organisms and plankton on reefs respond to deep water intrusions. Similarly, as internal waves and bores move vertically, surface-dwelling larval organisms are carried toward the shore. This has significant biological importance to cascading effects of food chains in coral reef ecosystems and may provide yet another key to unlocking the paradox.
Cyanobacteria provide soluble nitrates via nitrogen fixation.Coral reefs often depend on surrounding habitats, such as seagrass meadows and mangrove forests, for nutrients. Seagrass and mangroves supply dead plants and animals that are rich in nitrogen and serve to feed fish and animals from the reef by supplying wood and vegetation. Reefs, in turn, protect mangroves and seagrass from waves and produce sediment in which the mangroves and seagrass can root.
Biodiversity
Coral reefs form some of the world's most productive ecosystems, providing complex and varied marine habitats that support a wide range of organisms. Fringing reefs just below low tide level have a mutually beneficial relationship with mangrove forests at high tide level and sea grass meadows in between: the reefs protect the mangroves and seagrass from strong currents and waves that would damage them or erode the sediments in which they are rooted, while the mangroves and sea grass protect the coral from large influxes of silt, fresh water and pollutants. This level of variety in the environment benefits many coral reef animals, which, for example, may feed in the sea grass and use the reefs for protection or breeding.Reefs are home to a variety of animals, including fish, seabirds, sponges, cnidarians (which includes some types of corals and jellyfish), worms, crustaceans (including shrimp, cleaner shrimp, spiny lobsters and crabs), mollusks (including cephalopods), echinoderms (including starfish, sea urchins and sea cucumbers), sea squirts, sea turtles and sea snakes. Aside from humans, mammals are rare on coral reefs, with visiting cetaceans such as dolphins the main exception. A few species feed directly on corals, while others graze on algae on the reef. Reef biomass is positively related to species diversity.The same hideouts in a reef may be regularly inhabited by different species at different times of day. Nighttime predators such as cardinalfish and squirrelfish hide during the day, while damselfish, surgeonfish, triggerfish, wrasses and parrotfish hide from eels and sharks.: 49 The great number and diversity of hiding places in coral reefs, i.e. refuges, are the most important factor causing the great diversity and high biomass of the organisms in coral reefs.Coral reefs also have a very high degree of microorganism diversity compared to other environments.
Algae
Reefs are chronically at risk of algal encroachment. Overfishing and excess nutrient supply from onshore can enable algae to outcompete and kill the coral. Increased nutrient levels can be a result of sewage or chemical fertilizer runoff. Runoff can carry nitrogen and phosphorus which promote excess algae growth. Algae can sometimes out-compete the coral for space. The algae can then smother the coral by decreasing the oxygen supply available to the reef. Decreased oxygen levels can slow down calcification rates, weakening the coral and leaving it more susceptible to disease and degradation. Algae inhabit a large percentage of surveyed coral locations. The algal population consists of turf algae, coralline algae and macro algae. Some sea urchins (such as Diadema antillarum) eat these algae and could thus decrease the risk of algal encroachment.
Sponges
Sponges are essential for the functioning of the coral reef that system. Algae and corals in coral reefs produce organic material. This is filtered through sponges which convert this organic material into small particles which in turn are absorbed by algae and corals. Sponges are essential to the coral reef system however, they are quite different from corals. While corals are complex and many celled while sponges are very simple organisms with no tissue. They are alike in that they are both immobile aquatic invertebrates but otherwise are completely different.
Types of sponges-
There are several different species of sea sponge. They come in multiple shapes and sizes and all have unique characteristics. Some types of sea sponges include; the tube sponge, vase sponge, yellow sponge, bright red tree sponge, painted tunicate sponge, and the sea squirt sponge.
Medicinal Qualities of Sea Sponges-
Sea sponges have provided the base for many life saving medications. Scientists began to study them in the 1940s and after a few years, discovered that sea sponges contain properties that can stop viral infections. The first drug developed from sea sponges was released in 1969.
Fish
Over 4,000 species of fish inhabit coral reefs. The reasons for this diversity remain unclear. Hypotheses include the "lottery", in which the first (lucky winner) recruit to a territory is typically able to defend it against latecomers, "competition", in which adults compete for territory, and less-competitive species must be able to survive in poorer habitat, and "predation", in which population size is a function of postsettlement piscivore mortality. Healthy reefs can produce up to 35 tons of fish per square kilometer each year, but damaged reefs produce much less.
Invertebrates
Sea urchins, Dotidae and sea slugs eat seaweed. Some species of sea urchins, such as Diadema antillarum, can play a pivotal part in preventing algae from overrunning reefs. Researchers are investigating the use of native collector urchins, Tripneustes gratilla, for their potential as biocontrol agents to mitigate the spread of invasive algae species on coral reefs. Nudibranchia and sea anemones eat sponges.
A number of invertebrates, collectively called "cryptofauna", inhabit the coral skeletal substrate itself, either boring into the skeletons (through the process of bioerosion) or living in pre-existing voids and crevices. Animals boring into the rock include sponges, bivalve mollusks, and sipunculans. Those settling on the reef include many other species, particularly crustaceans and polychaete worms.
Seabirds
Coral reef systems provide important habitats for seabird species, some endangered. For example, Midway Atoll in Hawaii supports nearly three million seabirds, including two-thirds (1.5 million) of the global population of Laysan albatross, and one-third of the global population of black-footed albatross. Each seabird species has specific sites on the atoll where they nest. Altogether, 17 species of seabirds live on Midway. The short-tailed albatross is the rarest, with fewer than 2,200 surviving after excessive feather hunting in the late 19th century.
Other
Sea snakes feed exclusively on fish and their eggs. Marine birds, such as herons, gannets, pelicans and boobies, feed on reef fish. Some land-based reptiles intermittently associate with reefs, such as monitor lizards, the marine crocodile and semiaquatic snakes, such as Laticauda colubrina. Sea turtles, particularly hawksbill sea turtles, feed on sponges.
Ecosystem services
Coral reefs deliver ecosystem services to tourism, fisheries and coastline protection. The global economic value of coral reefs has been estimated to be between US$29.8 billion and $375 billion per year. About 500 million people benefit from ecosystem services provided by coral reefs.The economic cost over a 25-year period of destroying one square kilometer of coral reef has been estimated to be somewhere between $137,000 and $1,200,000.To improve the management of coastal coral reefs, the World Resources Institute (WRI) developed and published tools for calculating the value of coral reef-related tourism, shoreline protection and fisheries, partnering with five Caribbean countries. As of April 2011, published working papers covered St. Lucia, Tobago, Belize, and the Dominican Republic. The WRI was "making sure that the study results support improved coastal policies and management planning". The Belize study estimated the value of reef and mangrove services at $395–559 million annually.Bermuda's coral reefs provide economic benefits to the Island worth on average $722 million per year, based on six key ecosystem services, according to Sarkis et al (2010).
Shoreline protection
Coral reefs protect shorelines by absorbing wave energy, and many small islands would not exist without reefs. Coral reefs can reduce wave energy by 97%, helping to prevent loss of life and property damage. Coastlines protected by coral reefs are also more stable in terms of erosion than those without. Reefs can attenuate waves as well as or better than artificial structures designed for coastal defence such as breakwaters. An estimated 197 million people who live both below 10 m elevation and within 50 km of a reef consequently may receive risk reduction benefits from reefs. Restoring reefs is significantly cheaper than building artificial breakwaters in tropical environments. Expected damages from flooding would double, and costs from frequent storms would triple without the topmost meter of reefs. For 100-year storm events, flood damages would increase by 91% to $US 272 billion without the top meter.
Fisheries
About six million tons of fish are taken each year from coral reefs. Well-managed reefs have an average annual yield of 15 tons of seafood per square kilometer. Southeast Asia's coral reef fisheries alone yield about $2.4 billion annually from seafood.
Threats
Since their emergence 485 million years ago, coral reefs have faced many threats, including disease, predation, invasive species, bioerosion by grazing fish, algal blooms, and geologic hazards. Recent human activities present new threats. From 2009 to 2018, coral reefs worldwide declined 14%.Human activities that threaten coral include coral mining, bottom trawling, and the digging of canals and accesses into islands and bays, all of which can damage marine ecosystems if not done sustainably. Other localized threats include blast fishing, overfishing, coral overmining, and marine pollution, including use of the banned anti-fouling biocide tributyltin; although absent in developed countries, these activities continue in places with few environmental protections or poor regulatory enforcement. Chemicals in sunscreens may awaken latent viral infections in zooxanthellae and impact reproduction. However, concentrating tourism activities via offshore platforms has been shown to limit the spread of coral disease by tourists.Greenhouse gas emissions present a broader threat through sea temperature rise and sea level rise, resulting in widespread coral bleaching and loss of coral cover. Ocean acidification also affects corals by decreasing calcification rates and increasing dissolution rates, although corals can adapt their calcifying fluids to changes in seawater pH and carbonate levels to mitigate the impact. Volcanic and human-made aerosol pollution can modulate regional sea surface temperatures.In 2011, two researchers suggested that "extant marine invertebrates face the same synergistic effects of multiple stressors" that occurred during the end-Permian extinction, and that genera "with poorly buffered respiratory physiology and calcareous shells", such as corals, were particularly vulnerable.Corals respond to stress by "bleaching", or expelling their colorful zooxanthellate endosymbionts. Corals with Clade C zooxanthellae are generally vulnerable to heat-induced bleaching, whereas corals with the hardier Clade A or D are generally resistant, as are tougher coral genera like Porites and Montipora.Every 4–7 years, an El Niño event causes some reefs with heat-sensitive corals to bleach, with especially widespread bleachings in 1998 and 2010. However, reefs that experience a severe bleaching event become resistant to future heat-induced bleaching, due to rapid directional selection. Similar rapid adaption may protect coral reefs from global warming.A large-scale systematic study of the Jarvis Island coral community, which experienced ten El Niño-coincident coral bleaching events from 1960 to 2016, found that the reef recovered from almost complete death after severe events.
Protection
Marine protected areas (MPAs) are areas designated because they provide various kinds of protection to ocean and/or estuarine areas. They are intended to promote responsible fishery management and habitat protection. MPAs can also encompass social and biological objectives, including reef restoration, aesthetics, biodiversity and economic benefits.
The effectiveness of MPAs is still debated. For example, a study investigating the success of a small number of MPAs in Indonesia, the Philippines and Papua New Guinea found no significant differences between the MPAs and unprotected sites. Furthermore, in some cases they can generate local conflict, due to a lack of community participation, clashing views of the government and fisheries, effectiveness of the area and funding. In some situations, as in the Phoenix Islands Protected Area, MPAs provide revenue to locals. The level of income provided is similar to the income they would have generated without controls. Overall, it appears the MPA's can provide protection to local coral reefs, but that clear management and sufficient funds are required.
The Caribbean Coral Reefs - Status Report 1970–2012, states that coral decline may be reduced or even reversed. For this overfishing needs to be stopped, especially fishing on species key to coral reefs, such as parrotfish. Direct human pressure on coral reefs should also be reduced and the inflow of sewage should be minimised. Measures to achieve this could include restricting coastal settlement, development and tourism. The report shows that healthier reefs in the Caribbean are those with large, healthy populations of parrotfish. These occur in countries that protect parrotfish and other species, like sea urchins. They also often ban fish trapping and spearfishing. Together these measures help creating "resilient reefs".Protecting networks of diverse and healthy reefs, not only climate refugia, helps ensure the greatest chance of genetic diversity, which is critical for coral to adapt to new climates. A variety of conservation methods applied across marine and terrestrial threatened ecosystems makes coral adaption more likely and effective.Designating a reef as a biosphere reserve, marine park, national monument or world heritage site can offer protections. For example, Belize's barrier reef, Sian Ka'an, the Galapagos islands, Great Barrier Reef, Henderson Island, Palau and Papahānaumokuākea Marine National Monument are world heritage sites.In Australia, the Great Barrier Reef is protected by the Great Barrier Reef Marine Park Authority, and is the subject of much legislation, including a biodiversity action plan. Australia compiled a Coral Reef Resilience Action Plan. This plan consists of adaptive management strategies, including reducing carbon footprint. A public awareness plan provides education on the "rainforests of the sea" and how people can reduce carbon emissions.Inhabitants of Ahus Island, Manus Province, Papua New Guinea, have followed a generations-old practice of restricting fishing in six areas of their reef lagoon. Their cultural traditions allow line fishing, but no net or spear fishing. Both biomass and individual fish sizes are significantly larger than in places where fishing is unrestricted.Increased levels of atmospheric CO2 contribute to ocean acidification, which in turn damages coral reefs. To help combat ocean acidification, several countries have put laws in place to reduce greenhouse gases such as carbon dioxide. Many land use laws aim to reduce CO2 emissions by limiting deforestation. Deforestation can release significant amounts of CO2 absent sequestration via active follow-up forestry programs. Deforestation can also cause erosion, which flows into the ocean, contributing to ocean acidification. Incentives are used to reduce miles traveled by vehicles, which reduces carbon emissions into the atmosphere, thereby reducing the amount of dissolved CO2 in the ocean. State and federal governments also regulate land activities that affect coastal erosion. High-end satellite technology can monitor reef conditions.The United States Clean Water Act puts pressure on state governments to monitor and limit run-off of polluted water.
Restoration
Coral reef restoration has grown in prominence over the past several decades because of the unprecedented reef die-offs around the planet. Coral stressors can include pollution, warming ocean temperatures, extreme weather events, and overfishing. With the deterioration of global reefs, fish nurseries, biodiversity, coastal development and livelihood, and natural beauty are under threat. Fortunately, researchers have taken it upon themselves to develop a new field, coral restoration, in the 1970s-1980s
Coral farming
Coral aquaculture, also known as coral farming or coral gardening, is showing promise as a potentially effective tool for restoring coral reefs. The "gardening" process bypasses the early growth stages of corals when they are most at risk of dying. Coral seeds are grown in nurseries, then replanted on the reef. Coral is farmed by coral farmers whose interests range from reef conservation to increased income. Due to its straight forward process and substantial evidence of the technique having a significant effect on coral reef growth, coral nurseries became the most widespread and arguably the most effective method for coral restoration.
Coral gardens take advantage of a coral's natural ability to fragment and continuing to grow if the fragments are able to anchor themselves onto new substrates. This method was first tested by Baruch Rinkevich in 1995 which found success at the time. By today's standards, coral farming has grown into a variety of different forms, but still has the same goals of cultivating corals. Consequently, coral farming quickly replaced previously used transplantation methods or the act of physically moving sections or whole colonies of corals into a new area. Transplantation has seen success in the past and decades of experiments have led to a high success and survival rate. However, this method still requires the removal of corals from existing reefs. With the current state of reefs, this kind of method should generally be avoided if possible. Saving healthy corals from eroding substrates or reefs that are doomed to collapse could be a major advantage of utilizing transplantation.
Coral gardens generally take on the safe forms no matter where you go. It begins with the establishment of a nursery where operators can observe and care for coral fragments. It goes without saying that nurseries should be established in areas that are going to maximize growth and minimize mortality. Floating offshore coral trees or even aquariums are possible locations where corals can grow. After a location has been determined, collection and cultivation can occur.
The major benefit of using coral farms is it lowers polyp and juvenile mortality rates. By removing predators and recruitment obstacles, corals are able to mature without much hindrance. However, nurseries cannot stop climate stressors. Warming temperatures or hurricanes can still disrupt or even kill nursery corals.
Creating substrates
Efforts to expand the size and number of coral reefs generally involve supplying substrate to allow more corals to find a home. Substrate materials include discarded vehicle tires, scuttled ships, subway cars and formed concrete, such as reef balls. Reefs grow unaided on marine structures such as oil rigs. In large restoration projects, propagated hermatypic coral on substrate can be secured with metal pins, superglue or milliput. Needle and thread can also attach A-hermatype coral to substrate.
Biorock is a substrate produced by a patented process that runs low voltage electrical currents through seawater to cause dissolved minerals to precipitate onto steel structures. The resultant white carbonate (aragonite) is the same mineral that makes up natural coral reefs. Corals rapidly colonize and grow at accelerated rates on these coated structures. The electrical currents also accelerate the formation and growth of both chemical limestone rock and the skeletons of corals and other shell-bearing organisms, such as oysters. The vicinity of the anode and cathode provides a high-pH environment which inhibits the growth of competitive filamentous and fleshy algae. The increased growth rates fully depend on the accretion activity. Under the influence of the electric field, corals display an increased growth rate, size and density.
Simply having many structures on the ocean floor is not enough to form coral reefs. Restoration projects must consider the complexity of the substrates they are creating for future reefs. Researchers conducted an experiment near Ticao Island in the Philippines in 2013 where several substrates in varying complexities were laid in the nearby degraded reefs. Large complexity consisted of plots that had both a human-made substrates of both smooth and rough rocks with a surrounding fence, medium consisted of only the human-made substrates, and small had neither the fence or substrates. After one month, researchers found that there was a positive correlation between structure complexity and recruitment rates of larvae. The medium complexity performed the best with larvae favoring rough rocks over smooth rocks. Following one year of their study, researchers visited the site and found that many of the sites were able to support local fisheries. They came to the conclusion that reef restoration could be done cost-effectively and will yield long term benefits given they are protected and maintained.
Relocation
One case study with coral reef restoration was conducted on the island of Oahu in Hawaii. The University of Hawaii operates a Coral Reef Assessment and Monitoring Program to help relocate and restore coral reefs in Hawaii. A boat channel from the island of Oahu to the Hawaii Institute of Marine Biology on Coconut Island was overcrowded with coral reefs. Many areas of coral reef patches in the channel had been damaged from past dredging in the channel.
Dredging covers corals with sand. Coral larvae cannot settle on sand; they can only build on existing reefs or compatible hard surfaces, such as rock or concrete. Because of this, the university decided to relocate some of the coral. They transplanted them with the help of United States Army divers, to a site relatively close to the channel. They observed little if any damage to any of the colonies during transport and no mortality of coral reefs was observed on the transplant site. While attaching the coral to the transplant site, they found that coral placed on hard rock grew well, including on the wires that attached the corals to the site.
No environmental effects were seen from the transplantation process, recreational activities were not decreased, and no scenic areas were affected.
As an alternative to transplanting coral themselves, juvenile fish can also be encouraged to relocate to existing coral reefs by auditory simulation. In damaged sections of the Great Barrier Reef, loudspeakers playing recordings of healthy reef environments were found to attract fish twice as often as equivalent patches where no sound was played, and also increased species biodiversity by 50%.
Heat-tolerant symbionts
Another possibility for coral restoration is gene therapy: inoculating coral with genetically modified bacteria, or naturally-occurring heat-tolerant varieties of coral symbiotes, may make it possible to grow corals that are more resistant to climate change and other threats. Warming oceans are forcing corals to adapt to unprecedented temperatures. Those that do not have a tolerance for the elevated temperatures experience coral bleaching and eventually mortality. There is already research that looks to create genetically modified corals that can withstand a warming ocean. Madeleine J. H. van Oppen, James K. Oliver, Hollie M. Putnam, and Ruth D. Gates described four different ways that gradually increase in human intervention to genetically modify corals. These methods focus on altering the genetics of the zooxanthellae within coral rather than the alternative.
The first method is to induce acclimatization of the first generation of corals. The idea is that when adult and offspring corals are exposed to stressors, the zooxanthellae will gain a mutation. This method is based mostly on the chance that the zooxanthellae will acquire the specific trait that will allow it to better survive in warmer waters. The second method focuses on identifying what different kinds of zooxanthellae are within the coral and configuring how much of each zooxanthella lives within the coral at a given age. Use of zooxanthellae from the previous method would only boost success rates for this method. However, this method would only be applicable to younger corals, for now, because previous experiments of manipulation zooxanthellae communities at later life stages have all failed. The third method focuses on selective breeding tactics. Once selected, corals would be reared and exposed to simulated stressors in a laboratory. The last method is to genetically modify the zooxanthellae itself. When preferred mutations are acquired, the genetically modified zooxanthellae will be introduced to an aposymbiotic poly and a new coral will be produced. This method is the most laborious of the fourth, but researchers believe this method should be utilized more and holds the most promise in genetic engineering for coral restoration.
Invasive algae
Hawaiian coral reefs smothered by the spread of invasive algae were managed with a two-prong approach: divers manually removed invasive algae, with the support of super-sucker barges. Grazing pressure on invasive algae needed to be increased to prevent the regrowth of the algae. Researchers found that native collector urchins were reasonable candidate grazers for algae biocontrol, to extirpate the remaining invasive algae from the reef.
Invasive algae in Caribbean reefs
Macroalgae, or better known as seaweed, has to potential to cause reef collapse because they can outcompete many coral species. Macroalgae can overgrow on corals, shade, block recruitment, release biochemicals that can hinder spawning, and potentially form bacteria harmful to corals. Historically, algae growth was controlled by herbivorous fish and sea urchins. Parrotfish are a prime example of reef caretakers. Consequently, these two species can be considered as keystone species for reef environments because of their role in protecting reefs.
Before the 1980s, Jamaica's reefs were thriving and well cared for, however, this all changed after Hurricane Allen occurred in 1980 and an unknown disease spread across the Caribbean. In the wake of these events, massive damage was caused to both the reefs and sea urchin population across Jamaican's reefs and into the Caribbean Sea. As little as 2% of the original sea urchin population survived the disease. Primary macroalgae succeeded the destroyed reefs and eventually larger, more resilient macroalgae soon took its place as the dominant organism. Parrotfish and other herbivorous fish were few in numbers because of decades of overfishing and bycatch at the time. Historically, the Jamaican coast had 90% coral cover and was reduced to 5% in the 1990s. Eventually, corals were able to recover in areas where sea urchin populations were increasing. Sea urchins were able to feed and multiply and clear off substrates, leaving areas for coral polyps to anchor and mature. However, sea urchin populations are still not recovering as fast as researchers predicted, despite being highly fecundate. It is unknown whether or not the mysterious disease is still present and preventing sea urchin populations from rebounding. Regardless, these areas are slowly recovering with the aid of sea urchin grazing. This event supports an early restoration idea of cultivating and releasing sea urchins into reefs to prevent algal overgrowth.
Microfragmentation and fusion
In 2014, Christopher Page, Erinn Muller, and David Vaughan from the International Center for Coral Reef Research & Restoration at Mote Marine Laboratory in Summerland Key, Florida developed a new technology called "microfragmentation", in which they use a specialized diamond band saw to cut corals into 1 cm2 fragments instead of 6 cm2 to advance the growth of brain, boulder, and star corals. Corals Orbicella faveolata and Montastraea cavernosa were outplanted off the Florida's shores in several microfragment arrays. After two years, O. faveolata had grown 6.5x its original size while M. cavernosa had grown nearly twice its size. Under conventional means, both corals would have required decades to reach the same size. It is suspected that if predation events had not occurred near the beginning of the experiment O. faveolata would have grown at least ten times its original size. By using this method, Mote Marine Laboratory produced 25,000 corals and planted 10,000 in the Florida Keys in only one year. Shortly after, they discovered that these microfragments fused with other microfragments from the same parent coral. Typically, corals that are not from the same parent fight and kill nearby corals in an attempt to survive and expand. This new technology is known as "fusion" and has been shown to grow coral heads in just two years instead of the typical 25–75 years. After fusion occurs, the reef will act as a single organism rather than several independent reefs. Currently, there has been no published research into this method.
See also
Deep-water coral — Corals living in the cold waters of deeper, darker parts of the oceans
Mesophotic coral reef — Corals living in the mesopelagic or twilight zone
Fossil Coral Reef – National Natural Landmark in Le Roy, New York
Census of Coral Reefs – Field project of the Census of Marine Life
Catlin Seaview Survey
Coral reef organizations – U.S. Coral Reef Task ForcePages displaying wikidata descriptions as a fallback
Sponge reef
Pseudo-atoll – Island that encircles a lagoon
References
Further references
Coral Reef Protection: What Are Coral Reefs?. US EPA.
UNEP. 2004. Coral Reefs in the South China Sea. UNEP/GEF/SCS Technical Publication No. 2.
UNEP. 2007. Coral Reefs Demonstration Sites in the South China Sea. UNEP/GEF/SCS Technical Publication No. 5.
UNEP, 2007. National Reports on Coral Reefs in the Coastal Waters of the South China Sea. UNEP/GEF/SCS Technical Publication No. 11.
External links
"Coral Reef Factsheet". Waitt Institute. Archived from the original on 9 June 2015. Retrieved 8 June 2015.
Corals and Coral Reefs overview at the Smithsonian Ocean Portal
About Corals Archived 26 December 2013 at the Wayback Machine Australian Institute of Marine Science.
International Coral Reef Initiative
Moorea Coral Reef Long Term Ecological Research Site (US NSF)
ARC Centre of Excellence for Coral Reef Studies
NOAA's Coral-List Listserver for Coral Reef Information and News
NOAA's Coral Reef Conservation Program
NOAA's Coral Reef Information System
ReefBase: A Global Information System on Coral Reefs Archived 31 August 2012 at the Wayback Machine
National Coral Reef Institute Archived October 23, 2012, at the Wayback Machine Nova Southeastern University
Marine Aquarium Council
NCORE National Center for Coral Reef Research University of Miami
Science and Management of Coral Reefs in the South China Sea and Gulf of Thailand
Microdocs Archived 27 July 2011 at the Wayback Machine: 4 kinds of Reef Archived 24 October 2012 at the Wayback Machine & Reef structure Archived 24 October 2012 at the Wayback Machine
Reef Relief Active Florida environmental non-profit focusing on coral reef education and protection
Global Reef Record – Catlin Seaview Survey of reef, a database of images and other information
"Corals and Coral Reefs" (archived). Nancy Knowlton, iBioSeminars, 2011.
Nancy Knowlton's Seminar: "Corals and Coral Reefs". Nancy Knowlton, iBioSeminars, 2011.
About coral reefs Living Reefs Foundation, Bermuda
Caribbean Coral Reefs - Status Report 1970-2012 by the IUCN. - Video on YouTube, featuring the report. |
geology of wales | The geology of Wales is complex and varied; its study has been of considerable historical significance in the development of geology as a science. All geological periods from the Cryogenian (late Precambrian) to the Jurassic are represented at outcrop, whilst younger sedimentary rocks occur beneath the seas immediately off the Welsh coast. The effects of two mountain-building episodes have left their mark in the faulting and folding of much of the Palaeozoic rock sequence. Superficial deposits and landforms created during the present Quaternary period by water and ice are also plentiful and contribute to a remarkably diverse landscape of mountains, hills and coastal plains.
Wales' modern character derives in substantial part from the exploitation of its diverse mineral wealth; slate in Snowdonia, coal in the South Wales Valleys and metal ores in Anglesey and mid Wales, to name but three. Wales' geology influences farming practices and building stone choices but also planning of developments which must take into account ground stability and liability to flooding - geohazards which an appreciation of the geology can help deal with.
History of geological study
South Wales has a written record of geological interest going back to the 12th century when Giraldus Cambrensis noted pyritous shales near Newport. George Owen in 1603 correctly identified the stratigraphic relationship between the Carboniferous Limestone and the Coal Measures. Some of the first published representations of fossils were those of fossil plants taken from the coal measures near Neath (Gibson late 17th century).
In the mid-19th century, two prominent geologists, Roderick Murchison and Adam Sedgwick used their studies of the geology of Wales to establish certain principles of stratigraphy and palaeontology. They did fundamental work on the Old Red Sandstone but are remembered more for their work on the lower Palaeozoic sequence. It was Sedgwick who established the Cambrian system and Murchison first described the Silurian, naming it for the ancient Silures tribe which occupied mid Wales. An overlap between the two systems as mapped led eventually to protracted dispute between the two erstwhile collaborators. After their deaths, Charles Lapworth erected the Ordovician system (again named for an ancient tribe of northwest Wales, the Ordovices), to account for the sequence of rocks at the heart of the controversy.
More recently two locations in mid Wales have been selected to globally define stages of the Silurian period. Cefn-cerig Road near Cefn-cerig Farm, Llandovery, is the location of the Global Boundary Stratotype Section and Point (GSSP) which marks the boundary between the Aeronian and Telychian stages of the Silurian period on the geologic time scale. Similarly Trefawr Track, a forestry road north of Cwm-coed-aeron Farm, Llandovery, is the location of the GSSP marking the boundary between the Rhuddanian and Aeronian stages. Both GSSPs were ratified in 1984. :See main articles on Cefn-cerig Road and Trefawr Track.
Precambrian
Late Precambrian rocks are widespread on Anglesey, Llŷn and Arfon with other, more restricted occurrences in north Pembrokeshire, Radnorshire and Carmarthenshire. The often intensive metamorphism which these originally volcanic and sedimentary rocks have been subjected to and their generally faulted relationship to neighbouring rocks has meant that geologists’ understanding of them has been limited. The majority lie on or close to the margins of terranes, blocks of the Earth's crust which have had differing geological histories before assuming their present configuration. However, in recent years there has been a progressive elucidation of the way in which Wales’ many terranes came together during the late Precambrian and the Palaeozoic era.
The Stanner-Hanter Complex on the English border comprises volcanic rocks around 700 million years old which puts them within the Cryogenian period.
Palaeozoic
Cambrian
Rocks of Cambrian age occur most extensively in an inlier in Merionethshire where the up-arched rocks of the Harlech Dome form the Rhinogydd. The Harlech Grits Group comprises sandstones, mudstones and greywackes forms the eroded core of the dome and within this sequence it is specifically the greywackes of the 'Rhinog Formation' which provides the higher hills. Cambrian rocks are also to be found in north Pembrokeshire, Anglesey and Llŷn.
Ordovician
The Ordovician period gave rise to a sequence of sedimentary rocks which stretch from Pembrokeshire eastwards through Carmarthenshire up the Vale of Towy and which are intricately intermixed with those of the succeeding period northwards to the Vale of Conwy. In Snowdonia many Ordovician volcanic rocks give rise to a more rugged landscape than elsewhere in the country. Snowdon itself is largely formed of volcanic ash (tuff) with some sedimentary rock and igneous intrusions folded into a syncline. Cadair Idris is also largely formed of Ordovician igneous rocks. Anglesey and Llŷn are also Ordovician territory. The Ordovician rocks of Wales are typically intensely faulted and folded, having been affected by the earth movements of the Caledonian Orogeny.
A notable feature of the Ordovician system is a major downwarp known as the Welsh geosyncline.
Silurian
Rocks dating from the Silurian period are, by one measure, the most significant for Wales’ landscape; a greater percentage of the country's land area is directly underlain by rocks of this age than any other. Much of central Wales is formed in Silurian sandstones and mudstones as is the more gentle landscape of central Monmouthshire where the Usk Anticline gives rise to the Usk Inlier. In the north it is the Ludlow age mudstones and sandstones of the Elwy and Nantglyn Formations which form the Clwydian Range, and the Nantglyn Flags and Wenlockian Denbigh Grits which form the Denbigh Moors, Llantysilio Mountain and the Dee Valley around Llangollen. In west Wales, parts of south and central Pembrokeshire around Haverfordwest and Narberth and between Marloes and Daugleddau are formed by Llandovery aged mudstones, sandstones and conglomerates.
The Caledonian orogeny
A long and complex series of continental collisions known collectively as the Caledonian orogeny began in the Ordovician and continued through the Silurian into Devonian times. The effect in this area was to cause folding and faulting of the existing rock sequence, most particularly within the Welsh Basin, a process which intensified northwards. Parts of the sequence were subjected to low grade metamorphism, the most significant of which, from an economic point of view, would be the Cambrian and Ordovician slates of North Wales. The northeast to southwest 'grain' of much of the country was imparted at this time with a series of major fault zones persisting from that time to the present, some of which, particularly in the northwest, are believed to represent terrane boundaries. The siliciclastic deposits of the succeeding Devonian period represent in large part the rapid attrition of the extensive Caledonian Mountain belt created by the Caledonian collision.
Devonian
Devonian age rocks are broadly synonymous with the Old Red Sandstone (commonly referred to as ‘the ORS’) though the lowermost ORS is late Silurian in age. The Anglo-Welsh Basin which stretches from the border with England westwards through the Brecon Beacons National Park into Pembrokeshire includes the larger part of this sequence. It is the sandstones and mudstones of the Lower Devonian Brownstones and Senni Formations, sometimes capped by the hard wearing sandstones of the Plateau Beds which form such striking peaks as Pen y Fan and Sugar Loaf and the dramatic scarps of the Black Mountains and Black Mountain. There are restricted occurrences of Devonian rocks on Anglesey too.
Carboniferous
The Carboniferous period is represented by extensive outcrops across South Wales from the Wye Valley in the east, through the South Wales Coalfield, the Vale of Glamorgan and Gower westwards to southern Pembrokeshire. There are less extensive areas in northeast Wales and along the north coast into Anglesey where similarly aged rocks characterize the landscape. The sequence includes Carboniferous Limestone at its base, followed by coarse sandstones (The ‘Millstone Grit’ of the north and the ‘Twrch Sandstone’ of the south), then mudstones and finally the Coal Measures which comprise a thick succession of mudstones, sandstones and of course coal seams.
Limestone
Though mid Wales lay above sea level during Carboniferous times, shallow tropical seas extended across much of north and south Wales and it was in these environments that a succession of types of limestone were deposited.
The limestone gives rise to impressive cliffed landscapes both on the coast as at the Great Orme in the north and at St Govan's Head and the Gower Peninsula in the south, and inland at the escarpments of Eglwyseg Mountain near Llangollen and Llangattock hillside in the Usk Valley. Karst landscapes characterize the limestone outcrop and, particularly along the ‘north crop’ of the South Wales Coalfield basin, where the limestone is shallowly buried beneath adjacent sandstones, extensive development of solution hollows has taken place.
Namurian sequence
The Namurian age mudstones and sandstones which overlie/succeed the limestone give rise to rugged landscapes; typically either poorly drained moorland or else wooded gorges as in the Waterfall Country of southern Powys.
Coal Measures
Landscapes developed over Coal Measures rocks are extensively altered by humans, as the coal and iron found within this thick sequence of rocks have long been economically important, particularly since the Industrial Revolution. The former coalfields of Flintshire, Denbighshire and South Wales are witness to this period. In South Wales, the Coal Measures are overlain by the thick sandstones of the Pennant Measures which often provides craggy edges to the plateau which has been deeply dissected to form the South Wales Valleys. The Pennant Sandstone is widely used as a building stone.
A major geological feature of the Upper Carboniferous sub-period in South Wales is the South Wales Coalfield syncline. The rocks comprising this important area were laid down during the Westphalian Age approximately 314-308 million years ago (Ma), when climatic conditions were equatorial. This Westphalian succession includes a sequence with a thickness of more than 1800 m in the west. The Coal Measures were laid down on a low-lying waterlogged plain with peat mires immediately south of an ancient geological feature known as the Wales-London-Brabant High.
Variscan Orogeny
From late Carboniferous times, through the Permian, South Wales lay on the northern margin of the Variscan orogen, an area affected by a complex continental collision taking place to the south. The most intensely affected rocks are those of south and central Pembrokeshire where steeply dipping and vertical strata are commonplace and multiple folding, faulting and overthrusting are well seen in coastal sections. Southern Carmarthenshire and the western part of the South Wales Coalfield were affected to a lesser extent. Old Caledonoid weaknesses such as the Neath Disturbance were reactivated at this time.
Permian
Rocks dating from the Permian period occur in North Wales underlying the Vale of Clwyd and extend into the northeastern fringes of the country from the larger bodies of such rock in Cheshire and Shropshire. The Permo-Triassic rocks in the northeast of Wales are largely concealed by recent material deposited by rivers and the Devensian icesheet. Thicker sequences of Permo-Triassic rock are known to underlie the Bristol Channel, Cardigan Bay and the Irish Sea off the North Wales coast.
Mesozoic
Triassic
Triassic sandstones form much of the coast between Barry and Penarth and extend eastwards along the Monmouthshire coast to the English border at Chepstow. They also occur more sporadically further west between Ogmore-by-Sea and Kenfig. There are very localized occurrences of Triassic material in Gower and south Pembrokeshire, much of it breccia-fill of fissures in underlying Carboniferous Limestone. Triassic sandstones are also found along the border with Cheshire and Shropshire, though most often concealed beneath recent fluvial and glacially derived material.
Jurassic
Rocks dating from the Jurassic period occur widely across the Vale of Glamorgan. Much of the Glamorgan coast between Ogmore-by-Sea and Barry is formed by cliffs of layered Jurassic limestone known as the Lias. Extensive and spectacular shore platforms have been developed e.g. near Southerndown, as these cliffs have retreated inland through frequent rockfall.
Cretaceous
There are no rocks of Cretaceous age in Wales but they are known to be present within the sub-sea basins off the Welsh coast e.g. Celtic Sea and the Bristol Channel.
Cenozoic
Palaeogene and Neogene
There is scant evidence for rocks of the Palaeogene and Neogene periods in Wales though they are known to occur offshore. The exceptions are the sequence revealed in the Mochras borehole on the coastal strip south of Harlech and the 'pocket deposits' where sediments fill depressions in the Carboniferous Limestone in northeast Wales. In the south, poorly cemented sands occur sporadically in the central and western part of the Brecon Beacons National Park; these are thought to be a product of the Cenozoic weathering of the underlying Twrch Sandstone.
Quaternary
The landscape of Wales has assumed its present shape over the last 2.6 million years i.e. during the Quaternary period which reaches to the present day. Ice sheets and valley glaciers which developed during a series of ice ages have significantly altered a landscape which had developed as rivers drained a tilted upland surface which is thought to have emerged from beneath the sea during earlier Cainozoic times.
Glacial legacy
The effects of the last (Devensian) ice age are the most readily understood. An ice sheet which at its maximum extent covered virtually all of Wales and reached as far south as Cardiff, Bridgend and Gower left in its wake suites of both erosional and depositional landforms. The glacial cirques of Snowdonia and to a lesser extent of the Cambrian Mountains and the Brecon Beacons are well known. Many pre-existing valleys were further deepened by glacial ice. Cirque moraines in the mountains and terminal and recessional moraines in the major valleys are the most striking depositional legacy of the glaciation. Three substantial medial moraines extend beneath the waters of Cardigan Bay, parts being exposed at low spring tides as Sarn Badrig, Sarn y Bwch and Sarn Cynfelin.There are too, swarms of drumlins and a widespread plastering of glacial till elsewhere. The greatest concentration of drumlins is in Denbighshire though there are also distinct areas around the Severn valley.
Coastal deposits
Following the end of the last ice age, sea levels rose to roughly their current levels by around 6000 years ago. Forests which had become established at or below this level were destroyed though the preserved stumps of trees in growth position can still be seen in the intertidal zone in places, as can the remains of peat deposits which again had originally formed above the high-water mark. Redistribution of glacial and fluvial sands has given rise to extensive dune systems around the Welsh coast, notably at Newborough Warren on Anglesey, Morfa Harlech and Morfa Dyffryn in Gwynedd and at Pendine and Pembrey Burrows in Carmarthenshire and at Merthyr-mawr Warren and Kenfig Burrows in Glamorgan.
See also Coastline of Wales
Karstic landforms
Within the limestone areas of Wales, there have arisen karstic landscapes during the postglacial period, though elements of these were initiated during and even before successive ice ages. Limestone pavements are best developed along the 'north crop' within the Brecon Beacons National Park and there are numerous sinkholes and shakeholes, together with sinks, sections of dry valley and resurgences. Cave development is extensive and includes systems such as Ogof Ffynnon Ddu (Britain's deepest cave), Dan-yr-ogof (partly showcave) and Wales' most extensive system Ogof Draenen.
Economic geology
Metals
Humans have mined metals and metal ores in Wales for millennia. There are Bronze Age copper workings on the Great Orme near Llandudno and at Parys Mountain on Anglesey. Gold has been obtained since pre-Roman times at places like Dolaucothi. Lead and zinc were intensively mined in the Cwmystwyth area of mid Wales and a lead mine operated at Minera near Wrexham from the Middle Ages until the early twentieth century. In Victorian times the Sygun Copper Mine was opened near Beddgelert in Snowdonia. Ironstone is a component of the Lower Coal Measures rock sequence and where it outcrops along the northern edge of the South Wales Coalfield, it was extensively worked for the production of iron and was important in the initiation of the Industrial Revolution in South Wales.
Slate
The slate industry of Snowdonia was once of world importance. Purple and green slates of Cambrian age were worked at vast quarries on the flanks of Snowdon and at Bethesda, Dinorwig, Corris and Blaenau Ffestiniog.
Building stone
The abundance of hard rock in Wales means that it has found use in building since the earliest times. The 'bluestones' (of Ordovician dolerite) which form the lintels of Stonehenge were sourced in the Preseli Hills of Pembrokeshire around 2500 BC. Bronze Age and Iron Age peoples made extensive use of local materials in erecting a variety of cairns, standing stones and defensive works as manifest in Wales' many hill forts.
Wales' many fine cathedrals, abbeys and castles have used a variety of stones in their construction; Caerbwdi Sandstone in St David's Cathedral, Old Red Sandstone at Llanthony Priory and Tintern Abbey, 'Blue Pennant' sandstone in Caerphilly Castle and Sudbrook Sandstone at Caldicot Castle to name but a few. Triassic rocks provided the Radyr stone and also the Quarella stone which was worked at Bridgend.Sutton Stone from South Wales' Jurassic outcrop is a highly regarded limestone freestone that has been used in construction throughout the Vale of Glamorgan, it was also shipped over the Bristol Channel to North Devon and North Cornwall which are both deficient in limestone.
The micaceous sandstones of Carmarthenshire's Tilestones Formation were formerly worked to provide roofing material, as were similar flaggy sandstones elsewhere, at least until the burgeoning of the North Wales slate industry in the nineteenth century.
Limestone
Limestone has been worked on a small scale for burning in limekilns over many centuries. In more recent times it has been quarried for use as aggregate, as a flux for the steel industry and as a feed for the chemical industry.
Coal
The working of coal in Wales' various coalfields began in earnest with the initiation of the Industrial Revolution. Easily the most significant is the South Wales Coalfield though the contiguous Flintshire and Denbighshire Coalfields were of importance to the economy of northeast Wales. A rather smaller coalfield was worked in Pembrokeshire and a tiny one in Anglesey.
Sand and gravel
Deposits of glacial and fluvial sands and gravels have been and continue to be worked in numerous areas, principally for the construction industry.
Geohazards
Wales is not a particularly seismically active country, nevertheless earthquakes of lesser magnitude occur from time to time. Ground stability is more of an issue due both to natural causes and, in former areas of coal and other mineral exploitation, due to mining, surface excavation and spoil deposition. Deep-mining of coal in particular has led to reactivation of pre-existing landslips, notably in the steeply-sided valleys of the South Wales Coalfield. Inappropriate placing of spoil material on such slopes has both overloaded them and disturbed drainage patterns with occasional catastrophic effect as in the Aberfan Disaster of 1966. An extensive programme of stabilisation works across the coalfield followed that event.
The contamination of land, groundwater and watercourses is a risk in areas where mineral exploitation has taken place, notably in the Central Wales Orefield and in former coal mining districts.
Geological conservation and interpretation
Numerous sites have been identified as important earth science localities within the Geological Conservation Review and afforded protection as geological SSSIs. See here for complete list of both biological and geological SSSIs in Wales - some sites are protected in respect of both types of interest. In addition, two extensive areas are designated as Geoparks; the entire island of Anglesey as 'GeoMôn' in the north and Fforest Fawr within the Brecon Beacons National Park in the south.
The Geoparks have a range of roles; conservation and promotion of the two areas' geological heritage are important ones. These objectives are partly achieved through educational and interpretive programmes. 'RIGS groups' are being established in different parts of Wales with the aim of supporting locations designated as regionally important geodiversity sites and assisting in the implementation of Local Geodiversity Action Plans ('LGAPs'). Local authorities and other agencies in the public sector continue to be involved in the acquisition of significant earth heritage sites, their conservation and interpretation. Charities such as Wales' wildlife trusts also have a similar role.
See also
Geology of the British Isles
Geology of England
Geological groups of Great Britain
Geological structure of Great Britain
Geology of Monmouthshire
Geology of Carmarthenshire
List of geological faults of Wales
List of geological folds in Great Britain
Geology of South Wales
Geology of Snowdonia National Park
Geology of Brecon Beacons National Park
Palaeontology in Wales
Geology of Great Britain
References
Howells, M.F. 2007 British Regional Geology: Wales Keyworth, Nottingham: British Geological Survey 230pp ISBN 978-0-85272-584-9
Snowdonia National Park Authority
Official site of the Brecon Beacons National Park Authority
The Gower Information Center: Broad Pool
Ogg, James. "GSSP for the Base of Telychian". Archived from the original on 2006-06-18. Retrieved 2006-07-01.
Ogg, James. "GSSP for the Base of Aeronian". Archived from the original on 2006-06-18. Retrieved 2006-07-01.
John L. Morton, King of Siluria — How Roderick Murchison Changed the Face of Geology (Brocken Spectre Publishing, 2004, ISBN 0-9546829-0-4)
Chisholm, Hugh, ed. (1911). "Wales" . Encyclopædia Britannica. Vol. 28 (11th ed.). Cambridge University Press. p. 260.
Chisholm, Hugh, ed. (1911). "Denbighshire" . Encyclopædia Britannica. Vol. 8 (11th ed.). Cambridge University Press. p. 18.
Martin J. S. Rudwick, The Great Devonian Controversy: The Shaping of Scientific Knowledge among Gentlemanly Specialists (University of Chicago Press, 1985) — the rise of Murchison to power
James A. Secord, Controversy in Victorian Geology: The Cambrian-Silurian Dispute (Princeton University Press, 1986) — documents the battle between Murchison and Adam Sedgwick |
clam shrimp | Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classified in the former order Conchostraca, which later proved to be paraphyletic, due to the fact that water fleas are nested within clam shrimps. Clam shrimp are now divided into three orders, Cyclestherida, Laevicaudata, and Spinicaudata, in addition to the fossil family Leaiidae.
Characteristics
Both valves of the shell are held together by a strong closing muscle. The animals react to danger by contracting the muscle, so that the valves close tightly and the crustacean, as if dead, lies motionlessly at the bottom of the pool.
In most species the head is dorsoventrally compressed. The sessile compound eyes are close together and located on the forehead; in the genus Cyclestheria they are truly fused. In front of them is a simple naupliar eye. The first pair of antennae is reduced and unsegmented. The second pair of antennae, however, is long and biramous. Both branches are covered with numerous bristles. The crustaceans swim primarily by swooping the antennae. In the common genus Lynceus, which can open its spherical valves wide, the thoracic legs move in an oar-like manner along with the antennae.
The number of segments constituting the thorax varies from 10 to 32, and the number of legs varies accordingly. They are similar in structure to the legs of tadpole shrimp, and similarly, their size decreases from front to back. In females, the outer lobes of several middle legs are modified into long, upward-bending threadlike outgrowths, used to hold the eggs on the dorsal side of the body under the shell. However, the main functions of the thoracic legs are respiration and carrying food forward to the mouth. The gills are basically the outer lobes of all thoracic legs that are closest to the base of the leg. The legs are in constant movement, and the water between the valves of the carapace is quickly renewed. The body ends in a large chitinised telson, which is either laterally compressed and bears a pair of large hooks, or dorsoventrally compressed, with short hooks.
Reproduction and development
Reproduction
Clam shrimp have different reproductive strategies. For example, within the family Limnadiidae are found dioecious (male-female), hermaphroditic (only hermaphrodites), and androdioecious (male-hermaphrodite) species.
Life cycle
The eggs are surrounded by a tough shell and can withstand drying out, freezing and other hostile conditions. In some species these eggs can hatch after as long as 7 years.
When the egg arrives in a suitable pool, a larva hatches out at the nauplius stage (the nauplius stage is absent in Cyclestherida). Clam shrimp nauplii are distinguished by very small front antennae. At the second stage (metanauplius), the larva develops the small shell. They develop very quickly. For instance, Cyzicus reaches sexual maturity in 19 days after hatching.
Taxonomy
Extant clam shrimp belong to three orders, divided into five families; some notable genera and prehistoric taxa are also listed:
Geological history
Modern clam shrimp have little significance to humans. However, extinct species of these crustaceans are often studied by geologists. In freshwater deposits, generally poor in fossils, the well-preserved clam shrimp shells are found quite often. They help identify the age of the corresponding strata.During the past geological periods clam shrimp were apparently more numerous and diverse than they are now. 300 extinct species are known, and half as many living species. The oldest clam shrimp, such as Asmussia murchisoniana, were found in Devonian deposits. Many extinct species, mostly Triassic specimens, once lived in marine environments, where no extant clam shrimp inhabit today.
References
External links
[1]
Introduction to the Branchiopoda
Data related to Cyclestherida at Wikispecies
Data related to Laevicaudata at Wikispecies
Data related to Spinicaudata at Wikispecies |
fossil | A fossil (from Classical Latin fossilis, lit. 'obtained by digging') is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the fossil record.
Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years old to 4.1 billion years old. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host.
There are many processes that lead to fossilization, including permineralization, casts and molds, authigenic mineralization, replacement and recrystallization, adpression, carbonization, and bioimmuration.
Fossils vary in size from one-micrometre (1 µm) bacteria to dinosaurs and trees, many meters long and weighing many tons. A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces (coprolites). These types of fossil are called trace fossils or ichnofossils, as opposed to body fossils. Some fossils are biochemical and are called chemofossils or biosignatures.
Reliability
Though the fossil record is incomplete, numerous studies have demonstrated that there is enough information available to give us a good understanding of the pattern of diversification of life on Earth. In addition, the record can predict and fill gaps such as the discovery of Tiktaalik in the arctic of Canada.
Fossilization processes
The process of fossilization varies according to tissue type and external conditions:
Permineralization
Permineralization is a process of fossilization that occurs when an organism is buried. The empty spaces within an organism (spaces filled with liquid or gas during life) become filled with mineral-rich groundwater. Minerals precipitate from the groundwater, occupying the empty spaces. This process can occur in very small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce very detailed fossils. For permineralization to occur, the organism must become covered by sediment soon after death, otherwise the remains are destroyed by scavengers or decomposition. The degree to which the remains are decayed when covered determines the later details of the fossil. Some fossils consist only of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. This is a form of diagenesis.
Casts and molds
In some cases, the original remains of the organism completely dissolve or are otherwise destroyed. The remaining organism-shaped hole in the rock is called an external mold. If this void is later filled with sediment, the resulting cast resembles what the organism looked like. An endocast, or internal mold, is the result of sediments filling an organism's interior, such as the inside of a bivalve or snail or the hollow of a skull. Endocasts are sometimes termed Steinkerns, especially when bivalves are preserved this way.
Authigenic mineralization
This is a special form of cast and mold formation. If the chemistry is right, the organism (or fragment of organism) can act as a nucleus for the precipitation of minerals such as siderite, resulting in a nodule forming around it. If this happens rapidly before significant decay to the organic tissue, very fine three-dimensional morphological detail can be preserved. Nodules from the Carboniferous Mazon Creek fossil beds of Illinois, US, are among the best documented examples of such mineralization.
Replacement and recrystallization
Replacement occurs when the shell, bone, or other tissue is replaced with another mineral. In some cases mineral replacement of the original shell occurs so gradually and at such fine scales that microstructural features are preserved despite the total loss of original material. A shell is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form, as from aragonite to calcite.
Adpression (compression-impression)
Compression fossils, such as those of fossil ferns, are the result of chemical reduction of the complex organic molecules composing the organism's tissues. In this case the fossil consists of original material, albeit in a geochemically altered state. This chemical change is an expression of diagenesis. Often what remains is a carbonaceous film known as a phytoleim, in which case the fossil is known as a compression. Often, however, the phytoleim is lost and all that remains is an impression of the organism in the rock—an impression fossil. In many cases, however, compressions and impressions occur together. For instance, when the rock is broken open, the phytoleim will often be attached to one part (compression), whereas the counterpart will just be an impression. For this reason, one term covers the two modes of preservation: adpression.
Soft tissue, cell and molecular preservation
Because of their antiquity, an unexpected exception to the alteration of an organism's tissues by chemical reduction of the complex organic molecules during fossilization has been the discovery of soft tissue in dinosaur fossils, including blood vessels, and the isolation of proteins and evidence for DNA fragments. In 2014, Mary Schweitzer and her colleagues reported the presence of iron particles (goethite-aFeO(OH)) associated with soft tissues recovered from dinosaur fossils. Based on various experiments that studied the interaction of iron in haemoglobin with blood vessel tissue they proposed that solution hypoxia coupled with iron chelation enhances the stability and preservation of soft tissue and provides the basis for an explanation for the unforeseen preservation of fossil soft tissues. However, a slightly older study based on eight taxa ranging in time from the Devonian to the Jurassic found that reasonably well-preserved fibrils that probably represent collagen were preserved in all these fossils and that the quality of preservation depended mostly on the arrangement of the collagen fibers, with tight packing favoring good preservation. There seemed to be no correlation between geological age and quality of preservation, within that timeframe.
Carbonization and coalification
Fossils that are carbonized or coalified consist of the organic remains which have been reduced primarily to the chemical element carbon. Carbonized fossils consist of a thin film which forms a silhouette of the original organism, and the original organic remains were typically soft tissues. Coalified fossils consist primarily of coal, and the original organic remains were typically woody in composition.
Bioimmuration
Bioimmuration occurs when a skeletal organism overgrows or otherwise subsumes another organism, preserving the latter, or an impression of it, within the skeleton. Usually it is a sessile skeletal organism, such as a bryozoan or an oyster, which grows along a substrate, covering other sessile sclerobionts. Sometimes the bioimmured organism is soft-bodied and is then preserved in negative relief as a kind of external mold. There are also cases where an organism settles on top of a living skeletal organism that grows upwards, preserving the settler in its skeleton. Bioimmuration is known in the fossil record from the Ordovician to the Recent.
Types
Index
Index fossils (also known as guide fossils, indicator fossils or zone fossils) are fossils used to define and identify geologic periods (or faunal stages). They work on the premise that, although different sediments may look different depending on the conditions under which they were deposited, they may include the remains of the same species of fossil. The shorter the species' time range, the more precisely different sediments can be correlated, and so rapidly evolving species' fossils are particularly valuable. The best index fossils are common, easy to identify at species level and have a broad distribution—otherwise the likelihood of finding and recognizing one in the two sediments is poor.
Trace
Trace fossils consist mainly of tracks and burrows, but also include coprolites (fossil feces) and marks left by feeding. Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily fossilized hard parts, and they reflect animal behaviours. Many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them. Whilst exact assignment of trace fossils to their makers is generally impossible, traces may for example provide the earliest physical evidence of the appearance of moderately complex animals (comparable to earthworms).Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. They were first described by William Buckland in 1829. Prior to this they were known as "fossil fir cones" and "bezoar stones." They serve a valuable purpose in paleontology because they provide direct evidence of the predation and diet of extinct organisms. Coprolites may range in size from a few millimetres to over 60 centimetres.
Transitional
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation.
Microfossils
Microfossil is a descriptive term applied to fossilized plants and animals whose size is just at or below the level at which the fossil can be analyzed by the naked eye. A commonly applied cutoff point between "micro" and "macro" fossils is 1 mm. Microfossils may either be complete (or near-complete) organisms in themselves (such as the marine plankters foraminifera and coccolithophores) or component parts (such as small teeth or spores) of larger animals or plants. Microfossils are of critical importance as a reservoir of paleoclimate information, and are also commonly used by biostratigraphers to assist in the correlation of rock units.
Resin
Fossil resin (colloquially called amber) is a natural polymer found in many types of strata throughout the world, even the Arctic. The oldest fossil resin dates to the Triassic, though most dates to the Cenozoic. The excretion of the resin by certain plants is thought to be an evolutionary adaptation for protection from insects and to seal wounds. Fossil resin often contains other fossils called inclusions that were captured by the sticky resin. These include bacteria, fungi, other plants, and animals. Animal inclusions are usually small invertebrates, predominantly arthropods such as insects and spiders, and only extremely rarely a vertebrate such as a small lizard. Preservation of inclusions can be exquisite, including small fragments of DNA.
Derived or reworked
A derived, reworked or remanié fossil is a fossil found in rock that accumulated significantly later than when the fossilized animal or plant died. Reworked fossils are created by erosion exhuming (freeing) fossils from the rock formation in which they were originally deposited and their redeposition in a younger sedimentary deposit.
Wood
Fossil wood is wood that is preserved in the fossil record. Wood is usually the part of a plant that is best preserved (and most easily found). Fossil wood may or may not be petrified. The fossil wood may be the only part of the plant that has been preserved; therefore such wood may get a special kind of botanical name. This will usually include "xylon" and a term indicating its presumed affinity, such as Araucarioxylon (wood of Araucaria or some related genus), Palmoxylon (wood of an indeterminate palm), or Castanoxylon (wood of an indeterminate chinkapin).
Subfossil
The term subfossil can be used to refer to remains, such as bones, nests, or fecal deposits, whose fossilization process is not complete, either because the length of time since the animal involved was living is too short or because the conditions in which the remains were buried were not optimal for fossilization. Subfossils are often found in caves or other shelters where they can be preserved for thousands of years. The main importance of subfossil vs. fossil remains is that the former contain organic material, which can be used for radiocarbon dating or extraction and sequencing of DNA, protein, or other biomolecules. Additionally, isotope ratios can provide much information about the ecological conditions under which extinct animals lived. Subfossils are useful for studying the evolutionary history of an environment and can be important to studies in paleoclimatology.
Subfossils are often found in depositionary environments, such as lake sediments, oceanic sediments, and soils. Once deposited, physical and chemical weathering can alter the state of preservation, and small subfossils can also be ingested by living organisms. Subfossil remains that date from the Mesozoic are exceptionally rare, are usually in an advanced state of decay, and are consequently much disputed. The vast bulk of subfossil material comes from Quaternary sediments, including many subfossilized chironomid head capsules, ostracod carapaces, diatoms, and foraminifera.
For remains such as molluscan seashells, which frequently do not change their chemical composition over geological time, and may occasionally even retain such features as the original color markings for millions of years, the label 'subfossil' is applied to shells that are understood to be thousands of years old, but are of Holocene age, and therefore are not old enough to be from the Pleistocene epoch.
Chemical fossils
Chemical fossils, or chemofossils, are chemicals found in rocks and fossil fuels (petroleum, coal, and natural gas) that provide an organic signature for ancient life. Molecular fossils and isotope ratios represent two types of chemical fossils. The oldest traces of life on Earth are fossils of this type, including carbon isotope anomalies found in zircons that imply the existence of life as early as 4.1 billion years ago.
Dating
Estimating dates
Paleontology seeks to map out how life evolved across geologic time. A substantial hurdle is the difficulty of working out fossil ages. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating. This technique is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better. Although radiometric dating requires careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so the ratio of the radioactive element to its decay products shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers, which may provide termini for the intervening sediments.
Stratigraphy
Consequently, palaeontologists rely on stratigraphy to date fossils. Stratigraphy is the science of deciphering the "layer-cake" that is the sedimentary record. Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age is claimed to lie between the two known ages. Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is very difficult to match up rock beds that are not directly adjacent. However, fossils of species that survived for a relatively short time can be used to match isolated rocks: this technique is called biostratigraphy. For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period. If rocks of unknown age have traces of E. pseudoplanus, they have a mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and occupy a short time range to be useful. Misleading results are produced if the index fossils are incorrectly dated. Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of the problems involved in matching rocks of the same age across continents. Family-tree relationships also help to narrow down the date when lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved earlier.
It is also possible to estimate how long ago two living clades diverged, in other words approximately how long ago their last common ancestor must have lived, by assuming that DNA mutations accumulate at a constant rate. These "molecular clocks", however, are fallible, and provide only approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different techniques may vary by a factor of two.
Limitations
Organisms are only rarely preserved as fossils in the best of circumstances, and only a fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived. Because of the specialized and rare circumstances required for a biological structure to fossilize, only a small percentage of life-forms can be expected to be represented in discoveries, and each discovery represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, which will never demonstrate an exact half-way point.The fossil record is strongly biased toward organisms with hard-parts, leaving most groups of soft-bodied organisms with little to no role. It is replete with the mollusks, the vertebrates, the echinoderms, the brachiopods and some groups of arthropods.
Sites
Lagerstätten
Fossil sites with exceptional preservation—sometimes including preserved soft tissues—are known as Lagerstätten—German for "storage places". These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus slowing decomposition. Lagerstätten span geological time from the Cambrian period to the present. Worldwide, some of the best examples of near-perfect fossilization are the Cambrian Maotianshan shales and Burgess Shale, the Devonian Hunsrück Slates, the Jurassic Solnhofen limestone, and the Carboniferous Mazon Creek localities.
Stromatolites
Stromatolites are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria. Stromatolites provide some of the most ancient fossil records of life on Earth, dating back more than 3.5 billion years ago.Stromatolites were much more abundant in Precambrian times. While older, Archean fossil remains are presumed to be colonies of cyanobacteria, younger (that is, Proterozoic) fossils may be primordial forms of the eukaryote chlorophytes (that is, green algae). One genus of stromatolite very common in the geologic record is Collenia. The earliest stromatolite of confirmed microbial origin dates to 2.724 billion years ago.A 2009 discovery provides strong evidence of microbial stromatolites extending as far back as 3.45 billion years ago.Stromatolites are a major constituent of the fossil record for life's first 3.5 billion years, peaking about 1.25 billion years ago. They subsequently declined in abundance and diversity, which by the start of the Cambrian had fallen to 20% of their peak. The most widely supported explanation is that stromatolite builders fell victims to grazing creatures (the Cambrian substrate revolution), implying that sufficiently complex organisms were common over 1 billion years ago.The connection between grazer and stromatolite abundance is well documented in the younger Ordovician evolutionary radiation; stromatolite abundance also increased after the end-Ordovician and end-Permian extinctions decimated marine animals, falling back to earlier levels as marine animals recovered. Fluctuations in metazoan population and diversity may not have been the only factor in the reduction in stromatolite abundance. Factors such as the chemistry of the environment may have been responsible for changes.While prokaryotic cyanobacteria themselves reproduce asexually through cell division, they were instrumental in priming the environment for the evolutionary development of more complex eukaryotic organisms. Cyanobacteria (as well as extremophile Gammaproteobacteria) are thought to be largely responsible for increasing the amount of oxygen in the primeval earth's atmosphere through their continuing photosynthesis. Cyanobacteria use water, carbon dioxide and sunlight to create their food. A layer of mucus often forms over mats of cyanobacterial cells. In modern microbial mats, debris from the surrounding habitat can become trapped within the mucus, which can be cemented by the calcium carbonate to grow thin laminations of limestone. These laminations can accrete over time, resulting in the banded pattern common to stromatolites. The domal morphology of biological stromatolites is the result of the vertical growth necessary for the continued infiltration of sunlight to the organisms for photosynthesis. Layered spherical growth structures termed oncolites are similar to stromatolites and are also known from the fossil record. Thrombolites are poorly laminated or non-laminated clotted structures formed by cyanobacteria common in the fossil record and in modern sediments.The Zebra River Canyon area of the Kubis platform in the deeply dissected Zaris Mountains of southwestern Namibia provides an extremely well exposed example of the thrombolite-stromatolite-metazoan reefs that developed during the Proterozoic period, the stromatolites here being better developed in updip locations under conditions of higher current velocities and greater sediment influx.
Astrobiology
It has been suggested that biominerals could be important indicators of extraterrestrial life and thus could play an important role in the search for past or present life on the planet Mars. Furthermore, organic components (biosignatures) that are often associated with biominerals are believed to play crucial roles in both pre-biotic and biotic reactions.On 24 January 2014, NASA reported that current studies by the Curiosity and Opportunity rovers on Mars will now be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic and/or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars is now a primary NASA objective.
Pseudofossils
Pseudofossils are visual patterns in rocks that are produced by geologic processes rather than biologic processes. They can easily be mistaken for real fossils. Some pseudofossils, such as geological dendrite crystals, are formed by naturally occurring fissures in the rock that get filled up by percolating minerals. Other types of pseudofossils are kidney ore (round shapes in iron ore) and moss agates, which look like moss or plant leaves. Concretions, spherical or ovoid-shaped nodules found in some sedimentary strata, were once thought to be dinosaur eggs, and are often mistaken for fossils as well.
History of the study of fossils
Gathering fossils dates at least to the beginning of recorded history. The fossils themselves are referred to as the fossil record. The fossil record was one of the early sources of data underlying the study of evolution and continues to be relevant to the history of life on Earth. Paleontologists examine the fossil record to understand the process of evolution and the way particular species have evolved.
Ancient civilizations
Fossils have been visible and common throughout most of natural history, and so documented human interaction with them goes back as far as recorded history, or earlier.
There are many examples of paleolithic stone knives in Europe, with fossil echinoderms set precisely at the hand grip, going all the way back to Homo heidelbergensis and Neanderthals. These ancient peoples also drilled holes through the center of those round fossil shells, apparently using them as beads for necklaces.
The ancient Egyptians gathered fossils of species that resembled the bones of modern species they worshipped. The god Set was associated with the hippopotamus, therefore fossilized bones of hippo-like species were kept in that deity's temples. Five-rayed fossil sea urchin shells were associated with the deity Sopdu, the Morning Star, equivalent of Venus in Roman mythology.
Fossils appear to have directly contributed to the mythology of many civilizations, including the ancient Greeks. Classical Greek historian Herodotos wrote of an area near Hyperborea where gryphons protected golden treasure. There was indeed gold mining in that approximate region, where beaked Protoceratops skulls were common as fossils.
A later Greek scholar, Aristotle, eventually realized that fossil seashells from rocks were similar to those found on the beach, indicating the fossils were once living animals. He had previously explained them in terms of vaporous exhalations, which Persian polymath Avicenna modified into the theory of petrifying fluids (succus lapidificatus). Recognition of fossil seashells as originating in the sea was built upon in the 14th century by Albert of Saxony, and accepted in some form by most naturalists by the 16th century.Roman naturalist Pliny the Elder wrote of "tongue stones", which he called glossopetra. These were fossil shark teeth, thought by some classical cultures to look like the tongues of people or snakes. He also wrote about the horns of Ammon, which are fossil ammonites, whence the group of shelled octopus-cousins ultimately draws its modern name. Pliny also makes one of the earlier known references to toadstones, thought until the 18th century to be a magical cure for poison originating in the heads of toads, but which are fossil teeth from Lepidotes, a Cretaceous ray-finned fish.The Plains tribes of North America are thought to have similarly associated fossils, such as the many intact pterosaur fossils naturally exposed in the region, with their own mythology of the thunderbird.There is no such direct mythological connection known from prehistoric Africa, but there is considerable evidence of tribes there excavating and moving fossils to ceremonial sites, apparently treating them with some reverence.In Japan, fossil shark teeth were associated with the mythical tengu, thought to be the razor-sharp claws of the creature, documented some time after the 8th century AD.In medieval China, the fossil bones of ancient mammals including Homo erectus were often mistaken for "dragon bones" and used as medicine and aphrodisiacs. In addition, some of these fossil bones are collected as "art" by scholars, who left scripts on various artifacts, indicating the time they were added to a collection. One good example is the famous scholar Huang Tingjian of the Song Dynasty during the 11th century, who kept a specific seashell fossil with his own poem engraved on it. In his Dream Pool Essays published in 1088, Song dynasty Chinese scholar-official Shen Kuo hypothesized that marine fossils found in a geological stratum of mountains located hundreds of miles from the Pacific Ocean was evidence that a prehistoric seashore had once existed there and shifted over centuries of time. His observation of petrified bamboos in the dry northern climate zone of what is now Yan'an, Shaanxi province, China, led him to advance early ideas of gradual climate change due to bamboo naturally growing in wetter climate areas.In medieval Christendom, fossilized sea creatures on mountainsides were seen as proof of the biblical deluge of Noah's Ark. After observing the existence of seashells in mountains, the ancient Greek philosopher Xenophanes (c. 570 – 478 BC) speculated that the world was once inundated in a great flood that buried living creatures in drying mud.In 1027, the Persian Avicenna explained fossils' stoniness in The Book of Healing:
If what is said concerning the petrifaction of animals and plants is true, the cause of this (phenomenon) is a powerful mineralizing and petrifying virtue which arises in certain stony spots, or emanates suddenly from the earth during earthquake and subsidences, and petrifies whatever comes into contact with it. As a matter of fact, the petrifaction of the bodies of plants and animals is not more extraordinary than the transformation of waters.
From the 13th century to the present day, scholars pointed out that the fossil skulls of Deinotherium giganteum, found in Crete and Greece, might have been interpreted as being the skulls of the Cyclopes of Greek mythology, and are possibly the origin of that Greek myth. Their skulls appear to have a single eye-hole in the front, just like their modern elephant cousins, though in fact it's actually the opening for their trunk.
In Norse mythology, echinoderm shells (the round five-part button left over from a sea urchin) were associated with the god Thor, not only being incorporated in thunderstones, representations of Thor's hammer and subsequent hammer-shaped crosses as Christianity was adopted, but also kept in houses to garner Thor's protection.These grew into the shepherd's crowns of English folklore, used for decoration and as good luck charms, placed by the doorway of homes and churches. In Suffolk, a different species was used as a good-luck charm by bakers, who referred to them as fairy loaves, associating them with the similarly shaped loaves of bread they baked.
Early modern explanations
More scientific views of fossils emerged during the Renaissance. Leonardo da Vinci concurred with Aristotle's view that fossils were the remains of ancient life.: 361 For example, Leonardo noticed discrepancies with the biblical flood narrative as an explanation for fossil origins:
If the Deluge had carried the shells for distances of three and four hundred miles from the sea it would have carried them mixed with various other natural objects all heaped up together; but even at such distances from the sea we see the oysters all together and also the shellfish and the cuttlefish and all the other shells which congregate together, found all together dead; and the solitary shells are found apart from one another as we see them every day on the sea-shores.
And we find oysters together in very large families, among which some may be seen with their shells still joined together, indicating that they were left there by the sea and that they were still living when the strait of Gibraltar was cut through. In the mountains of Parma and Piacenza multitudes of shells and corals with holes may be seen still sticking to the rocks....
In 1666, Nicholas Steno examined a shark, and made the association of its teeth with the "tongue stones" of ancient Greco-Roman mythology, concluding that those were not in fact the tongues of venomous snakes, but the teeth of some long-extinct species of shark.Robert Hooke (1635–1703) included micrographs of fossils in his Micrographia and was among the first to observe fossil forams. His observations on fossils, which he stated to be the petrified remains of creatures some of which no longer existed, were published posthumously in 1705.William Smith (1769–1839), an English canal engineer, observed that rocks of different ages (based on the law of superposition) preserved different assemblages of fossils, and that these assemblages succeeded one another in a regular and determinable order. He observed that rocks from distant locations could be correlated based on the fossils they contained. He termed this the principle of faunal succession. This principle became one of Darwin's chief pieces of evidence that biological evolution was real.
Georges Cuvier came to believe that most if not all the animal fossils he examined were remains of extinct species. This led Cuvier to become an active proponent of the geological school of thought called catastrophism. Near the end of his 1796 paper on living and fossil elephants he said:
All of these facts, consistent among themselves, and not opposed by any report, seem to me to prove the existence of a world previous to ours, destroyed by some kind of catastrophe.
Interest in fossils, and geology more generally, expanded during the early nineteenth century. In Britain, Mary Anning's discoveries of fossils, including the first complete ichthyosaur and a complete plesiosaurus skeleton, sparked both public and scholarly interest.
Linnaeus and Darwin
Early naturalists well understood the similarities and differences of living species leading Linnaeus to develop a hierarchical classification system still in use today. Darwin and his contemporaries first linked the hierarchical structure of the tree of life with the then very sparse fossil record. Darwin eloquently described a process of descent with modification, or evolution, whereby organisms either adapt to natural and changing environmental pressures, or they perish.
When Darwin wrote On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, the oldest animal fossils were those from the Cambrian Period, now known to be about 540 million years old. He worried about the absence of older fossils because of the implications on the validity of his theories, but he expressed hope that such fossils would be found, noting that: "only a small portion of the world is known with accuracy." Darwin also pondered the sudden appearance of many groups (i.e. phyla) in the oldest known Cambrian fossiliferous strata.
After Darwin
Since Darwin's time, the fossil record has been extended to between 2.3 and 3.5 billion years. Most of these Precambrian fossils are microscopic bacteria or microfossils. However, macroscopic fossils are now known from the late Proterozoic. The Ediacara biota (also called Vendian biota) dating from 575 million years ago collectively constitutes a richly diverse assembly of early multicellular eukaryotes.
The fossil record and faunal succession form the basis of the science of biostratigraphy or determining the age of rocks based on embedded fossils. For the first 150 years of geology, biostratigraphy and superposition were the only means for determining the relative age of rocks. The geologic time scale was developed based on the relative ages of rock strata as determined by the early paleontologists and stratigraphers.
Since the early years of the twentieth century, absolute dating methods, such as radiometric dating (including potassium/argon, argon/argon, uranium series, and, for very recent fossils, radiocarbon dating) have been used to verify the relative ages obtained by fossils and to provide absolute ages for many fossils. Radiometric dating has shown that the earliest known stromatolites are over 3.4 billion years old.
Modern era
Paleontology has joined with evolutionary biology to share the interdisciplinary task of outlining the tree of life, which inevitably leads backwards in time to Precambrian microscopic life when cell structure and functions evolved. Earth's deep time in the Proterozoic and deeper still in the Archean is only "recounted by microscopic fossils and subtle chemical signals." Molecular biologists, using phylogenetics, can compare protein amino acid or nucleotide sequence homology (i.e., similarity) to evaluate taxonomy and evolutionary distances among organisms, with limited statistical confidence. The study of fossils, on the other hand, can more specifically pinpoint when and in what organism a mutation first appeared. Phylogenetics and paleontology work together in the clarification of science's still dim view of the appearance of life and its evolution.
Niles Eldredge's study of the Phacops trilobite genus supported the hypothesis that modifications to the arrangement of the trilobite's eye lenses proceeded by fits and starts over millions of years during the Devonian. Eldredge's interpretation of the Phacops fossil record was that the aftermaths of the lens changes, but not the rapidly occurring evolutionary process, were fossilized. This and other data led Stephen Jay Gould and Niles Eldredge to publish their seminal paper on punctuated equilibrium in 1971.
Synchrotron X-ray tomographic analysis of early Cambrian bilaterian embryonic microfossils yielded new insights of metazoan evolution at its earliest stages. The tomography technique provides previously unattainable three-dimensional resolution at the limits of fossilization. Fossils of two enigmatic bilaterians, the worm-like Markuelia and a putative, primitive protostome, Pseudooides, provide a peek at germ layer embryonic development. These 543-million-year-old embryos support the emergence of some aspects of arthropod development earlier than previously thought in the late Proterozoic. The preserved embryos from China and Siberia underwent rapid diagenetic phosphatization resulting in exquisite preservation, including cell structures. This research is a notable example of how knowledge encoded by the fossil record continues to contribute otherwise unattainable information on the emergence and development of life on Earth. For example, the research suggests Markuelia has closest affinity to priapulid worms, and is adjacent to the evolutionary branching of Priapulida, Nematoda and Arthropoda.Despite significant advances in uncovering and identifying paleontological specimens, it is generally accepted that the fossil record is vastly incomplete. Approaches for measuring the completeness of the fossil record have been developed for numerous subsets of species, including those grouped taxonomically, temporally, environmentally/geographically, or in sum. This encompasses the subfield of taphonomy and the study of biases in the paleontological record.
Art
According to one hypothesis, a Corinthian vase from the 6th century BCE is the oldest artistic record of a vertebrate fossil, perhaps a Miocene giraffe combined with elements from other species. However, a subsequent study using artificial intelligence and expert evaluations reject this idea, because mammals do not have the eye bones shown in the painted monster. Morphologically, the vase painting correspond to a carnivorous reptile of the Varanidae family that still lives in regions occupied by the ancient Greek.
Trading and collecting
Fossil trading is the practice of buying and selling fossils. This is many times done illegally with artifacts stolen from research sites, costing many important scientific specimens each year. The problem is quite pronounced in China, where many specimens have been stolen.Fossil collecting (sometimes, in a non-scientific sense, fossil hunting) is the collection of fossils for scientific study, hobby, or profit. Fossil collecting, as practiced by amateurs, is the predecessor of modern paleontology and many still collect fossils and study fossils as amateurs. Professionals and amateurs alike collect fossils for their scientific value.
As medicine
The use of fossils to address health issues is rooted in traditional medicine and include the use of fossils as talismans. The specific fossil to use to alleviate or cure an illness is often based on its resemblance to the symptoms or affected organ. The usefulness of fossils as medicine is almost entirely a placebo effect, though fossil material might conceivably have some antacid activity or supply some essential minerals. The use of dinosaur bones as "dragon bones" has persisted in Traditional Chinese medicine into modern times, with mid-Cretaceous dinosaur bones being used for the purpose in Ruyang County during the early 21st century.
Gallery
See also
References
Further reading
"Grand Canyon cliff collapse reveals 313 million-year-old fossil footprints" 21 August 2020, CNN
"Hints of fossil DNA discovered in dinosaur skull" by Michael Greshko, 3 March 2020, National Geographic
"Fossils for Kids | Learn all about how fossils are formed, the types of fossils and more!" Video (2:23), 27 January 2020, Clarendon Learning
"Fossil & their formation" Video (9:55), 15 November 2019, Khan Academy
"How are dinosaur fossils formed? by Lisa Hendry, Natural History Museum, London
"Fossils 101" Video (4:27), 22 August 2019, National Geographic
"How to Spot the Fossils Hiding in Plain Sight" by Jessica Leigh Hester, 23 February 2018, Atlas Obscura
"It's extremely hard to become a fossil" Archived 4 September 2009 at the Wayback Machine, by Olivia Judson, 30 December 2008, The New York Times
"Bones Are Not the Only Fossils" Archived 15 March 2009 at the Wayback Machine, by Olivia Judson, 4 March 2008, The New York Times
External links
Fossils on In Our Time at the BBC
The Virtual Fossil Museum throughout Time and Evolution
Paleoportal, geology and fossils of the United States
The Fossil Record, a complete listing of the families, orders, class and phyla found in the fossil record (archived 3 May 2012)
Paleontology at Curlie
Ernest Ingersoll (1920). "Fossils" . Encyclopedia Americana.
"Fossil" . New International Encyclopedia. 1905. |
geography of ireland | Ireland is an island in Northern Europe in the north Atlantic Ocean. The island lies on the European continental shelf, part of the Eurasian Plate. The island's main geographical features include low central plains surrounded by coastal mountains. The highest peak is Carrauntoohil (Irish: Corrán Tuathail), which is 1,039 metres (3,409 ft) above sea level. The western coastline is rugged, with many islands, peninsulas, headlands and bays. The island is bisected by the River Shannon, which at 360.5 km (224 mi) with a 102.1 km (63 mi) estuary is the longest river in Ireland and flows south from County Cavan in Ulster to meet the Atlantic just south of Limerick. There are a number of sizeable lakes along Ireland's rivers, of which Lough Neagh is the largest.
Politically, the island consists of the Republic of Ireland, with jurisdiction over about five-sixths of the island, and Northern Ireland, a constituent country of the United Kingdom, with jurisdiction over the remaining sixth. Located west of the island of Great Britain, it lies at approximately 53°N 8°W. It has a total area of 84,421 km2 (32,595 sq mi). It is separated from Great Britain by the Irish Sea and from mainland Europe by the Celtic Sea.
Ireland forms the second largest landmass in the North-West European Archipelago, together with nearby islands including Great Britain and the Isle of Man, known in the United Kingdom as the British Isles.
Geological development
The geology of Ireland is diverse. Different regions contain rocks belonging to different geological periods, dating back almost 2 billion years. The oldest known Irish rock is about 1.7 billion years old and is found on Inishtrahull Island off the north coast of Inishowen and on the mainland at Annagh Head on the Mullet Peninsula. The newer formations are the drumlins and glacial valleys as a result of the last ice age, and the sinkholes and cave formations in the limestone regions of Clare.Ireland's geological history covers everything from volcanism and tropical seas to the last glacial period. Ireland was formed in two distinct parts and slowly joined, uniting about 440 million years ago. As a result of tectonics and the effect of ice, the sea level has risen and fallen. In every area of the country the rocks which formed can be seen as a result. Finally, the impact of the glaciers shaped the landscape seen today. The variation between the two areas, along with the differences between volcanic areas and shallow seas, led to a range of soils. There are extensive bogs and free-draining brown earths. The mountains are granite, sandstone, limestone with karst areas, and basalt formations.Most of Ireland was probably above sea level during the last 60 million years. As such its landscapes have been shaped by erosion and weathering on land. Protracted erosion also means most of the Paleogene and Neogene sediments have been eroded away or, as known in a few cases, buried by Quaternary deposits. Before the Quaternary glaciations affected Ireland the landscape had developed thick weathered regolith on the uplands and karst in the lowlands. There has been some controversy regarding the origin of the planation surfaces found in Ireland. While some have argued for an origin in marine planation others regard these surfaces as peneplains formed by weathering and fluvial erosion. Not only is their origin disputed but also their actual extent and the relative role of sea-level change and tectonics in their shaping. Most river systems in Ireland formed in the Cenozoic before the Quaternary glaciations. Rivers follow for most of their course structural features of the geology of Ireland. Marine erosion since the Miocene may have made Ireland's western coast retreat more than 100 km. Pre-Quaternary relief was more dramatic than today's glacier-smoothened landscapes.
Physical geography
Mountain ranges
Ireland consists of a mostly flat low-lying area in the Midlands, ringed by mountain ranges such as (beginning in County Kerry and working counter-clockwise) the MacGillycuddy's Reeks, Comeragh Mountains, Blackstairs Mountains, Wicklow Mountains, the Mournes, Glens of Antrim, Sperrin Mountains, Bluestack Mountains, Derryveagh Mountains, Ox Mountains, Nephinbeg Mountains and the Twelve Bens/Maumturks group. Some mountain ranges are further inland in the south of Ireland, such as the Galtee Mountains (the highest inland range), Silvermine and Slieve Bloom Mountains. The highest peak Carrauntoohil, at 1,038.6 m (3,407 ft) high, is in the MacGillycuddy's Reeks, a range of glacier-carved sandstone mountains. Only three peaks on the island are over 1,000 m (3,300 ft) and another 457 exceed 500 m (1,600 ft). Ireland is sometimes known as the "Emerald Isle" because of its green landscape.
Forests
Ireland, like the neighbouring Great Britain, was once covered in forest. Clearing of forests began in the Neolithic Age and accelerated following the Tudor Conquest, resulting in forest cover of only 1% by the start of the twentieth century. As of 2017, total tree cover in the Republic of Ireland stood at 11% of land area. The figure for native forest stood at 2% in 2018; the third lowest in Europe behind Iceland and Malta.
Rivers and lakes
The River Shannon, at 360.5 km (224.0 mi) in length, is the longest river in Ireland and Britain. With a drainage area of 16,865 km2 (6,512 sq mi), the Shannon River Basin covers one-fifth of the island. The Shannon crosses 11 counties and divides the west of Ireland from the south and east. The river develops into three large lakes along its course, Lough Allen, Lough Ree, and Lough Derg. The River Shannon enters the Atlantic Ocean at Limerick city along the Shannon Estuary. Other major rivers include the River Liffey, River Lee, River Blackwater, River Nore, River Suir, River Barrow, River Bann, River Foyle, River Erne, and River Boyne.Lough Neagh, in Ulster, is the largest lake in Ireland and Britain with an area of 392 km2 (151 sq mi). The largest lake in the Republic of Ireland is Lough Corrib 176 km2 (68 sq mi). Other large lakes include Lough Erne, Lough Mask and Lough Conn.
Inlets
In County Donegal, Lough Swilly separates the western side of the Inishowen peninsula. Lough Foyle on the other side, is one of Ireland's larger inlets, situated between County Donegal and County Londonderry. Clockwise round the coast is Belfast Lough, between County Antrim and County Down. Also in County Down is Strangford Lough, actually an inlet partially separating the Ards peninsula from the mainland. Further south, Carlingford Lough is situated between Down and County Louth.Dublin Bay is the next sizeable inlet. The east coast of Ireland has no major inlets until Wexford Harbour at the mouth of the River Slaney. On the south coast, Waterford Harbour is situated at the mouth of the River Suir (into which the other two of the Three Sisters (River Nore and River Barrow) flow). The next major inlet is Cork Harbour, at the mouth of the River Lee, in which Great Island is situated.Dunmanus Bay, Kenmare estuary and Dingle Bay are all inlets between the peninsulas of County Kerry. North of these is the Shannon Estuary. Between north County Clare and County Galway is Galway Bay. Clew Bay is located on the coast of County Mayo, south of Achill Island, while Broadhaven Bay, Blacksod Bay and Sruth Fada Conn bays are situated in northwest Connacht, in North Mayo. Killala Bay is on the northeast coast of Mayo. Donegal Bay is a major inlet between County Donegal and County Sligo.A recent global remote sensing analysis suggested that there were 565 km2 of tidal flats in Ireland, making it the 43rd ranked country in terms of tidal flat area.
Headlands
Malin Head is the most northerly point in Ireland, while Mizen Head is one of the most southern points, hence the term "from Malin to Mizen" (or the reverse) is used for anything applying to the island of Ireland as a whole. Carnsore Point is another extreme point of Ireland, being the southeasternmost point of Ireland. Hook Head and the Old Head of Kinsale are two of many headlands along the south coast. Loop Head is the headland at which County Clare comes to a point on the west coast of Ireland, with the Atlantic on the north, and the Shannon estuary to the south. Hag's Head is another headland further up Clare's north/western coastline, with the Cliffs of Moher along the coastline north of the point. Erris Head is the northwesternmost point of Connacht.
Islands and peninsulas
Apart from Ireland itself, Achill Island to its northwest is now considered the largest island in the group. The island is inhabited, and is connected to the mainland by a bridge. Some of the next largest islands are the Aran Islands, off the coast of southern Connacht, host to an Irish-speaking community, or Gaeltacht. Valentia Island off the Iveragh peninsula is also one of Ireland's larger islands, and is relatively settled, as well as being connected by a bridge at its southeastern end. Omey Island, off the coast of Connemara is a tidal island.Some of the best-known peninsulas in Ireland are in County Kerry; the Dingle peninsula, the Iveragh peninsula and the Beara peninsula. The Ards peninsula is one of the larger peninsulas outside Kerry. The Inishowen peninsula in County Donegal includes Ireland's most northerly point, Malin Head and several important towns including Buncrana on Lough Swilly, Carndonagh and Moville on Lough Foyle. Ireland's most northerly land feature is Inishtrahull island, off Malin Head. Rockall Island may deserve this honour but its status is disputed, being claimed by the United Kingdom, Republic of Ireland, Denmark (for the Faroe Islands) and Iceland. The most southerly point is the Fastnet Rock.The Hebrides off Scotland and Anglesey off Wales were grouped with Ireland ("Hibernia") by the Greco-Roman geographer Ptolemy, but this is no longer common.
Climate
The climate of Ireland is mild, humid and changeable with abundant rainfall and a lack of temperature extremes. Ireland's climate is defined as a temperate oceanic climate, or Cfb on the Köppen climate classification system, a classification it shares with most of northwest Europe. The country receives generally warm summers and mild winters. It is considerably warmer than other areas at the same latitude on the other side of the Atlantic, such as in Newfoundland, because it lies downwind of the Atlantic Ocean. It is also warmer than maritime climates near the same latitude, such as the Pacific Northwest as a result of heat released by the Atlantic overturning circulation that includes the North Atlantic Current and Gulf Stream. For comparison, Dublin is 9 °C warmer than St. John's in Newfoundland in winter and 4 °C warmer than Seattle in the Pacific Northwest in winter.The influence of the North Atlantic Current also ensures the coastline of Ireland remains ice-free throughout the winter. The climate in Ireland does not experience extreme weather, with tornadoes and similar weather features being rare. However, Ireland is prone to eastward moving cyclones which come in from the North Atlantic.The prevailing wind comes from the southwest, breaking on the high mountains of the west coast. Rainfall is therefore a particularly prominent part of western Irish life, with Valentia Island, off the west coast of County Kerry, getting over twice as much annual rainfall as Dublin on the east (1,557 mm or 61.3 in vs. 714 mm or 28.1 in).January and February are the coldest months of the year, and mean daily air temperatures fall between 4 and 7 °C (39.2 and 44.6 °F) during these months. July and August are the warmest, with mean daily temperatures of 14 to 16 °C (57.2 to 60.8 °F), whilst mean daily maximums in July and August vary from 17 to 18 °C (62.6 to 64.4 °F) near the coast, to 19 to 21 °C (66.2 to 69.8 °F) inland. The sunniest months are May and June, with an average of five to seven hours sunshine per day.Though extreme weather events in Ireland are comparatively rare when compared with other countries in the European Continent, they do occur. Atlantic depressions, occurring mainly in the months of December, January and February, can occasionally bring winds of up to 160 km/h or 99 mph to Western coastal counties; while the summer months, and particularly around late July/early August, thunderstorms can develop.The tables below show mean 30-year climate averages for Ireland's two largest cities, taken from the weather stations at Dublin Airport and Belfast International Airport respectively. The state metrological service for the Republic of Ireland is Met Éireann, while the Met Office monitors climate data for Northern Ireland.
Political and human geography
Ireland is divided into four provinces—Connacht, Leinster, Munster and Ulster—and 32 administrative counties of Ireland. Six of the nine Ulster counties form Northern Ireland and the other 26 form the state, Ireland. The map shows the county boundaries for all 32 counties.
From an administrative viewpoint, 21 of the counties in the Republic are units of local government. The other six have more than one local council area, resulting in a total of 31 county-level authorities. County Tipperary had two ridings, North Tipperary and South Tipperary, originally established in 1838, renamed in 2001 and amalgamated in 2014. The cities of Dublin, Cork and Galway have city councils and are administered separately from the counties bearing those names. The cities of Limerick and Waterford were merged with their respective county councils in 2014 to form new city and county councils. The remaining part of County Dublin is divided into Dún Laoghaire–Rathdown, Fingal, and South Dublin.Electoral areas in Ireland (the state) are called constituencies in accordance with Irish law, mostly follow county boundaries. Maintaining links to the county system is a mandatory consideration in the re-organisation of constituency boundaries by a Constituency Commission.In Northern Ireland, a major re-organisation of local government in 1973 replaced the six traditional counties and two county boroughs (Belfast and Derry) by 26 single-tier districts, which, apart from Fermanagh cross the traditional county boundaries. The six counties and two county-boroughs remain in use for purposes such as Lieutenancy. In November 2005, proposals were announced which would see the number of local authorities reduced to seven.
The island's total population of nearly 7 million people is concentrated in the east and south, particularly in Dublin, Belfast, Cork and their surrounding areas.
Natural resources
Bogs
Ireland has 12,000 km2 (about 4,600 sq miles) of bogland, consisting of two distinct types: blanket bogs and raised bogs. Blanket bogs are the more widespread of the two types. They are essentially a product of human activity aided by the moist Irish climate. Blanket bogs formed on sites where Neolithic farmers cleared trees for farming. As the land so cleared fell into disuse, the soil began to leach and become more acidic, producing a suitable environment for the growth of heather and rushes. The debris from these plants accumulated and a layer of peat formed. One of the largest expanses of Atlantic blanket bog in Ireland is to be found in County Mayo.Raised bogs are most common in the Shannon basin. They formed when depressions left behind after the ice age filled with water to form lakes. Debris from reeds in these lakes formed a layer of at the bottom of the water. This eventually choked the lakes and raised above the surface, forming raised bogs.Since the 17th century, peat has been cut for fuel for domestic heating and cooking, and it is called turf when so used. The process accelerated as commercial exploitation of bogs grew. In the 1940s, machines for cutting turf were introduced and larger-scale harvesting became possible. In the Republic, this became the responsibility of a semi-state company called Bord na Móna. In addition to domestic uses, commercially extracted turf is used in a number of industries, producing peat briquettes for domestic fuel and milled peat for electricity generation. More recently peat is being combined with biomass for dual-firing electricity generation.In recent years, the destruction of bogs has raised environmental concerns. The issue is particularly acute for raised bogs which were more widely mined as they yield a higher-grade fuel than blanket bogs. Plans are now in place in both the Republic and Northern Ireland to conserve most of the remaining raised bogs on the island.
Oil, natural gas and minerals
Offshore exploration for natural gas began in 1970. The first major discovery was the Kinsale Head gas field in 1971. Next were the smaller Ballycotton gas field in 1989, and the Corrib gas field in 1996. Gas from these fields is pumped ashore and used for both domestic and industrial purposes. The Helvick oil field, estimated to contain over 28 million barrels (4,500,000 m3) of oil, was discovered in 2000, and Barryroe, estimated to contain 1.6 billion barrels (250,000,000 m3) of oil, was discovered in 2012, although neither have been exploited. Ireland is the largest European producer of zinc, with one zinc-lead mine currently in operation at Tara, which is Europe's largest and deepest active mine. Other mineral deposits with actual or potential commercial value include gold, silver, gypsum, talc, calcite, dolomite, roofing slate, limestone aggregate, building stone, sand and gravel.In May 2007 the Department of Communications, Marine and Natural Resources (now replaced by the Department of Communications, Energy and Natural Resources) reported that there may be volumes over 130 billion barrels (2.1×1010 m3) of petroleum and 50 trillion cubic feet (1,400 km3) of natural gas in Irish waters – worth trillions of Euro, if true. The minimum confirmed amount of oil in the Irish Atlantic waters is 10 billion barrels (1.6×109 m3), worth over €450 billion. There are also areas of petroleum and natural gas on shore, for example the Lough Allen basin, with 9.4 trillion cubic feet (270 km3) of gas and 1.5 billion barrels (240,000,000 m3) of oil, valued at €74.4 billion. Already some fields are being exploited, such as the Spanish Point field, with 1.25 trillion cubic feet (35 km3) of gas and 206 million barrels (32,800,000 m3) of oil, valued at €19.6 billion. The Corrib Basin is also quite large, worth anything up to €87 billion, while the Dunquin gas field, initially estimated to have 25 trillion cubic feet (710 km3) of natural gas and 4.13 billion barrels (657,000,000 m3) of petroleum but 2012 revised estimates suggest only 14 trillion cubic feet (400 km3) of natural gas and .5 billion barrels (79,000,000 m3) barrels of oil condensate.In March 2012 the first commercial oil well was drilled 70 km off the Cork coast by Providence Resources, renamed Barryroe Offshore. At the time, Providence's executive Tony O'Reilly, Jr., said: It’s a defining moment for the Irish offshore oil and gas industry. The Barryroe oil well is yielding 3500 barrels per day in exploratory drilling; at current oil prices of $120 a barrel Barryroe oil well is worth in excess of €2.14bn annually. However, in 2023, the Department of the Environment, Climate and Communications declined approval of the "Lease Undertaking" that would be necessary to finish appraisal drilling and Barryroe Offshore Energy will now wind down their business by a voluntary liquidation so the field may not be developed. Legal action may be taken by investors against the Irish government including the minor 20% investor Lansdowne Oil & Gas.
Renewable energy
Under the original 2009 Renewable Energy Directive the Republic of Ireland had set a target of producing 16% of all its energy needs from renewable energy sources by 2020 but in 2018 the second Renewable Energy Directive increased the target to 32% by 2030. Between 2005 and 2014 the percentage of energy from renewable energy sources grew from just 3.1% to 8.6% of total final consumption. By 2020 the overall renewable energy share was 13.5%, short of its Renewable Energy Drive target of 16%. Renewable electricity accounted for 69% of all renewable energy used in 2020, up from two thirds (66.8%) in 2019.
Wind
While hydro generated power contributed most to Ireland's renewable energy during the during the 20th century, so far in the 21st century there has been a significant increase in the production of energy by wind spurred by climate change concerns.Bellacorick wind farm, built by Bord na Móna in 1992, was the first Irish wind farm with an individual turbine capacity of 0.3MW which compared with the current capacity of 4–5MW means that when turbines age out, replacements will produce significantly more power per installation. As of 2022 the Republic of Ireland had more than 300 wind farms but the number will have to double by 2030 if the current 40% of renewable energy is to double. Most of the energy will have to come from inshore wind farms because the sole offshore wind farm, Arklow Bank Wind Park, only produces 0.6% of the nation's total wind energy. The 80% target is an ambitious aspect of the Climate Action Plan some impediments, such as planning permission and the age of existing wind farms, may hinder this aspiration.A floating 400MW wind farm off the coast of Northern Ireland was proposed for the North Channel in 2022 to be operating by 2029. Another northern project, opened in October 2023, was set up under a corporate power purchase agreement in which Amazon, who backed the project, will be the off-taker of all the power produced by the 16-MW Ballykeel 7-turbine wind farm in County Antrim.In November 2023, EDF Renewables announced their Carrowkeel Wind Farm which will be a 30 Megawatt project for County Roscommon for completion in 2028 which should power more than 20,000 homes.
See also
Extreme points of Ireland
Gravity anomalies of Britain and Ireland
Coastal landforms of Ireland
Geographical centre of Ireland
Notes
References
Bibliography
Print
Mitchell, Frank and Ryan, Michael. Reading the Irish landscape (1998). ISBN 1-86059-055-1
Whittow, J. B. Geography and Scenery in Ireland (Penguin Books 1974)
Holland, Charles, H and Sanders, Ian S. The Geology of Ireland 2nd ed. (2009). ISBN 1903765722
Place-names, Diarmuid O Murchadha and Kevin Murray, in The Heritage of Ireland, ed. N. Buttimer et al., The Collins Press, Cork, 2000, pp. 146–155.
A paper landscape:the Ordnance Survey in nineteenth-century Ireland, J.H. Andrews, London, 1975
Monasticon Hibernicum, M. Archdall, 1786
Etymological aetiology in Irish tradition, R. Baumgarten, Eiru 41, pp. 115–122, 1990
The Origin and History of Irish names of Places, Patrick Weston Joyce, three volumes, Dublin, 1869, 1875, 1913.
Irish Place Names, D. Flanagan and L. Flanagan, Dublin, 1994
Census of Ireland:general alphabetical index to the townlands and towns, parishes and paronies of Ireland, Dublin, 1861
The Placenames of Westmeath, Paul Walsh, 1957
The Placenames of Decies, P. Power, Cork, 1952
The place-names of county Wicklow, Liam Price, seven volumes, Dublin, 1945–67
Online
Abbot, Patrick. Ireland's Peat Bogs. Retrieved on 23 January 2008.
Ireland – The World Factbook. Central Intelligence Agency. Retrieved on 23 January 2008.
OnlineWeather.com – climate details for Ireland. Retrieved 2011-01-12
External links
OSI FAQ – lists of the longest, highest and other statistics
A discussion on RTÉ Radio 1's science show Quantum Leap about the quality of GPS mapping in Ireland is available here (archived link). The discussion starts 8mins 18sec into the show. It aired on 18 Jan 2002 (archived link). Requires RealPlayer. |
gubbio | Gubbio (Italian pronunciation: [ˈgubbjo]) is an Italian town and comune in the far northeastern part of the Italian province of Perugia (Umbria). It is located on the lowest slope of Mt. Ingino, a small mountain of the Apennines.
History
The city's origins are very ancient. The hills above the town were already occupied in the Bronze Age. As Ikuvium, it was an important town of the Umbri in pre-Roman times, made famous for the discovery there in 1444 of the Iguvine Tablets, a set of bronze tablets that together constitute the largest surviving text in the Umbrian language. After the Roman conquest in the 2nd century BC – it kept its name as Iguvium – the city remained important, as attested by its Roman theatre, the second-largest surviving in the world.
Gubbio became very powerful in the beginning of the Middle Ages. The town sent 1000 knights to fight in the First Crusade under the lead of Girolamo of the prominent Gabrielli family, who according to an undocumented local tradition, they were the first to reach the Church of the Holy Sepulchre when Jerusalem was seized (1099).
The following centuries in Gubbio were turbulent, featuring wars against the neighboring towns of Umbria. One of these wars saw the miraculous intervention of its bishop, Ubald, who secured Gubbio an overwhelming victory (1151) and a period of prosperity. In the struggles of Guelphs and Ghibellines, the Gabrielli, such as the condottiero Cante dei Gabrielli (c. 1260–1335), fought for the Guelph faction, supporting the papacy. As Podestà of Florence, Cante exiled Dante Alighieri, ensuring his own lasting notoriety.
In 1350 Giovanni Gabrielli, count of Borgovalle seized power as the lord of Gubbio. His rule was short, and he was forced to hand over the town to Cardinal Gil Álvarez Carrillo de Albornoz, representing the Papal states (1354).
A few years later, Gabriello Gabrielli, the bishop of Gubbio, also proclaimed himself lord of Gubbio (Signor d'Agobbio). Betrayed by a group of noblemen which included many of his relatives, the bishop was forced to leave the town and seek refuge at his home castle at Cantiano.
With the decline of the political prestige of the Gabrielli, Gubbio was thereafter incorporated into the territories of the House of Montefeltro. The lord of Urbino, Federico da Montefeltro rebuilt the ancient Palazzo Ducale in Gubbio, incorporating in it a studiolo veneered with intarsia like his studiolo at Urbino. The maiolica industry at Gubbio reached its apogee in the first half of the 16th century, with metallic lustre glazes imitating gold and copper.
Gubbio became part of the Papal States in 1631, when the della Rovere family, to whom the Duchy of Urbino had been granted, was extinguished. In 1860 Gubbio was incorporated into the Kingdom of Italy along with the rest of the Papal States.
The name of the Pamphili family, a great papal family, originated in Gubbio then went to Rome under the pontificate of Pope Innocent VIII (1484–1492), and is immortalized by Diego Velázquez and his portrait of Pope Innocent X.
Geography
Overview
The town is located in northern Umbria, near the border with Marche. The municipality borders Cagli (PU), Cantiano (PU), Costacciaro, Fossato di Vico, Gualdo Tadino, Perugia, Pietralunga, Scheggia e Pascelupo, Sigillo, Umbertide and Valfabbrica.
Frazioni
The frazioni (territorial subdivisions) of the comune of Gubbio are the villages of: Belvedere, Bevelle, Biscina, Branca, Burano, Camporeggiano, Carbonesca, Casamorcia-Raggio, Cipolleto, Colonnata, Colpalombo, Ferratelle, Loreto, Magrano, Mocaiana, Monteleto, Monteluiano, Nogna, Padule, Petroia, Ponte d'Assi, Raggio, San Benedetto Vecchio, San Marco, San Martino in Colle, Santa Cristina, Scritto, Semonte, Spada, Torre Calzolari and Villa Magna.
Monuments and sites of interest
The historical centre of Gubbio has a decidedly medieval aspect: the town is austere in appearance because of the dark grey stone, narrow streets, and Gothic architecture. Many houses in central Gubbio date to the 14th and 15th centuries, and were originally the dwellings of wealthy merchants. They often have a second door fronting on the street, usually just a few inches from the main entrance. This secondary entrance is narrower, and a foot or so above the actual street level. This type of door is called a porta dei morti (door of the dead) because it was proposed that they were used to remove the bodies of any who might have died inside the house. This is almost certainly false, but there is no agreement as to the purpose of the secondary doors. A more likely theory is that the door was used by the owners to protect themselves when opening to unknown persons, leaving them in a dominating position.
Religious architecture or sites
Duomo: This Cathedral was built in the late 12th century. The most striking feature is the rose-window in the façade with, at its sides, the symbols of the Evangelists: the eagle for John the Evangelist, the lion for Mark the Evangelist, the angel for Matthew the Apostle and the ox for Luke the Evangelist. The interior has latine cross plan with a single nave. The most precious art piece is the wooden Christ over the altar, of Umbrian school.
San Francesco: This church from the second half of the 13th century is the sole religious edifice in the city having a nave with two aisles. The vaults are supported by octagonal pilasters. The frescoes in the left side date from the 15th century.
Santa Maria Nuova: This is a typical Cistercian church of the 13th century. In the interior is a 14th-century fresco portraying the so-called Madonna del Belvedere (1413), by Ottaviano Nelli. It also has a work by Guido Palmeruccio. Also from the Cistercians is the Convent of St. Augustine, with some frescoes by Nelli.
Basilica of Sant'Ubaldo, with a nave and four aisles is a sanctuary outside the city. Noteworthy are the marble altar and the great windows with episodes of the life of Ubald, patron of Gubbio. The finely sculpted portals and the fragmentary frescoes give a hint of the magnificent 15th-century decoration once boasted by the basilica.
San Giovanni Battista, Gubbio: 13th-century church withone nave only with four transversal arches supporting the pitched roof,a model for later Gubbio churches.
San Domenico, once known as San Martino
Sant'Agostino
Santa Croce della Foce
Secular architecture or sites
Roman Theater: This ancient open air theater built in the 1st century BC using square blocks of local limestone. Traces of mosaic decoration have been found. Originally, the diameter of the cavea was 70 metres, and could house up to 6,000 spectators.
Roman Mausoleum: This Mausoleum is sometimes said to be of Gaius Pomponius Graecinus, but on no satisfactory grounds.
Palazzo dei Consoli: Dating to the first half of the 14th century, this massive palace, is now a museum housing the Iguvine Tablets.
Palazzo and Torre Gabrielli
Palazzo Ducale: The Palace built from 1470 by Luciano Laurana or Francesco di Giorgio Martini for Federico da Montefeltro. Famous is the inner court, reminiscent of the Palazzo Ducale, Urbino.
Museo Cante Gabrielli: This museum is housed in the Palazzo del Capitano del Popolo, which once belonged to the Gabrielli family.
Vivian Gabriel Oriental Collection: This is a museum of Tibetan, Nepalese, Chinese and Indian art. The collection was donated to the municipality by Edmund Vivian Gabriel (1875–1950), British colonial officer and adventurer, collateral descendant of the Gabrielli who were lords of Gubbio in the Middle Ages.
Culture
Gubbio is home to the Corsa dei Ceri, a run held every year always on Saint Ubaldo Day, the 15th day of May, in which three teams, devoted to Ubald, Saint George and Saint Anthony the Great run through throngs of cheering supporters clad in the distinctive colours of yellow, blue and black, with white trousers and red belts and neckbands, up much of the mountain from the main square in front of the Palazzo dei Consoli to the basilica of St. Ubaldo, each team carrying a statue of their saint mounted on a wooden octagonal prism, similar to an hour-glass shape 4 metres (13 ft) tall and weighing about 280 kg (617 lb).
The race has strong devotional, civic, and historical overtones and is one of the best-known folklore manifestations in Italy; the Ceri were chosen as the heraldic emblem on the coat of arms of Umbria as a modern administrative region.
A celebration like the Corsa dei Ceri is held also in Jessup, Pennsylvania. In this small town the people carry out the same festivities as the residents of Gubbio do by "racing" the three statues through the streets during the Memorial Day weekend. This remains an important and sacred event in both towns.
Gubbio was also one of the centres of production of the Italian pottery (maiolica), during the Renaissance. The most important Italian potter of that period, Giorgio Andreoli, was active in Gubbio during the early 16th century.
The town's most famous story is that of "The Wolf of Gubbio"; a man eating wolf that was tamed by St. Francis of Assisi and who then became a docile resident of the city. The legend is related in the 14th-century Little Flowers of St. Francis.
The Gubbio Layer
Gubbio is also known among geologists and palaeontologists as the discovery place of what was at first called the "Gubbio layer", a sedimentary layer enriched in iridium that was exposed by a roadcut outside of town. This thin, dark band of sediment marks the Cretaceous–Paleogene boundary, also known as the K–T boundary or K–Pg boundary, between the Cretaceous and Paleogene geological periods about 66 million years ago, and was formed by infalling debris from the gigantic meteor impact probably responsible for the mass extinction of the dinosaurs. Its iridium, a heavy metal rare on Earth's surface, is plentiful in extraterrestrial material such as comets and asteroids. It also contains small globules of glassy material called tektites, formed in the initial impact. Discovered at Gubbio, the Cretaceous–Paleogene boundary is also visible at many places all over the world. The characteristics of this boundary layer support the theory that a devastating meteorite impact, with accompanying ecological and climatic disturbance, was directly responsible for the Cretaceous–Paleogene extinction event.
Gubbio in fiction
In Hermann Hesse's novel Steppenwolf (1927) the isolated and tormented protagonist – a namesake of the wolf – consoles himself at one point by recalling a scene that the author might have beheld during his travels: "(...) that slender cypress on the hill over Gubbio that, though split and riven by a fall of stone, yet held fast to life and put forth with its last resources a new sparse tuft at the top".The town is a backdrop in Antal Szerb's novel Journey by Moonlight (1937) as well as Danièle Sallenave's Les Portes de Gubbio (1980).
The TV series Don Matteo, where the title character ministers to his parish while solving crimes, was shot on location in Gubbio between 2000 and 2011.
Other
Anna Moroni, a popular cook on the Italian daytime TV series "La Prova del Cuoco" discusses Gubbio in many of her TV segments. She often cooks dishes from the region on TV, and she featured Gubbio in her first book.
Sport
A.S. Gubbio 1910 football club play in Serie C at the Pietro Barbetti Stadium.
Transportation
The city is served by Fossato di Vico–Gubbio railway station located in Fossato di Vico; until 1945 was also operating the Central Apennine railway (Ferrovia Appenino Centrale abbreviation FAC) with a narrow gauge which departed from Arezzo and reached as far as Fossato di Vico and in Gubbio had his own railway station located in via Beniamino Ubaldi 2, now completely demolished.
International relations
Twin towns – Sister cities
Gubbio is twinned with:
Notable people
Giosuè Fioriti (born 1989), Italian footballer
See also
Roman Catholic Diocese of Gubbio
Mount Ingino Christmas Tree
References
External links
Official website
Official site of the Festa dei Ceri
Gubbio at Associazione Eugubini nel Mondo website
Thayer's Gazetteer
Rugby Gubbio - Official Web Site
Paradoxplace Gubbio Photo Pages
Sbandieratori di Gubbio (flag-wavers, flag-throwers)
Harris, W., R. Talbert, T. Elliott, S. Gillies (13 July 2020). "Places: 413174 (Iguvium)". Pleiades. Retrieved March 7, 2012.{{cite web}}: CS1 maint: multiple names: authors list (link)
The Gubbio Studiolo and its conservation, volumes 1 & 2, from The Metropolitan Museum of Art Libraries (fully available online as PDF), which contains material on Gubbio (see index)
Period Rooms in the Metropolitan Museum of Art , from The Metropolitan Museum of Art Libraries (fully available online as PDF), which contains material on Gubbio (see index) |
riversleigh world heritage area | Riversleigh World Heritage Area is Australia's most famous fossil location, recognised for the series of well preserved fossils deposited from the Late Oligocene to more recent geological periods. The fossiliferous limestone system is located near the Gregory River in the north-west of Queensland, an environment that was once a very wet rainforest that became more arid as the Gondwanan land masses separated and the Australian continent moved north. The approximately 100 square kilometres (39 sq mi) area has fossil remains of ancient mammals, birds, and reptiles of the Oligocene and Miocene ages, many of which were discovered and are only known from the Riversleigh area; the species that have occurred there are known as the Riversleigh fauna.The fossils at Riversleigh are unusual because they are found in soft freshwater limestone which has not been compacted. This means the animal remains retain their three-dimensional structure, rather than being partially crushed like in most fossil sites. The area is located within the catchment of the Gregory River.
Many of the fossil sites were crevices and limestone caves created by the action of large amounts of water on the karst formation, creating pitfall traps and feeding spots for predators which periodically and perhaps suddenly became covered and preserved; these conditions are responsible for the large assemblages of fossilised bats whose guano helped to conserve the remains of themselves and others.
Fossils were first noted to exist in the area in 1901. An initial exploration survey was conducted in 1963. Since 1976, the area has been the subject of systemic exploration. The site was co-listed with the Naracoorte Caves National Park in South Australia as a World Heritage Site in 1994, and by itself, it is an extension of the Boodjamulla National Park.
Description
Fossils at Riversleigh are found in limestone by lime-rich freshwater pools, and in caves, when the ecosystem was evolving from rich rainforest to semiarid grassland community. Some of the fossils at Riversleigh are 25 million years old. High concentrations of calcium carbonate have meant the fossils are extremely well preserved. The fossil collection reveals mammalian evolution across more than 20 million years. Fossils have been found in more than 200 individual locations. The fossil record here is significant because it provides evidence on evolution and the distribution of species across Gondwana.
The presence of Riversleigh fauna in the Oligo-Miocene has been classified by four "faunal zones", and used to denote the presence of fossil taxa in these time periods. These may be summarised as
Faunal Zone A (FZA): Late or Upper Oligocene, 28.4 to 23.03 million years ago
Faunal Zone B (FZB): Early or Lower Miocene, 23.03 to 15.97 Ma
Faunal Zone C (FZC): Middle Miocene, 15.97 to 11.608 Ma
Faunal Zone D (FZD): Late or Upper Miocene, 11.608 to 5.332 MaThirty-five fossil bat species have been identified at the site, which is the richest in the world. Cave deposits have been particularly rich in bat species.The skull and nearly complete dentition of a 15-million-year-old monotreme, Obdurodon dicksoni, provide a window into the evolution of this characteristically Australian group. Fossil ancestors of the recently extinct thylacine, Thylacinus cynocephalus, have also been identified among Riversleigh's fauna. In 1993, skulls of the koala-like Nimbadon were unearthed in a previously unknown cave in the region. Researchers estimate that this marsupial first appeared about 15 million years ago and died out about 12 million years ago, perhaps from climate change-induced losses in habitat. A well-preserved skull of the ancient Nimbacinus dicksoni, an extinct relative of the thylacine, has been used to determine the hunting behavior of the species.Other fossils have provided evidence of how the koala has evolved in response to Australia's change from predominant rainforest vegetation to drier eucalypt forests. The fossil bird fauna at Riversleigh includes an artamid Kurrartapu johnnguyeni, a fossil sittella, and representatives of various other families of modern birds. Some fossil insects and plants have also been discovered.The fossil species identified at the sites are collectively known as the Riversleigh fauna.
Research
Scientific studies are mostly conducted by a group of palaeontologists from the University of New South Wales. Mike Archer is a paleontologist who has been working at Riversleigh since 1983. He and his co-workers discovered that diluted acetic acid was the most effective method of extracting fossils. Karen Black, a palaeontologist from UNSW, discovered a new species of extinct koala, at Riversleigh, which was then named after Dick Smith.
See also
List of fossil sites
Agate Fossil Beds National Monument
Santa Rosa local fauna
Messel pit
Laguna del Hunco Formation
Posidonia Shale
References
Further reading
Archer, M. et al. 1991. Riversleigh: the Story of Australia's Inland Rainforests, (Sydney: Reed Books)
External links
World heritage listing for Riversleigh
UNESCO site with information on Riversleigh, Australia
Information about fossils from Riversleigh, Australian Museum
The Riversleigh Society supports scientific research at Riversleigh |
mount kumgang | Mount Kumgang (Korean: 금강산; RR: Geumgangsan; MR: Kŭmgangsan; lit. Diamond Mountain) or the Kumgang Mountains is a mountain massif, with a 1,638-metre-high (5,374 ft) peak, in Kangwon-do, North Korea. It is located on the east coast of the country, in Mount Kumgang Tourist Region, formerly part of Kangwŏn Province, and is part of the Taebaek mountain range which runs along the east of the Korean Peninsula. The mountain is about 50 kilometres (31 mi) from the South Korean city of Sokcho in Gangwon-do.
Seasonal names
Mount Kumgang has been known for its scenic beauty since ancient times and is the subject of many different works of art. Including its spring name, Kŭmgangsan (Korean: 금강산; Hanja: 金剛山, Korean pronunciation: [kɯmɡaŋsʰan]), it has many different names for each season, but it is most widely known today in the Korean language as Kŭmgangsan. In summer it is called Pongraesan (봉래산, 蓬萊山: the place where a Spirit dwells); in autumn, Phung'aksan (풍악산, 楓岳山: hill of colored leaves, or 楓骨山: great mountain of colored leaves); in winter, Kaegolsan (개골산, 皆骨山: stone bone mountain).
Formation
The creation of Mt. Kŭmgang is closely related to the unique climate and distinctive geological activity of the area. Mt. Kŭmgang is a region where rain and snow fall relatively heavily, and the climate varies depending on altitude and even east-west location. The Kŭmgang geological layer is composed of several types of rocks from ancient geological periods. The most widely distributed rocks are granites of two types (mica mixed and stained), with granite-gneissic fertilization zones being formed in some areas. The rocks are transversely oriented and form a joint in various directions, forming unusual terrains and strange rocks, which have been formed as a result of erosion for a long period of crustal activity and weathering, from 10 million years to the present.
Geography
Kŭmgang Mountain ranges from Tongcheon-gun, Gangwon-do in the Democratic People's Republic of Korea, to Inje-gun, Gangwon-do in the Republic of Korea. The area is up to 40 km long east–west, 60 km north–south, with a total size of 530 km² to the back of Baekdudaegan. It is divided between the "Inner Kumgang" in the west and the "Outer Kumgang" in the east. The area on the east side of the Yeongeum River is called "Hae Kumgang" ("Sea Kumgang"). The main peak of Mt. Kŭmgang is Pirobong, and there are more than 60 peaks over 1,000 meters. Combined with countless sub-peaks, they were historically called "12,000 peaks". Many scenic spots in the area are designated as natural monuments of the Democratic People's Republic of Korea. The southern part of the "Outer Kumgang" is also called "New Kumgang". There are 11 areas in Outer Kumgang, 8 in Inner Kumgang and 3 in Hae Kumgang, although not all have been opened.
Inner Kumgang
Since ancient times, the name Kumgang has been mainly used for the "Inner Kumgang" (내금강), which, located in the western part of the central pole, contains the main peak of Mount Kŭmgang.
Outer Kumgang
"Outer Kumgang" (외금강) is located to the east of the "Inner kumgang" and covers an area along the east coast. The Outer Kŭmgang area is noted for the large number of peaks. Chipson Peak (literally "rock of ten thousand forms") is known for its many waterfalls. It includes many mountain peaks including Moonjoo Peak, Ho Peak, Sangdeung Peak, etc. The "Sea Kŭmgang" area is known for the lagoons and stone pillars.
Kuryong Falls ("Nine Dragons Falls") in Kuryongyeon is one of the three major waterfalls in Korea along with Daeseung Falls in Seoraksan. It is 74 meters in height and 4 meters in width. The waterfall cliffs and the bottom are made of one granite mass. Bibbong Waterfall is 139 meters higher, and is named for its refreshing water stream. The rocks there are associated with unique legends.
Environment
Much of the mountain is covered by mixed broadleaf and coniferous forest and protected in a 60,000 ha national park. Some 25,000 ha has been identified by BirdLife International as an Important Bird Area (IBA) because it supports endangered red-crowned cranes.
Climate
It belongs to the alpine region and has relatively high rainfall, with heavy rainfall in July and August. The East-West difference is severe, and the rainfall increases from Haegeumgang to Oegeumgang, but due to the phenomenon of Foehn, the rainfall decreases from Naegeumgang to Naegeumgang. It is also warm and humid in preparation for the overall climate in Korea.However, depending on the altitude, cold temperatures of minus 10 to 30 degrees Celsius will continue in the winter, and depending on the region, snow will fall as early as October. These climatic conditions lie at the intersection of the northern and southern plants.
Mount Kumgang Tourist Region
Starting in 1998, South Korean tourists were allowed to visit Mount Kumgang, initially travelling by cruise ship, and later more commonly by coach. In 2002, the area around the mountain was separated from Kangwŏn Province and organized as a separately-administered Tourist Region. The land route was opened in 2003. A rail link exists on the North Korean side up to the border, but no tracks are laid between Gangneung and the border in South Korea.
In 1998, there were 15,500 tourists in November and December, in 1999 there were 148,000, and in 2000 213,000. In 2001 tourist numbers dropped to 58,000 amidst disagreements over the access over land. As of 2002, almost 500,000 had visited the Mount Kumgang Tourist Region. Tourist numbers then reached about 240,000 a year. In June 2005, Hyundai Asan announced the one millionth South Korean visit to the area.The Mount Kumgang Tourist Region, developed by Hyundai Asan, was thought to be one way for the North Korean government to earn hard currency. The currency at the resort was neither the South Korean won nor the North Korean won, but the Chinese RMB and US dollar. Food and services to South Korean tourists were provided by some North Koreans. But most of the staff in the hotels are Chinese citizens of Korean heritage with Korean language skills. There had been plans to expand the site but as of late 2022 there were reports based on satellite imagery that the resort's facilities, including a golf course and a floating hotel, were being dismantled pursuant to directives from leader Kim Jong-un.On the morning of July 11, 2008, a 53-year-old South-Korean tourist was shot and killed while walking on the resort's beach. Park Wang-ja entered a military area by crossing over a sand dune and was shot twice by North Korean soldiers. North Korea claimed that sentries had no choice but to shoot her because, despite their order to stop, she fled. South Korea demanded an on-the-spot survey, but North Korea declined it, claiming all the facts were clear and all responsibilities were the victim's and South Korea's. Due to the shooting, South Korea temporarily suspended all trips to Mount Kumgang.In March 2010, the DPRK government warned of "extraordinary measures" if the tourism ban were not lifted. On April 23, 2010, the North Korean government seized 5 properties owned by South Korea at the resort, saying that it was done "in compensation for the damage the North side suffered due to the suspension of the tour for a long period." In seizing the properties, North Korea also alluded to the Baengnyeong incident, showing displeasure with South Korea blaming North Korea for the sinking of the ship.Since April 2010, North Korea is now permitting companies to run tours from the North Korean side, making it appear increasingly unlikely that tours will be resumed from the South. However, on October 1, 2010, news reports said, "Red Cross officials from the two Koreas agreed Friday to hold reunions for families separated by the Korean War amid mixed signals from North Korea on easing tensions over the sinking of a South Korean warship. One hundred families from each country will attend the meetings from Oct. 30 to Nov. 5 at a hotel and reunion center at the North's scenic Diamond Mountain resort, Unification Ministry spokeswoman Lee Jong-joo said."As of September 2011 North Korea have begun operating cruises directly from Rason in north-eastern North Korea, to the port in Mount Kumgang, offering visitors the chance to stay in the resorts previously run by the south. Although they are aimed primarily at Chinese guests, western companies are also offering the tours.
Cultural significance
Koreans have perceived Kŭmgangsan as their muse since well before the Middle Ages. Practically every poet and artist who lived during the Joseon dynasty (1392-1910) made a pilgrimage to Kŭmgangsan. Among other well-known works, are the Geumgang jeondo and the Pungaknaesan chongramdo, painted in the 1740s by Jeong Seon.
The division of the Korean peninsula in 1950 resulted in the South Korean people finding themselves unable to visit this beloved mountain for the better part of 50 years. The 155-mile-long (249 km) barbed-wire fence erected as part of the DMZ (Demilitarized zone) separating the two Koreas proved to be an obstacle stronger than any other barrier.In 1894 the British writer Isabella Bird Bishop referred to it in her travelogue as "Diamond Mountain".Kŭmgangsan is the subject of a 1962 South Korean folk song, Longing for Mt. Geumgang. It is also the setting of the 1973 North Korean revolutionary opera The Song of Mount Kumgang, and is a central motif in the South Korea TV drama Saimdang, Memoir of Colors.
See also
Mount Kumgang Tourist Region
List of mountains in Korea
Geography of North Korea
Notes and references
Further reading
Legends of the Kumgang Mountains. Translated by Chol, Su Ryom. Pyongyang: Foreign Languages Publishing House. 1990. OCLC 35310597.
External links
Kuryong Falls Geumgangsan Kangwon Province DPRK on YouTube
Mt. Kumgang 100 famous views on YouTube |
skaro | Skaro is a fictional planet in the British science fiction television series Doctor Who. It was created by the writer Terry Nation as the home planet of the Daleks.
In The Daleks (1963–64), Skaro is described as being the twelfth planet from its sun, while in Genesis of the Daleks (1975) it is stated that Skaro is situated in the "Seventh Galaxy". It is portrayed as having various moons: Flidor, Falkus and Omega Mysterium, with Falkus being presented as an artificial construct created by the Daleks as a last refuge. Falkus and Omega Mysterium are also referenced in the Big Finish Productions I, Davros audio dramas I, Davros: Innocence (2006) and I, Davros: Purity (2006). In Destiny of the Daleks (1979) the Movellans refer to Skaro as D–5–Gamma–Z–Alpha.
Geography
The BBC-licensed The Dalek Book (1964) includes a map entitled "The Dalography of Skaro" on which three continents are shown; Dalazar, Darren and Davius. Dalazar is described as the most habitable part of Skaro, having a subtropical climate and being the location of the Dalek city. To the south-east is the Lake of Mutations and to the south the Drammankins mountain range, which stretches across the entire continent from the east to west coast. To the north-east Dalazar is joined to the continent of Darren by a land bridge. Darren is indicated to be the site of the neutron bomb explosion which transformed the Daleks from their humanoid form into mutants. The north and south regions are separated by the "Radiation Range" mountains. The third continent, Davius, is shown divided into east and west regions by the "River of Whirling Waters", with the eastern region being identified as the home of the Thals. Five seas are shown; the Ocean of Ooze, Sea of Acid, Sea of Rust, Serpent Sea and the land-locked Bottomless Sea. Other major features are the Island of Moving Mountains and an island chain named the Forbidden Islands, both situated in the Ocean of Ooze, and the Island of Gushing Gold located in the Sea of Rust.The BBC-Licensed The Dalek Outer Space Book (1966) confirms some of these details in a cutaway illustration entitled "The Strata of Skaro". A sea called The Ocean of Death is added, together with the Islands of Mist which, from the description, is an alternative name for the Dalek Book's Forbidden Islands. Further information is added by the 1977 Dalek Annual article "The Dark Side of Skaro", which mentions the Crystal Continent, Serpent Island and a feature called The Rocks, consisting of stone needles projecting thousands of feet high out of the sea and populated by gigantic flying creatures. Other areas listed are a prison colony, a region populated by the mutated descendants of prisoners used in early Dalek neutron weapon tests and The Swamp Lands, described as possibly being a vast, living organism that engulfs and feeds upon anything coming near its surface.Other Skarosian geographical features are mentioned in the TV21 comic strip The Daleks (1965-1967). In the story "Duel of the Daleks" an acid river and mercury geysers appear. In "Legacy of Yesteryear" a desert area called Tarran, volcanic plains and a northern polar region are portrayed, the latter area stated to have been created when the explosion of the Daleks' neutron bomb shifted the planet on its axis.The novelisation of Remembrance of the Daleks (1990) states that the Dalek city is called Mensvat Esc-Dalek and is located in the Vekis Nar-Kangji (Plain of Swords). In the computer game Doctor Who Adventure Game "City of the Daleks" (2010) the Dalek city is named Kaalann.
Flora
In most media, Skaro is portrayed as a nuclear wasteland and almost entirely devoid of plant life, with only a petrified forest located close to the Dalek city. Several exceptions are mentioned, however. Varga plants, resembling large, motile cacti studded with poisonous thorns, are seen in Mission to the Unknown (1965). Native to Skaro, they have been deliberately mutated by the Daleks to act as sentries and deter other life forms from interfering with their activities. An individual poisoned by the thorns develops an urge to kill and eventually transforms into another Varga plant. The Arkellis flower is described as being rare and only able to root in metal, with its sap being a constituent of the Golden Emperor Dalek's metallic casing. In the TV21 comic strip The Daleks, dense undergrowth is depicted on several occasions, most notably in the mercury geyser swamps and the mutated forest.
Fauna
The Doctor Who television programme has shown only a few examples of Skaro's native wildlife. In The Daleks, a small, dead reptilian creature with long teeth, a pointed snout and pliable metal skin is discovered, the First Doctor surmising that its body is held together by a magnetic field. This is later identified by a Thal as a "Magnedon". (In the 1965 film Dr. Who and the Daleks, which is based upon The Daleks television serial, this creature is portrayed as a rather larger, petrified, dragon-like animal). A multi-tentacled creature with two luminous eyes is also shown inhabiting the Lake of Mutations. A large, aggressive, tentacled animal called a "Slyther" appears in The Dalek Invasion of Earth (1964). It is described as the Black Dalek's "pet" and is used to patrol the Dalek mine workings. Giant land-based clams, capable of crushing bone, are seen in Genesis of the Daleks (1975). They are described as being the discarded results of Davros' genetic experiments. In "Asylum of the Daleks" (2012) a flock of bird-like creatures are seen briefly, flying in the distance above the ruins of the Dalek City.Other media have introduced additional creatures. The Dalek Book's Dalography of Skaro states that vast serpents, mutated from earthworms by a neutron bomb explosion, live below the surface of the continent of Darren. The book also contains The Dalek Dictionary, which includes entries for "Lallapalange" (an extinct harmony bird which sang with two voices) and "Urvacryl" (a two-headed eel inhabiting the Lake of Mutations). Later, the TV21 "The Daleks" comic strip added giant eels, Terrorkons (large aquatic creatures resembling wingless, two-headed dragons) and amorphous Sand Creatures. The Dalek Outer Space Book contains illustrations of several subterranean creatures including "Sponge People", a "Sucker" (resembling a red beetle), the tentacled Krakis and an unnamed squirrel-like animal. To this can be added yellow and black beetles and "rock leopards", mentioned in the novelisation of Remembrance of the Daleks.
Sapient inhabitants
In the television serial The Daleks two sapient, humanoid species are described as having existed on Skaro; the Dals, teachers and philosophers, and the Thals, a race of warriors. Radiation from a neutronic war caused both species to mutate. By the time of the story, the Thals are a blond-haired caucasian people, their physical mutation having come full circle. They have renounced violence and survive by farming. In contrast, the Dals have evolved into hideous, aggressive, xenophobic creatures which have encased themselves in protective metal shells and rely upon technology for survival. They now refer to themselves as Daleks.This evolution of the Dalek and Thal races is contradicted in the TV serial Genesis of the Daleks. The story depicts the Dalek progenitors as being a humanoid race called the Kaleds. They have been at war with the Thals for generations, turning Skaro into a wasteland devastated by chemical and nuclear weapons. While the Daleks and Thals have each engineered their own huge, protective dome in which to shelter, the disfigured victims of chemical and radioactive contamination are banished to roam the surface as "mutos". The Kaled scientists realise that the planet's toxic environment will eventually cause the mutation of their species, bringing their genetic purity to an end. Their chief scientist, Davros, decides to accelerate the mutation to find the ultimate Kaled form, in the process "improving" it by removing all traces of conscience, feeling and emotion. The resulting organisms are placed into armoured travel machines and referred to by Davros as Daleks.The TV Century 21 Dalek comic strip presents a different description of Skaro's sapient life. One race, the Daleks, are depicted as short, blue-skinned, aggressive humanoids. They are engaged in a vicious war against the Thals who, although not shown in the strip, are described as tall, handsome, peaceful and living in constant fear of Dalek attack. The Daleks build a neutron bomb to finally bring the conflict to an end but a meteorite storm detonates the device prematurely, apparently destroying most of the life on Skaro. A mutated Dalek commandeers a prototype war machine, created shortly before the holocaust, to act as a mobile protective casing. It then convinces the last two humanoid Daleks, Yarvelling and Zolfian, to build more casings for the many other mutants which have survived. No further mention of the Thals is made in the strip, the implication being that they all perished in the nuclear conflagration.
The Big Finish Productions I, Davros series of audio plays (2006) places the divergence of the Kaled and Thal species at a point 10 million years prior to the events depicted in Genesis of the Daleks and refers to two other species, the Tharons and the Dals, as both being extinct due to Kaled genocide by the time of the Kaled-Thal war.
Fictional history
The central plot device of the Doctor Who television programme, and of the Whoniverse, is time travel. Coupled with successive programme producers' and scriptwriters' uneven approach to continuity, attempts at imposing a strict chronology upon Skaro's fictional history are problematic.
The events leading to the creation of the Daleks, as depicted in Genesis of the Daleks (1975), apparently pre-date those of The Daleks (1963–64) while in The Evil of the Daleks (1967), the story of which concludes with the apparent destruction of the Daleks due to a civil war on Skaro, the Second Doctor states that this is the creatures' "final end".In Destiny of the Daleks (1979), set many centuries after the events of Genesis of the Daleks, the Daleks return to an abandoned and still radioactive Skaro to retrieve their creator, Davros. In the subsequent serial Revelation of the Daleks (1985), the Daleks are shown to have re-occupied Skaro; those loyal to the Dalek Supreme travelling from there to capture Davros and destroy his new Dalek army on the planet Necros.Skaro's final appearance in the classic series is in the story Remembrance of the Daleks (1988), in which the Seventh Doctor tricks Davros and his Imperial Daleks into using a Time Lord device called the Hand of Omega on Skaro's sun to recreate the Gallifreyan time travel experiments. The Doctor sabotages the device, however, causing their sun to turn into a supernova which completely obliterates the planet.An image of Skaro is shown briefly at the start of the 1996 Doctor Who television movie, the narrative indicating that it is the site of a trial of the Master. No reference to the destruction of the planet is made. An attempt to explain this incongruity is made in the novel War of the Daleks (1997) in which, at the climax of the events portrayed in Remembrance of the Daleks, the Daleks manipulate Davros and the Seventh Doctor into destroying a planet called Antalin which they have terraformed to resemble Skaro and take its place. The novel further places the story Destiny of the Daleks on the disguised Antalin, and not Skaro.In the revived Doctor Who series, Skaro is referenced by the introduction of the Cult of Skaro in "Doomsday" (2006) and "Daleks in Manhattan" (2007), where the character Dalek Caan states that the planet is "gone... destroyed in a great war". Later, in the episode "Asylum of the Daleks" (2012), the Eleventh Doctor is lured to Skaro briefly. The planet is depicted as having been abandoned once again and is shown with a stormy, rain-swept red sky, the landscape filled with derelict structures and skyscrapers. This is consistent with the appearance of post-Time War Skaro as seen in the downloadable computer game City of the Daleks and an article written by Russell T Davies in the Doctor Who Annual 2006, which states that Skaro was devastated at the end of the Time War.Skaro appears in "The Magician's Apprentice" and "The Witch's Familiar" (2015), where Davros is shown first as an adolescent lost on a desert battlefield, and then having returned to the planet many years later to die with his "children", the Daleks. The planet has been made invisible and, when questioned by the Doctor, Davros states that the Daleks have rebuilt it.The Dalek Outer Space Book (1967) contains a chart entitled "The Evolution of Skaro" which traces the development of the planet from its creation, through various geological periods, to the advent of the Daleks.
Other appearances
Skaro is the setting for the feature film Dr. Who and the Daleks (1965), starring Peter Cushing. Although it is not named in the film, it is retroactively identified in its sequel, Daleks' Invasion Earth 2150 A.D. (1966).
Skaro appears in the Big Finish Doctor Who audio stories The Mutant Phase (2000) and Davros (2003), and features prominently in the I, Davros spin-off series (2006), which focuses on Davros' life and the events that led to his creating the Daleks.Skaro makes an appearance in the Doctor Who: The Adventure Games episode "City of the Daleks". In the narrative the Daleks remove Skaro from the Time War, preventing its destruction. The Eleventh Doctor thwarts the Dalek's plan, negating the planet's survival and restoring the proper timeline. In April 2010 Piers Wenger, executive producer of Doctor Who at the time, stated that the games constitute "episodes" and form part of the Doctor Who universe.Skaro appears in Daleks!, a five part CGI animated series launched by the BBC on its YouTube channel in November 2020 as part of its multi-platform story, Time Lord Victorious!.
Exterior filming locations
For Genesis of the Daleks exterior scenes supposedly taking place on Skaro were shot at Betchworth Quarry, Surrey and for Destiny of the Daleks at Winspit Quarry, Dorset. In "The Magician's Apprentice" and "The Witch's Familiar", exterior scenes set on Skaro were filmed in Tenerife.
See also
Dalek
Dalek variants
History of the Daleks
References
Bibliography
External links
Skaro on Tardis at Fandom, an external wiki
Skaro Home of the Daleks, article at The Doctor Who Site |
list of periods and events in climate history | The list of periods and events in climate history includes some notable climate events known to paleoclimatology. Knowledge of precise climatic events decreases as the record goes further back in time. The timeline of glaciation covers ice ages specifically, which tend to have their own names for phases, often with different names used for different parts of the world. The names for earlier periods and events come from geology and paleontology. The marine isotope stages (MIS) are often used to express dating within the Quaternary.
Before 1 million years ago
Scale: Millions of years before present, earlier dates approximate.
Pleistocene
All dates are approximate. "(B-S)" means this is one of the periods from the Blytt-Sernander sequence, originally based on studies of Danish peat bogs.
Holocene
All dates are BC (BCE) and approximate. "(B-S)" means this is one of the periods from the Blytt-Sernander sequence, originally based on studies of Danish peat bogs.
Common Era/AD
Climate changes of 535-536 (535–536 AD), sudden cooling and failure of harvests, perhaps caused by volcanic dust
900–1300 Medieval Warm Period, wet in Europe, arid in North America, may have depopulated the Great Plains of North America, associated with the Medieval renaissances in Europe
Great Famine of 1315–1317 in Europe
Little Ice Age: Various dates between 1250 and 1550 or later are held to mark the start of the Little ice age, ending at equally varied dates around 1850
1460–1550 Spörer Minimum cold
1656–1715 Maunder Minimum low sunspot activity
1790–1830 Dalton Minimum low sunspot activity, cold
1816 Year Without a Summer, caused by volcanic dust of Mount Tambora eruption
1850–present Retreat of glaciers since 1850, instrumental temperature record
Present and recent past global warming, perhaps to be named the Anthropocene period
See also
Climate change (modern day)
Climate change (general concept)
Climate across Cretaceous–Paleogene boundary
Thermal history of Earth
Geologic temperature record |
geological hazard | A geologic hazard or geohazard is an adverse of geologic condition capable of causing widespread damage or loss of property and life. These hazards are geological and environmental conditions and involve long-term or short-term geological processes. Geohazards can be relatively small features, but they can also attain huge dimensions (e.g., submarine or surface landslide) and affect local and regional socio-economics to a large extent (e.g., tsunamis).
Sometimes the hazard is instigated by the careless location of developments or construction in which the conditions were not taken into account. Human activities, such as drilling through overpressured zones, could result in significant risk, and as such mitigation and prevention are paramount, through improved understanding of geohazards, their preconditions, causes and implications. In other cases, particularly in montane regions, natural processes can cause catalytic events of a complex nature, such as an avalanche hitting a lake and causing a debris flow, with consequences potentially hundreds of miles away, or creating a lahar by volcanism.
Marine geohazards in particular constitute a fast-growing sector of research as they involve seismic, tectonic, volcanic processes now occurring at higher frequency, and often resulting in coastal sub-marine avalanches or devastating tsunamis in some of the most densely populated areas of the world Such impacts on vulnerable coastal populations, coastal infrastructures, offshore exploration platforms, obviously call for a higher level of preparedness and mitigation.
Speed of development
Sudden phenomena
Sudden phenomena include:
avalanches (snow or rock) and its runout
earthquakes and earthquake-triggered phenomena such as tsunamis
forest fires (espec. in Mediterranean areas) leading to deforestation
geomagnetic storms
gulls (chasms) associated with cambering of valley sides
ice jams (Eisstoß) on rivers or glacial lake outburst floods below a glacier
landslide (displacement of earth materials on a slope or hillside)
mudflows (avalanche-like muddy flow of soft/wet soil and sediment materials, narrow landslides)
pyroclastic flows
rockfalls, rock slides, (rock avalanche) and debris flows
torrents (flash floods, rapid floods or heavy current creeks with irregular course)
liquefaction (settlement of the ground in areas underlain by loose saturated sand/silt during an earthquake event)
volcanic eruptions, lahars and ash falls.
Slow phenomena
Gradual or slow phenomena include:
alluvial fans (e.g. at the exit of canyons or side valleys)
caldera development (volcanoes)
geyser deposits
ground settlement due to consolidation of compressible soils or due to collapseable soils (see also compaction)
ground subsidence, sags and sinkholes
sand dune migration
shoreline and stream erosion
thermal springs
Evaluation and mitigation
Geologic hazards are typically evaluated by engineering geologists who are educated and trained in interpretation of landforms and earth process, earth-structure interaction, and in geologic hazard mitigation. The engineering geologist provides recommendations and designs to mitigate for geologic hazards. Trained hazard mitigation planners also assist local communities to identify strategies for mitigating the effects of such hazards and developing plans to implement these measures. Mitigation can include a variety of measures:
Geologic hazards may be avoided by relocation. Publicly available databases, via searchable platforms, can help people evaluate hazards in locations of interest.
The stability of sloping earth can be improved by the construction of retaining walls, which may use techniques such as slurry walls, shear pins, tiebacks, soil nails or soil anchors. Larger projects may use gabions and other forms of earth buttress.
Shorelines and streams are protected against scour and erosion using revetments and riprap.
The soil or rock itself may be improved by means such as dynamic compaction, injection of grout or concrete, and mechanically stabilized earth.
Additional mitigation methods include deep foundations, tunnels, surface and subdrain systems, and other measures.
Planning measures include regulations prohibiting development near hazard-prone areas and adoption of building codes.
In paleohistory
Eleven distinct flood basalt episodes occurred in the past 250 million years, resulting in large volcanic provinces, creating lava plateaus and mountain ranges on Earth. Large igneous provinces have been connected to five mass extinction events. The timing of six out of eleven known provinces coincide with periods of global warming and marine anoxia/dysoxia. Thus, suggesting that volcanic CO2 emissions can force an important effect on the climate system.
Known hazards
2004 Indian Ocean earthquake and tsunami
2008 Sichuan earthquake
2011 Tōhoku earthquake and tsunami
The Barrier (located in Garibaldi Provincial Park)
Usoi Dam a natural landslide dam
See also
Earthquake engineering
Physical impacts of climate change
References
External links
Media related to Geological hazards at Wikimedia Commons
International Centre for Geohazards (ICG) |
tree of life (biology) | The tree of life or universal tree of life is a metaphor, model and research tool used to explore the evolution of life and describe the relationships between organisms, both living and extinct, as described in a famous passage in Charles Darwin's On the Origin of Species (1859).
The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth.
Tree diagrams originated in the medieval era to represent genealogical relationships. Phylogenetic tree diagrams in the evolutionary sense date back to the mid-nineteenth century.
The term phylogeny for the evolutionary relationships of species through time was coined by Ernst Haeckel, who went further than Darwin in proposing phylogenic histories of life. In contemporary usage, tree of life refers to the compilation of comprehensive phylogenetic databases rooted at the last universal common ancestor of life on Earth. Two public databases for the tree of life are TimeTree, for phylogeny and divergence times, and the Open Tree of Life, for phylogeny.
History
Early natural classification
Although tree-like diagrams have long been used to organise knowledge, and although branching diagrams known as claves ("keys") were omnipresent in eighteenth-century natural history, it appears that the earliest tree diagram of natural order was the 1801 "Arbre botanique" (Botanical Tree) of the French schoolteacher and Catholic priest Augustin Augier. Yet, although Augier discussed his tree in distinctly genealogical terms, and although his design clearly mimicked the visual conventions of a contemporary family tree, his tree did not include any evolutionary or temporal aspect. Consistent with Augier's priestly vocation, the Botanical Tree showed rather the perfect order of nature as instituted by God at the moment of Creation.In 1809, Augier's more famous compatriot Jean-Baptiste Lamarck (1744–1829), who was acquainted with Augier's "Botanical Tree", included a branching diagram of animal species in his Philosophie zoologique. Unlike Augier, however, Lamarck did not discuss his diagram in terms of a genealogy or a tree, but instead named it a tableau ("depiction"). Lamarck believed in the transmutation of life forms, but he did not believe in common descent; instead he believed that life developed in parallel lineages (repeated, spontaneous generation) advancing from more simple to more complex.In 1840, the American geologist Edward Hitchcock (1793–1864) published the first tree-like paleontology chart in his Elementary Geology, with two separate trees for the plants and the animals. These are crowned (graphically) with the Palms and Man.The first edition of Robert Chambers' Vestiges of the Natural History of Creation, published anonymously in 1844 in England, contained a tree-like diagram in the chapter "Hypothesis of the development of the vegetable and animal kingdoms". It shows a model of embryological development where fish (F), reptiles (R), and birds (B) represent branches from a path leading to mammals (M). In the text this branching tree idea is tentatively applied to the history of life on earth: "there may be branching".In 1858, a year before Darwin's Origin, the paleontologist Heinrich Georg Bronn (1800–1862) published a hypothetical tree labelled with letters. Although not a creationist, Bronn did not propose a mechanism of change.
Darwin
Charles Darwin (1809–1882) used the metaphor of a "tree of life" to conceptualise his theory of evolution. In On the Origin of Species (1859) he presented an abstract diagram of a portion of a larger timetree for species of an unnamed large genus (see figure). On the horizontal base line hypothetical species within this genus are labelled A – L and are spaced irregularly to indicate how distinct they are from each other, and are above broken lines at various angles suggesting that they have diverged from one or more common ancestors. On the vertical axis divisions labelled I – XIV each represent a thousand generations. From A, diverging lines show branching descent producing new varieties, some of which become extinct, so that after ten thousand generations descendants of A have become distinct new varieties or even sub-species a10, f10, and m10. Similarly, the descendants of I have diversified to become the new varieties w10 and z10. The process is extrapolated for a further four thousand generations so that the descendants of A and I become fourteen new species labelled a14 to z14. While F has continued for fourteen thousand generations relatively unchanged, species B,C,D,E,G,H,K and L have gone extinct. In Darwin's own words: "Thus the small differences distinguishing varieties of the same species, will steadily tend to increase till they come to equal the greater differences between species of the same genus, or even of distinct genera." Darwin's tree is not a tree of life, but rather a small portion created to show the principle of evolution. Because it shows relationships (phylogeny) and time (generations), it is a timetree. In contrast, Ernst Haeckel illustrated a phylogenetic tree (branching only) in 1866, not scaled to time, and of real species and higher taxa. In his summary to the section, Darwin put his concept in terms of the metaphor of the tree of life:
The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have tried to overmaster other species in the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs; and this connexion of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear all the other branches; so with the species which lived during long-past geological periods, very few now have living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped off; and these lost branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and which are known to us only from having been found in a fossil state. As we here and there see a thin straggling branch springing from a fork low down in a tree, and which by some chance has been favoured and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its affinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.
The meaning and importance of Darwin's use of the tree of life metaphor have been extensively discussed by scientists and scholars. Stephen Jay Gould, for one, has argued that Darwin placed the famous passage quoted above "at a crucial spot in his text", where it marked the conclusion of his argument for natural selection, illustrating both the interconnectedness by descent of organisms as well as their success and failure in the history of life. David Penny has written that Darwin did not use the tree of life to describe the relationship between groups of organisms, but to suggest that, as with branches in a living tree, lineages of species competed with and supplanted one another. Petter Hellström has argued that Darwin consciously named his tree after the biblical Tree of Life, as described in Genesis, thus relating his theory to the religious tradition.
Haeckel
Ernst Haeckel (1834–1919) constructed several trees of life. His first sketch, in the 1860s, shows "Pithecanthropus alalus" as the ancestor of Homo sapiens. His 1866 tree of life from Generelle Morphologie der Organismen shows three kingdoms: Plantae, Protista and Animalia. This has been described as "the earliest 'tree of life' model of biodiversity". His 1879 "Pedigree of Man" was published in his 1879 book The Evolution of Man. It traces all life forms to the Monera, and places Man (labelled "Menschen") at the top of the tree.
Developments since 1990
In 1990, Carl Woese, Otto Kandler and Mark Wheelis proposed a novel "tree of life" consisting of three lines of descent for which they introduced the term domain as the highest rank of classification. They also suggested the terms Bacteria, Archaea and Eukarya for the three domains. It is the very first tree that is founded on molecular phylogenetics and for the first time it also includes microorganisms. The history of the research on microbial evolution resulting in this natural tree of life and of the different tree-concepts has been documented by Jan Sapp.The model of a tree is still considered valid for eukaryotic life forms. Trees have been proposed with either four or two supergroups. There does not yet appear to be a consensus; in a 2009 review article, Roger and Simpson conclude that "with the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution."In 2015, the third version of TimeTree was released, with 2,274 studies and 50,632 species, represented in a spiral tree of life, free to download.
In 2015, the first draft of the Open Tree of Life was published, in which information from nearly 500 previously published trees was combined into a single online database, free to browse and download. Another database, TimeTree, helps biologists to evaluate phylogeny and divergence times.In 2016, a new tree of life (unrooted), summarising the evolution of all known life forms, was published, illustrating the latest genetic findings that the branches were mainly composed of bacteria. The new study incorporated over a thousand newly discovered bacteria and archaea.In 2022, the fifth version of TimeTree was released, incorporating 4,185 published studies and 148,876 species, representing the largest timetree of life from actual data (non-imputed).
Horizontal gene transfer and rooting the tree of life
The prokaryotes (the two domains of bacteria and archaea) and certain animals such as bdelloid rotifers freely pass genetic information between unrelated organisms by horizontal gene transfer. Recombination, gene loss, duplication, and gene creation are a few of the processes by which genes can be transferred within and between bacterial and archaeal species, causing variation that is not due to vertical transfer. There is emerging evidence of horizontal gene transfer within the prokaryotes at the single and multicell level, so the tree of life does not explain the full complexity of the situation in the prokaryotes. This is a major problem for the tree of life because there is consensus that eukaryotes arose from a fusion between bacteria and archaea, meaning that the tree of life is not fully bifurcating and should not be represented as such for that important node. Secondly, unrooted phylogenetic networks are not true evolutionary trees (or trees of life) because there is no directionality, and therefore the tree of life needs a root.
See also
References
Further reading
Darwin, Charles (1859). On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (1st ed.). London: John Murray. ISBN 978-1-4353-9386-8.
Darwin, Charles (1872). The Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (6th ed.). London: John Murray. ISBN 978-1-4353-9386-8.
Doolittle, W. F.; Bapteste, E. (2007). "Inaugural Article: Pattern pluralism and the Tree of Life hypothesis". Proceedings of the National Academy of Sciences. 104 (7): 2043–2049. Bibcode:2007PNAS..104.2043D. doi:10.1073/pnas.0610699104. PMC 1892968. PMID 17261804.
External links
Tree of Life Web Project - explore complete phylogenetic tree interactively
Tree of Life Evolution Links species on Earth through a shared evolutionary history
The Tree of Life by Garrett Neske, The Wolfram Demonstrations Project: "presents an interactive tree of life that allows you to explore the relationships between many different kinds of organisms by allowing you to select an organism and visualize the clade to which it belongs."
The Green Tree of Life - Hyperbolic tree University of California/Jepson Herbaria
NCBI's taxonomy database common tree
OneZoom Tree of Life Explorer |
viluppuram | Viluppuram, Villupuram, or Vizhuppuram (Tamil: [ʋiɻɯppɯɾam] ) is a Municipality and the administrative headquarters of Viluppuram district.
Located 61 kilometres (38 mi) south west of a Tiruvannamalai and 45 kilometres (28 mi) north west of Cuddalore null The town serves as a major railway junction, and National Highway 45 passes through it. Agriculture is a main source of income. As Government of India 2011 census data indicated, Viluppuram had a population of 96,253. and the town's literacy rate has been recorded as 90.16% by Census 2011.In 1919, Vilppuram was officially constituted as a municipality, which today comprises 42 wards, making it the largest town and municipality in Viluppuram district.
History
In 1677, Shivaji took Gingee area with the assistance of Golkonda forces. Later in 18th century, both the English and French acquired settlements in South Arcot. During the Anglo-French rivalry, the entire district was turned into a war land. After some time, the entire area came under the control of East India Company. It remained under British authority till 1947 when India became independent.After independence, the district as we know it today, was part of the larger South Arcot District headquartered at Cuddalore . On 30 September 1993, Villupuram became the headquarters of the newly created Vizhuppuram District as a result of the division of the South Arcot District.
Geography
Vizhuppuram is located in 11° 56' N 79° 29' E. which is in the far southeast part of India, situated 160 kilometres (99 mi) south of Chennai, 160 kilometres (99 mi) north of Trichy, 177 kilometres (110 mi) east of Salem, 45 kilometres (28 mi) North west of Cuddalore, 40 kilometres (25 mi) west of Pondicherry shares the seashore of the Bay of Bengal.The area contains metamorphic rocks formed by pressure and heat belonging to the granite-like gneiss family. There are also three major groups of sedimentary rocks, layers of particles that settled in different geological periods. Kalrayan Hills forest park is located 116 kilometres (72 mi) to the west and Gingee Hills forest park 50 kilometres (31 mi) to the north. The Thatagiri Murugan Temple is about 191 kilometres (119 mi) to the southeast in Senthamangalam with the Lord Siva temple in Koppampatti 153 kilometres (95 mi) southwest of the town.
Climate
Since the town is landlocked, the weather in Viluppuram is generally humid and hot. It relies on the monsoon for rain from July to December. Summers are very hot, and temperatures can get up to 40 °C (104 °F). Winters are moderate with temperatures ranging between 30 and 35 °C (86 and 95 °F) Viluppuram has a tropical climate. In winter, there is much less rainfall in Viluppuram than in summer. This climate is considered to be Aw/As according to the Köppen-Geiger climate classification.
The average annual temperature is 28.4 °C (83.1 °F) in Viluppuram with average annual rainfall of 1,046 millimetres (41.2 in). The driest month is March, with 6 millimetres (0.24 in) of rainfall. With an average of 222 millimetres (8.7 in) per annum, the most precipitation falls in October. The warmest month of the year is May, with an average temperature of 32.0 °C (89.6 °F). January has the lowest average temperature of the year at 24.6 °C (76.3 °F).
The difference in precipitation between the driest month and the wettest month is 216 millimetres (8.5 in). During the year, the average temperatures vary by 7.4 °C (45.3 °F).
Demographics
As of the 2011 census, Viluppuram municipality was divided into 44 wards for which elections are held every five years and had a population of 96,253 of which 47,670 were male and 48,583 female.
Administration
Politically, Viluppuram is part of the Vizhuppuram Lok Sabha constituency and the Vizhuppuram State Assembly constituency. The municipality was established in 1919 and was upgraded to a second-grade municipality in 1953, the first-grade municipality in 1973, and a selection grade municipality in 1988. The town is divided into 42 wards. The municipal council is composed of 42 ward councilors and is headed by a chairperson elected by voters of the town. Councilors-elect a vice-chairperson among themselves while the executive wing is headed by a commissioner, who is assisted by a team of officials including the health officer, municipal engineer, town planning officer, manager, revenue officer and other staff.
Transport
Road
Viluppuram is connected by roads to major cities and to the rest of the state. The major national highways of the town are:
NH 38, which connects Vellore and Thoothukudi, via Tiruvannamalai - Viluppuram – Tiruchirapalli –Madurai – Aruppukottai.
SH 07 connects Villupuram -- Tirukoilur.
NH 332, which connects Viluppuram and Pondicherry.
NH 132, which Connects Villupuram and Tindivanam.
NH NH 45A, which Connects Villupuram and Nagapattinam.
NH 36, which connects Vikravandi and Manamadurai via Panruti – Neyveli – Kumbakonam - Thanjavur - Pudukottai bypasses Villupuram at 5 km in Koliyanur.
Rail
The Viluppuram Railway Junction at Vizhuppuram serves as the distribution point of rail traffic from Chennai, the state capital of Tamil Nadu, towards the southern part of the state. Five railway lines branch out of Vizhuppuram:
Fully Electrified Double BG (Broad Gauge) line (FEDL) towards Chennai Beach via Chengulpattu Junction.
Fully Electrified Double BG (Broad Gauge) line (FEDL) towards Tiruchirapalli Junction via Vridhachalam Junction and Ariyalur. Also called "Chord Line" to Tiruchirapalli.
Fully Electrified Single BG (Broad Gauge) line (FEDL) towards Tiruchirapalli Junction via Cuddalore Port Junction, Mayiladuthurai, Kumbakonam and Thanjavur Junction. Also called Main Line.
Fully Electrified Single BG (Broad Gauge) line towards Katpadi Junction via Tirukoilur Tiruvannamalai and Vellore Cantonment.
Fully Electrified Single BG (Broad Gauge) line to Pondicherry.
Air
The nearest airport is Pondicherry Airport at Pondicherry, in Puducherry, approximately 40 km from Viluppuram. Pondicherry Airport is connected to Bangalore by commercial airlines.
The nearest major airport is the Chennai International Airport (MAA), approximately 147 km from the town; the next closest major airport is Tiruchirapalli international Airport, approximately 170 km from the town.
References
External links
Viluppuram District Official Website |
list of mnemonics | This article contains a list of notable mnemonics used to remember various objects, lists, etc.
Astronomy
Order of planets from the Sun: (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto)
obsolete (per the IAU definition of planet):
Most Vegetables Eat More Juice So Usually Never Pee
My Very Educated Mother Just Served Us Nine Potatoes
Many Vicious Elephants Met Just Slightly Under New Pineapples
My Very Easy Method Just Speeds Up Naming Planets
Mark's Very Extravagant Mother Just Sent Us Ninety Parakeets
Mother Very Eagerly Made A (Asteroids) Jelly Sandwich Under No ProtestStellar classification sequence: O B A F G K M R N SOh Be A Fine Girl/Guy, Kiss Me Right Now, Sweetheart!Revised stellar classification sequence: O B A F G K M L T YOld, Bald, And Fat Generals Kiss More Ladies Than YouSigns of the zodiac:Average distances of the outer planets from the Sun in astronomical units approximate nice round numbers:Jupiter: 5 AU, Saturn: 10 AU, Uranus: 20 AU, Neptune: 30 AU, Pluto: 40 AU
Biology
To remember the order of taxa in biology (Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species, [Variety]):
"Dear King Philip Came Over For Good Soup" is often cited as a non-vulgar method for teaching students to memorize the taxonomic classification of system. Other variations tend to start with the mythical king, with one author noting "The nonsense about King Philip, or some ribald version of it, has been memorized by generations of biology students".
Dear King Philip Claps Often For Good Science
Dark King Prawns Curl Over Fresh Green Salad
Do Kings Play Chess On Fine Green Silk?: 69
Dumb Kids Prefer Cheese Over Fried Greasy Spinach: 69
Do Kindly Place Cover On Fresh Green Spring Vegetables: 69
Darn Kernel Panics Crash Our Family Game System
Do Keep Pond Clean Or Frog Gets Sick
Dumb Kids Play Catch Over Father's Grave Stone
Daniel Keeps Philip Cat On Friday Getting Salsa
To remember the processes that define living things:
MRS GREN: Movement; Respiration; Sensation; Growth; Reproduction; Excretion; Nutrition: 135
To remember the number of humps on types of camels:: 67 D in Dromedary has one hump; B in Bactrian has twoTo recognize poison ivy
Leaves of three, leave it be.
COWS stand for Cold Opposite Warm Same, which are the relation between the components of the Caloric reflex test
Chemistry
To recall the names of the first 20 elements in the periodic table:Harry, he likes beer by cupfuls, not over frothy, never nasty mugs allowed. Since past six closing, are kegs cancelled?(H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca.)To remember the different charges of the anode and cathode in electrolysis (PANIC):Positive Anode Negative Is CathodeAN OIL RIG CAT:At the ANode, Oxidation Involves electron Loss.
Reduction Involves electron Gain at the CAThode.CHON: to remember the four most common elements in organismsCarbon, Hydrogen, Oxygen, NitrogenCHNOPS: to remember the six most common elements in organismsCarbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur
Engineering
For the EIA electronic color code, Black(0), Brown(1), Red(2), Orange(3), Yellow(4), Green(5), Blue(6), Violet(7), Gray(8), White(9), Gold(5%), Silver(10%), None(20%)
Big brown rabbits often yield great big vocal groans when gingerly slapped
Bad boys run our young girls behind victory garden walls
B .B Roy [of] Great Britain [has] Very Good Wife.A mnemonic to remember which way to turn common (right-hand thread) screws and nuts, including light bulbs, is "Righty-tighty, Lefty-loosey"; another is "Right on, Left off".: 165
For the OSI Network Layer model Please Do Not Throw Sausage Pizza Away correspond to the Physical, Datalink, Network, Transport, Session, Presentation and Application layers.
For power in watts: Twinkle twinkle little star, Power equals I squared R.[1]
Geography
Both names of the northern major circles of latitude (the Arctic Circle and Tropic of Cancer) have six letters; both southern ones (the Antarctic Circle and Tropic of Capricorn) have nine.
The countries of South America in order of largest to smallest by area: Brazil, Argentina, Peru, Colombia, Bolivia, Venezuela, Chile, Paraguay, Ecuador, Guyana, Uruguay, SurinameBoring, Average Politics Can Become Very Corrupt. People Everywhere Get Used SometimesThe countries of Central America from North to South: Belize, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, PanamaBig Gorillas Eat Hotdogs, Not Cold Pizza
Including Mexico, My Grandma's Bunny Eats Hamburgers, Not Canned PeasThe Great Lakes in order of largest to smallest: Superior, Huron, Michigan, Erie, OntarioSuper Heroes Must Eat OatsA more common mnemonic for the Great Lakes, disregarding order:Huron Ontario Michigan Erie Superior: HOMESThe principal factors affecting climate: LABDOWALatitude, Altitude, Build, Distance from the sea, Ocean currents, Wind, AspectThe countries bordering Germany (clockwise from top): Denmark, Poland, Czechia, Austria, Switzerland, France, Luxembourg, Belgium, Netherlands.
Do Polish Checks Always Say "France Look Back Now"!
Geology
Geological periods: Precambrian, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous; Post-Cretaceous Epochs: Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Recent (Holocene)Pregnant Camels Often Sit Down Carefully, Perhaps Their Joints Creak? Possibly Early Oiling Might Prevent Permanent Rheumatism: 62–63
Paleozoic to Cenozoic: Pregnant Camels Ordinarily Sit Down Carefully, Perhaps Their Joints Creak
Post-Cretaceous Epochs: Please Eat Oats My Pretty Pet Horse (Holocene)Mohs scale of mineral hardness 1-10:For Talc(=1), Gypsum(=2), Calcite(=3), Fluorite(=4), Apatite(=5), Orthoclase(=6), Quartz(=7), Topaz(=8), Corundum(=9), Diamond(=10)
Tall Girls Can Fight And Other Queer Things Can Develop: 64
TAll GYroscopes CAn FLy APart ORbiting QUickly TO COmplete DIsintegration: 64
Toronto Girls Can Flirt And Only Quit To Chase Dwarves
Terrible Giants Can Find Alligators Or Quaint Trolls Conveniently Digestible
Tall Gene Calls Florence At Our Quarters To Correct DumbnessDifferentiating stalactites from stalagmites.The 'mites go up and the 'tites come down. When one has ants in one's pants, the mites go up and the tights come down.: 66 (In a strict scientific sense, a mite is not an ant, although "mite" in common speech can refer to any small creature.)
Stalactites hang tight, hang down like tights on a line; stalagmites might bite (if you sit on them), might reach the roof.: 66
Tights hang from the Ceiling, and Mites crawl around on the Ground
You need might to do push-ups (from the floor). You must hold tight doing chin-ups (off the ceiling).
Stalactites are on the ceiling. Stalagmites are on the ground.: 66
Stalactites cling tight to the ceiling; stalagmites might reach the ceiling.
History
Chinese dynasties (simplified): Xia (Hsia), Shang, Zhou (Chou), Qin (Ch'in), Han, Jin, Southern and Northern, Sui, Tang, Song, Yuan, Ming, Qing (Ching)She Shamefully Chose Chinese Hand Jingles (and) SiNfully Sweet Tango Songs: "You (and) Me, Chickadee!"English dynasties (simplified): Norman, Plantagenet, Lancaster, York, Tudor, Stuart, Hanover, WindsorNo Plan Like Yours To Study History Wisely.
Wives of Henry VIII (names): Aragon, Boleyn, Seymour, Cleves, Howard, ParrAll Boys Should Come Home Please: 103 Wives of Henry VIII (manner of death): Divorced, beheaded, died / Divorced, beheaded, survived.: 104
British nobility rank order (simplified): Duke, Marquess, Earl, Viscount, BaronsDo Men Ever Visit Boston?Assassinated US presidents and perpetrators: Lincoln by Booth, Garfield by Guiteau, McKinley by Czolgosz and Kennedy by Oswald.Losers Bearing Grudges Grieve Mainly Cowards Killing Orators
Languages
Characteristic sequence of letters
I always comes before E (but after C, E comes before I)In most words like friend, field, piece, pierce, mischief, thief, tier, it is "i" which comes before "e". But on some words with c just before the pair of e and i, like receive, perceive, "e" comes before "i". This can be remembered by the following mnemonic,
I before E, except after CBut this is not always obeyed as in case of weird and weigh, weight, height, neighbor etc. and can be remembered by extending that mnemonic as given below
I before E, except after C
Or when sounded "A" as in neighbor, weigh and weight
Or when sounded like "eye" as in height
And "weird" is just weirdAnother variant, which avoids confusion when the two letters represent different sounds instead of a single sound, as in atheist or being, runs
When it says ee
Put i before e
But not after cWhere ever there is a Q there is a U tooMost frequently u follows q. e.g.: Que, queen, question, quack, quark, quartz, quarry, quit, Pique, torque, macaque, exchequer. Hence the mnemonic:
Where ever there is a Q there is a U too (But this is violated by some words; see:List of English words containing Q not followed by U)
Letters of specific syllables in a word
BELIEVEDo not believe a lie.SECRETARYA secretary must keep a secretTEACHERThere is an ache in every teacher.MEASUREMENTBe sure of your measurements before you start work.FRIENDFri the end of your friendSPECIALThe CIA have special agentsBEAUTIFULBig Elephants Are UglySEPARATEAlways smell a rat when you spell separate
There was a farmer named Sep and one day his wife saw a rat. She yelled, “Sep! A rat – E!!!”CEMETERYThere are three "e"s buried in "cemetery".PRINCIPALThe principal is your pal.
Distinguishing between similar words
Difference between Advice & Advise, Practice & Practise, Licence & License etc.Advice, Practice, Licence etc. (those with c) are nouns and Advise, Practise, License etc. are verbs.
One way of remembering this is that the word ‘noun’ comes before the word ‘verb’ in the dictionary; likewise ‘c’ comes before ‘s’, so the nouns are ‘practice, licence, advice’ and the verbs are ‘practise, license, advise’.Here or HearWe hear with our ear.Complement and Complimentcomplement adds something to make it enough
compliment puts you in the limelightPrinciple and PrincipalYour principal is your pal
A rule can be called a principleRemedial and MenialRemedial work is meant to remedy.
Menial work is boring but it's mean (-ial) to complain.Their, There and They'reTheirs is not mine even though 'I' is in it.
There is where we'll be.
They're is a contraction of 'they are.'Stationary and stationeryStationery contains er and so does paper; stationary (not moving) contains ar and so does car
A for "at rest", e for envelopeGray and greyGray is preferred in America while grey is preferred in England
First letter mnemonics of spelling
DIARRH(O)EADashing In A Rush, Running Harder (or) Else Accident!
Dining In A Rough Restaurant: Hurry, (otherwise)Expect Accidents!
Diarrhea Is A Really Runny Heap (of) Endless AmountsARITHMETICA Rat In The House May Eat The Ice CreamNECESSARYNot Every Cat Eats Sardines (Some Are Really Yummy)
Never Eat Chocolate, Eat Sardine Sandwiches And Remain YoungBECAUSEBig Elephants Can Always Understand Small Elephants
Big Elephants Cause Accidents Under Small Elephants
Big Elephants Can't Always Use Small Exits
Big Elephants Can’t Always Use Small EntrancesMNEMONICSMnemonics Now Erase Man's Oldest Nemesis, Insufficient Cerebral StorageGEOGRAPHYGeorge's Elderly Old Grandfather Rode A Pig Home Yesterday.TOMORROWTrails Of My Old Red Rose Over WindowRHYTHMRhythm Helps Your Two Hips Move
Grammar
Adjective order in English: OSASCOMP (Opinion, Size, Age, Shape, Color, Origin, Material, Purpose)On Saturday And Sunday Cold Ovens Make Pastry
Commonly-used coordinating conjunctions in English: FANBOYSFor, And, Nor, But, Or, Yet, So
The verbs in French that use the auxiliary verb être in the compound past (sometimes called "verbs of motion") can be memorized using the phrase "Dr. (and) Mrs. Vandertramp":devenir, revenir, monter, rester, sortir, venir, aller, naître, descendre, entrer, rentrer, tomber, retourner, arriver, mourir, partir
Mathematics
Pi
The first 15 numbers of Pi can be remembered by counting the letters in the phrase, "How I want a drink, alcoholic of course, after the heavy lectures involving quantum mechanics."
Quadratic equation
The articulation of the quadratic equation can be sung to the tune of various songs as a mnemonic device.
Mathematical operations
For helping students in remembering the rules in adding and multiplying two signed numbers, Balbuena and Buayan (2015) made the letter strategies LAUS (like signs, add; unlike signs, subtract) and LPUN (like signs, positive; unlike signs, negative), respectively.Order of Operations
PEMDAS
Please - Parenthesis
Excuse - Exponents
My - Multiplication
Dear - Division
Aunt - Addition
Sally - Subtraction
(In the UK, the phrase BIDMAS is used instead; Brackets, Indices, Division, Multiplication, Addition, Subtraction.)
Trigonometry
The mnemonic "SOHCAHTOA" (occasionally spelt "SOH CAH TOA") is often used to remember the basic trigonometric functions:
Sine = Opposite / Hypotenuse
Cosine = Adjacent / Hypotenuse
Tangent = Opposite / AdjacentOther mnemonics that have been used for this include:
Some Old Hippie
Caught Another Hippie
Tripping On Acid.
Ships Of Holland Call At Harwich To Obtain Apples.
Sighs Of Happiness Come After Having Tankards Of Ale.
Some Old Hen Caught Another Hen Taking Off Alone.
Silly Old Hitler Can't Advance His Troops On Africa.
Topology
Mnemonics for Euler's characteristic are "fav. me", for "F add V, minus E ", and "veryfun".
Calculus
The mnemonic "LIATE" is commonly used to determine which functions are to be chosen as u and DV in integration by parts.
Logarithmic functions
Inverse trigonometric functions
Algebraic functions
Trigonometric functions
Exponential functions
Medicine
To remember the signs of a stroke:
FAST
Face (Has the victim's face fallen on one side?)
Arms (Can the victim raise both arms and keep them raised?)
Speech (Is the victim's speech slurred? Can they repeat a simple sentence?)
Time (It is time to contact emergency services.)
To remember the steps for Resuscitation:
D.R.S. A.B.C.D
Danger (Check for danger to yourself or others before starting)
Response (Check for signs of life or response)
Send for help (Call for backup, or Emergency services)
Airway (Check for obstruction in the throat)
Breaths (Check for breaths)
CPR (Commence CPR)
Defib (Apply Defibrillator)
Anatomy
To remember the 10 organ systems of the human body:NICER DRUMS (Nervous, Integumentary, Circulatory, Endocrine, Respiratory, Digestive, Reproductive, Urinary, Muscular, Skeletal)
Intrinsic muscles of hand'A OF A OF A'
Thenar (lateral to medial-palmar surface):
Abductor pollicis brevis
Opponens pollicis
Flexor pollicis brevis
Adductor pollicis
Hypothenar (lateral to medial-palmar surface):
Opponens digiti minimi
Flexor digiti minimi
Abductor digiti minimi
Muscles of mandibular nerve (V3 of trigeminal nerve) : Mylohyoid, Tensor tympani + Tensor veli palatini, Digastric (Anterior) – 4 Muscles of Mastication (temporalis, masseter, medial and lateral pterygoidsMy Tensors Dig Ants for Mom
2 big ones, 2 small ones, 2 tensors, 2 pterygoidsBones of the wrist:Scaphoid bone, Lunate bone, Triquetral bone, Pisiform bone, Trapezium (bone), Trapezoid bone, Capitate bone & Hamate boneSome Lovers Try Positions That They Can't Handle
She Looks Too Pretty Try To Catch Her
So Long To Pinky, Here Comes The Thumb
Simply Learn The Positions That The Carpus Has
Send Louis To Paris To Tame Carnal Hungers
Stop Letting Those People Touch The Cadaver's HandsDifferential DiagnosisVINDICATECranial nerves
Music
Bowed strings
Mnemonics are used in remembering string names in violin standard tuning.
Good Dogs Always Eat
Greedy Dogs Always Eat
Mnemonics are used in remembering string names in viola standard tuning.
Cats Give Dogs Advice
Guitar
Mnemonics are used in remembering guitar string names in standard tuning.Every Average Dude Gets Better Eventually
Eggs Are Deliciously Good Breakfast Energy
Eddy Ate Dynamite Good Bye Eddy
Every Adult Dog Growls Barks Eats.
Every Acid Dealer Gets Busted Eventually
Even After Dinner Giant Boys Eat
Elephants All Dine Generally Before Eight
Elephants And Donkeys Grow Big Ears
Every American Dog Gets Bones Easily
Every Angel Does Good Before Evil
Eat All Day Get Big Easy
Eine Alte Dame Geht Heute Einkaufen (German: an old lady goes shopping today)
Een Aap Die Geen Bananen Eet (Dutch: A monkey that doesn't eat bananas)Thus we get the names of the strings from 6th string to the 1st string in that order.
Conversely, a mnemonic listing the strings in the reverse order is:
Every Beginning Guitarist Does All Exercises!
Elvis' Big Great Dane Ate Everything
Every Big Girl Deserves An Elephant
Easter Bunny Gets Drunk At Easter
Easter Bunnies Go Dancing After Easter
Ukulele
As for guitar tuning, there is also a mnemonic for ukuleles.
Good Cooks Eat A-lotIn the other direction it is Aunt Evy Cooks Grits
Reading music
Musicians can remember the notes associated with the five lines of the treble clef using any of the following mnemonics, EGBDF: (from the bottom line to the top) Every Good Boy Does Fine.
Every Good Boy Deserves Fudge (or Friendship, Fun, Fruit, etc.)
Eggnog Gets Better During February
Empty Garbage Before Dad FlipsThe four spaces of the treble clef spell out (from the bottom to the top) FACE and can be remembered as FACE fits in the space (between lines)
The five lines of the bass clef from the bottom to the top Good Boys Do Fine Always
Good Birds Don't Fly Away
Grizzly Bears Don't Fly Airplanes
Great Basses Dig Fine Altos
Goblins Bring Death For All
George Bush Didn't Find Anything
Good Burritos Don't Fall ApartThe four spaces of the bass clef from the bottom to the top All Cows Eat Grass
All Cars Eat GasThe five lines of the alto clef from the bottom to the top Fat Alley Cat Eats GarbageThe four spaces of the alto clef from the bottom to the top Green Birds Do Fly
The order of sharps in key signature notation is F♯, C♯, G♯, D♯, A♯, E♯, B♯, which can be remembered using the phrase Father Charles Goes Down And Ends Battle
Father Christmas Gave Dad An Electric Blanket.
Fat Cats Go Down Alleys Eating Birds.
Fidel Castro Gets Drunk And Eats Babies.
Fat Cats Greedy Dogs All Eat Bananas.The order of flats is B♭, E♭, A♭, D♭, G♭, C♭, and F♭ (reverse order of sharps), which can be remembered using the phrase: Battle Ends And Down Goes Charles' Father
Blanket Exploded And Dad Got Cold Feet.
Before Eating A Doughnut Get Coffee First.To remember the difference between the whole rest and the half rest:
A whole rest looks like a "hole in the ground", and a half rest looks like a hat.
Philosophy
THE LAD ZAPPA is a mnemonic for the first 11 (and most important) Ionian philosophers: Thales, Heraclitus, Empedocles, Leucippus, Anaximander, Democritus, Zeno, Anaximenes, Protagoras, Parmenides, Anaxagoras .
THE PLAZA PAD is another mnemonic for the first 11 (and most important) Ionian philosophers: Thales, Heraclitus, Empedocles, Protagoras, Leucippus, Anaximander, Zeno, Anaximenes, Parmenides, Anaxagoras, Democritus.
SPA is a mnemonic for the philosophers Socrates, Plato, and Aristotle in their order of appearance, Socrates first.
Physics
Sequence of colors in a rainbow or visible spectrum (red, orange, yellow, green, blue, indigo, violet):"Richard Of York Gave Battle In Vain"
Roy G. Biv is also used as a fictitious name
Transportation
Marine"Red, Right, Return" reminds the skipper entering ("returning to") an IALA region B port to keep red markers to the starboard of the vessel. Conversely the opposite convention exists in IALA region A ports, where a similar (but significantly different) mnemonic of "Red on the Right Returning To Sea" can be used.
The phrase "there's always some red port (wine) left" is used to remember the basics in seafaring. "Red" refers to the color of navigation lights on the port (left) side of a vessel (as opposed to green on the starboard side).
"Nuclear Restrictions Constrain Fishing and Sailing, People Say" is used to encode the "order of priority" for which vessels have right of way (earlier in the list has priority over later): Not under command; Restricted; Constrained by draft; Fishing vessel; Sailboat; Powerboat; Seaplane.
Aviation uses many mnemonics in addition to written checklists. See also Category: Aviation mnemonicsCRAFT - Clearance limit, Route, Altitude, Frequency, Transponder.
pre-landing: GUMPS - Gas, Undercarriage, Mixture, Propeller, Speed.
pre-final: MARTHA - Missed (procedure), Altitude (limit), Radios (set), Time (limit), Heading (final), Airspeed (descent)
pre-high-altitude - FLOWER - Flow (enabled), Lights (test), Oxygen (charged), Water (humidity), Electricity (on), Radio (check)
pre-flight-paperwork - ARROW - Airworthiness (certificate), Registration, Required (charts), Operating (checklists), Weight and balance
night collision avoidance: Red, Right, Returning - Red nav light on Right implies target is Returning (closing)
radio loss Instrument course - CDEF - as Cleared, else Direct to last fix, else as directed to Expect, else as flight plan Filed
spin recovery - POKER - Power (off), Opposite (full rudder), Klean (flaps, ...), Elevator (briskly forward), Recover (from dive)
Units of measure
Common SI prefixes:kilo-, hecto-, deca-, deci-, centi-, milli-, in descending order of magnitude:"Base" (Meters, liters, grams) come in between "deca" and "deci".
Kangaroos Hop Down British Driveways Carrying M&Ms
King Henry Drank Both Diet Cokes Monday
King Henry Died By Drinking Chocolate Milkdeca-, hecto-, kilo-, mega-, giga-, tera-, in ascending order of magnitude:Decadent Hector Killed Meg's Gigantic Terrierdeci-,-, milli-, micro-, nano-, pico-, femto-, atto- in descending order of magnitude:Darn Clever Mnemonic Makes No Prefix Forgettable, Absolutely
See also
Mnemonic
List of firefighting mnemonics
List of visual mnemonics
Category: Science mnemonics
References
Further reading
Evans, Rod L. (2007). Every good boy deserves fudge : the book of mnemonic devices (1st ed.). New York, N.Y.: Perigee. ISBN 978-0-399-53351-8.
Parkinson, Judy (2008). I before E (except after C) : old-school ways to remember stuff. Pleasantville, N.Y.: Reader's Digest Association. ISBN 978-0-7621-0917-3.
External links
List of hundreds of mnemonics belonging to several topics
Medical mnemonics pdf (consisting of 22 pages full of) mnemonics on medical topics ordered alphabetically
Medical mnemonics
Searchable database of Medical mnemonics
Mnemonics generator for numbers
Collection of Mnemonics
Collection of Mnemonics by Category
Community website to collaborate and create new mnemonics |
space colonization | Space colonization (also called space settlement or extraterrestrial colonization) is the use of outer space or celestial bodies other than Earth for permanent habitation or as extraterrestrial territory.
The inhabitation and territorial use of extraterrestrial space has been proposed, for example, for space settlements or extraterrestrial mining enterprises. To date, no permanent space settlement other than temporary space habitats have been set up, nor has any extraterrestrial territory or land been legally claimed. Making territorial claims in space is prohibited by international space law, defining space as a common heritage. International space law has had the goal to prevent colonial claims and militarization of space, and has advocated the installation of international regimes to regulate access to and sharing of space, particularly for specific locations such as the limited space of geostationary orbit or the Moon.
Many arguments for and against space settlement have been made. The two most common in favor of colonization are survival of human civilization and life from Earth in the event of a planetary-scale disaster (natural or human-made), and the availability of additional resources in space that could enable expansion of human society. The most common objections include concerns that the commodification of the cosmos may be likely to enhance the interests of the already powerful, including major economic and military institutions; enormous opportunity cost as compared to expending the same resources here on Earth; exacerbation of pre-existing detrimental processes such as wars, economic inequality, and environmental degradation.A space settlement would set a precedent that would raise numerous socio-political questions. The mere construction of the needed infrastructure presents daunting technological and economic challenges. Space settlements are generally conceived as providing for nearly all (or all) the needs of larger numbers of humans, in an environment out in space that is very hostile to human life and inaccessible for maintenance and supply from Earth. It would involve much development of currently primitive technologies, such as controlled ecological life-support systems. With the high cost of orbital spaceflight (around $1400 per kg, or $640 per pound, to low Earth orbit by Falcon Heavy), a space settlement would currently be massively expensive. On the technological front, there is ongoing progress in making access to space cheaper (reusable launch systems could reach $20 per kg to orbit), and in creating automated manufacturing and construction techniques.
There are yet no plans for building space settlement by any large-scale organization, either government or private. However, many proposals, speculations, and designs for space settlements have been made through the years, and a considerable number of space colonization advocates and groups are active. Several famous scientists, such as Freeman Dyson, have come out in favor of space settlement.
Definition
The term has been used very broadly, being applied to any permanent human presence, even robotic, particularly along with the term "settlement", being imprecisely applied to any human space habitat, from research stations to self-sustaining communities in space.
The word colony and colonization are terms rooted in colonial history on Earth, making it a human geographic as well as particularly a political term.
This broad use for any permanent human activity and development in space has been criticized, particularly as colonialist and undifferentiated (see below Objections).
In this sense, a colony is a settlement that claims territory and exploits it for the settlers or their metropole. Therefore a human outpost, while possibly a space habitat or even a space settlement, does not automatically constitute a space colony. Though entrepôts like trade factories did often grow into colonies.
Therefore any basing can be part of colonization, while colonization can be understood as a process that is open to more claims, beyond basing. The International Space Station, the longest-occupied extraterrestrial habitat thus far, does not claim territory and thus is not usually considered a colony.
History
When the first space flight programs commenced, they partly used - and have continued to use - colonial spaces on Earth, such as places of indigenous peoples at the RAAF Woomera Range Complex, Guiana Space Centre or contemporarily for astronomy at the Mauna Kea telescope.
When orbital spaceflight was achieved in the 1950s colonialism was still a strong international project, e.g. easing the United States to advance its space program and space in general as part of a "New Frontier". But during the initial decades of the space age, decolonization also gained again in force producing many newly independent countries. These newly independent countries confronted spacefaring countries, demanding an anti-colonial stance and regulation of space activity when space law was raised and negotiated internationally.
Fears of confrontations because of land grabs and an arms race in space between the few countries with spaceflight capabilities grew and were ultimately shared by the spacefaring countries themselves. This produced the wording of the agreed on international space law, starting with the Outer Space Treaty of 1967, calling space a "province of all mankind" and securing provisions for international regulation and sharing of outer space.
The advent of geostationary satellites raised the case of limited space in outer space. A group of equatorial countries, all of which were countries that were once colonies of colonial empires, but without spaceflight capabilities, signed in 1976 the Bogota Declaration. These countries declared that geostationary orbit is a limited natural resource and belongs to the equatorial countries directly below, seeing it not as part of outer space, humanity's common. Through this, the declaration challenged the dominance of geostationary orbit by spacefaring countries through identifying their dominance as imperialistic. Furthermore this dominance in space has foreshadowed threats to the Outer Space Treaty guaranteed accessibility to space, as in the case of space debris which is ever increasing because of a lack of access regulation.In 1977, the first sustained space habitat, the Salyut 6 station, was put into Earth's orbit. Eventually the first space stations were succeeded by the ISS, today's largest human outpost in space and closest to a space settlement.
Built and operated under a multilateral regime, it has become a blueprint for future stations, such as around and possibly on the Moon. An international regime for lunar activity was demanded by the international Moon Treaty, but is currently developed multilaterally as with the Artemis Accords.
The only habitation on a different celestial body so far have been the temporary habitats of the crewed lunar landers.
Conceptual
Early suggestions for future colonizers like Francis Drake and Christoph Columbus to reach the Moon and people consequently living there were made by John Wilkins in A Discourse Concerning a New Planet in the first half of the 17th century.The first known work on space colonization was the 1869 novella The Brick Moon by Edward Everett Hale, about an inhabited artificial satellite. In 1897 Kurd Lasswitz also wrote about space colonies.
The Russian rocket science pioneer Konstantin Tsiolkovsky foresaw elements of the space community in his book Beyond Planet Earth written about 1900. Tsiolkovsky had his space travelers building greenhouses and raising crops in space. Tsiolkovsky believed that going into space would help perfect human beings, leading to immortality and peace.In the 1920s John Desmond Bernal, Hermann Oberth, Guido von Pirquet and Herman Noordung further developed the idea. Wernher von Braun contributed his ideas in a 1952 Colliers article. In the 1950s and 1960s, Dandridge M. Cole published his ideas.
Another seminal book on the subject was the book The High Frontier: Human Colonies in Space by Gerard K. O'Neill in 1977 which was followed the same year by Colonies in Space by T. A. Heppenheimer.Marianne J. Dyson wrote Home on the Moon; Living on a Space Frontier in 2003; Peter Eckart wrote Lunar Base Handbook in 2006 and then Harrison Schmitt's Return to the Moon written in 2007.
Locations
Location is a frequent point of contention between space colonization advocates. The location of colonization can be on a physical body planet, dwarf planet, natural satellite, or asteroid or orbiting one. Colonization of the Solar System has received the most attention.
For settlements not on a body see also space habitat.
Near-Earth space
The Moon
The Moon is discussed as a target for colonization, due to its proximity to Earth and lower escape velocity. Abundant ice is trapped in permanently shadowed craters near the poles, which could provide support for the water needs of a lunar colony, though indications that mercury is also similarly trapped there may pose health concerns. Native precious metals, such as gold, silver, and probably platinum, are also concentrated at the lunar poles by electrostatic dust transport. However, the Moon's lack of atmosphere provides no protection from space radiation or meteoroids, so lunar lava tubes have been proposed sites to gain protection. The Moon's low surface gravity is also a concern, as it is unknown whether 1/6g is enough to maintain human health for long periods. Interest in establishing a moonbase has increased in the 21st century as an intermediate to Mars colonization, with such proposals as the Moon Village for research, mining, and trade facilities with permanent habitation.A number of government space agencies such as Russia (2014), China (2012) and the US have periodically floated lunar plans for constructing the first lunar outpost.
The European Space Agency (ESA) head Jan Woerner has proposed cooperation among countries and companies on lunar capabilities, a concept referred to as Moon Village.In a December 2017 directive, the Trump Administration steered NASA to include a lunar mission on the pathway to other beyond Earth orbit (BEO) destinations.In a May 2018 interview, Blue Origin CEO Jeff Bezos indicated Blue Origin would build and fly the Blue Moon lunar lander on its own, with private funding, but that they would build it a lot faster, and accomplish more, if it were done in a partnership with existing government space agencies. Bezos specifically mentioned the December 2017 NASA direction and the ESA Moon Village concepts.
Lagrange points
Another near-Earth possibility are the stable Earth–Moon Lagrange points L4 and L5, at which point a space colony can float indefinitely. The L5 Society was founded to promote settlement by building space stations at these points. Gerard K. O'Neill suggested in 1974 that the L5 point, in particular, could fit several thousands of floating colonies, and would allow easy travel to and from the colonies due to the shallow effective potential at this point.
The inner planets
Many planets within the Solar System have been considered for colonization and terraforming. The main candidates for colonization in the inner Solar System are Mars and Venus. Other possible candidates for colonization include the Moon and even Mercury.
Mercury
Once thought to be a volatile-depleted body like the Moon, Mercury is now known to be volatile-rich, surprisingly richer in volatiles than any other terrestrial body in the inner Solar System. The planet also receives six and a half times the solar flux as the Earth/Moon system, making solar energy a very effective energy source; it could be harnessed through orbital solar arrays and beamed to the surface or exported to other planets.Geologist Stephen Gillett suggested in 1996 that this could make Mercury an ideal place to build and launch solar sail spacecraft, which could launch as folded-up "chunks" by mass driver from Mercury's surface. Once in space, the solar sails would deploy. Solar energy for the mass driver should be easy to come by, and solar sails near Mercury would have 6.5 times the thrust they do near Earth. This could make Mercury an ideal place to acquire materials useful in building hardware to send to (and terraform) Venus. Vast solar collectors could also be built on or near Mercury to produce power for large-scale engineering activities such as laser-pushed light sails to nearby star systems.As Mercury has essentially no axial tilt, crater floors near its poles lie in eternal darkness, never seeing the Sun. They function as cold traps, trapping volatiles for geological periods. It is estimated that the poles of Mercury contain 1014–1015 kg of water, likely covered by about 5.65×109 m3 of hydrocarbons. This would make agriculture possible. It has been suggested that plant varieties could be developed to take advantage of the high light intensity and the long day of Mercury. The poles do not experience the significant day-night variations the rest of Mercury do, making them the best place on the planet to begin a colony.Another option is to live underground, where day-night variations would be damped enough that temperatures would stay roughly constant. There are indications that Mercury contains lava tubes, like the Moon and Mars, which would be suitable for this purpose. Underground temperatures in a ring around Mercury's poles can even reach room temperature on Earth, 22±1 °C; and this is achieved at a depths starting from only about 0.7 m. This presence of volatiles and abundance of energy has led Alexander Bolonkin and James Shifflett to consider Mercury preferable to Mars for colonization.Yet a third option could be to continually move to stay on the night side, as Mercury's 176-day-long day-night cycle means that the terminator travels very slowly.Because Mercury is very dense, its surface gravity is 0.38g like Mars, even though it is a smaller planet. This would be easier to adjust to than lunar gravity (0.16g), but still present advantages regarding lower escape velocity from the planet. Mercury's proximity gives it advantages over the asteroids and outer planets, and its low synodic period means that launch windows from Earth to Mercury are more frequent than those from Earth to Venus or Mars.On the downside, a Mercury colony would require significant shielding from radiation and solar flares, and since Mercury is airless, decompression and temperature extremes would be constant risks.
Venus
Surface conditions on Venus are extremely hostile to human life: average surface temperature is 464 °C (hot enough to melt lead), and average surface pressure is 92 times Earth's atmospheric pressure – roughly equivalent to a depth of one kilometre under Earth's oceans. (There is some variation; due to its altitude, the peak of Maxwell Montes is at only 380 °C and 45 bar, making it the coolest and least pressurised location on Venus' surface. There are also some hot spots at about 700 °C.) Solar energy is not available at the surface due to the constant cloud cover, and the carbon dioxide atmosphere is poisonous.However, the upper atmosphere of Venus has much more Earthlike conditions and has been suggested as a plausible colonization location since at least 1971 by Soviet scientists. At just over 50 km altitude (the cloud tops), atmospheric pressure is roughly equal to that on Earth's surface, and temperatures range from 0–50 °C. The volatile elements necessary for life are present (hydrogen, carbon, nitrogen, oxygen, and sulfur), and above the clouds, solar energy is abundant. Pressurization would not be required; humans could even go outside the habitats safely with oxygen provision and clothing to protect against the sulfuric acid droplets. Geoffrey Landis has pointed out that breathable air is a lifting gas in Venus' atmosphere: a cubic meter of air would lift half a kilogram, and an oxygen- and nitrogen-filled aerostat the size of a city on Venus would be able to lift the mass of a city. This suggests floating aerostat cities as a colonization method for Venus. The lack of pressure differences between the outside and inside means that there is ample time to repair habitat breaches. With just over three times the land area of Earth, there would be space even for a billion such cities. The atmosphere provides enough radiation shielding at this altitude, and Venus' 0.90g gravity is likely sufficient to prevent the negative health effects of microgravity.A day on Venus is very long on the surface, but the atmosphere rotates much faster than the planet (a phenomenon called superrotation), so a floating habitat would only have a day of about a hundred hours. Landis compares this favorably with polar days and nights on Earth, which are much longer. A floating habitat at higher latitudes on Venus would approach a normal 24-hour cycle. Mining the surface would give access to important industrial metals, and it could be accessed via airplanes, balloons, or fullerene cables meant to withstand high temperatures. To avoid the problem of the habitat being in motion relative to its mining devices, the habitat could descend into the lower atmosphere: this region is hotter, but Landis argues that a large-sized habitat would have enough heat capacity to have no problem with a short stay at higher temperatures.The colonization of Venus has been a subject of many works of science fiction since before the dawn of spaceflight and is still discussed from both a fictional and a scientific standpoint. Proposals for Venus are focused on colonies floating in the upper-middle atmosphere and on terraforming.
Mars
The hypothetical colonization of Mars has received interest from public space agencies and private corporations and has received extensive treatment in science fiction writing, film, and art. The most recent commitments to researching permanent settlement include those by public space agencies—NASA, ESA, Roscosmos, ISRO, and the CNSA—and private organizations—SpaceX, Lockheed Martin, and Boeing.
Asteroid belt
The asteroid belt has significant overall material available, but it is thinly distributed as it covers a vast region of space. The largest asteroid is Ceres, which at about 940 km in diameter is big enough to be a dwarf planet. The next two largest are Pallas and Vesta, both about 520 km in diameter. Uncrewed supply craft should be practical with little technological advance, even crossing 500 million kilometers of space. The colonists would have a strong interest in assuring their asteroid did not hit Earth or any other body of significant mass, but would have extreme difficulty in moving an asteroid of any size. The orbits of the Earth and most asteroids are very distant from each other in terms of delta-v and the asteroidal bodies have enormous momentum. Rockets or mass drivers can perhaps be installed on asteroids to direct their path into a safe course.
Ceres has readily available water, ammonia, and methane, important for survival, fuel, and possibly terraforming of Mars and Venus. The colony could be established on a surface crater or underground. However, even Ceres only manages a tiny surface gravity of 0.03g, which is not enough to stave off the negative effects of microgravity (though it does make transportation to and from Ceres easier). Either medical treatments or artificial gravity would thus be required. Additionally, colonizing the main asteroid belt would likely require infrastructure to already be present on the Moon and Mars.Some have suggested that Ceres could act as a main base or hub for asteroid mining. However, Geoffrey A. Landis has pointed out that the asteroid belt is a poor place for an asteroid-mining base if more than one asteroid is to be exploited: the asteroids are not close to each other, and two asteroids chosen at random are quite likely to be on opposite sides from the Sun from each other. He suggests that it would be better to construct such a base on an inner planet, such as Venus: inner planets have higher orbital velocities, making the transfer time to any specific asteroid shorter, and orbit the Sun faster, so that the launch windows to the asteroid are more frequent (a lower synodic period). Thus Venus is closer to the asteroids than Earth or Mars in terms of flight time. Transfer times for the journeys Venus–Ceres and Venus–Vesta are only 1.15 and 0.95 years respectively along minimum-energy trajectories, which is shorter even than Earth–Ceres and Earth–Vesta at 1.29 and 1.08 years respectively.
Moons of outer planets
Human missions to the outer planets would need to arrive quickly due to the effects of space radiation and microgravity along the journey. In 2012, Thomas B. Kerwick wrote that the distance to the outer planets made their human exploration impractical for now, noting that travel times for round trips to Mars were estimated at two years, and that the closest approach of Jupiter to Earth is over ten times farther than the closest approach of Mars to Earth. However, he noted that this could change with "significant advancement on spacecraft design". Nuclear-thermal or nuclear-electric engines have been suggested as a way to make the journey to Jupiter in a reasonable amount of time. The cold would also be a factor, necessitating a robust source of heat energy for spacesuits and bases. Most of the larger moons of the outer planets contain water ice, liquid water, and organic compounds that might be useful for sustaining human life.Robert Zubrin has suggested Saturn, Uranus, and Neptune as advantageous locations for colonization because their atmospheres are good sources of fusion fuels, such as deuterium and helium-3. Zubrin suggested that Saturn would be the most important and valuable as it is the closest and has an excellent satellite system. Jupiter's high gravity makes it difficult to extract gases from its atmosphere, and its strong radiation belt makes developing its system difficult. On the other hand, fusion power has yet to be achieved, and fusion power from helium-3 is more difficult to achieve than conventional deuterium–tritium fusion. Jeffrey Van Cleve, Carl Grillmair, and Mark Hanna instead focus on Uranus, because the delta-v required to get helium-3 from the atmosphere into orbit is half that needed for Jupiter, and because Uranus' atmosphere is five times richer in helium than Saturn's.Jupiter's Galilean moons (Io, Europa, Ganymede, and Callisto) and Saturn's Titan are the only moons that have gravities comparable to Earth's Moon. The Moon has a 0.17g gravity; Io, 0.18g; Europa, 0.13g; Ganymede, 0.15g; Callisto, 0.13g; and Titan, 0.14g. Neptune's Triton has about half the Moon's gravity (0.08g); other round moons provide even less (starting from Uranus' Titania and Oberon at about 0.04g).
Jovian moons
The Jovian system in general has particular disadvantages for colonization, including a deep gravity well. The magnetosphere of Jupiter bombards the moons of Jupiter with intense ionizing radiation delivering about 36 Sv per day to unshielded colonists on Io and about 5.40 Sv per day on Europa. Exposure to about 0.75 Sv over a few days is enough to cause radiation poisoning, and about 5 Sv over a few days is fatal.Jupiter itself, like the other gas giants, has further disadvantages. There is no accessible surface on which to land, and the light hydrogen atmosphere would not provide good buoyancy for some kind of aerial habitat as has been proposed for Venus.
Radiation levels on Io and Europa are extreme, enough to kill unshielded humans within an Earth day. Therefore, only Callisto and perhaps Ganymede could reasonably support a human colony. Callisto orbits outside Jupiter's radiation belt. Ganymede's low latitudes are partially shielded by the moon's magnetic field, though not enough to completely remove the need for radiation shielding. Both of them have available water, silicate rock, and metals that could be mined and used for construction.Although Io's volcanism and tidal heating constitute valuable resources, exploiting them is probably impractical. Europa is rich in water (its subsurface ocean is expected to contain over twice as much water as all Earth's oceans together) and likely oxygen, but metals and minerals would have to be imported. If alien microbial life exists on Europa, human immune systems may not protect against it. Sufficient radiation shielding might, however, make Europa an interesting location for a research base. The private Artemis Project drafted a plan in 1997 to colonize Europa, involving surface igloos as bases to drill down into the ice and explore the ocean underneath, and suggesting that humans could live in "air pockets" in the ice layer. Ganymede and Callisto are also expected to have internal oceans. It might be possible to build a surface base that would produce fuel for further exploration of the Solar System.
In 2003, NASA performed a study called HOPE (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the Solar System. The target chosen was Callisto due to its distance from Jupiter, and thus the planet's harmful radiation. It could be possible to build a surface base that would produce fuel for further exploration of the Solar System. HOPE estimated a round trip time for a crewed mission of about 2–5 years, assuming significant progress in propulsion technologies.Io is not ideal for colonization, due to its hostile environment. The moon is under influence of high tidal forces, causing high volcanic activity. Jupiter's strong radiation belt overshadows Io, delivering 36 Sv a day to the moon. The moon is also extremely dry. Io is the least ideal place for the colonization of the four Galilean moons.
Despite this, its volcanoes could be energy resources for the other moons, which are better suited to colonization.
The Artemis Project proposed a plan to colonize Europa. Scientists would inhabit igloos and drill down into the Europan ice crust, exploring any subsurface ocean. The report also discusses the use of air pockets for human habitation.
Ganymede is the largest moon in the Solar System. Ganymede is the only moon with a magnetosphere, albeit overshadowed by Jupiter's magnetic field. Because of this magnetic field, Ganymede is one of only two Jovian moons where surface settlements would be feasible because it receives about 0.08 Sv of radiation per day. Ganymede could be terraformed.The Keck Observatory announced in 2006 that the binary Jupiter trojan 617 Patroclus, and possibly many other Jupiter trojans, are likely composed of water ice, with a layer of dust. This suggests that mining water and other volatiles in this region and transporting them elsewhere in the Solar System, perhaps via the proposed Interplanetary Transport Network, may be feasible in the not-so-distant future. This could make colonization of the Moon, Mercury and main-belt asteroids more practical.
Saturnian moons
Saturn has seven moons large enough to be round: in order of increasing distance from Saturn, they are Mimas, Enceladus, Tethys, Dione, Rhea, Titan, and Iapetus. Titan is the largest and the only one with a Moon-like gravity: it is the only moon in the Solar System to have a dense atmosphere and is rich in carbon-bearing compounds, suggesting it as a colonization target. Titan has water ice and large methane oceans. Robert Zubrin identified Titan as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization.The small moon Enceladus is also of interest, having a subsurface ocean that is separated from the surface by only tens of meters of ice at the south pole, compared to kilometers of ice separating the ocean from the surface on Europa. Volatile and organic compounds are present there, and the moon's high density for an ice world (1.6 g/cm3) indicates that its core is rich in silicates.Saturn's radiation belt is much weaker than Jupiter's, so radiation is less of an issue here. Dione, Rhea, Titan, and Iapetus all orbit outside the radiation belt, and Titan's thick atmosphere would adequately shield against cosmic radiation.Robert Zubrin identified Saturn, Uranus and Neptune as "the Persian Gulf of the Solar System", as the largest sources of deuterium and helium-3 to drive a fusion economy, with Saturn the most important and most valuable of the three, because of its relative proximity, low radiation, and large system of moons. On the other hand, planetary scientist John Lewis in his 1997 book Mining the Sky, insists that Uranus is the likeliest place to mine helium-3 because of its significantly shallower gravity well, which makes it easier for a laden tanker spacecraft to thrust itself out. Furthermore, Uranus is an Ice giant, which would likely make it easier to separate the helium out of the atmosphere.
Zubrin identified Titan as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization. He said, "In certain ways, Titan is the most hospitable extraterrestrial world within the Solar System for human colonization." A widely published expert on terraforming, Christopher McKay, is also a co-investigator on the Huygens probe that landed on Titan in January 2005.
The surface of Titan is mostly uncratered and thus inferred to be very young and active, and probably composed of mostly water ice, and lakes of liquid hydrocarbons (methane/ethane) in its polar regions. While the temperature is cryogenic (95 K) it should be able to support a base, but more information regarding Titan's surface and the activities on it is necessary. The thick atmosphere and the weather, such as potential flash floods, are also factors to consider.
On 9 March 2006, NASA's Cassini space probe found possible evidence of liquid water on Enceladus. According to that article, "pockets of liquid water may be no more than tens of meters below the surface." These findings were confirmed in 2014 by NASA. This means liquid water could be collected much more easily and safely on Enceladus than, for instance, on Europa (see above). Discovery of water, especially liquid water, generally makes a celestial body a much more likely candidate for colonization. An alternative model of Enceladus's activity is the decomposition of methane/water clathrates – a process requiring lower temperatures than liquid water eruptions. The higher density of Enceladus indicates a larger than Saturnian average silicate core that could provide materials for base operations.
Trans-Neptunian region
Freeman Dyson suggested that within a few centuries human civilization will have relocated to the Kuiper belt. Several hundred billion to trillion comet-like ice-rich bodies exist outside the orbit of Neptune, in the Kuiper belt and Inner and Outer Oort cloud. These may contain all the ingredients for life (water ice, ammonia, and carbon-rich compounds), including significant amounts of deuterium and helium-3. Since Dyson's proposal, the number of trans-Neptunian objects known has increased greatly.
Colonists could live in the dwarf planet's icy crust or mantle, using fusion or geothermal heat[citation needed] and mining the soft-ice or liquid inner ocean for volatiles and minerals. Given the light gravity and resulting lower pressure in the ice mantle or inner ocean, colonizing the rocky core's outer surface might give colonists the largest number of mineral and volatile resources as well as insulating them from cold.[citation needed] Surface habitats or domes are another possibility, as background radiation levels are likely to be low.
Orbit around gas giants
There have also been proposals to place robotic aerostats in the upper atmospheres of the Solar System's gas giant planets for exploration and possibly mining of helium-3, which could have a very high value per unit mass as a thermonuclear fuel.Because Uranus has the lowest escape velocity of the four gas giants, it has been proposed as a mining site for helium-3. If human supervision of the robotic activity proved necessary, one of Uranus's natural satellites might serve as a base.
It is hypothesized that one of Neptune's satellites could be used for colonization. Triton's surface shows signs of extensive geological activity that implies a subsurface ocean, perhaps composed of ammonia/water. If technology advanced to the point that tapping such geothermal energy was possible, it could make colonizing a cryogenic world like Triton feasible, supplemented by nuclear fusion power.
Beyond the Solar System
Looking beyond the Solar System, there are up to several hundred billion potential stars with possible colonization targets. The main difficulty is the vast distances to other stars: roughly a hundred thousand times farther away than the planets in the Solar System. This means that some combination of very high speed (some more-than-fractional percentage of the speed of light), or travel times lasting centuries or millennia, would be required. These speeds are far beyond what current spacecraft propulsion systems can provide.
Space colonization technology could in principle allow human expansion at high, but sub-relativistic speeds, substantially less than the speed of light, c. An interstellar colony ship would be similar to a space habitat, with the addition of major propulsion capabilities and independent energy generation.
Hypothetical starship concepts proposed both by scientists and in hard science fiction include:
A generation ship would travel much slower than light, with consequent interstellar trip times of many decades or centuries. The crew would go through generations before the journey was complete, so none of the initial crew would be expected to survive to arrive at the destination, assuming current human lifespans.
A sleeper ship, where most or all of the crew spend the journey in some form of hibernation or suspended animation, allowing some or all to reach the destination.
An embryo-carrying interstellar starship (EIS), much smaller than a generation ship or sleeper ship, transporting human embryos or DNA in a frozen or dormant state to the destination. (Obvious biological and psychological problems in birthing, raising, and educating such voyagers, neglected here, may not be fundamental.)
A nuclear fusion or fission powered ship (e.g. ion drive) of some kind, achieving velocities of up to perhaps 10% c permitting one-way trips to nearby stars with durations comparable to a human lifetime.
A Project Orion-ship, a nuclear-powered concept proposed by Freeman Dyson which would use nuclear explosions to propel a starship. A special case of the preceding nuclear rocket concepts, with similar potential velocity capability, but possibly easier technology.
Laser propulsion concepts, using some form of beaming of power from the Solar System might allow a light-sail or other ship to reach high speeds, comparable to those theoretically attainable by the fusion-powered electric rocket, above. These methods would need some means, such as supplementary nuclear propulsion, to stop at the destination, but a hybrid (light-sail for acceleration, fusion-electric for deceleration) system might be possible.
Uploaded human minds or artificial intelligence may be transmitted via radio or laser at light speed to interstellar destinations where self-replicating spacecraft have traveled subluminally and set up infrastructure and possibly also brought some minds. Extraterrestrial intelligence might be another viable destination.The above concepts appear limited to high, but still sub-relativistic speeds, due to fundamental energy and reaction mass considerations, and all would entail trip times which might be enabled by space colonization technology, permitting self-contained habitats with lifetimes of decades to centuries. Yet human interstellar expansion at average speeds of even 0.1% of c would permit settlement of the entire Galaxy in less than one-half of the Sun's galactic orbital period of ~240,000,000 years, which is comparable to the timescale of other galactic processes. Thus, even if interstellar travel at near relativistic speeds is never feasible (which cannot be determined at this time), the development of space colonization could allow human expansion beyond the Solar System without requiring technological advances that cannot yet be reasonably foreseen. This could greatly improve the chances for the survival of intelligent life over cosmic timescales, given the many natural and human-related hazards that have been widely noted.
If humanity does gain access to a large amount of energy, on the order of the mass-energy of entire planets, it may eventually become feasible to construct Alcubierre drives. These are one of the few methods of superluminal travel which may be possible under current physics. However, it is probable that such a device could never exist, due to the fundamental challenges posed. For more on this see Difficulties of making and using an Alcubierre Drive.
Intergalactic travel
The distances between galaxies are on the order of a million times farther than those between the stars, and thus intergalactic colonization would involve voyages of millions of years via special self-sustaining methods.
Law, governance, and sovereignty
Space activity is legally based on the Outer Space Treaty, the main international treaty. But space law has become a larger legal field, which includes other international agreements such as the significantly less ratified Moon Treaty and diverse national laws.
The Outer Space Treaty established the basic ramifications for space activity in article one:"The exploration and use of outer space, including the Moon and other celestial bodies, shall be carried out for the benefit and in the interests of all countries, irrespective of their degree of economic or scientific development, and shall be the province of all mankind."
And continued in article two by stating:"Outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means."The development of international space law has revolved much around outer space being defined as common heritage of mankind. The Magna Carta of Space presented by William A. Hyman in 1966 framed outer space explicitly not as terra nullius but as res communis, which subsequently influenced the work of the United Nations Committee on the Peaceful Uses of Outer Space.
Reasons
Survival of human civilization
A primary argument calling for space colonization is the long-term survival of human civilization and terrestrial life. By developing alternative locations off Earth, the planet's species, including humans, could live on in the event of natural or human-made disasters on our own planet.On two occasions, theoretical physicist and cosmologist Stephen Hawking argued for space colonization as a means of saving humanity. In 2001, Hawking predicted that the human race would become extinct within the next thousand years unless colonies could be established in space. In 2010, he stated that humanity faces two options: either we colonize space within the next two hundred years, or we will face the long-term prospect of extinction.In 2005, then NASA Administrator Michael Griffin identified space colonization as the ultimate goal of current spaceflight programs, saying:
... the goal isn't just scientific exploration ... it's also about extending the range of human habitat out from Earth into the solar system as we go forward in time ... In the long run, a single-planet species will not survive ... If we humans want to survive for hundreds of thousands of millions of years, we must ultimately populate other planets. Now, today the technology is such that this is barely conceivable. We're in the infancy of it. ... I'm talking about that one day, I don't know when that day is, but there will be more human beings who live off the Earth than on it. We may well have people living on the Moon. We may have people living on the moons of Jupiter and other planets. We may have people making habitats on asteroids ... I know that humans will colonize the solar system and one day go beyond.
Louis J. Halle, formerly of the United States Department of State, wrote in Foreign Affairs (Summer 1980) that the colonization of space will protect humanity in the event of global nuclear warfare. The physicist Paul Davies also supports the view that if a planetary catastrophe threatens the survival of the human species on Earth, a self-sufficient colony could "reverse-colonize" Earth and restore human civilization. The author and journalist William E. Burrows and the biochemist Robert Shapiro proposed a private project, the Alliance to Rescue Civilization, with the goal of establishing an off-Earth "backup" of human civilization.Based on his Copernican principle, J. Richard Gott has estimated that the human race could survive for another 7.8 million years, but it is not likely to ever colonize other planets. However, he expressed a hope to be proven wrong, because "colonizing other worlds is our best chance to hedge our bets and improve the survival prospects of our species".In a theoretical study from 2019, a group of researchers have pondered the long-term trajectory of human civilization. It is argued that due to Earth's finitude as well as the limited duration of the Solar System, mankind's survival into the far future will very likely require extensive space colonization.: 8, 22f This 'astronomical trajectory' of mankind, as it is termed, could come about in four steps: First step, plenty of space colonies could be established at various habitable locations — be it in outer space or on celestial bodies away from Earth – and allowed to remain dependent on support from Earth for a start. In the second step, these colonies could gradually become self-sufficient, enabling them to survive if or when the mother civilization on Earth fails or dies. Third step, the colonies could develop and expand their habitation by themselves on their space stations or celestial bodies, for example via terraforming. In the fourth step, the colonies could self-replicate and establish new colonies further into space, a process that could then repeat itself and continue at an exponential rate throughout the cosmos. However, this astronomical trajectory may not be a lasting one, as it will most likely be interrupted and eventually decline due to resource depletion or straining competition between various human factions, bringing about some 'star wars' scenario.: 23–25
Vast resources in space
Resources in space, both in materials and energy, are enormous. The Solar System alone has, according to different estimates, enough material and energy to support anywhere from several thousand to over a billion times that of the current Earth-based human population, mostly from the Sun itself.Asteroid mining will also be a key player in space colonization. Water and materials to make structures and shielding can be easily found in asteroids. Instead of resupplying on Earth, mining and fuel stations need to be established on asteroids to facilitate better space travel. Optical mining is the term NASA uses to describe extracting materials from asteroids. NASA believes by using propellant derived from asteroids for exploration to the moon, Mars, and beyond will save $100 billion. If funding and technology come sooner than estimated, asteroid mining might be possible within a decade.Although some items of the infrastructure requirements above can already be easily produced on Earth and would therefore not be very valuable as trade items (oxygen, water, base metal ores, silicates, etc.), other high-value items are more abundant, more easily produced, of higher quality, or can only be produced in space. These would provide (over the long-term) a very high return on the initial investment in space infrastructure.Some of these high-value trade goods include precious metals, gemstones, power, solar cells, ball bearings, semi-conductors, and pharmaceuticals.The mining and extraction of metals from a small asteroid the size of 3554 Amun or (6178) 1986 DA, both small near-Earth asteroids, would be 30 times as much metal as humans have mined throughout history. A metal asteroid this size would be worth approximately US$20 trillion at 2001 market pricesThe main impediments to commercial exploitation of these resources are the very high cost of initial investment, the very long period required for the expected return on those investments (The Eros Project plans a 50-year development), and the fact that the venture has never been carried out before—the high-risk nature of the investment.
Expansion with fewer negative consequences
Expansion of humans and technological progress has usually resulted in some form of environmental devastation, and destruction of ecosystems and their accompanying wildlife. In the past, expansion has often come at the expense of displacing many indigenous peoples, the resulting treatment of these peoples ranging anywhere from encroachment to genocide. Because space has no known life, this need not be a consequence, as some space settlement advocates have pointed out. However, on some bodies of the Solar System, there is the potential for extant native lifeforms and so the negative consequences of space colonization cannot be dismissed.Counterarguments state that changing only the location but not the logic of exploitation will not create a more sustainable future.
Alleviating overpopulation and resource demand
An argument for space colonization is to mitigate proposed impacts of overpopulation of Earth, such as resource depletion. If the resources of space were opened to use and viable life-supporting habitats were built, Earth would no longer define the limitations of growth. Although many of Earth's resources are non-renewable, off-planet colonies could satisfy the majority of the planet's resource requirements. With the availability of extraterrestrial resources, demand on terrestrial ones would decline. Proponents of this idea include Stephen Hawking and Gerard K. O'Neill.Others including cosmologist Carl Sagan and science fiction writers Arthur C. Clarke, and Isaac Asimov, have argued that shipping any excess population into space is not a viable solution to human overpopulation. According to Clarke, "the population battle must be fought or won here on Earth". The problem for these authors is not the lack of resources in space (as shown in books such as Mining the Sky), but the physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth.
Other arguments
Advocates for space colonization cite a presumed innate human drive to explore and discover, and call it a quality at the core of progress and thriving civilizations.Nick Bostrom has argued that from a utilitarian perspective, space colonization should be a chief goal as it would enable a very large population to live for a very long period of time (possibly billions of years), which would produce an enormous amount of utility (or happiness). He claims that it is more important to reduce existential risks to increase the probability of eventual colonization than to accelerate technological development so that space colonization could happen sooner. In his paper, he assumes that the created lives will have positive ethical value despite the problem of suffering.
In a 2001 interview with Freeman Dyson, J. Richard Gott and Sid Goldstein, they were asked for reasons why some humans should live in space. Their answers were:
Spread life and beauty throughout the universe
Ensure the survival of our species
Make money through new forms of space commercialization such as solar-power satellites, asteroid mining, and space manufacturing
Save the environment of Earth by moving people and industry into spaceBiotic ethics is a branch of ethics that values life itself. For biotic ethics, and their extension to space as panbiotic ethics, it is a human purpose to secure and propagate life and to use space to maximize life.
Difficulties
There would be many problems in colonizing the outer Solar System. These include:
Distance from Earth: The outer planets are much farther from Earth than the inner planets, and would therefore be harder and more time-consuming to reach. In addition, return voyages may well be prohibitive considering the time and distance.
Extreme cold: temperatures are near absolute zero in many parts of the outer Solar System.
Power: Solar power is many times less concentrated in the outer Solar System than in the inner Solar System. It is unclear as to whether it would be usable there, using some form of concentration mirrors, or whether nuclear power would be necessary. There have also been proposals to use the gravitational potential energy of planets or dwarf planets with moons.
Effects of low gravity on the human body: All moons of the gas giants and all outer dwarf planets have a very low gravity, the highest being Io's gravity (0.183 g) which is less than 1/5 of the Earth's gravity. Since the Apollo program all crewed spaceflight has been constrained to Low Earth orbit and there has been no opportunity to test the effects of such low gravitational accelerations on the human body. It is speculated that the low gravity environments might have very similar effects to long-term exposure in weightlessness. Such effects can be avoided by rotating spacecraft creating artificial gravity.
Criticisms
Space colonization has been seen as a relief to the problem of human overpopulation as early as 1758, and listed as one of Stephen Hawking's reasons for pursuing space exploration. Critics note, however, that a slowdown in population growth rates since the 1980s has alleviated the risk of overpopulation.Critics also argue that the costs of commercial activity in space are too high to be profitable against Earth-based industries, and hence that it is unlikely to see significant exploitation of space resources in the foreseeable future.Other objections include concerns that the forthcoming colonization and commodification of the cosmos is likely to enhance the interests of the already powerful, including major economic and military institutions e.g. the large financial institutions, the major aerospace companies and the military–industrial complex, to lead to new wars, and to exacerbate pre-existing exploitation of workers and resources, economic inequality, poverty, social division and marginalization, environmental degradation, and other detrimental processes or institutions.Additional concerns include creating a culture in which humans are no longer seen as human, but rather as material assets. The issues of human dignity, morality, philosophy, culture, bioethics, and the threat of megalomaniac leaders in these new "societies" would all have to be addressed in order for space colonization to meet the psychological and social needs of people living in isolated colonies.As an alternative or addendum for the future of the human race, many science fiction writers have focused on the realm of the 'inner-space', that is the computer-aided exploration of the human mind and human consciousness—possibly en route developmentally to a Matrioshka Brain.Robotic spacecraft are proposed as an alternative to gain many of the same scientific advantages without the limited mission duration and high cost of life support and return transportation involved in human missions.A corollary to the Fermi paradox—"nobody else is doing it"—is the argument that, because no evidence of alien colonization technology exists, it is statistically unlikely to even be possible to use that same level of technology ourselves.
Colonialism
Space colonization has been discussed as postcolonial continuation of imperialism and colonialism, calling for decolonization instead of colonization. Critics argue that the present politico-legal regimes and their philosophic grounding advantage imperialist development of space and that key decisionmakers in space colonization are often wealthy elites affiliated with private corporations, and that space colonization would primarily appeal to their peers rather than ordinary citizens. Furthermore, it is argued that there is a need for inclusive and democratic participation and implementation of any space exploration, infrastructure or habitation. According to space law expert Michael Dodge, existing space law, such as the Outer Space Treaty, guarantees access to space, but does not enforce social inclusiveness or regulate non-state actors.Particularly the narrative of the "New Frontier" has been criticized as unreflected continuation of settler colonialism and manifest destiny, continuing the narrative of exploration as fundamental to the assumed human nature. Joon Yun considers space colonization as a solution to human survival and global problems like pollution to be imperialist; others have identified space as a new sacrifice zone of colonialism.Natalie B. Trevino argues that not colonialism but coloniality will be carried into space if not reflected on.More specifically the advocacy for territorial colonization of Mars opposed to habitation in the atmospheric space of Venus has been called surfacism, a concept similar to Thomas Golds surface chauvinism.
More generally space infrastructure such as the Mauna Kea Observatories have also been criticized and protested against as being colonialist. Guiana Space Centre has also been the site of anti-colonial protests, connecting colonization as an issue on Earth and in space.In regard to the scenario of extraterrestrial first contact it has been argued that being used to employ colonial language would endanger such first impressions and encounters.Furthermore spaceflight as a whole and space law more particularly has been criticized as a postcolonial project by being built on a colonial legacy and by not facilitating the sharing of access to space and its benefits, too often allowing spaceflight to be used to sustain colonialism and imperialism, most of all on Earth instead.
Planetary protection
Robotic spacecraft to Mars are required to be sterilized, to have at most 300,000 spores on the exterior of the craft—and more thoroughly sterilized if they contact "special regions" containing water, or it could contaminate life-detection experiments or the planet itself.It is impossible to sterilize human missions to this level, as humans are host to typically a hundred trillion microorganisms of thousands of species of the human microbiome, and these cannot be removed while preserving the life of the human. Containment seems the only option, but it is a major challenge in the event of a hard landing (i.e. crash). There have been several planetary workshops on this issue, but with no final guidelines for a way forward yet. Human explorers could also inadvertently contaminate Earth if they return to the planet while carrying extraterrestrial microorganisms.
Physical, mental and emotional health risks to colonizers
The health of the humans who may participate in a colonization venture would be subject to increased physical, mental and emotional risks. NASA learned that – without gravity – bones lose minerals, causing osteoporosis. Bone density may decrease by 1% per month, which may lead to a greater risk of osteoporosis-related fractures later in life. Fluid shifts towards to the head may cause vision problems. NASA found that isolation in closed environments aboard the International Space Station led to depression, sleep disorders, and diminished personal interactions, likely due to confined spaces and the monotony and boredom of long space flight. Circadian rhythm may also be susceptible to the effects of space life due to the effects on sleep of disrupted timing of sunset and sunrise. This can lead to exhaustion, as well as other sleep problems such as insomnia, which can reduce their productivity and lead to mental health disorders. High-energy radiation is a health risk that colonizers would face, as radiation in deep space is deadlier than what astronauts face now in low Earth orbit. Metal shielding on space vehicles protects against only 25-30% of space radiation, possibly leaving colonizers exposed to the other 70% of radiation and its short and long-term health complications.
Implementation
Building colonies in space would require access to water, food, space, people, construction materials, energy, transportation, communications, life support, simulated gravity, radiation protection and capital investment. It is likely the colonies would be located near the necessary physical resources. The practice of space architecture seeks to transform spaceflight from a heroic test of human endurance to a normality within the bounds of comfortable experience. As is true of other frontier-opening endeavors, the capital investment necessary for space colonization would probably come from governments, an argument made by John Hickman and Neil deGrasse Tyson.
Life support
In space settlements, a life support system must recycle or import all the nutrients without "crashing." The closest terrestrial analogue to space life support is possibly that of a nuclear submarine. Nuclear submarines use mechanical life support systems to support humans for months without surfacing, and this same basic technology could presumably be employed for space use. However, nuclear submarines run "open loop"—extracting oxygen from seawater, and typically dumping carbon dioxide overboard, although they recycle existing oxygen. Another commonly proposed life-support system is a closed ecological system such as Biosphere 2.
Solutions to health risks
Although there are many physical, mental, and emotional health risks for future colonizers and pioneers, solutions have been proposed to correct these problems. Mars500, HI-SEAS, and SMART-OP represent efforts to help reduce the effects of loneliness and confinement for long periods of time. Keeping contact with family members, celebrating holidays, and maintaining cultural identities all had an impact on minimizing the deterioration of mental health. There are also health tools in development to help astronauts reduce anxiety, as well as helpful tips to reduce the spread of germs and bacteria in a closed environment. Radiation risk may be reduced for astronauts by frequent monitoring and focusing work away from the shielding on the shuttle. Future space agencies can also ensure that every colonizer would have a mandatory amount of daily exercise to prevent degradation of muscle.
Radiation protection
Cosmic rays and solar flares create a lethal radiation environment in space. In Earth orbit, the Van Allen belts make living above the Earth's atmosphere difficult. To protect life, settlements must be surrounded by sufficient mass to absorb most incoming radiation, unless magnetic or plasma radiation shields were developed.Passive mass shielding of four metric tons per square meter of surface area will reduce radiation dosage to several mSv or less annually, well below the rate of some populated high natural background areas on Earth. This can be leftover material (slag) from processing lunar soil and asteroids into oxygen, metals, and other useful materials. However, it represents a significant obstacle to manoeuvring vessels with such massive bulk (mobile spacecraft being particularly likely to use less massive active shielding). Inertia would necessitate powerful thrusters to start or stop rotation, or electric motors to spin two massive portions of a vessel in opposite senses. Shielding material can be stationary around a rotating interior.
Psychological adjustment
The monotony and loneliness that comes from a prolonged space mission can leave astronauts susceptible to cabin fever or having a psychotic break. Moreover, lack of sleep, fatigue, and work overload can affect an astronaut's ability to perform well in an environment such as space where every action is critical.
Economics
Space colonization can roughly be said to be possible when the necessary methods of space colonization become cheap enough (such as space access by cheaper launch systems) to meet the cumulative funds that have been gathered for the purpose, in addition to estimated profits from commercial use of space.Although there are no immediate prospects for the large amounts of money required for space colonization to be available given traditional launch costs, there is some prospect of a radical reduction to launch costs in the 2010s, which would consequently lessen the cost of any efforts in that direction. With a published price of US$56.5 million per launch of up to 13,150 kg (28,990 lb) payload to low Earth orbit, SpaceX Falcon 9 rockets are already the "cheapest in the industry". Advancements currently being developed as part of the SpaceX reusable launch system development program to enable reusable Falcon 9s "could drop the price by an order of magnitude, sparking more space-based enterprise, which in turn would drop the cost of access to space still further through economies of scale." If SpaceX is successful in developing the reusable technology, it would be expected to "have a major impact on the cost of access to space", and change the increasingly competitive market in space launch services.The President's Commission on Implementation of United States Space Exploration Policy suggested that an inducement prize should be established, perhaps by government, for the achievement of space colonization, for example by offering the prize to the first organization to place humans on the Moon and sustain them for a fixed period before they return to Earth.
Money and currency
Experts have debated on the possible usage of money and currencies in societies that will be established in space. The Quasi Universal Intergalactic Denomination, or QUID, is a physical currency made from a space-qualified polymer PTFE for inter-planetary travelers. QUID was designed for the foreign exchange company Travelex by scientists from Britain's National Space Centre and the University of Leicester.Other possibilities include the incorporation of cryptocurrency as the primary form of currency, as suggested by Elon Musk.
Resources
Colonies on the Moon, Mars, asteroids, or the metal-rich planet Mercury, could extract local materials. The Moon is deficient in volatiles such as argon, helium and compounds of carbon, hydrogen and nitrogen. The LCROSS impacter was targeted at the Cabeus crater which was chosen as having a high concentration of water for the Moon. A plume of material erupted in which some water was detected. Mission chief scientist Anthony Colaprete estimated that the Cabeus crater contains material with 1% water or possibly more. Water ice should also be in other permanently shadowed craters near the lunar poles. Although helium is present only in low concentrations on the Moon, where it is deposited into regolith by the solar wind, an estimated million tons of He-3 exists over all. It also has industrially significant oxygen, silicon, and metals such as iron, aluminum, and titanium.
Launching materials from Earth is expensive, so bulk materials for colonies could come from the Moon, a near-Earth object (NEO), Phobos, or Deimos. The benefits of using such sources include: a lower gravitational force, no atmospheric drag on cargo vessels, and no biosphere to damage. Many NEOs contain substantial amounts of metals. Underneath a drier outer crust (much like oil shale), some other NEOs are inactive comets which include billions of tons of water ice and kerogen hydrocarbons, as well as some nitrogen compounds.Farther out, Jupiter's Trojan asteroids are thought to be rich in water ice and other volatiles.Recycling of some raw materials would almost certainly be necessary.
Energy
Solar energy in orbit is abundant, reliable, and is commonly used to power satellites today. There is no night in free space, and no clouds or atmosphere to block sunlight. Light intensity obeys an inverse-square law. So the solar energy available at distance d from the Sun is E = 1367/d2 W/m2, where d is measured in astronomical units (AU) and 1367 watts/m2 is the energy available at the distance of Earth's orbit from the Sun, 1 AU.In the weightlessness and vacuum of space, high temperatures for industrial processes can easily be achieved in solar ovens with huge parabolic reflectors made of metallic foil with very lightweight support structures. Flat mirrors to reflect sunlight around radiation shields into living areas (to avoid line-of-sight access for cosmic rays, or to make the Sun's image appear to move across their "sky") or onto crops are even lighter and easier to build.
Large solar power photovoltaic cell arrays or thermal power plants would be needed to meet the electrical power needs of the settlers' use. In developed parts of Earth, electrical consumption can average 1 kilowatt/person (or roughly 10 megawatt-hours per person per year.) These power plants could be at a short distance from the main structures if wires are used to transmit the power, or much farther away with wireless power transmission.
A major export of the initial space settlement designs was anticipated to be large solar power satellites (SPS) that would use wireless power transmission (phase-locked microwave beams or lasers emitting wavelengths that special solar cells convert with high efficiency) to send power to locations on Earth, or to colonies on the Moon or other locations in space. For locations on Earth, this method of getting power is extremely benign, with zero emissions and far less ground area required per watt than for conventional solar panels. Once these satellites are primarily built from lunar or asteroid-derived materials, the price of SPS electricity could be lower than energy from fossil fuel or nuclear energy; replacing these would have significant benefits such as the elimination of greenhouse gases and nuclear waste from electricity generation.Transmitting solar energy wirelessly from the Earth to the Moon and back is also an idea proposed for the benefit of space colonization and energy resources. Physicist Dr. David Criswell, who worked for NASA during the Apollo missions, came up with the idea of using power beams to transfer energy from space. These beams, microwaves with a wavelength of about 12 cm, will be almost untouched as they travel through the atmosphere. They can also be aimed at more industrial areas to keep away from humans or animal activities. This will allow for safer and more reliable methods of transferring solar energy.
In 2008, scientists were able to send a 20 watt microwave signal from a mountain in Maui to the island of Hawaii. Since then JAXA and Mitsubishi has teamed up on a $21 billion project in order to place satellites in orbit which could generate up to 1 gigawatt of energy. These are the next advancements being done today in order to make energy be transmitted wirelessly for space-based solar energy.
However, the value of SPS power delivered wirelessly to other locations in space will typically be far higher than to Earth. Otherwise, the means of generating the power would need to be included with these projects and pay the heavy penalty of Earth launch costs. Therefore, other than proposed demonstration projects for power delivered to Earth, the first priority for SPS electricity is likely to be locations in space, such as communications satellites, fuel depots or "orbital tugboat" boosters transferring cargo and passengers between low Earth orbit (LEO) and other orbits such as geosynchronous orbit (GEO), lunar orbit or highly-eccentric Earth orbit (HEEO).: 132 The system will also rely on satellites and receiving stations on Earth to convert the energy into electricity. Because of this energy can be transmitted easily from dayside to nightside meaning power is reliable 24/7.Nuclear power is sometimes proposed for colonies located on the Moon or on Mars, as the supply of solar energy is too discontinuous in these locations; the Moon has nights of two Earth weeks in duration. Mars has nights, relatively high gravity, and an atmosphere featuring large dust storms to cover and degrade solar panels. Also, Mars' greater distance from the Sun (1.52 astronomical units, AU) means that only 1/1.522 or about 43% of the solar energy is available at Mars compared with Earth orbit. Another method would be transmitting energy wirelessly to the lunar or Martian colonies from solar power satellites (SPSs) as described above; the difficulties of generating power in these locations make the relative advantages of SPSs much greater there than for power beamed to locations on Earth. In order to also be able to fulfill the requirements of a Moon base and energy to supply life support, maintenance, communications, and research, a combination of both nuclear and solar energy will be used in the first colonies.For both solar thermal and nuclear power generation in airless environments, such as the Moon and space, and to a lesser extent the very thin Martian atmosphere, one of the main difficulties is dispersing the inevitable heat generated. This requires fairly large radiator areas.
Self-replication
Space manufacturing could enable self-replication. Some think it's the ultimate goal because it allows an exponential increase in colonies, while eliminating costs to and dependence on Earth. It could be argued that the establishment of such a colony would be Earth's first act of self-replication. Intermediate goals include colonies that expect only information from Earth (science, engineering, entertainment) and colonies that just require periodic supply of light weight objects, such as integrated circuits, medicines, genetic material and tools.
Population size
In 2002, the anthropologist John H. Moore estimated that a population of 150–180 would permit a stable society to exist for 60 to 80 generations—equivalent to 2,000 years.
Assuming a journey of 6,300 years, the astrophysicist Frédéric Marin and the particle physicist Camille Beluffi calculated that the minimum viable population for a generation ship to reach Proxima Centauri would be 98 settlers at the beginning of the mission (then the crew will breed until reaching a stable population of several hundred settlers within the ship) .In 2020, Jean-Marc Salotti proposed a method to determine the minimum number of settlers to survive on an extraterrestrial world. It is based on the comparison between the required time to perform all activities and the working time of all human resources. For Mars, 110 individuals would be required.
Advocacy
Several private companies have announced plans toward the colonization of Mars. Among entrepreneurs leading the call for space colonization are Elon Musk, Dennis Tito and Bas Lansdorp.
Involved organizations
Organizations that contribute to space colonization include:
The National Space Society is an organization with the vision of people living and working in thriving communities beyond the Earth. The NSS also maintains an extensive library of full-text articles and books on space settlement.
The Space Frontier Foundation performs space advocacy including strong free market, capitalist views about space development.
The Mars Society promotes Robert Zubrin's Mars Direct plan and the settlement of Mars.
The Space Settlement Institute is searching for ways to make space colonization happen within a lifetime.
SpaceX is developing extensive spaceflight transportation infrastructure with the express purpose of enabling long-term human settlement of Mars.
The Space Studies Institute funds the study of outer space settlements, especially O'Neill cylinders.
The Alliance to Rescue Civilization plans to establish backups of human civilization on the Moon and other locations away from Earth.
The Artemis Project plans to set up a private lunar surface station.[2]
The British Interplanetary Society promotes ideas for the exploration and utilization of space, including a Mars colony, future propulsion systems (see Project Daedalus), terraforming, and locating other habitable worlds.In June 2013 the BIS began the SPACE project to re-examine Gerard O'Neill's 1970s space colony studies in light of the advances made since then. The progress of this effort were detailed in a special edition of the journal in September 2019.
Asgardia (nation) – an organization searching to circumvent limitations placed by Outer Space Treaty.
The Cyprus Space Exploration Organisation (CSEO) promotes space exploration and colonization, and fosters collaboration in space.
Terrestrial analogues to space settlement
Many space agencies build "testbeds", which are facilities on Earth for testing advanced life support systems, but these are designed for long duration human spaceflight, not permanent colonization.
The most famous attempt to build an analogue to a self-sufficient settlement is Biosphere 2, which attempted to duplicate Earth's biosphere.
BIOS-3 is another closed ecosystem, completed in 1972 in Krasnoyarsk, Siberia.
The Mars Desert Research Station has a habitat for similar reasons, but the surrounding climate is not strictly inhospitable.
Devon Island Mars Arctic Research Station, can also provide some practice for off-world outpost construction and operation.
In media and fiction
Although established space habitats are a stock element in science fiction stories, fictional works that explore the themes, social or practical, of the settlement and occupation of a habitable world are much rarer.
Solaris is noted for its critique of space colonization of inhabited planets. At one point, one of the characters says:We are humanitarian and chivalrous; we don't want to enslave other races, we simply want to bequeath them our values and take over their heritage in exchange. We think of ourselves as the Knights of the Holy Contact. This is another lie. We are only seeking Man. We have no need of other worlds. We need mirrors. (§6:72)
In 2022 Rudolph Herzog and Werner Herzog presented an in-depth documentary with Lucianne Walkowicz called Last exit: Space.
See also
References
Further reading
PapersYap, Xiao-Shan & Rakhyun E. Kim (2023). "Towards Earth-Space Governance in a Multi-Planetary Era". Earth System Governance, 16: 100173.
Ferrando, Francesca (July 2016). "Why Space Migration Must be Posthuman". The Ethics of Space Exploration. Space and Society. New York, US: Springer. pp. 137–152. doi:10.1007/978-3-319-39827-3_10. ISBN 978-3-319-39825-9.
Tiziani, Moreno (Jun 2013). "The Colonization of Space - An Anthropological Outlook" (PDF). Antrocom Online Journal of Anthropology. Rome, Italy: Antrocom. 9 (1): 225–236. ISSN 1973-2880. Archived from the original (PDF) on 2013-12-02. Retrieved 2013-12-01.
Foss, Nicole (December 2016). Mass Extinction and Mass Insanity.
Harrison, Albert A. (2002). Spacefaring: The Human Dimension. Berkeley, CA, US: University of California Press. ISBN 978-0-520-23677-6.
Seedhouse, Erik (2009). Lunar Outpost: The Challenges of Establishing a Human Settlement on the Moon. Chichester, UK: Praxis Publishing Ltd. ISBN 978-0-387-09746-6. Also see [3]
Seedhouse, Erik (2009). Martian Outpost: The Challenges of Establishing a Human Settlement on Mars. Bibcode:2009maou.book.....S. ISBN 978-0-387-98190-1. {{cite book}}: |journal= ignored (help)
Seedhouse, Erik (2012). Interplanetary Outpost: The Human and Technological Challenges of Exploring the Outer Planets. Berlin: Springer. ISBN 978-1-4419-9747-0.
Cameron M. Smith, Evan T. Davies (2012). Emigrating Beyond Earth: Human Adaptation and Space Colonization. Berlin: Springer-Verlag. ISBN 978-1-4614-1164-2.VideoRees, Martin (March 2017). Brief talk on some key issues in space exploration and colonization. Archived from the original on 2021-12-11. Posted on the official YouTube channel of Casina Pio IV.
Sarmont, Eagle (December 2018). Opening the High Frontier. Affordable to everyone spaceflight is the key to building a spacefaring civilization. Posted on Vimeo. |
great unconformity | Of the many unconformities (gaps) observed in geological strata, the term Great Unconformity is frequently applied to either the unconformity observed by James Hutton in 1787 at Siccar Point in Scotland, or that observed by John Wesley Powell in the Grand Canyon in 1869. Both instances are exceptional examples of where the contacts between sedimentary strata and either sedimentary or crystalline strata of greatly different ages, origins, and structure represent periods of geologic time sufficiently long to raise great mountains and then erode them away.
Background
Unconformities tend to reflect long-term changes in the pattern of the accumulation of sedimentary or igneous strata in low-lying areas (often ocean basins, such as the Gulf of Mexico or the North Sea, but also Bangladesh and much of Brazil), then being uplifted and eroded (such as the ongoing Himalayan orogeny, the older Laramide orogeny of the Rocky Mountains, or much older Appalachian (Alleghanian) and Ouachita orogenies), then subsequently subsiding, eventually to be buried under younger sediments. The intervening periods of tectonic uplift are generally periods of mountain building, often due to the collision of tectonic plates. The "great" unconformities of regional or continental scale (in both geography and chronology) are associated with either global changes in eustatic sea level or the supercontinent cycle, the periodic merger of all the continents into one approximately every 500 million years.
Hutton's Unconformity
Hutton's Unconformity at Siccar Point, in county of Berwickshire on the east coast of Scotland, is an angular unconformity that consists of gently dipping, reddish, Upper Devonian and Lower Carboniferous breccias, sandstones, and conglomerates of the Old Red Sandstone overlying deeply eroded, near-vertical, greyish, Silurian (Llandovery) greywackes and shales. The Llandovery greywackes and graptolite-bearing shales of the Gala Group were deposited by turbidity currents in a deep sea environment about 425 million years ago. The overlying Devonian strata were deposited by rivers and streams about 345 million years ago. Thus, this unconformity reflects a gap of about 80 million years during which deep sea sediments were lithified, folded, and uplifted; later deeply eroded and weathered subaerially; and finally buried by river and stream sediments.Exposures of the unconformity at Siccar Point, provided James Hutton, accompanied by John Playfair and Sir James Hall, the clearest example of an unconformable relationship between two sets of sedimentary strata that involved a complex geological history. The clear truncation of near-vertical Silurian sedimentary strata by well-bedded conglomerates and sandstones belonging to the Upper Old Red Sandstone allowed Hutton to demonstrate the existence of significant breaks in the geological record, in this case a break separating strata that were then called alpine schistus and secondary strata. This and other unconformities provided evidence for Hutton's ideas about the recycling of geological materials and for unconformities representing very large time periods. He argued that these concepts pointed to the great antiquity of the Earth and the vastness of the geological time-scale.
Powell’s Unconformity, Grand Canyon
The Great Unconformity of Powell in the Grand Canyon is a regional unconformity that separates the Tonto Group from the underlying, faulted and tilted sedimentary rocks of the Grand Canyon Supergroup and vertically foliated metamorphic and igneous rocks of the Vishnu Basement Rocks. The unconformity between the Tonto Group and the Vishnu Basement Rocks is a nonconformity. The break between the Tonto Group and the Grand Canyon Supergroup is an angular unconformity.Powell's Great Unconformity is part of a continent-wide unconformity that extends across Laurentia, the ancient core of North America. It was first recognized twelve years before Powell's expedition by John Newberry in New Mexico, during the Ives expedition of 1857–1858. However, the disruption of the American Civil War kept Newberry's work from becoming widely known. This Great Unconformity marks the progressive submergence of this landmass by a shallow cratonic sea and its burial by shallow marine sediments of the Cambrian-Early Ordovician Sauk sequence. The submergence of Laurentia ended a lengthy period of widespread continental denudation that exhumed and deeply eroded Precambrian rocks and exposed them to extensive physical and chemical weathering at the Earth's surface. As a result, Powell's Great Unconformity is unusual in its geographic extent and its stratigraphic significance.The length of time represented by Powell's Great Unconformity varies along its length. Within the Grand Canyon, the Great Unconformity represents a period of about 175 million years between the Tonto Group and the youngest subdivision, the Sixtymile Formation, of the Grand Canyon Supergroup. At the base of the Grand Canyon Supergroup, where it truncates the Bass Formation, the period of time represented by this angular unconformity increases to about 725 million years. Where the Tonto Group overlies the Vishnu Basement Rocks, the Great Unconformity represents a period as much as 1.2 to 1.6 billion years. (See also geological timescale.)
Frenchman Mountain, Nevada
A prominent exposure of Powell's Great Unconformity occurs in Frenchman Mountain in Nevada. Frenchman Mountain exposes a sequence of Phanerozoic strata equivalent to those found in the Grand Canyon. At the base of this sequence, the Great Unconformity, with the Tapeats Sandstone of the Tonto Group overlying the Vishnu Basement Rocks, is well exposed in a manner that is atypical and scientifically significant in its combination of extent and accessibility. This exposure is frequently illustrated in popular and educational publications, and is often part of geological fieldtrips. There is a gap of about 1.2 billion years where 550 million year old strata of the Tapeats Sandstone rests on 1.7 billion (1700 million) year old Vishnu Basement Rocks.
As a widespread phenomenon
The term "Great Unconformity" has also been used to refer to the anomalous concentration of unconformities, including basement nonconformities, below the base of the Cambrian. Charles Walcott was among the first to note this phenomenon, remarking in 1910:
I do not know of a case of proven conformity between Cambrian and pre-Cambrian Algonkian rocks on the North American continent. In all localities where the contact is sufficiently extensive, or where fossils have been found in the basal Cambrian beds or above the basal conglomerate and coarser sandstones, an unconformity has been found to exist. Stated in another way, the pre-Cambrian land surface was formed of sedimentary, eruptive, and crystalline rocks that did not in any known instance immediately precede in deposition or origin the Cambrian sediments. Everywhere there is a stratigraphic and time break between the known pre-Cambrian rocks and Cambrian sediments of the North American continent.
A potential link has been proposed between such sub-Cambrian unconformities and glacial erosion during the Neoproterozoic Snowball Earth glaciations. Alternatively, it has been proposed that multiple smaller events, such as the formation and breakup of Rodinia, created many unconformities worldwide. Evidence indicates that the Pikes Peak unconformity was formed before the Snowball Earth glaciations.
Possible causes of the Great Unconformity
There is currently no widely accepted explanation for the Great Unconformity among geoscientists. There are hypotheses that have been proposed; it is widely accepted that there was a combination of more than one event which may have caused such an extensive phenomenon. One example is a large glaciation event which took place during the Neoproterozoic, starting around 720 million years ago. This is also when a significant glaciation event known as 'Snowball Earth' occurred. Snowball Earth covered almost the entire planet with ice. The areas that underwent glaciation were approximately those where the Great Unconformity is located today. When glaciers move, they drag and erode sediment away from the underlying rock. This would explain how a large section of rock was taken away from widespread areas around the same time.
See also
Geology of the Grand Canyon area (with time scale)
List of orogenies
Orogeny (mountain building)
References
External links
Hutton's UnconformityAnonymous (2003) Siccar Point Field Excursion Preview. School of GeoSciences, University of Edinburgh, Edinburgh, Scotland. last accessed September 22, 2013.
Moore, R (2009) Siccar Point. Reports of the National Center for Science Education. 29(1):26. last accessed September 22, 2013.
Rowan, C (2011) The making of an angular unconformity: Hutton’s unconformity at Siccar Point. Highly Allochthonous. last accessed September 22, 2013.Powell's UnconformityGorvett, Zaria (1 September 2021). "The strange race to track down a missing billion years". BBC.
Abbott, W (2001) Revisiting the Grand Canyon – Through the Eyes of Seismic Sequence Stratigraphy. AAPG Datapages / Search and Discovery, American Association of Petroleum Geologist, Tulsa, Oklahoma. last accessed September 22, 2013.
Brandriss, M. (2004) Angular unconformity between Proterozoic and Cambrian rocks, Grand Canyon, Arizona. GeoDIL, A Geoscience Digital Image Library, University of North Dakota, Grand Forks, North Dakota. last accessed September 22, 2013.
Share, J. (2012a) The Great Unconformity of the Grand Canyon and the Late Proterozoic-Cambrian Time Interval: Part I – Defining It. last accessed September 22, 2013.
Share, J. (2012a) The Great Unconformity and the Late Proterozoic-Cambrian Time Interval: Part II – The Rifting of Rodinia and the "Snowball Earth" Glaciations That Followed. last accessed September 22, 2013.
The Unconformity in Wyoming |
flood geology | Flood geology (also creation geology or diluvial geology) is a pseudoscientific attempt to interpret and reconcile geological features of the Earth in accordance with a literal belief in the Genesis flood narrative, the flood myth in the Hebrew Bible. In the early 19th century, diluvial geologists hypothesized that specific surface features provided evidence of a worldwide flood which had followed earlier geological eras; after further investigation they agreed that these features resulted from local floods or from glaciers. In the 20th century, young-Earth creationists revived flood geology as an overarching concept in their opposition to evolution, assuming a recent six-day Creation and cataclysmic geological changes during the biblical flood, and incorporating creationist explanations of the sequences of rock strata.
In the early stages of development of the science of geology, fossils were interpreted as evidence of past flooding. The "theories of the Earth" of the 17th century proposed mechanisms based on natural laws, within a timescale set by the Ussher chronology. As modern geology developed, geologists found evidence of an ancient Earth, and evidence inconsistent with the notion that the Earth had developed in a series of cataclysms, like the Genesis flood. In early 19th-century Britain, "diluvialism" attributed landforms and surface features (such as beds of gravel and erratic boulders) to the destructive effects of this supposed global deluge, but by 1830 geologists increasingly found that the evidence supported only relatively local floods. So-called scriptural geologists attempted to give primacy to literal biblical explanations, but they lacked a background in geology and were marginalised by the scientific community, as well as having little influence in the churches.
Creationist flood geology was only supported by a minority of the 20th century anti-evolution movement, mainly in the Seventh-day Adventist Church, until the 1961 publication of The Genesis Flood by Morris and Whitcomb. Around 1970, proponents adopted the terms "scientific creationism" and creation science.Proponents of flood geology hold to a literal reading of Genesis 6–9 and view its passages as historically accurate; they use the Bible's internal chronology to place the Genesis flood and the story of Noah's Ark within the last five thousand years.Scientific analysis has refuted the key tenets of flood geology. Flood geology contradicts the scientific consensus in geology, stratigraphy, geophysics, physics, paleontology, biology, anthropology, and archaeology. Modern geology, its sub-disciplines and other scientific disciplines use the scientific method. In contrast, flood geology does not adhere to the scientific method, making it a pseudoscience.
The great flood in the history of geology
In pre-Christian times, fossils found on land were thought by Greek philosophers, including Xenophanes, Xanthus and Aristotle, to be evidence that the sea had in past ages covered the land. Their concept of vast time periods in an eternal cosmos was rejected by early Christian writers as incompatible with their belief in Creation by God. Among the church fathers, Tertullian spoke of fossils demonstrating that mountains had been overrun by water without explicitly saying when. Chrysostom and Augustine believed that fossils were the remains of animals that were killed and buried during the brief duration of the Genesis flood, and later Martin Luther viewed fossils as having resulted from the flood.Other scholars, including Avicenna, thought fossils were produced in the rock by "petrifying virtue" acting on "seeds" of plants and animals. In 1580, Bernard Palissy speculated that fossils had formed in lakes, and natural historians subsequently disputed the alternatives. Robert Hooke made empirical investigations, and doubted that the numbers of fossil shells or depth of shell beds could have formed in the one year of Noah's Flood. In 1616, Nicolas Steno showed how chemical processes changed organic remains into stone fossils. His fundamental principles of stratigraphy published in 1669 established that rock strata formed horizontally and were later broken and tilted, though he assumed these processes would occur within 6,000 years including a worldwide Flood.
Theories of the Earth
In his influential Principles of Philosophy of 1644, René Descartes applied his mechanical physical laws to envisage swirling particles forming the Earth as a layered sphere. This natural philosophy was recast in biblical terms by the theologian Thomas Burnet, whose Sacred Theory of the Earth published in the 1680s proposed complex explanations based on natural laws, and explicitly rejected the simpler approach of invoking miracles as incompatible with the methodology of natural philosophy (the precursor to science). Burnet maintained that less than 6,000 years ago the Earth had emerged from chaos as a perfect sphere, with paradise on land over a watery abyss. This crust had dried out and cracked, and its collapse caused the biblical deluge, forming mountains as well as caverns where the water retreated. He made no mention of fossils, but inspired other diluvial theories that did.In 1695, John Woodward's An Essay Toward a Natural History of the Earth viewed the Genesis flood as dissolving rocks and earth into a thick slurry that caught up all living things, which, when the waters settled, formed strata according to the specific gravity of these materials, including fossils of the organisms. When it was pointed out that lower layers were often less dense and forces that shattered rock would destroy organic remains, he resorted to the explanation that a divine miracle had temporarily suspended gravity. William Whiston's New Theory of the Earth of 1696 combined scripture with Newtonian physics to propose that the original chaos was the atmosphere of a comet with the days of creation each taking a year, and the Genesis flood had resulted from a second comet. His explanation of how the flood caused mountains and the fossil sequence was similar to Woodward's. Johann Jakob Scheuchzer wrote in support of Woodward's ideas in 1708, describing some fossil vertebrae as bones of sinners who had perished in the flood. A skeleton found in a quarry was described by him in 1726 as Homo diluvii testis, a giant human testifying to the flood. This was accepted for some time, but in 1812 it was shown to be a prehistoric salamander.
Beginnings of modern geology
The modern science of geology developed in the 18th century, the term "geology" itself was popularised by the Encyclopédie of 1751. Steno's categorisation of strata was expanded by several geologists, including Johann Gottlob Lehmann who believed that the oldest mountains had formed early in the Creation, and categorised as Flötz-Gebürge stratified mountains with few ore deposits but with thin layers containing fossils, overlain by a third category of superficial deposits. In his 1756 publication he identified 30 different layers in this category which he attributed to the action of the Genesis Deluge, possibly including debris from the older mountains. Others including Giovanni Arduino attributed secondary strata to natural causes: Georg Christian Füchsel said that geologists had to take as standard the processes in which nature currently produces solids, "we know no other way", and only the most recent deposits could be attributed to a great Flood.Lehman's classification was developed by Abraham Gottlob Werner who thought that rock strata had been deposited from a primeval global ocean rather than by Noah's Flood, a doctrine called Neptunism. The idea of a young Earth was further undermined in 1774 by Nicolas Desmarest, whose studies of a succession of extinct volcanoes in Europe showed layers which would have taken long ages to build up. The fact that these layers were still intact indicated that any later Flood had been local rather than universal. Against Neptunism, James Hutton proposed an indefinitely old cycle of eroded rocks being deposited in the sea, consolidated and heaved up by volcanic forces into mountains which in turn eroded, all in natural processes which continue to operate.
Catastrophism and diluvialism
The first professional geological society, the Geological Society of London, was founded in 1807. By this time, geologists were convinced that an immense time had been needed to build up the huge thickness of rock strata visible in quarries and cliffs, implying extensive pre-human periods. Most accepted a basic time scale classifying rocks as primitive, transition, secondary, or tertiary. Several researchers independently found that strata could be identified by characteristic fossils: secondary strata in southern England were mapped by William Smith from 1799 to 1815.
Cuvier and Jameson
Georges Cuvier, working with Alexandre Brongniart, examined tertiary strata in the region around Paris. Cuvier found that fossils identified rock formations as alternating between marine and terrestrial deposits, indicating "repeated irruptions and retreats of the sea" which he identified with a long series of sudden catastrophes which had caused extinctions. In his 1812 Discours préliminaire to his Recherches sur les ossemens fossiles de quadrupeds put forward a synthesis of this research into the long prehistoric period, and a historical approach to the most recent catastrophe. His historical approach tested empirical claims in the biblical text of Genesis against other ancient writings to pick out the "real facts" from "interested fictions". In his assessment, Moses had written the account around 3,300 years ago, long after the events described. Cuvier only discussed the Genesis Flood in general terms, as the most recent example of "an event of an [sic] universal catastrophe, occasioned by an irruption of the waters" not set "much further back than five or six thousand years ago". The historical texts could be loosely related to evidence such as overturned strata and "heaps of debris and rounded pebbles". An English translation was published in 1813 with a preface and notes by Robert Jameson, Regius Professor of Natural history at the University of Edinburgh. He began the preface with a sentence which ignored Cuvier's historical approach and instead deferred to revelation:
"Although the Mosaic account of the creation of the world is an inspired writing, and consequently rests on evidence wholly independent of human observation and experience, still it is interesting, and in many respects important, to know that it coincides with the various phenomena observable in the mineral kingdom." This sentence was removed after the second edition, and Jameson's position changed as shown by his notes in successive editions, but it influenced British views of Cuvier's concept. In 1819, George Bellas Greenough, first president of The Geological Society, issued A Critical Examination of the First Principles of Geology stating that unless erratic boulders deposited hundreds of miles from their original sources had been moved by seas, rivers, or collapsing lakes, "the only remaining cause, to which these effects can be ascribed, is a Debacle or Deluge."
Buckland and the English school of geologists
Conservative geologists in Britain welcomed Cuvier's theory to replace Werner's Neptunism, and the Church of England clergyman William Buckland became the foremost proponent of Flood geology as he sought to get the new science of geology accepted on the curriculum of the University of Oxford. In 1818, he was visited by Cuvier, and in his inaugural speech in 1819 as the first professor of geology at the university he defended the subject against allegations that it undermined religion. His speech, published as Vindiciae Geologicae; or, The Connexion of Geology with Religion Explained, equated the last of a long series of catastrophes with the Genesis flood, and said that "the grand fact of an universal deluge at no very remote period is proved on grounds so decisive and incontrovertible, that, had we never heard of such an event from Scripture, or any other, authority, Geology of itself must have called in the assistance of some such catastrophe, to explain the phenomena of diluvian action which are universally presented to us, and which are unintelligible without recourse to a deluge exerting its ravages at a period not more ancient than that announced in the Book of Genesis." The evidence he proposed included erratic boulders, extensive areas of gravel, and landforms which appeared to have been scoured by water.This inaugural address influenced the geologists William Conybeare and William Phillips. In their 1822 book on Outlines of the Geology of England and Wales Conybeare referred to the same features in an introduction about the relationship between geology and religion, describing how a deluge causing "the last great geological change to which the surface of our planet appears to have been exposed" left behind the debris (which he named in Latin Diluvium) as evidence for "that great and universal catastrophe to which it seems most properly assignable". In 1823, Buckland published his detailed account of "Relics of the Flood", Reliquiae Diluvianae; or, Observations on the Organic Remains Contained in Caves, Fissures, and Diluvial Gravel and on Other Geological Phenomena Attesting the Action of an Universal Deluge, incorporating his research suggesting that animal fossils had been dragged into the Kirkdale Cave by hyenas then covered by a layer of red mud washed in by the Deluge.Buckland's views were supported by other Church of England clergymen naturalists: his Oxford colleague Charles Daubeny proposed in 1820 that the volcanoes of the Auvergne showed a sequence of lava flows from before and after the Flood had cut valleys through the region. In an 1823 article "On the deluge", John Stevens Henslow, professor of mineralogy at the University of Cambridge, affirmed the concept and proposed that the Flood had originated from a comet, but this was his only comment on the topic. Adam Sedgwick, Woodwardian Professor of Geology at Cambridge, presented two supportive papers in 1825, "On the origin of alluvial and diluvial deposits", and "On diluvial formations". At this time, most of what Sedgwick called "The English school of geologists" distinguished superficial deposits which were "diluvial", showing "great irregular masses of sand, loam, and coarse gravel, containing through its mass rounded blocks sometimes of enormous magnitude" and supposedly caused by "some great irregular inundation", from "alluvial" deposits of "comminuted gravel, silt, loam, and other materials" attributed to lesser events, the "propelling force" of rivers, or "successive partial inundations".In America, Benjamin Silliman at Yale College spread the concept, and in an 1833 essay dismissed the earlier idea that most stratified rocks had been formed in the Flood, while arguing that surface features showed "wreck and ruin" attributable to "mighty floods and rushing torrents of water". He said that "we must charge to moving waters the undulating appearance of stratified sand and gravel, often observed in many places, and very conspicuously in the plain of New Haven, and in other regions of Connecticut and New England", while both "bowlder stones" and sandy deserts across the world could be attributed to "diluvial agency".
Criticisms and retractions: the downfall of Diluvialism
Other naturalists were critical of Diluvialism: the Church of Scotland pastor John Fleming published opposing arguments in a series of articles from 1823 onwards. He was critical of the assumption that fossils resembling modern tropical species had been swept north "by some violent means", which he regarded as absurd considering the "unbroken state" of fossil remains. For example, fossil mammoths demonstrated adaptation to the same northern climates now prevalent where they were found. He criticized Buckland's identification of red mud in the Kirkdale cave as diluvial, when near identical mud in other caves had been described as fluvial. While Cuvier had reconciled geology with a loose reading of the biblical text, Fleming argued that such a union was "indiscreet" and turned to a more literal view of Genesis:
But if the supposed impetuous torrent excavated valleys, and transported masses of rocks to a distance from their original repositories, then must the soil have been swept from off the earth to the destruction of the vegetable tribes. Moses does not record such an occurrence. On the contrary, in his history of the dove and the olive-leaf plucked off, he furnishes a proof that the flood was not so violent in its motions as to disturb the soil, nor to overturn the trees which it supported.
When Sedgwick visited Paris at the end of 1826 he found hostility to Diluvialism: Alexander von Humboldt ridiculed it "beyond measure", and Louis-Constant Prévost "lectured against it". In the summer of 1827 Sedgwick and Roderick Murchison travelled to investigate the geology of the Scottish Highlands, where they found "so many indications of local diluvial operations" that Sedgwick began to change his mind about it being worldwide. When George Poulett Scrope published his investigations into the Auvergne in 1827, he did not use the term "diluvium". He was followed by Murchison and Charles Lyell whose account appeared in 1829. All three agreed that the valleys could well have been formed by rivers acting over a long time, and a deluge was not needed. Lyell, formerly a pupil of Buckland, put strong arguments against diluvialism in the first volume of his Principles of Geology published in 1830, though suggesting the possibility of a deluge affecting a region such as the low-lying area around the Caspian Sea. Sedgwick responded to this book in his presidential address to the Geological Society in February 1830, agreeing that diluvial deposits had formed at differing times. At the society a year later, when retiring from the presidency, Sedgwick described his former belief that "vast masses of diluvial gravel" had been scattered worldwide in "one violent and transitory period" as "a most unwarranted conclusion", and therefore thought "it right, as one of my last acts before I quit this Chair, thus publicly to read my recantation." However, he remained convinced that a flood as described in Genesis was not excluded by geology.One student had seen the gradual abandonment of diluvialism: Charles Darwin had attended Jameson's geology lectures in 1826, and at Cambridge became a close friend of Henslow before learning geology from Sedgwick in 1831. At the outset of the Beagle voyage Darwin was given a copy of Lyell's Principles of Geology, and at the first landfall began his career as a geologist with investigations which supported Lyell's concept of slow uplift while also describing loose rocks and gravel as "part of the long disputed Diluvium". Debates continued over the part played by repeated exceptional catastrophes in geology, and in 1832 William Whewell dubbed this view catastrophism, while naming Lyell's insistence on explanations based on current processes uniformitarianism.Buckland, too, gradually modified his views on the Deluge. In 1832 a student noted Buckland's view on cause of diluvial gravel, "whether is Mosaic inundation or not, will not say". In a footnote to his Bridgewater Treatise of 1836, Buckland backed down from his former claim that the "violent inundation" identified in his Reliquiae Diluvianae was the Genesis flood:
it seems more probable, that the event in question, was the last of the many geological revolutions that have been produced by violent irruptions of water, rather than the comparatively tranquil inundation described in the Inspired Narrative. It has been justly argued, against the attempt to identity these two great historical and natural phenomena, that, as the rise and fall of the waters of the Mosaic deluge are described to have been gradual and of short duration, they would have produced comparatively little change on the surface of the country they overflowed.
For a while, Buckland had continued to insist that some geological layers were related to the Great Flood, but grew to accept the idea that they represented multiple inundations which occurred well before humans existed. In 1840 he made a field trip to Scotland with the Swiss geologist Louis Agassiz, and became convinced that the "diluvial" features which he had attributed to the Deluge had, in fact, been produced by ancient ice ages. Buckland became one of the foremost champions of Agassiz's theory of glaciations, and diluvialism went out of use in geology. Active geologists no longer posited sudden ancient catastrophes with unknown causes, and instead increasingly explained phenomena by observable processes causing slow changes over great periods.
Scriptural geologists, and later commentary
Scriptural geologists were a heterogeneous group of writers in the early nineteenth century, who claimed "the primacy of literalistic biblical exegesis" and a short Young Earth time-scale. Their views were marginalised and ignored by the scientific community of their time. They generally lacked any background in geology, and had little influence even in church circles.Many of them quoted obsolete geological writings. Among the most prominent, Granville Penn argued in 1822 that "mineral geology" rejected revelation, while true "Mosaical geology" showed that God had created primitive rock formations directly, in correspondence with the laws which God then made to produce subsequent effects. A first revolution on the third day of creation deepened the oceans so water rushed in, and in the Deluge 1,656 years afterwards a second revolution sank land areas and raised the sea bed to cause a swirling flood which moved soil and fossil remains into stratified layers, after which God created new vegetation. As Genesis appeared to show that the rivers of Eden had survived this catastrophe, he argued that the verses concerned were an added "parenthesis" which should be disregarded. In 1837 George Fairholme expressed disappointment about disappearing belief in the deluge, and about Sedgwick and Buckland recanting diluvialism, while putting forward his own New and Conclusive Physical Demonstrations which ignored geological findings to claim that strata had been deposited in a quick continuous process while still moist.Geology was popularized by several authors. John Pye Smith's lectures published in 1840 reconciled an extended time frame with Genesis by the increasingly common gap theology or day-age theology, and said it was likely that the gravel and boulder formations were not "diluvium", but had taken long ages predating the creation of humans. He reaffirmed that the Flood was historical as a local event, something which the 17th century theologians Edward Stillingfleet and Matthew Poole had already suggested on a purely biblical basis. Smith also denounced the "fanciful" writings of the scriptural geologists. Edward Hitchcock sought to ensure that geological findings could be corroborated by scripture, and dismissed the scriptural geology of Penn and Fairholme as misrepresenting both scripture and the facts of geology. He noted the difficulty of equating a violent deluge with the more tranquil Genesis account. Hugh Miller supported similar points with considerable detail.Little attention was paid to Flood geology over the rest of the 19th century, its few supporters included the author Eleazar Lord in the 1850s and the Lutheran scholar Carl Friedrich Keil in 1860 and 1878. The visions of Ellen G. White published in 1864 formed Seventh-day Adventist Church views, and influenced 20th century creationism.
Creationist flood geology
The Seventh-day Adventist Church, led by Ellen G. White, took a six-day creation literally, and believed that she received divine messages supplementing and supporting the Bible. Her visions of the flood and its aftermath, published in 1864, described a catastrophic deluge which reshaped the entire surface of the Earth, followed by a powerful wind which piled up new high mountains, burying the bodies of men and beasts. Buried forests became coal and oil, and where God later caused these to burn, they reacted with limestone and water to cause "earthquakes, volcanoes and fiery issues".
George McCready Price
Ellen G. White's visions prompted several books by one of her followers, George McCready Price, leading to the 20th-century revival of flood geology. After years selling White's books door-to-door, Price took a one-year teacher-training course and taught in several schools. When shown books on evolution and the fossil sequence which contradicted his beliefs, he found the answer in White's "revealing word pictures" which suggested how the fossils had been buried. He studied textbooks on geology and "almost tons of geological documents", finding "how the actual facts of the rocks and fossils, stripped of mere theories, splendidly refute this evolutionary theory of the invariable order of the fossils, which is the very backbone of the evolution doctrine". In 1902, he produced a manuscript for a book proposing geology based on Genesis, in which the sequence of fossils resulted from the different responses of animals to the encroaching flood. He agreed with White on the origins of coal and oil, and conjectured that mountain ranges (including the Alps and Himalaya) formed from layers deposited by the flood which had then been "folded and elevated to their present height by the great lateral pressure that accompanied its subsidence". He then found a report describing paraconformities and a paper on thrust faults. He concluded from these "providential discoveries" that it was impossible to prove the age or overall sequence of fossils, and included these points in his self-published paperback of 1906, Illogical Geology: The Weakest Point in the Evolution Theory. His arguments continued this focus on disproving the sequence of strata, and he ultimately sold more than 15,000 copies of his 1923 college textbook The New Geology.Price increasingly gained attention outside Adventist groups, and in the creation–evolution controversy other leading Christian fundamentalists praised his opposition to evolution – though none of them followed his young Earth arguments, retaining their belief in the gap or in the day-age interpretation of Genesis. Price corresponded with William Jennings Bryan and was invited to be a witness in the Scopes Trial of 1925, but declined as he was teaching in England and opposed to teaching Genesis in public schools as "it would be an infringement on the cardinal American principle of separation of church and state". Price returned from England in 1929 to rising popularity among fundamentalists as a scientific author. In the same year his former student Harold W. Clark self-published the short book Back to Creationism, which recommended Price's flood geology as the new "science of creationism", introducing the label "creationism" as a replacement for "anti-evolution" of "Christian Fundamentals".In 1935, Price and Dudley Joseph Whitney (a rancher who had co-founded the Lindcove Community Bible Church, and now followed Price) founded the Religion and Science Association (RSA). They aimed to resolve disagreements among fundamentalists with "a harmonious solution" which would convert them all to flood geology. Most of the organising group were Adventists, others included conservative Lutherans with similarly literalist beliefs. Bryon C. Nelson of the Norwegian Lutheran Church of America had included Price's geological views in a 1927 book, and in 1931 published The Deluge Story in Stone: A History of the Flood Theory of Geology, which described Price as the "one very outstanding advocate of the Flood" of the century. The first public RSA conference in March 1936 invited various fundamentalist views, but opened up differences between the organisers on the antiquity of creation and on life before Adam. The RSA went defunct in 1937, and a dispute continued between Price and Nelson, who now viewed Creation as occurring over 100,000 years previously.In 1938, Price, with a group of Adventists in Los Angeles, founded what became the Deluge Geology Society (DGS), with membership restricted to those believing that the creation week comprised "six literal days, and that the Deluge should be studied as the cause of the major geological changes since creation". Not all DGS-adherents were Adventists; early members included the Independent Baptist Henry M. Morris and the Missouri Lutheran Walter E. Lammerts. The DGS undertook field-work: in June 1941 their first Bulletin hailed the news that the Paluxy River dinosaur trackways in Texas appeared to include human footprints. Though Nelson had advised Price in 1939 that this was "absurd" and that the difficulty of human footprints forming during the turmoil of the deluge would "knock the Flood theory all to pieces", in 1943 the DGS began raising funds for "actual excavation" by a Footprint Research Committee of members including the consulting geologist Clifford L. Burdick. Initially they tried to keep their research secret from "unfriendly scientists". Then in 1945, to encourage backing, they announced giant human footprints, allegedly defeating "at a single stroke" the theory of evolution. The revelation that locals had carved the footprints, and an unsuccessful field trip that year, failed to dampen their hopes. However, by then doctrinal arguments had riven the DGS. The most extreme dispute began in late 1938 after Harold W. Clark observed deep drilling in oil fields and had discussions with practical geologists which dispelled the belief that the fossil sequence was random, convincing him that the evidence of thrust faults was "almost incontrovertible". He wrote to Price, telling his teacher that the "rocks do lie in a much more definite sequence than we have ever allowed", and proposing that the fossil sequence was explained by ecological zones before the flood. Price reacted with fury, and despite Clark emphasising their shared belief in literal recent Creation, the dispute continued. In 1946 Clark set out his views in a book, The New Diluvialism, which Price denounced as Theories of Satanic Origin.In 1941, F. Alton Everest co-founded the American Scientific Affiliation (ASA) as a less confrontational forum for evangelical scientists. Some deluge geologists, including Lammerts and Price, urged close cooperation with the DGS, but Everest began to see their views as presenting an "insurmountable problem" for the ASA. In 1948, he requested J. Laurence Kulp, a geologist in fellowship with the Plymouth Brethren, to explore the issue. At the convention that year, Kulp examined hominid antiquity demonstrated by radiocarbon dating. At the 1949 convention a paper by Kulp was presented, giving a detailed critique of Deluge Geology, which he said had "grown and infiltrated the greater portion of fundamental Christianity in America primarily due to the absence of trained Christian geologists". Kulp demonstrated that "major propositions of the theory are contraindicated by established physical and chemical laws". He focused on "four basic errors" commonly made by flood geologists:
saying that geology was the same as evolution
assuming "that life has been on the earth only for a few thousand years, [and] therefore the flood must account for geological strata"
misunderstanding "the physical and chemical conditions under which rocks are formed"
ignoring recent discoveries such as radiometric dating that undermined their assumptionsKulp accused Price of ignorance and deception, and concluded that "this unscientific theory of flood geology has done and will do considerable harm to the strong propagation of the gospel among educated people". Price said nothing during the presentation and discussion. When invited to speak, he "said something very brief which missed what everyone was waiting for". Further publications made the ASA's opposition to flood geology clear.
Morris and Whitcomb
In 1942, Irwin A. Moon's Sermons from Science persuaded the engineer Henry M. Morris (1918–2006) of the importance of harmonising science and the Bible, and introduced him to the concepts of a vapor canopy causing the Flood and its geological effects. About a year later Morris found George McCready Price's New Geology a "life-changing experience", and joined the Deluge Geology Society. His book That You Might Believe (1946) for college students included Price's flood geology.Morris had joined the American Scientific Affiliation (ASA) in 1949, and in the summer of 1953 he made a presentation on The Biblical Evidence for a Recent Creation and Universal Deluge at their annual conference, held at the Grace Theological Seminary's campus. He impressed a graduate student there, John C. Whitcomb, Jr. who was teaching Old Testament and Hebrew. To Whitcomb's distress, the ASA members at the presentation "politely denounced" Morris.In 1955, the ASA held a joint meeting with the Evangelical Theological Society (ETS) at the same campus, where theologian Bernard Ramm's The Christian View of Science and Scripture (1954) caused considerable discussion. This book dismissed flood geology as typifying the "ignoble tradition" of fundamentalism, and stated that Price could not be taken seriously, as lacking the necessary competence, training and integrity. Instead, Ramm proposed what he called progressive creationism, in which the Genesis days functioned as pictorial images revealing a process that had taken place over millions of years. ASA scientists praised Ramm's views, but the ETS theologians proved unwilling to follow Ramm.This encouraged Whitcomb to make his doctoral dissertation a response to Ramm and a defence of Price's position. He systematically asked evangelical professors of apologetics, archaeology and the Old Testament about creation and the flood, and in October told Morris that Ramm's book had been sufficient incentive for him to devote his dissertation to the topic. In 1957 Whitcomb completed his 450-page dissertation, "The Genesis Flood", and he promptly began summarising it for a book. Moody Publishers responded positively and agreed with him that chapters on scientific aspects should be carefully checked or written by someone with a PhD in science, but Whitcomb's attempts to find someone with a doctorate in geology were unsuccessful. Morris gave helpful advice, expressing concern that sections were too closely based on Price and on Velikovsky who were "both considered by scientists generally as crackpots". Morris produced an outline of his planned three chapters, and in December 1957 agreed to co-author the book.Morris sent on his draft for comment in early 1959. His intended 100 pages grew to almost 350, around twice the length of Whitcomb's eventual contribution. Recalling Morris's earlier concerns about how Price was viewed by scientists, Whitcomb suggested that "For many people, our position would be somewhat discredited" by multiple references to Price in the draft, including a section headed "Price and Seventh-Day Adventism". Morris agreed, and even suggested avoiding the term "flood geology" but it proved too useful. After discussion, the co-authors minimised these references and removed any mention of Price's Adventist affiliation. By early 1960 they became impatient at delays when Moody Publishers expressed misgivings about the length and literal views of the book, and they went along with Rousas Rushdoony's recommendation of a small Philadelphia publisher.
The Genesis Flood (1961)
The Presbyterian and Reformed Publishing Company of Philadelphia published Whitcomb and Morris's The Genesis Flood in February 1961. The authors took as their premise biblical infallibility: "the basic argument of this volume is that the Scriptures are true". For Whitcomb, Genesis described a worldwide Flood which covered all the high mountains, Noah's ark with a capacity equivalent to eight freight-trains, flood waters from a canopy and the deeps, and subsequent dispersal of animals from Ararat to all the continents via land bridges. He disputed the views published by Arthur Custance (1910–1985) and Bernard Ramm (1916-1992). Morris then confronted readers with the dilemma of whether to believe Scripture or to accept the interpretations of trained geologists, and instead of the latter proposed "a new scheme of historical geology" - true both to Scripture and to "God's work" revealed in nature. This was essentially Price's The New Geology of 1923 updated for the 1960s, though with few direct references to Price.Like Price before him, Morris argued that most fossil-bearing strata had formed during a global deluge, disputing uniformitarianism, multiple ice-ages, and the geologic column. He explained the apparent fossil sequence as the outcome of marine organisms dying in the slurry of sediments in early stages of the flood, of moving currents sorting objects by size and shape, and of the mobility of vertebrates (allowing them to initially escape the floodwaters). He cited Lammerts in support of Price's views about the thrust fault at Chief Mountain disproving the sequence.
The book went beyond Price in some areas. Morris extended the six-day creation from the Earth to the entire universe, and wrote that death and decay had only begun with the Fall of Man, which had therefore introduced entropy and the second law of thermodynamics. He proposed that a vapor canopy, before providing water for the flood, created a mild, even climate and shielded the Earth from cosmic rays – so radiocarbon dating of antediluvian samples would not work. He cited the testimony of Clifford L. Burdick (1919-2005) from the 1950s that some of the Glen Rose Formation dinosaur trackways near the Paluxy River in Dinosaur Valley State Park overlapped human footprints, but Burdick failed to confirm this, and the claim disappeared from the third edition of The Genesis Flood.
Creation Research Society
In a 1957 discussion with Whitcomb, Walter E. Lammerts suggested an "informal association" to exchange ideas, and possibly research, on flood geology. Morris was unavailable to get things started, then c. 1961 William J. Tinkle got in touch, and they set about recruiting others. They had difficulty in finding supporters with scientific qualifications. The Creation Research Committee of ten they put together on 9 February 1962 had varying views on the age of the Earth, but all opposed evolution. They then succeeded in recruiting others into what became the Creation Research Society (CRS) in June 1963, and grew rapidly. Getting an agreed statement of belief was problematic, they affirmed that the Bible was "historically and scientifically true in the original autographs" so that "the account of origins in Genesis is a factual presentation of simple historical truths" and "The great flood described in Genesis, commonly referred to as the Noachian Flood, was an historic event worldwide in its extent and effect", but to Morris's disappointment they did not make flood geology mandatory. They lacked a qualified geologist, and Morris persuaded the group to appoint Clifford L. Burdick as their only Earth scientist, overcoming initial concerns raised by Lammerts. The CRS grew rapidly, with an increasing proportion of the membership adhering to strict young Earth flood geology.The resources of the CRS for its first decade went into publication of the CRS Quarterly, and a project to publish a creationist school book. Since the 1920s most U.S. schools had not taught pupils about evolution, but Sputnik exposed apparent weaknesses of U.S. science education and the Biological Sciences Curriculum Study produced textbooks in 1963 which included the topic. When the Texas Education Agency held a hearing in October 1964 about adopting these textbooks, creationist objectors were unable to name suitable creationist alternatives. Lammerts organised a CRS textbook committee which lined up a group of authors, with John N. Moore as senior editor bringing their contributions together into a suitable textbook.
Creation science
The teaching of evolution, reintroduced in 1963 by the Biological Sciences Curriculum Study textbooks, was prohibited by laws in some states. These bans were contested; the Epperson v. Arkansas case which began late in 1965 was decided in 1968 by the United States Supreme Court ruling that such laws violated the Establishment Clause of the First Amendment to the United States Constitution.Some creationists thought a legal decision requiring religious neutrality in schools should shield their children from teachings hostile to their religion; Nell J. Segraves and Jean E. Sumrall (a friend of Lammerts who was also associated with the Creation Research Society and the Bible-Science Association) petitioned the California State Board of Education to require that school biology texts designate evolution a theory. In 1966 Max Rafferty as California State Superintendent of Public Instruction suggested that they demand equal time for creation, as the Civil Rights Act of 1964 allowed teachers to mention religion as long as they did not promote specific doctrines. Their first attempt failed, but in 1969 controversy arose over a proposed Science Framework for California Schools. Anticipating success, they and others in the Bible-Science Association formed Creation Science, Inc., to produce textbooks. A compromise acceptable to Segraves, Sumrall and the Board was suggested by Vernon L. Grose, and the revised 1970 Framework included "While the Bible and other philosophical treatises also mention creation, science has independently postulated the various theories of creation. Therefore, creation in scientific terms is not a religious or philosophical belief." The result kept school texts free of creationism, but downgraded evolution to mere speculative theory.Creationists reacted to the California developments with a new confidence that they could introduce their ideas into schools by minimizing biblical references. Henry M. Morris declared that "Creationism is on the way back, this time not primarily as a religious belief, but as an alternative scientific explanation of the world in which we live." In 1970 Creation Science, Inc., combined with a planned studies center at Christian Heritage College as the Creation-Science Research Center. Morris moved to San Diego to become director of the center and academic vice-president of the college. In the fall he presented a course at the college on "Scientific Creationism", the first time he is known to have used the term in public. (Two years later, the Creation-Science Research Center split with part becoming the Institute for Creation Research (ICR) led by Morris.)The Creation Research Society (CRS) had found schoolbook publishers reluctant to take on their textbook, and eventually the Christian publishing company Zondervan brought out Biology: A Search for Order in Complexity in 1970. The ten thousand copies printed sold out within a year, and they produced 25,000 as the second impression, but hardly any public schools adopted the book. A preface by Morris claimed that there were two philosophies of creation, "the doctrine of evolution and the doctrine of special creation", attempting to give both equal validity. The book mostly covered uncontroversial details of biology, but asserted that these were correctly seen as "God's creation" or "divine creation", and presented biblical creation as the correct scientific view. A chapter on "Weaknesses of Geologic Evidence" disputed evolutionary theories while asserting a "fact that most fossil material was laid down by the flood in Noah's time". Another chapter disputed evolutionary theory.In the Creation Research Society Quarterly for September 1971 Morris introduced the "two-model approach" asserting that evolution and creation were both equally scientific and equally religious, and soon afterwards he said they were "competing scientific hypotheses". For the third printing of Biology: A Search for Order in Complexity in 1974, the editor John N. Moore added a preface setting out this approach as "the two basic viewpoints of origins", the "evolution model" and the "creation model". When an Indiana school decided to use the book as their biology text, the Hendren v. Campbell district court case banned its use in public schools as infringing the Establishment Clause. Judge Michael T. Dugan, II, described it as "a text obviously designed to present only the view of Biblical Creationism in a favorable light", contravening the constitution by promotion of a specific sectarian religious view.As a tactic to gain the same scientific status as evolution, flood geology proponents had effectively relabeled the Bible-based flood geology of George McCready Price as "creation science" or "scientific creationism" by the mid 1970s. At the CRS board meeting in the Spring of 1972, members were told to start using "scientific creationism", a phrase used interchangeably with "creation science"; Morris explained that preferences differed, though neither was ideal as "one simple term" could not "identify such a complex and comprehensive subject." In the 1974 ICR handbook for high-school teachers titled Scientific Creationism, Morris used the two-model approach to support his argument that creationism could "be taught without reference to the book of Genesis or to other religious literature or to religious doctrines", and in public schools only the "basic scientific creation model" should be taught, rather than biblical creationism which "would open the door to wide interpretations of Genesis" or to non-Christian cosmogonies. He did not deny having been influenced by the Bible. In his preface to the book dated July 1974, Morris as editor outlined how the "Public School Edition" of the book evaluated evidence from a "strictly scientific point of view" without "reference to the Bible or other religious literature", while the "General Edition" was "essentially identical" except for an additional chapter on "Creation according to Scripture" that "places the scientific evidence in its proper biblical and theological context."The main ideas in creation science are: the belief in "creation ex nihilo" (Latin: out of nothing); the conviction that the Earth was created within the last 6,000 years; the belief that mankind and other life on Earth were created as distinct fixed "baraminological" kinds; and the idea that fossils found in geological strata were deposited during a cataclysmic flood which completely covered the entire Earth. As a result, creation science also challenges the commonly accepted geologic and astrophysical theories for the age and origins of the Earth and Universe, which creationists acknowledge are irreconcilable to the account in the Book of Genesis.
Creationist arguments for a global flood
Fossils
The geologic column and the fossil record are used as major pieces of evidence in the modern scientific explanation of the development and evolution of life on Earth as well as a means to establish the age of the Earth. Young Earth Creationists such as Morris and Whitcomb in their 1961 book, The Genesis Flood, say that the age of the fossils depends on the amount of time credited to the geologic column, which they ascribe to be about one year. Some flood geologists dispute geology's assembled global geologic column since index fossils are used to link geographically isolated strata to other strata across the map. Fossils are often dated by their proximity to strata containing index fossils whose age has been determined by its location on the geologic column. Oard and others say that the identification of fossils as index fossils has been too error-prone for index fossils to be used reliably to make those correlations, or to date local strata using the assembled geologic scale.Other creationists accept the existence of the geological column and believe that it indicates a sequence of events that might have occurred during the global flood. Institute for Creation Research creationists such as Andrew Snelling, Steven A. Austin and Kurt Wise take this approach, as does Creation Ministries International. They cite the Cambrian explosion – the appearance of abundant fossils in the upper Ediacaran (Vendian) Period and lower Cambrian Period – as the pre-Flood/Flood boundary, the presence in such sediments of fossils that do not occur later in the geological record as part of a pre–flood biota that perished and the absence of fossilized organisms that appear later (such as angiosperms and mammals) as due to erosion of sediments deposited by the flood as waters receded off the land. Creationists say that fossilization can only take place when the organism is buried quickly to protect the remains from destruction by scavengers or decomposition. They say that the fossil record provides evidence of a single cataclysmic flood and not of a series of slow changes accumulating over millions of years.Flood geologists have proposed numerous hypotheses to reconcile the sequence of fossils evident in the fossil column with the literal account of Noah's flood in the Bible. Whitcomb and Morris proposed three possible factors:
hydrological, whereby the relative buoyancies of the remains (based on the organisms' shapes and densities) determined the sequence in which their remains settled to the bottom of the flood-waters
ecological, suggesting organisms living at the ocean bottom succumbed first in the flood and those living at the highest altitudes last
anatomical/behavioral, the ordered sequence in the fossil column resulting from the very different responses to the rising waters between different kinds of organisms due to their diverse mobilities and original habitats. In a scenario put forth by Morris, the remains of marine life settled to the bottom first, followed by the slower-moving lowland reptiles, and culminating with humans, whose superior intelligence and ability to flee enabled them to reach higher elevations before the flood waters overcame them.Some creationists believe that oil and coal deposits formed rapidly in sedimentary layers as volcanoes or flood waters flattened forests and buried the debris. They believe the vegetation decomposed rapidly into oil or coal due to the heat of the subterranean waters as they were unleashed from the Earth during the flood or by the high temperatures created as the remains were compressed by water and sediment.Creationists continue to search for evidence in the natural world that they consider consistent with the above description, such as evidence of rapid formation. For example, there have been claims of raindrop marks and water ripples at layer boundaries, sometimes associated with the claimed fossilized footprints of men and dinosaurs walking together. Such footprint evidence has been debunked and some have been shown to be fakes.
Widespread flood stories
Proponents of Flood Geology state that "native global flood stories are documented as history or legend in almost every region on earth". "These flood tales are frequently linked by common elements that parallel the biblical account including the warning of the coming flood, the construction of a boat in advance, the storage of animals, the inclusion of family, and the release of birds to determine if the water level had subsided." They suggest that "the overwhelming consistency among flood legends found in distant parts of the globe indicates they were derived from the same origin, but oral transcription has changed the details through time".Anthropologist Patrick Nunn rejects this view and highlights the fact that much of the human population lives near water sources such as rivers and coasts, where unusually severe floods can be expected to occur occasionally and will be recorded in local mythology.
Proposed mechanisms of flood geology
George McCready Price attempted to fit a great deal of earth's geological history into a model based on a few accounts from the Bible. Price's simple model was used by Whitcomb and Morris initially but they did not build on the model in the 60s and 70s. However, a rough sketch of a creationist model could be constructed from creationist publications and debate material. Recent creationist efforts attempt to build complex models that incorporate as much scientific evidence as possible into the biblical narrative. Some scientific evidence used for these models was formerly rejected by creationists. These models attempt to explain continental movements in a short time frame, the order of the fossil record, and the Pleistocene ice age.
Runaway subduction
In the 60s and 70s a simple creationist model proposed that, "The Flood split the land mass into the present continents." Steve Austin and other creationists proposed a preliminary model of catastrophic plate tectonics (CPT) in 1994. Their work built on earlier papers by John Baumgardner and Russell Humphreys in 1986. Baumgardner proposed a model of mantle convection that allows for runaway subduction and Humphrey associated mantle convection with rapid magnetic reversals in earth history. Baumgardner's proposal holds that the rapid plunge of former oceanic plates into the mantle (caused by an unknown trigger-mechanism) increased local mantle pressures to the point that its viscosity dropped several magnitudes according to known properties of mantle silicates. Once initiated, sinking plates caused the spread of low viscosity throughout the mantle resulting in runaway mantle-convection and catastrophic tectonic motion which dragged continents across the surface of the earth. Once the former ocean plates, which are thought to be denser than the mantle, reached the bottom of the mantle an equilibrium resulted. Pressures dropped, viscosity increased, runaway mantle-convection stopped, leaving the surface of the earth rearranged. Proponents point to subducted slabs in the mantle which are still relatively cool, which they regard as evidence that they have not been there for millions of years which would result in temperature equilibration.Given that conventional plate tectonics accounts for much of the geomorphic features of continents and oceans, it is natural that creationists would seek to develop a high speed version of the same process. CPT explains many geological features, provides mechanisms for the biblical flood, and minimizes appeals to miracles.Some prominent creationists (Froede, Oard, Read) oppose CPT for various technical reasons. One main objection is that the model assumes the super continent Pangaea was intact at the initiation of the year-long flood. The CPT process then tore Pangaea apart creating the current configuration of the continents. But the breakup of Pangaea started early in the Mesozoic, meaning that CPT only accounts for part of the entire Phanerozoic geological record. CPT in this form only explains part of the geological column that flood geology normally explains. Modifying the CPT model to account for the entire Phanerozoic including multiple Wilson Cycles would complicate the model considerably.Other objections of CPT include the amount of heat produced for the rapid plate movements, and the fact that the cooling of hot oceanic plates and the raising of continental plates would take a great deal of time and require multiple small scale catastrophes after the flood ended. The original CPT proposal of Austin and others in 1994 was admittedly preliminary but the major issues have not been solved.The vast majority of geologists regard the hypothesis of catastrophic plate tectonics as pseudoscience; they reject it in favor of the conventional geological theory of plate tectonics. It has been argued that the tremendous release of energy necessitated by such an event would boil off the Earth's oceans, making a global flood impossible. Not only does catastrophic plate tectonics lack any plausible geophysical mechanism by which its changes might occur, it also is contradicted by considerable geological evidence (which is in turn consistent with conventional plate tectonics), including:
The fact that a number of volcanic oceanic island chains, such as the Hawaiian islands, yield evidence of the ocean floor having moved over volcanic hot-spots. These islands have widely ranging ages (determined via both radiometric dating and relative erosion) that contradict the catastrophic tectonic hypothesis of rapid development and thus a similar age.
Radiometric dating and sedimentation rates on the ocean floor likewise contradict the hypothesis that it all came into existence nearly contemporaneously.
Catastrophic tectonics does not allow sufficient time for guyots to have their peak eroded away (leaving these seamounts' characteristic flat tops).
Runaway subduction does not explain the kind of continental collision illustrated by that of the Indian and Eurasian Plates. (For further information see Orogeny.)Conventional plate tectonics accounts for the geological evidence already, including innumerable details that catastrophic plate tectonics cannot, such as why there is gold in California, silver in Nevada, salt flats in Utah, and coal in Pennsylvania, without requiring any extraordinary mechanisms to do so.
Vapor/water canopy
Isaac Newton Vail (1840–1912), a Quaker schoolteacher, in his 1912 work The Earth's Annular System, extrapolated from the nebular hypothesis what he called the annular system of earth history, with the earth being originally surrounded by rings resembling those of Saturn, or "canopies" of water vapor. Vail hypothesised that, one by one, these canopies collapsed on the Earth, resulting in fossils being buried in a "succession of stupendous cataclysms, separated by unknown periods of time". The Genesis flood was thought to have been caused by "the last remnant" of this vapor. Although this final flood was geologically significant, it was not held to account for as much of the fossil record as George McCready Price had asserted.Vail's ideas about geology appeared in Charles Taze Russell's 1912 The Photo-Drama of Creation and subsequently in Joseph Franklin Rutherford's Creation of 1927 and later publications. The Seventh-day Adventist physicist Robert W. Woods also proposed a vapor canopy, before The Genesis Flood gave it prominent and repeated mention in 1961.Although the vapor-canopy theory has fallen into disfavour among most creationists, Dillow in 1981 and Vardiman in 2003 attempted to defend the idea. Among its more vocal adherents, controversial young earth creationist Kent Hovind uses it as the basis for his eponymous "Hovind Theory". Jehovah's Witnesses propose as the water source of the deluge a "heavenly ocean" that was over the earth from the second creative day until the Flood.
Modern geology and flood geology
Modern geology, its sub-disciplines and other scientific disciplines use the scientific method to analyze the geology of the earth. The key tenets of flood geology are refuted by scientific analysis and do not have any standing in the scientific community. Modern geology relies on a number of established principles, one of the most important of which is Charles Lyell's principle of uniformitarianism. In relation to geological forces it states that the shaping of the Earth has occurred by means of mostly slow-acting forces that can be seen in operation today. By applying these principles, geologists have determined that the Earth is approximately 4.54 billion years old. They study the lithosphere of the Earth to gain information on the history of the planet. Geologists divide Earth's history into eons, eras, periods, epochs, and faunal stages characterized by well-defined breaks in the fossil record (see Geologic time scale). In general, there is a lack of any evidence for any of the above effects proposed by flood geologists and their claims of fossil layering are not taken seriously by scientists.
Erosion
The global flood cannot explain geological formations such as angular unconformities, where sedimentary rocks have been tilted and eroded then more sedimentary layers deposited on top, needing long periods of time for these processes. There is also the time needed for the erosion of valleys in sedimentary rock mountains. In another example, the flood, had it occurred, should also have produced large-scale effects spread throughout the entire world. Erosion should be evenly distributed, yet the levels of erosion in, for example, the Appalachians and the Rocky Mountains differ significantly.
Geochronology
Geochronology is the science of determining the absolute age of rocks, fossils, and sediments by a variety of techniques. These methods indicate that the Earth as a whole is about 4.54 billion years old, and that the strata that, according to flood geology, were laid down during the Flood some 6,000 years ago, were actually deposited gradually over many millions of years.
Paleontology
If the flood were responsible for fossilization, then all the animals now fossilized must have been living together on the Earth just before the flood. Based on estimates of the number of remains buried in the Karoo fossil formation in Africa, this would correspond to an abnormally high density of vertebrates worldwide, close to 2100 per acre.
Creationists argue that evidence for the geological column is fragmentary, and all the complex layers of chalk occurred in the approach to the 150th day of Noah's flood. However, the entire geologic column is found in several places, and shows multiple features, including evidence of erosion and burrowing through older layers, which are inexplicable on a short timescale. Carbonate hardgrounds and the fossils associated with them show that the so-called flood sediments include evidence of long hiatuses in deposition that are not consistent with flood dynamics or timing.
Geochemistry
Proponents of Flood Geology are also unable to account for the alternation between calcite seas and aragonite seas through the Phanerozoic. The cyclical pattern of carbonate hardgrounds, calcitic and aragonitic ooids, and calcite-shelled fauna has apparently been controlled by seafloor spreading rates and the flushing of seawater through hydrothermal vents which changes its Mg/Ca ratio.
Sedimentary rock features
Phil Senter's 2011 article, "The Defeat of Flood Geology by Flood Geology", in the journal Reports of the National Center for Science Education, discusses "sedimentologic and other geologic features that Flood geologists have identified as evidence that particular strata cannot have been deposited during a time when the entire planet was under water ... and distribution of strata that predate the existence of the Ararat mountain chain." These include continental basalts, terrestrial tracks of animals, and marine communities preserving multiple in-situ generations included in the rocks of most or all Phanerozoic periods, and the basalt even in the younger Precambrian rocks. Others, occurring in rocks of several geologic periods, include lake deposits and eolian (wind) deposits. Using their own words, Flood geologists find evidence in every Paleozoic and Mesozoic period, and in every epoch of the Cenozoic period, indicating that a global flood could not have occurred during that interval. A single flood could also not account for such features as angular unconformities, in which lower rock layers are tilted while higher rock layers were laid down horizontally on top.
Physics
The engineer Jane Albright notes several scientific failings of the canopy theory, reasoning from first principles in physics. Among these are that enough water to create a flood of even 5 centimetres (2.0 in) of rain would form a vapor blanket thick enough to make the earth too hot for life, since water vapor is a greenhouse gas; the same blanket would have an optical depth sufficient to effectively obscure all incoming starlight.
See also
Baraminology
Creation biology
International Conference on Creationism
List of topics characterized as pseudoscience
Polystrate fossil
Pre-Adamite
Scriptural geologist
Searches for Noah's Ark
Notes
References
Books
Journals
Web
OtherBaumgardner, JR (1986). "Numerical Simulation of the Large-Scale Tectonic Changes Accompanying the Flood" (PDF). First International Conference on Creationism. Retrieved 15 July 2014.
Baumgardner, JR (2003). "Catastrophic Plate Tectonics: The Physics Behind the Genesis Flood". Fifth International Conference on Creationism. Archived from the original on 6 November 2016. Retrieved 29 March 2007.
Humphreys, Russell (1986). "Reversals of the Earth's Magnetic Field During the Genesis Flood" (PDF). First International Conference on Creationism. Retrieved 15 July 2014.
Further reading
Senter, Phil (May–June 2001). "The Defeat of Flood Geology by Flood Geology". Reports of the National Center for Science Education. 31 (3). Archived from the original on 18 February 2019. Retrieved 19 July 2011.
H. Neuville, "On the Extinction of the Mammoth," Annual Report of the Smithsonian Institution, 1919.
Patten, Donald W. The Biblical Flood and the Ice Epoch (Seattle: Pacific Meridian Publishing Company, 1966).
Patten, Donald W. Catastrophism and the Old Testament (Seattle: Pacific Meridian Publishing Company, 1988). ISBN 0-88070-291-5 |
soil formation | Soil formation, also known as pedogenesis, is the process of soil genesis as regulated by the effects of place, environment, and history. Biogeochemical processes act to both create and destroy order (anisotropy) within soils. These alterations lead to the development of layers, termed soil horizons, distinguished by differences in color, structure, texture, and chemistry. These features occur in patterns of soil type distribution, forming in response to differences in soil forming factors.Pedogenesis is studied as a branch of pedology, the study of soil in its natural environment. Other branches of pedology are the study of soil morphology, and soil classification. The study of pedogenesis is important to understanding soil distribution patterns in current (soil geography) and past (paleopedology) geologic periods.
Overview
Soil develops through a series of changes. The starting point is weathering of freshly accumulated parent material. A variety of soil microbes (bacteria, archaea, fungi) feed on simple compounds (nutrients) released by weathering, and produce organic acids and specialized proteins which contribute in turn to mineral weathering. They also leave behind organic residues which contribute to humus formation. Plant roots with their symbiotic mycorrhizal fungi are also able to extract nutrients from rocks.New soils increase in depth by a combination of weathering, and further deposition. The soil production rate due to weathering is approximately 1/10 mm per year. New soils can also deepen from dust deposition. Gradually soil is able to support higher forms of plants and animals, starting with pioneer species, and proceeding along ecological succession to more complex plant and animal communities. Topsoils deepen with the accumulation of humus originating from dead remains of higher plants and soil microbes. They also deepen through mixing of organic matter with weathered minerals. As soils mature, they develop soil horizons as organic matter accumulates and mineral weathering and leaching take place.
Factors of soil formation
Soil formation is influenced by at least five classic factors that are intertwined in the evolution of a soil. They are: parent material, climate, topography (relief), organisms, and time. When reordered to climate, organisms, relief, parent material, and time, they form the acronym CLORPT.
Parent material
The mineral material from which a soil forms is called parent material. Rock, whether its origin is igneous, sedimentary, or metamorphic, is the source of all soil mineral materials and the origin of all plant nutrients with the exceptions of nitrogen, hydrogen and carbon. As the parent material is chemically and physically weathered, transported, deposited and precipitated, it is transformed into a soil.Typical soil parent mineral materials are:
Quartz: SiO2
Calcite: CaCO3
Feldspar: KAlSi3O8
Mica (biotite): K(Mg,Fe)3(AlSi3O10)(F,OH)2Parent materials are classified according to how they came to be deposited. Residual materials are mineral materials that have weathered in place from primary bedrock. Transported materials are those that have been deposited by water, wind, ice or gravity. Cumulose material is organic matter that has grown and accumulates in place.Residual soils are soils that develop from their underlying parent rocks and have the same general chemistry as those rocks. The soils found on mesas, plateaux, and plains are residual soils. In the United States as little as three percent of the soils are residual.Most soils derive from transported materials that have been moved many miles by wind, water, ice and gravity.
Aeolian processes (movement by wind) are capable of moving silt and fine sand many hundreds of miles, forming loess soils (60–90 percent silt), common in the Midwest of North America, north-western Europe, Argentina and Central Asia. Clay is seldom moved by wind as it forms stable aggregates.
Water-transported materials are classed as either alluvial, lacustrine, or marine. Alluvial materials are those moved and deposited by flowing water. Sedimentary deposits settled in lakes are called lacustrine. Lake Bonneville and many soils around the Great Lakes of the United States are examples. Marine deposits, such as soils along the Atlantic and Gulf Coasts and in the Imperial Valley of California of the United States, are the beds of ancient seas that have been revealed as the land uplifted.
Ice moves parent material and makes deposits in the form of terminal and lateral moraines in the case of stationary glaciers. Retreating glaciers leave smoother ground moraines and in all cases, outwash plains are left as alluvial deposits are moved downstream from the glacier.
Parent material moved by gravity is obvious at the base of steep slopes as talus cones and is called colluvial material.Cumulose parent material is not moved but originates from deposited organic material. This includes peat and muck soils and results from preservation of plant residues by the low oxygen content of a high water table. While peat may form sterile soils, muck soils may be very fertile.
Weathering
The weathering of parent material takes the form of physical weathering (disintegration), chemical weathering (decomposition) and chemical transformation. Weathering is usually confined to the top few meters of geologic material, because physical, chemical, and biological stresses and fluctuations generally decrease with depth. Physical disintegration begins as rocks that have solidified deep in the Earth are exposed to lower pressure near the surface and swell and become mechanically unstable. Chemical decomposition is a function of mineral solubility, the rate of which doubles with each 10 °C rise in temperature, but is strongly dependent on water to effect chemical changes. Rocks that will decompose in a few years in tropical climates will remain unaltered for millennia in deserts. Structural changes are the result of hydration, oxidation, and reduction. Chemical weathering mainly results from the excretion of organic acids and chelating compounds by bacteria and fungi, thought to increase under present-day greenhouse effect.
Physical disintegration is the first stage in the transformation of parent material into soil. Temperature fluctuations cause expansion and contraction of the rock, splitting it along lines of weakness. Water may then enter the cracks and freeze and cause the physical splitting of material along a path toward the center of the rock, while temperature gradients within the rock can cause exfoliation of "shells". Cycles of wetting and drying cause soil particles to be abraded to a finer size, as does the physical rubbing of material as it is moved by wind, water, and gravity. Water can deposit within rocks minerals that expand upon drying, thereby stressing the rock. Finally, organisms reduce parent material in size and create crevices and pores through the mechanical action of plant roots and the digging activity of animals. Grinding of parent material by rock-eating animals also contributes to incipient soil formation.
Chemical decomposition and structural changes result when minerals are made soluble by water or are changed in structure. The first three of the following list are solubility changes and the last three are structural changes.The solution of salts in water results from the action of bipolar water molecules on ionic salt compounds producing a solution of ions and water, removing those minerals and reducing the rock's integrity, at a rate depending on water flow and pore channels.
Hydrolysis is the transformation of minerals into polar molecules by the splitting of intervening water. This results in soluble acid-base pairs. For example, the hydrolysis of orthoclase-feldspar transforms it to acid silicate clay and basic potassium hydroxide, both of which are more soluble.
In carbonation, the solution of carbon dioxide in water forms carbonic acid. Carbonic acid will transform calcite into more soluble calcium bicarbonate.
Hydration is the inclusion of water in a mineral structure, causing it to swell and leaving it stressed and easily decomposed.
Oxidation of a mineral compound is the inclusion of oxygen in a mineral, causing it to increase its oxidation number and swell due to the relatively large size of oxygen, leaving it stressed and more easily attacked by water (hydrolysis) or carbonic acid (carbonation).
Reduction, the opposite of oxidation, means the removal of oxygen, hence the oxidation number of some part of the mineral is reduced, which occurs when oxygen is scarce. The reduction of minerals leaves them electrically unstable, more soluble and internally stressed and easily decomposed. It mainly occurs in waterlogged conditions.Of the above, hydrolysis and carbonation are the most effective, in particular in regions of high rainfall, temperature and physical erosion. Chemical weathering becomes more effective as the surface area of the rock increases, thus is favoured by physical disintegration. This stems in latitudinal and altitudinal climate gradients in regolith formation.Saprolite is a particular example of a residual soil formed from the transformation of granite, metamorphic and other types of bedrock into clay minerals. Often called [weathered granite], saprolite is the result of weathering processes that include: hydrolysis, chelation from organic compounds, hydration and physical processes that include freezing and thawing. The mineralogical and chemical composition of the primary bedrock material, its physical features, including grain size and degree of consolidation, and the rate and type of weathering transforms the parent material into a different mineral. The texture, pH and mineral constituents of saprolite are inherited from its parent material. This process is also called arenization, resulting in the formation of sandy soils (granitic arenas), thanks to the much higher resistance of quartz compared to other mineral components of granite (micas, amphiboles, feldspars).
Climate
The principal climatic variables influencing soil formation are effective precipitation (i.e., precipitation minus evapotranspiration) and temperature, both of which affect the rates of chemical, physical, and biological processes. Temperature and moisture both influence the organic matter content of soil through their effects on the balance between primary production and decomposition: the colder or drier the climate the lesser atmospheric carbon is fixed as organic matter while the lesser organic matter is decomposed.Climate is the dominant factor in soil formation, and soils show the distinctive characteristics of the climate zones in which they form, with a feedback to climate through transfer of carbon stocked in soil horizons back to the atmosphere. If warm temperatures and abundant water are present in the profile at the same time, the processes of weathering, leaching, and plant growth will be maximized. According to the climatic determination of biomes, humid climates favor the growth of trees. In contrast, grasses are the dominant native vegetation in subhumid and semiarid regions, while shrubs and brush of various kinds dominate in arid areas.Water is essential for all the major chemical weathering reactions. To be effective in soil formation, water must penetrate the regolith. The seasonal rainfall distribution, evaporative losses, site topography, and soil permeability interact to determine how effectively precipitation can influence soil formation. The greater the depth of water penetration, the greater the depth of weathering of the soil and its development. Surplus water percolating through the soil profile transports soluble and suspended materials from the upper layers (eluviation) to the lower layers (illuviation), including clay particles and dissolved organic matter. It may also carry away soluble materials in the surface drainage waters. Thus, percolating water stimulates weathering reactions and helps differentiate soil horizons. Likewise, a deficiency of water is a major factor in determining the characteristics of soils of dry regions. Soluble salts are not leached from these soils, and in some cases they build up to levels that curtail plant and microbial growth. Soil profiles in arid and semi-arid regions are also apt to accumulate carbonates and certain types of expansive clays (calcrete or caliche horizons). In tropical soils, when the soil has been deprived of vegetation (e.g. by deforestation) and thereby is submitted to intense evaporation, the upward capillary movement of water, which has dissolved iron and aluminum salts, is responsible for the formation of a superficial hard pan of laterite or bauxite, respectively, which is improper for cultivation, a known case of irreversible soil degradation (lateritization, bauxitization).The direct influences of climate include:
A shallow accumulation of lime in low rainfall areas as caliche
Formation of acid soils in humid areas
Erosion of soils on steep hillsides
Deposition of eroded materials downstream
Very intense chemical weathering, leaching, and erosion in warm and humid regions where soil does not freezeClimate directly affects the rate of weathering and leaching. Wind moves sand and smaller particles (dust), especially in arid regions where there is little plant cover, depositing it close or far from the entrainment source. The type and amount of precipitation influence soil formation by affecting the movement of ions and particles through the soil, and aid in the development of different soil profiles. Soil profiles are more distinct in wet and cool climates, where organic materials may accumulate, than in wet and warm climates, where organic materials are rapidly consumed. The effectiveness of water in weathering parent rock material depends on seasonal and daily temperature fluctuations, which favour tensile stresses in rock minerals, and thus their mechanical disaggregation, a process called thermal fatigue. By the same process freeze-thaw cycles are an effective mechanism which breaks up rocks and other consolidated materials.Climate also indirectly influences soil formation through the effects of vegetation cover and biological activity, which modify the rates of chemical reactions in the soil.
Topography
The topography, or relief, is characterized by the inclination (slope), elevation, and orientation of the terrain (aspect). Topography determines the rate of precipitation or runoff and the rate of formation or erosion of the surface soil profile. The topographical setting may either hasten or retard the work of climatic forces.Steep slopes encourage rapid soil loss by erosion and allow less rainfall to enter the soil before running off and hence, little mineral deposition in lower profiles (illuviation). In semiarid regions, the lower effective rainfall on steeper slopes also results in less complete vegetative cover, so there is less plant contribution to soil formation. For all of these reasons, steep slopes prevent the formation of soil from getting very far ahead of soil destruction. Therefore, soils on steep terrain tend to have rather shallow, poorly developed profiles in comparison to soils on nearby, more level sites.Topography determines exposure to weather, fire, and other forces of man and nature. Mineral accumulations, plant nutrients, type of vegetation, vegetation growth, erosion, and water drainage are dependent on topographic relief. Soils at the bottom of a hill will get more water than soils on the slopes, and soils on the slopes that face the sun's path will be drier than soils on slopes that do not.In swales and depressions where runoff water tends to concentrate, the regolith is usually more deeply weathered and soil profile development is more advanced. However, in the lowest landscape positions, water may saturate the regolith to such a degree that drainage and aeration are restricted. Here, the weathering of some minerals and the decomposition of organic matter are retarded, while the loss of iron and manganese is accelerated. In such low-lying topography, special profile features characteristic of wetland soils may develop. Depressions allow the accumulation of water, minerals and organic matter and in the extreme, the resulting soils will be saline marshes or peat bogs.Recurring patterns of topography result in toposequences or soil catenas. These patterns emerge from topographic differences in erosion, deposition, fertility, soil moisture, plant cover, soil biology, fire history, and exposure to the elements. As a matter of rule, gravity transports water downslope, together with mineral and organic solutes and colloids, increasing particulate and base content at the foot of hills and mountains. However, many other factors like drainage and erosion interact with slope position, blurring its expected influence on crop yield.
Organisms
Each soil has a unique combination of microbial, plant, animal and human influences acting upon it. Microorganisms are particularly influential in the mineral transformations critical to the soil forming process. Additionally, some bacteria can fix atmospheric nitrogen and some fungi are efficient at extracting deep soil phosphorus and increasing soil carbon levels in the form of glomalin. Plants hold soil against erosion, and accumulated plant material build soil humus levels. Plant root exudation supports microbial activity. Animals serve to decompose plant materials and mix soil through bioturbation.Soil is the most speciose ecosystem on Earth, but the vast majority of organisms in soil are microbes, a great many of which have not been described. There may be a population limit of around one billion cells per gram of soil, but estimates of the number of species vary widely from 50,000 per gram to over a million per gram of soil. The total number of organisms and species can vary widely according to soil type, location, and depth.Plants, animals, fungi, bacteria and humans affect soil formation (see soil biomantle and stonelayer). Soil animals, including soil macrofauna and soil mesofauna, mix soils as they form burrows and pores, allowing moisture and gases to move about, a process called bioturbation. In the same way, plant roots penetrate soil horizons and open channels upon decomposition. Plants with deep taproots can penetrate many metres through the different soil layers to bring up nutrients from deeper in the profile. Plants have fine roots that excrete organic compounds (sugars, organic acids, mucilage), slough off cells (in particular at their tip) and are easily decomposed, adding organic matter to soil, a process called rhizodeposition. Micro-organisms, including fungi and bacteria, effect chemical exchanges between roots and soil and act as a reserve of nutrients in a soil biological hotspot called rhizosphere. The growth of roots through the soil stimulates microbial populations, stimulating in turn the activity of their predators (notably amoeba), thereby increasing the mineralization rate, and in last turn root growth, a positive feedback called the soil microbial loop. Out of root influence, in the bulk soil, most bacteria are in a quiescent stage, forming microaggregates, i.e. mucilaginous colonies to which clay particles are glued, offering them a protection against desiccation and predation by soil microfauna (bacteriophagous protozoa and nematodes). Microaggregates (20–250 μm) are ingested by soil mesofauna and macrofauna, and bacterial bodies are partly or totally digested in their guts.Humans impact soil formation by removing vegetation cover through tillage, application of biocides, fire and leaving soils bare. This can lead to erosion, waterlogging, lateritization or podzolization (according to climate and topography). Their tillage also mixes the different soil layers, restarting the soil formation process as less weathered material is mixed with the more developed upper layers, resulting in net increased rate of mineral weathering.Earthworms, ants, termites, moles, gophers, as well as some millipedes and tenebrionid beetles, mix the soil as they burrow, significantly affecting soil formation. Earthworms ingest soil particles and organic residues, enhancing the availability of plant nutrients in the material that passes through their bodies. They aerate and stir the soil and create stable soil aggregates, after having disrupted links between soil particles during the intestinal transit of ingested soil, thereby assuring ready infiltration of water. In addition, as ants and termites build mounds, earthworms transport soil materials from one horizon to another. Other important functions are fulfilled by earthworms in the soil ecosystem, in particular their intense mucus production, both within the intestine and as a lining in their galleries, exert a priming effect on soil microflora, giving them the status of ecosystem engineers, which they share with ants and termites.In general, the mixing of the soil by the activities of animals, sometimes called pedoturbation, tends to undo or counteract the tendency of other soil-forming processes that create distinct horizons. Termites and ants may also retard soil profile development by denuding large areas of soil around their nests, leading to increased loss of soil by erosion. Large animals such as gophers, moles, and prairie dogs bore into the lower soil horizons, bringing materials to the surface. Their tunnels are often open to the surface, encouraging the movement of water and air into the subsurface layers. In localized areas, they enhance mixing of the lower and upper horizons by creating, and later refilling the tunnels. Old animal burrows in the lower horizons often become filled with soil material from the overlying A horizon, creating profile features known as crotovinas.Vegetation impacts soils in numerous ways. It can prevent erosion caused by excessive rain that might result from surface runoff. Plants shade soils, keeping them cooler and slowing evaporation of soil moisture. Conversely, by way of transpiration, plants can cause soils to lose moisture, resulting in complex and highly variable relationships between leaf area index (measuring light interception) and moisture loss: more generally plants prevent soil from desiccation during driest months while they dry it during moister months, thereby acting as a buffer against strong moisture variation. Plants can form new chemicals that can break down minerals, both directly and indirectly through mycorrhizal fungi and rhizosphere bacteria, and improve the soil structure. The type and amount of vegetation depends on climate, topography, soil characteristics and biological factors, mediated or not by human activities. Soil factors such as density, depth, chemistry, pH, temperature and moisture greatly affect the type of plants that can grow in a given location. Dead plants and fallen leaves and stems begin their decomposition on the surface. There, organisms feed on them and mix the organic material with the upper soil layers; these added organic compounds become part of the soil formation process.The influence of humans, and by association, fire, are state factors placed within the organisms state factor. Humans can import, or extract, nutrients and energy in ways that dramatically change soil formation. Accelerated soil erosion due to overgrazing, and Pre-Columbian terraforming the Amazon basin resulting in Terra Preta are two examples of the effects of humans' management.
Human activities widely influence soil formation. For example, it is believed that Native Americans regularly set fires to maintain several large areas of prairie grasslands in Indiana and Michigan, although climate and mammalian grazers (e.g. bisons) are also advocated to explain the maintenance of the Great Plains of North America. In more recent times, human destruction of natural vegetation and subsequent tillage of the soil for crop production has abruptly modified soil formation. Likewise, irrigating soil in an arid region drastically influences soil-forming factors, as does adding fertilizer and lime to soils of low fertility.Distinct ecosystems produce distinct soils, sometimes in easily observable ways. For example, three species of land snails in the genus Euchondrus in the Negev desert are noted for eating lichens growing under the surface limestone rocks and slabs (endolithic lichens). The grazing activity of these ecosystem engineers disrupts and eats the limestone, resulting in the weathering of the stones, and the subsequent formation of soil. They have a significant effect on the region: the total population of snails is estimated to process between 0.7 and 1.1 metric ton per hectare per year of limestone in the Negev desert.The effects of ancient ecosystems are not as easily observed, and this challenges the understanding of soil formation. For example, the chernozems of the North American tallgrass prairie have a humus fraction nearly half of which is charcoal. This outcome was not anticipated because the antecedent prairie fire ecology capable of producing these distinct deep rich black soils is not easily observed. The role of soil engineers in the formation of charcoal-enriched horizons of Terra preta (Amazonian Black Earths) is now acknowledged and was verified experimentally on the pantropical earthworm Pontoscolex corethrurus.
Time
Time is a factor in the interactions of all the above. While a mixture of sand, silt and clay constitute the texture of a soil and the aggregation of those components produces peds, the development of a distinct B horizon marks the development of a soil or pedogenesis. With time, soils will evolve features that depend on the interplay of the prior listed soil-forming factors. It takes decades to several thousand years for a soil to develop a profile, although the notion of soil development has been criticized, soil being in a constant state-of-change under the influence of fluctuating soil-forming factors. That time period depends strongly on climate, parent material, relief, and biotic activity. For example, recently deposited material from a flood exhibits no soil development as there has not been enough time for the material to form a structure that further defines soil. The original soil surface is buried, and the formation process must begin anew for this deposit. Over time the soil will develop a profile that depends on the intensities of biota and climate. While a soil can achieve relative stability of its properties for extended periods, the soil life cycle ultimately ends in soil conditions that leave it vulnerable to erosion. Despite the inevitability of soil retrogression and degradation, most soil cycles are long.Soil-forming factors continue to affect soils during their existence, even on stable landscapes that are long-enduring, some for millions of years. Materials are deposited on top or are blown or washed from the surface. With additions, removals and alterations, soils are always subject to new conditions. Whether these are slow or rapid changes depends on climate, topography and biological activity.Time as a soil-forming factor may be investigated by studying soil chronosequences, in which soils of different ages but with minor differences in other soil-forming factors can be compared.Paleosols are soils formed during previous soil forming conditions.
History of research
Dokuchaev's equation
Russian geologist Vasily Dokuchaev, commonly regarded as the father of pedology, determined in 1883 that soil formation occurs over time under the influence of climate, vegetation, topography, and parent material. He demonstrated this in 1898 using the soil forming equation:
soil = f(cl, o, p) tr(where cl or c = climate, o = biological processes, p = parent material) tr = relative time (young, mature, old)
Hans Jenny's state equation
American soil scientist Hans Jenny published in 1941 a state equation for the factors influencing soil formation:
S = f(cl, o, r, p, t, …) S soil formation
cl (sometimes c) climate
o organisms (soil microbiology, soil mesofauna, soil biology)
r relief
p parent material
t timeThis is often remembered with the mnemonic Clorpt.
Jenny's state equation in Factors of Soil Formation differs from the Vasily Dokuchaev equation, treating time (t) as a factor, adding topographic relief (r), and pointedly leaving the ellipsis "open" for more factors (state variables) to be added as our understanding becomes more refined.
There are two principal methods by which the state equation may be solved: first in a theoretical or conceptual manner by logical deductions from certain premises, and second empirically by experimentation or field observation.
The empirical method is still mostly employed today, and soil formation can be defined by varying a single factor and keeping the other factors constant. This led to the development of empirical models to describe pedogenesis, such as climofunctions, biofunctions, topofunctions, lithofunctions, and chronofunctions. Since Hans Jenny published his formulation in 1941, it has been used by innumerable soil surveyors all over the world as a qualitative list for understanding the factors that may be important for producing the soil pattern within a region.
Soil forming processes
Soils develop from parent material by various weathering processes. Organic matter accumulation, decomposition, and humification are as critically important to soil formation as weathering. The zone of humification and weathering where pedogenic processes are dominant and where biota play an important role is termed the solum.Soil acidification resulting from soil respiration supports chemical weathering. Plants contribute to chemical weathering through root exudates.Soils can be enriched by deposition of sediments on floodplains and alluvial fans, and by wind-borne deposits.Soil mixing (pedoturbation) is often an important factor in soil formation. Pedoturbation includes churning clays, cryoturbation, and bioturbation. Types of bioturbation include faunal pedoturbation (animal burrowing), plant pedoturbation (root growth, tree uprooting), and fungal pedoturbation (mycelial growth). Pedoturbation transforms soils through destratification, mixing, and sorting, as well as creating preferential flow paths for soil gas and infiltrating water. The zone of active bioturbation is termed the soil biomantle.Soil moisture content and water flow through the soil profile support leaching of solutes, and eluviation. Eluviation is the translocation of colloid material, such as organic matter, clay and other mineral compounds. Transported constituents are deposited due to differences in soil moisture and soil chemistry, especially soil pH and redox potential. The interplay of removal (eluviation) and deposition (illuviation), also called pedotranslocation, results in contrasting soil horizons.Key soil-forming processes especially important to macro-scale patterns of soil formation are:
Laterization
Podsolization
Calcification
Salinization
Gleization
Examples
A variety of mechanisms contribute to soil formation, including siltation, erosion, overpressure and lake bed succession. A specific example of the evolution of soils in prehistoric lake beds is in the Makgadikgadi Pans of the Kalahari Desert, where change in an ancient river course led to millennia of salinity buildup and formation of calcretes and silcretes.
Notes
References
Stanley W. Buol, F.D. Hole and R.W. McCracken. 1997. Soil Genesis and Classification, 4th ed. Iowa State Univ. Press, Ames ISBN 0-8138-2873-2
C. Michael Hogan. 2008. Makgadikgadi, The Megalithic Portal, ed. A. Burnham [1]
Francis D. Hole and J.B. Campbell. 1985. Soil landscape analysis. Totowa Rowman & Allanheld, 214 p. ISBN 0-86598-140-X
Hans Jenny. 1994. Factors of Soil Formation. A System of Quantitative Pedology. New York: Dover Press. (Reprint, with foreword by R. Amundson, of the 1941 McGraw-Hill publication). pdf file format.
Ben van der Pluijm et al. 2005. Soils, Weathering, and Nutrients from the Global Change 1 Lectures. University of Michigan. Url last accessed on 2007-03-31 |
geologic record | The geologic record in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata. That is, deposits laid down by volcanism or by deposition of sediment derived from weathering detritus (clays, sands etc.). This includes all its fossil content and the information it yields about the history of the Earth: its past climate, geography, geology and the evolution of life on its surface. According to the law of superposition, sedimentary and volcanic rock layers are deposited on top of each other. They harden over time to become a solidified (competent) rock column, that may be intruded by igneous rocks and disrupted by tectonic events.
Correlating the rock record
At a certain locality on the Earth's surface, the rock column provides a cross section of the natural history in the area during the time covered by the age of the rocks. This is sometimes called the rock history and gives a window into the natural history of the location that spans many geological time units such as ages, epochs, or in some cases even multiple major geologic periods—for the particular geographic region or regions. The geologic record is in no one place entirely complete for where geologic forces one age provide a low-lying region accumulating deposits much like a layer cake, in the next may have uplifted the region, and the same area is instead one that is weathering and being torn down by chemistry, wind, temperature, and water. This is to say that in a given location, the geologic record can be and is quite often interrupted as the ancient local environment was converted by geological forces into new landforms and features. Sediment core data at the mouths of large riverine drainage basins, some of which go 7 miles (11 km) deep thoroughly support the law of superposition.However using broadly occurring deposited layers trapped within differently located rock columns, geologists have pieced together a system of units covering most of the geologic time scale using the law of superposition, for where tectonic forces have uplifted one ridge newly subject to erosion and weathering in folding and faulting the strata, they have also created a nearby trough or structural basin region that lies at a relative lower elevation that can accumulate additional deposits. By comparing overall formations, geologic structures and local strata, calibrated by those layers which are widespread, a nearly complete geologic record has been constructed since the 17th century.
Discordant strata example
Correcting for discordancies can be done in a number of ways and utilizing a number of technologies or field research results from studies in other disciplines.
In this example, the study of layered rocks and the fossils they contain is called biostratigraphy and utilizes amassed geobiology and paleobiological knowledge. Fossils can be used to recognize rock layers of the same or different geologic ages, thereby coordinating locally occurring geologic stages to the overall geologic timeline.
The pictures of the fossils of monocellular algae in this USGS figure were taken with a scanning electron microscope and have been magnified 250 times.
In the U.S. state of South Carolina three marker species of fossil algae are found in a core of rock whereas in Virginia only two of the three species are found in the Eocene Series of rock layers spanning three stages and the geologic ages from 37.2–55.8 MA.
Comparing the record about the discordance in the record to the full rock column shows the non-occurrence of the missing species and that portion of the local rock record, from the early part of the middle Eocene is missing there. This is one form of discordancy and the means geologists use to compensate for local variations in the rock record. With the two remaining marker species it is possible to correlate rock layers of the same age (early Eocene and latter part of the middle Eocene) in both South Carolina and Virginia, and thereby "calibrate" the local rock column into its proper place in the overall geologic record.
Lithology vs paleontology
Consequently, as the picture of the overall rock record emerged, and discontinuities and similarities in one place were cross-correlated to those in others, it became useful to subdivide the overall geologic record into a series of component sub-sections representing different sized groups of layers within known geologic time, from the shortest time span stage to the largest thickest strata eonothem and time spans eon. Concurrent work in other natural science fields required a time continuum be defined, and earth scientists decided to coordinate the system of rock layers and their identification criteria with that of the geologic time scale. This gives the pairing between the physical layers of the left column and the time units of the center column in the table at right.
Gallery
== References == |
shocked quartz | Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the crystalline structure of quartz is deformed along planes inside the crystal. These planes, which show up as lines under a microscope, are called planar deformation features (PDFs), or shock lamellae.
Discovery
Shocked quartz was discovered following underground nuclear weapons testing, which generated the intense pressures required to alter the quartz lattice. Eugene Shoemaker showed that shocked quartz is also found inside craters created by meteor impact, such as the Barringer Crater and Chicxulub crater. The presence of shocked quartz supports that such craters were formed by impact, because a volcanic eruption would not generate the required pressure.Lightning is now known to contribute to the surface record of shocked quartz grains, complicating identification of hypervelocity impact features.
Formation
Shocked quartz is usually associated in nature with two high-pressure polymorphs of silicon dioxide: coesite and stishovite. These polymorphs have a crystal structure different from standard quartz. This structure can be formed only by intense pressure (more than 2 gigapascals), but at moderate temperatures. Coesite and stishovite are usually viewed as indicative of impact events or eclogite facies metamorphism (or nuclear explosion), but are also found in sediments prone to lightning strikes and in fulgurites.
Occurrence
Shocked quartz is found worldwide, and occurs in the thin Cretaceous–Paleogene boundary layer, which occurs at the contact between Cretaceous and Paleogene rocks. This is further evidence (in addition to iridium enrichment) that the transition between the two geologic periods was caused by a large impact.Lightning also generates planar deformation features in quartz and is capable of propagating appropriate pressure/temperature gradients in rocks and sediments alike. This very common mechanism may significantly contribute to the accumulation of shocked quartz in the geologic record. Mantle xenoliths and sediments derived from them may contain coesite or stishovite.Though shocked quartz is only recently recognized, Eugene Shoemaker discovered it prior to its crystallographic description in building stones in the Bavarian town of Nördlingen, derived from shock-metamorphic rocks, such as breccia and pseudotachylite, of Ries crater.
See also
Lechatelierite
Seifertite
Shatter cone
Shock metamorphism
References
External links
Shocked quartz page
Coesite page
Stishovite page |
history of paleontology | The history of paleontology traces the history of the effort to understand the history of life on Earth by studying the fossil record left behind by living organisms. Since it is concerned with understanding living organisms of the past, paleontology can be considered to be a field of biology, but its historical development has been closely tied to geology and the effort to understand the history of Earth itself.
In ancient times, Xenophanes (570–480 BC), Herodotus (484–425 BC), Eratosthenes (276–194 BC), and Strabo (64 BC–24 AD) wrote about fossils of marine organisms, indicating that land was once under water. The ancient Chinese considered them to be dragon bones and documented them as such. During the Middle Ages, fossils were discussed by Persian naturalist Ibn Sina (known as Avicenna in Europe) in The Book of Healing (1027), which proposed a theory of petrifying fluids that Albert of Saxony would elaborate on in the 14th century. The Chinese naturalist Shen Kuo (1031–1095) would propose a theory of climate change based on evidence from petrified bamboo.
In early modern Europe, the systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason. The nature of fossils and their relationship to life in the past became better understood during the 17th and 18th centuries, and at the end of the 18th century, the work of Georges Cuvier had ended a long running debate about the reality of extinction, leading to the emergence of paleontology – in association with comparative anatomy – as a scientific discipline. The expanding knowledge of the fossil record also played an increasing role in the development of geology, and stratigraphy in particular.
In 1822, the word "paleontology" was used by the editor of a French scientific journal to refer to the study of ancient living organisms through fossils, and the first half of the 19th century saw geological and paleontological activity become increasingly well organized with the growth of geologic societies and museums and an increasing number of professional geologists and fossil specialists. This contributed to a rapid increase in knowledge about the history of life on Earth, and progress towards definition of the geologic time scale largely based on fossil evidence. As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. This would encourage early evolutionary theories on the transmutation of species. After Charles Darwin published On the Origin of Species in 1859, much of the focus of paleontology shifted to understanding evolutionary paths, including human evolution, and evolutionary theory.The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America. The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection, as demonstrated by a series of important discoveries in China near the end of the 20th century. Many transitional fossils have been discovered, and there is now considered to be abundant evidence of how all classes of vertebrates are related, much of it in the form of transitional fossils. The last few decades of the 20th century saw a renewed interest in mass extinctions and their role in the evolution of life on Earth. There was also a renewed interest in the Cambrian explosion that saw the development of the body plans of most animal phyla. The discovery of fossils of the Ediacaran biota and developments in paleobiology extended knowledge about the history of life back far before the Cambrian.
Prior to the 17th century
As early as the 6th century BC, the Greek philosopher Xenophanes of Colophon (570–480 BC) recognized that some fossil shells were remains of shellfish, which he used to argue that what was at the time dry land was once under the sea. Leonardo da Vinci (1452–1519), in an unpublished notebook, also concluded that some fossil sea shells were the remains of shellfish. However, in both cases, the fossils were complete remains of shellfish species that closely resembled living species, and were therefore easy to classify.In 1027, the Persian naturalist, Ibn Sina (known as Avicenna in Europe), proposed an explanation of how the stoniness of fossils was caused in The Book of Healing. He modified an idea of Aristotle's, which explained it in terms of vaporous exhalations. Ibn Sina modified this into the theory of petrifying fluids (succus lapidificatus), which was elaborated on by Albert of Saxony in the 14th century and was accepted in some form by most naturalists by the 16th century.Shen Kuo (Chinese: 沈括) (1031–1095) of the Song Dynasty used marine fossils found in the Taihang Mountains to infer the existence of geological processes such as geomorphology and the shifting of seashores over time. In 1088 AD, he discovered preserved petrified bamboos found underground in Yan'an, Shanbei region, Shaanxi province. Using his observation, he argued for a theory of gradual climate change, since Shaanxi was part of a dry climate zone that did not support a habitat for the growth of bamboos.As a result of a new emphasis on observing, classifying, and cataloging nature, 16th-century natural philosophers in Europe began to establish extensive collections of fossil objects (as well as collections of plant and animal specimens), which were often stored in specially built cabinets to help organize them. Conrad Gesner published a 1565 work on fossils that contained one of the first detailed descriptions of such a cabinet and collection. The collection belonged to a member of the extensive network of correspondents that Gesner drew on for his works. Such informal correspondence networks among natural philosophers and collectors became increasingly important during the course of the 16th century and were direct forerunners of the scientific societies that would begin to form in the 17th century. These cabinet collections and correspondence networks played an important role in the development of natural philosophy.However, most 16th-century Europeans did not recognize that fossils were the remains of living organisms. The etymology of the word fossil comes from the Latin for things having been dug up. As this indicates, the term was applied to a wide variety of stone and stone-like objects without regard to whether they might have an organic origin. 16th-century writers such as Gesner and Georg Agricola were more interested in classifying such objects by their physical and mystical properties than they were in determining the objects' origins. In addition, the natural philosophy of the period encouraged alternative explanations for the origin of fossils. Both the Aristotelian and Neoplatonic schools of philosophy provided support for the idea that stony objects might grow within the earth to resemble living things. Neoplatonic philosophy maintained that there could be affinities between living and non-living objects that could cause one to resemble the other. The Aristotelian school maintained that the seeds of living organisms could enter the ground and generate objects resembling those organisms.
Leonardo da Vinci and the development of paleontology
Leonardo da Vinci established a line of continuity between the two main branches of paleontology: body fossil palaeontology and ichnology. In fact, Leonardo dealt with both major classes of fossils: (1) body fossils, e.g. fossilized shells; (2) ichnofossils (also known as trace fossils), i.e. the fossilized products of life-substrate interactions (e.g. burrows and borings). In folios 8 to 10 of the Leicester code, Leonardo examined the subject of body fossils, tackling one of the vexing issues of his contemporaries: why do we find petrified seashells on mountains? Leonardo answered this question by correctly interpreting the biogenic nature of fossil mollusks and their sedimentary matrix. The interpretation of Leonardo da Vinci appears extraordinarily innovative as he surpassed three centuries of scientific debate on the nature of body fossils. Da Vinci took into consideration invertebrate ichnofossils to prove his ideas on the nature of fossil objects. To da Vinci, ichnofossils played a central role in demonstrating: (1) the organic nature of petrified shells and (2) the sedimentary origin of the rock layers bearing fossil objects. Da Vinci described what are bioerosion ichnofossils: ‘‘The hills around Parma and Piacenza show abundant mollusks and bored corals still attached to the rocks. When I was working on the great horse in Milan, certain peasants brought me a huge bagful of them’’— Leicester Code, folio 9rSuch fossil borings allowed Leonardo to confute the Inorganic theory, i.e. the idea that so-called petrified shells (mollusk body fossils) are inorganic curiosities. With the words of Leonardo da Vinci:‘‘[the Inorganic theory is not true] because there remains the trace of the [animal’s] movements on the shell which [it] consumed in the same manner of a woodworm in wood …’’— Leicester Code, folio 9vDa Vinci discussed not only fossil borings, but also burrows. Leonardo used fossil burrows as paleoenvironmental tools to demonstrate the marine nature of sedimentary strata:‘‘Between one layer and the other there remain traces of the worms that crept between them when they had not yet dried. All the sea mud still contains shells, and the shells are petrified together with the mud’’— Leicester Code, folio 10vOther Renaissance naturalists studied invertebrate ichnofossils during the Renaissance, but none of them reached such accurate conclusions. Leonardo's considerations of invertebrate ichnofossils are extraordinarily modern not only when compared to those of his contemporaries, but also to interpretations in later times. In fact, during the 1800s invertebrate ichnofossils were explained as fucoids, or seaweed, and their true nature was widely understood only by the early 1900s. For these reasons, Leonardo da Vinci is deservedly considered the founding father of both the major branches of palaeontology, i.e. the study of body fossils and ichnology.
17th century
During the Age of Reason, fundamental changes in natural philosophy were reflected in the analysis of fossils. In 1665 Athanasius Kircher attributed giant bones to extinct races of giant humans in his Mundus subterraneus. In the same year Robert Hooke published Micrographia, an illustrated collection of his observations with a microscope. One of these observations was entitled "Of Petrify'd wood, and other Petrify'd bodies", which included a comparison between petrified and ordinary wood. He concluded that petrified wood was ordinary wood that had been soaked with "water impregnated with stony and earthy particles". He then suggested that several kinds of fossil sea shells were formed from ordinary shells by a similar process. He argued against the prevalent view that such objects were "Stones form'd by some extraordinary Plastick virtue latent in the Earth itself". Hooke believed that fossils provided evidence about the history of life on Earth writing in 1668:
...if the finding of Coines, Medals, Urnes, and other Monuments of famous persons, or Towns, or Utensils, be admitted for unquestionable Proofs, that such Persons or things have, in former times had a being, certainly those Petrifactions may be allowed to be of equal Validity and Evidence, that there have formerly been such Vegetables or Animals... and are true universal Characters legible to all rational Men.
Hooke was prepared to accept the possibility that some such fossils represented species that had become extinct, possibly in past geological catastrophes.In 1667 Nicholas Steno wrote a paper about a shark head he had dissected. He compared the teeth of the shark with the common fossil objects known as "tongue stones" or glossopetrae. He concluded that the fossils must have been shark teeth. Steno then took an interest in the question of fossils, and to address some of the objections to their organic origin he began studying rock strata. The result of this work was published in 1669 as Forerunner to a Dissertation on a solid naturally enclosed in a solid. In this book, Steno drew a clear distinction between objects such as rock crystals that really were formed within rocks and those such as fossil shells and shark teeth that were formed outside of those rocks. Steno realized that certain kinds of rock had been formed by the successive deposition of horizontal layers of sediment and that fossils were the remains of living organisms that had become buried in that sediment. Steno who, like almost all 17th-century natural philosophers, believed that the earth was only a few thousand years old, resorted to the Biblical flood as a possible explanation for fossils of marine organisms that were far from the sea.Despite the considerable influence of Forerunner, naturalists such as Martin Lister (1638–1712) and John Ray (1627–1705) continued to question the organic origin of some fossils. They were particularly concerned about objects such as fossil Ammonites, which Hooke claimed were organic in origin, that did not resemble any known living species. This raised the possibility of extinction, which they found difficult to accept for philosophical and theological reasons. In 1695 Ray wrote to the Welsh naturalist Edward Lluyd complaining of such views: "... there follows such a train of consequences, as seem to shock the Scripture-History of the novity of the World; at least they overthrow the opinion received, & not without good reason, among Divines and Philosophers, that since the first Creation there have been no species of Animals or Vegetables lost, no new ones produced."
18th century
In his 1778 work Epochs of Nature Georges Buffon referred to fossils, in particular the discovery of fossils of tropical species such as elephants and rhinoceros in northern Europe, as evidence for the theory that the earth had started out much warmer than it currently was and had been gradually cooling.
In 1796 Georges Cuvier presented a paper on living and fossil elephants comparing skeletal remains of Indian and African elephants to fossils of mammoths and of an animal he would later name mastodon utilizing comparative anatomy. He established for the first time that Indian and African elephants were different species, and that mammoths differed from both and must be extinct. He further concluded that the mastodon was another extinct species that also differed from Indian or African elephants, more so than mammoths. Cuvier made another powerful demonstration of the power of comparative anatomy in paleontology when he presented a second paper in 1796 on a large fossil skeleton from Paraguay, which he named Megatherium and identified as a giant sloth by comparing its skull to those of two living species of tree sloth. Cuvier's ground-breaking work in paleontology and comparative anatomy led to the widespread acceptance of extinction. It also led Cuvier to advocate the geological theory of catastrophism to explain the succession of organisms revealed by the fossil record. He also pointed out that since mammoths and woolly rhinoceros were not the same species as the elephants and rhinoceros currently living in the tropics, their fossils could not be used as evidence for a cooling earth.
In a pioneering application of stratigraphy, William Smith, a surveyor and mining engineer, made extensive use of fossils to help correlate rock strata in different locations. He created the first geological map of England during the late 1790s and early 19th century. He established the principle of faunal succession, the idea that each strata of sedimentary rock would contain particular types of fossils, and that these would succeed one another in a predictable way even in widely separated geologic formations. At the same time, Cuvier and Alexandre Brongniart, an instructor at the Paris school of mine engineering, used similar methods in an influential study of the geology of the region around Paris.
Early to mid-19th century
The study of fossils and the origin of the word paleontology
The Smithsonian Libraries consider that the first edition of a work which laid the foundation to vertebrate paleontology was Georges Cuvier's Recherches sur les ossements fossiles de quadrupèdes (Researches on quadruped fossil bones), published in France in 1812. Referring to the second edition of this work (1821), Cuvier's disciple and editor of the scientific publication Journal de physique Henri Marie Ducrotay de Blainville published in January 1822, in the Journal de physique, an article titled "Analyse des principaux travaux dans les sciences physiques, publiés dans l'année 1821" ("Analysis of the main works in the physical sciences, published in the year 1821"). In this article Blainville unveiled for the first time the printed word palæontologie which later gave the English word "paleontology". Blainville had already coined the term paléozoologie in 1817 to refer to the work Cuvier and others were doing to reconstruct extinct animals from fossil bones. However, Blainville began looking for a term that could refer to the study of both fossil animal and plant remains. After trying some unsuccessful alternatives, he hit on "palaeontologie" in 1822. Blainville's term for the study of the fossilized organisms quickly became popular and was anglicized into "paleontology".In 1828 Alexandre Brongniart's son, the botanist Adolphe Brongniart, published the introduction to a longer work on the history of fossil plants. Adolphe Brongniart concluded that the history of plants could roughly be divided into four parts. The first period was characterized by cryptogams. The second period was characterized by the appearance of the conifers. The third period brought emergence of the cycads, and the fourth by the development of the flowering plants (such as the dicotyledons). The transitions between each of these periods was marked by sharp discontinuities in the fossil record, with more gradual changes within the periods. Brongniart's work is the foundation of paleobotany and reinforced the theory that life on earth had a long and complex history, and different groups of plants and animals made their appearances in successive order. It also supported the idea that the Earth's climate had changed over time as Brongniart concluded that plant fossils showed that during the Carboniferous the climate of Northern Europe must have been tropical. The term "paleobotany" was coined in 1884 and "palynology" in 1944.
The age of mammals
In 1804, Cuvier identified two fossil mammal genera from the gypsum quarries of the outskirts of Paris (known as the Paris Basin) in France (although the fossils were known by him as early as at least 1800). Unlike earlier-discovered fossil mammals like Megatherium and Mammut, the 1804-described fossil mammals were discovered from deeper deposits instead of surface deposits, indicating older ages (late Eocene epoch). He identified that the two genera were definitely mammals based on dental and postcranial evidence and were similar to extant mammals such as tapirs, camels, and pigs. However, he also identified that they differed from each other and extant mammals based on dental evidence. He named the two genera Palaeotherium and Anoplotherium. Later in 1807, he wrote about two incomplete skeletons of A. commune that were just recently uncovered from the communes of Pantin and Antony, respectively. Despite the skeletons being incomplete and the first being partially damaged from not being carefully collected by workers, he was able to determine based on postcranial evidence that A. commune was similar to animals that would eventually be classified in the order Artiodactyla after his lifetime. However, Cuvier expressed his surprise at how A. commune sported highly unusual traits of which there are no modern analogues in its extant relatives, such as a long and robust tail of 22 caudal vertebrae and third small fingers in its feet in addition to two long ones.In 1812, Cuvier followed up with published drawn reconstructions on known remains of "Palaeotherium" minor (= Plagiolophus minor), "Anoplotherium medium" (= Xiphodon gracilis), and, most famously, Anoplotherium commune. In A. commune, he was able to predict accurately that A. commune had robust muscles in its entire body to support its short limbs and long tail. He also described hypothesized paleobiologies of the different species assigned to Anoplotherium (some of which would eventually be assigned to different Paleogene artiodactyls such as Xiphodon and Dichobune). His skeletal reconstructions of fossil mammal genera and hypothesis of paleoecological behaviors are considered amongst the earliest instances within paleontology. He also drew muscle reconstructions of A. commune based on known skeletal remains of the species, which were reprinted but never published to the public out of his concern that they were too speculative. Today, however, his muscle reconstructions of A. commune are seen as accurate and having paved the way for paleoart and biomechanics.
The age of reptiles
In 1808, Cuvier identified a fossil found in Maastricht as a giant marine reptile that would later be named Mosasaurus. He also identified, from a drawing, another fossil found in Bavaria as a flying reptile and named it Pterodactylus. He speculated, based on the strata in which these fossils were found, that large reptiles had lived prior to what he was calling "the age of mammals". Cuvier's speculation would be supported by a series of finds that would be made in Great Britain over the course of the next two decades. Mary Anning, a professional fossil collector since age eleven, collected the fossils of a number of marine reptiles and prehistoric fish from the Jurassic marine strata at Lyme Regis. These included the first ichthyosaur skeleton to be recognized as such, which was collected in 1811, and the first two plesiosaur skeletons ever found in 1821 and 1823. Mary Anning was only 12 when she and her brother discovered the Ichthyosaurus skeleton. Many of her discoveries would be described scientifically by the geologists William Conybeare, Henry De la Beche, and William Buckland. It was Anning who observed that stony objects known as "bezoar stones" were often found in the abdominal region of ichthyosaur skeletons, and she noted that if such stones were broken open they often contained fossilized fish bones and scales as well as sometimes bones from small ichthyosaurs. This led her to suggest to Buckland that they were fossilized feces, which he named coprolites, and which he used to better understand ancient food chains. Mary Anning made many fossil discoveries that revolutionized science. However, despite her phenomenal scientific contributions, she was rarely recognized officially for her discoveries. Her discoveries were often credited to wealthy men who bought her fossils.In 1824, Buckland found and described a lower jaw from Jurassic deposits from Stonesfield. He determined that the bone belonged to a carnivorous land-dwelling reptile he called Megalosaurus. That same year Gideon Mantell realized that some large teeth he had found in 1822, in Cretaceous rocks from Tilgate, belonged to a giant herbivorous land-dwelling reptile. He called it Iguanodon, because the teeth resembled those of an iguana. All of this led Mantell to publish an influential paper in 1831 entitled "The Age of Reptiles" in which he summarized the evidence for there having been an extended time during which the earth had teemed with large reptiles, and he divided that era, based in what rock strata different types of reptiles first appeared, into three intervals that anticipated the modern periods of the Triassic, Jurassic, and Cretaceous. In 1832 Mantell would find, in Tilgate, a partial skeleton of an armored reptile he would call Hylaeosaurus. In 1841 the English anatomist Richard Owen would create a new order of reptiles, which he called Dinosauria, for Megalosaurus, Iguanodon, and Hylaeosaurus.
This evidence that giant reptiles had lived on Earth in the past caused great excitement in scientific circles, and even among some segments of the general public. Buckland did describe the jaw of a small primitive mammal, Phascolotherium, that was found in the same strata as Megalosaurus. This discovery, known as the Stonesfield mammal, was a much discussed anomaly. Cuvier at first thought it was a marsupial, but Buckland later realized it was a primitive placental mammal. Due to its small size and primitive nature, Buckland did not believe it invalidated the overall pattern of an age of reptiles, when the largest and most conspicuous animals had been reptiles rather than mammals.
Catastrophism, uniformitarianism and the fossil record
In Cuvier's landmark 1796 paper on living and fossil elephants, he referred to a single catastrophe that destroyed life to be replaced by the current forms. As a result of his studies of extinct mammals, he realized that animals such as Palaeotherium and Anoplotherium had lived before the time of the mammoths, which led him to write in terms of multiple geological catastrophes that had wiped out a series of successive faunas. By 1830, a scientific consensus had formed around his ideas as a result of paleobotany and the dinosaur and marine reptile discoveries in Britain. In Great Britain, where natural theology was very influential in the early 19th century, a group of geologists that included Buckland, and Robert Jameson insisted on explicitly linking the most recent of Cuvier's catastrophes to the biblical flood. Catastrophism had a religious overtone in Britain that was absent elsewhere.Partly in response to what he saw as unsound and unscientific speculations by William Buckland and other practitioners of flood geology, Charles Lyell advocated the geological theory of uniformitarianism in his influential work Principles of Geology. Lyell amassed evidence, both from his own field research and the work of others, that most geological features could be explained by the slow action of present-day forces, such as vulcanism, earthquakes, erosion, and sedimentation rather than past catastrophic events. Lyell also claimed that the apparent evidence for catastrophic changes in the fossil record, and even the appearance of directional succession in the history of life, were illusions caused by imperfections in that record. For instance he argued that the absence of birds and mammals from the earliest fossil strata was merely an imperfection in the fossil record attributable to the fact that marine organisms were more easily fossilized. Also Lyell pointed to the Stonesfield mammal as evidence that mammals had not necessarily been preceded by reptiles, and to the fact that certain Pleistocene strata showed a mixture of extinct and still surviving species, which he said showed that extinction occurred piecemeal rather than as a result of catastrophic events. Lyell was successful in convincing geologists of the idea that the geological features of the earth were largely due to the action of the same geologic forces that could be observed in the present day, acting over an extended period of time. He was not successful in gaining support for his view of the fossil record, which he believed did not support a theory of directional succession.
Transmutation of species and the fossil record
In the early 19th century Jean Baptiste Lamarck used fossils to argue for his theory of the transmutation of species. Fossil finds, and the emerging evidence that life had changed over time, fueled speculation on this topic during the next few decades. Robert Chambers used fossil evidence in his 1844 popular science book Vestiges of the Natural History of Creation, which advocated an evolutionary origin for the cosmos as well as for life on earth. Like Lamarck's theory it maintained that life had progressed from the simple to the complex. These early evolutionary ideas were widely discussed in scientific circles but were not accepted into the scientific mainstream. Many of the critics of transmutational ideas used fossil evidence in their arguments. In the same paper that coined the term dinosaur Richard Owen pointed out that dinosaurs were at least as sophisticated and complex as modern reptiles, which he claimed contradicted transmutational theories. Hugh Miller would make a similar argument, pointing out that the fossil fish found in the Old Red Sandstone formation were fully as complex as any later fish, and not the primitive forms alleged by Vestiges. While these early evolutionary theories failed to become accepted as mainstream science, the debates over them would help pave the way for the acceptance of Darwin's theory of evolution by natural selection a few years later.
Geological time scale and the history of life
Geologists such as Adam Sedgwick, and Roderick Murchison continued, in the course of disputes such as the Great Devonian controversy, to make advances in stratigraphy. They described newly recognized geological periods, such as the Cambrian, the Silurian, the Devonian, and the Permian. Increasingly, such progress in stratigraphy depended on the opinions of experts with specialized knowledge of particular types of fossils such as William Lonsdale (fossil corals), and John Lindley (fossil plants) who both played a role in the Devonian controversy and its resolution. By the early 1840s much of the geologic time scale had been developed. In 1841, John Phillips formally divided the geologic column into three major eras, the Paleozoic, Mesozoic, and Cenozoic, based on sharp breaks in the fossil record. He identified the three periods of the Mesozoic era and all the periods of the Paleozoic era except the Ordovician. His definition of the geological time scale is still used today. It remained a relative time scale with no method of assigning any of the periods' absolute dates. It was understood that not only had there been an "age of reptiles" preceding the current "age of mammals", but there had been a time (during the Cambrian and the Silurian) when life had been restricted to the sea, and a time (prior to the Devonian) when invertebrates had been the largest and most complex forms of animal life.
Expansion and professionalization of geology and paleontology
This rapid progress in geology and paleontology during the 1830s and 1840s was aided by a growing international network of geologists and fossil specialists whose work was organized and reviewed by an increasing number of geological societies. Many of these geologists and paleontologists were now paid professionals working for universities, museums and government geological surveys. The relatively high level of public support for the earth sciences was due to their cultural impact, and their proven economic value in helping to exploit mineral resources such as coal.Another important factor was the development in the late 18th and early 19th centuries of museums with large natural history collections. These museums received specimens from collectors around the world and served as centers for the study of comparative anatomy and morphology. These disciplines played key roles in the development of a more technically sophisticated form of natural history. One of the first and most important examples was the Museum of Natural History in Paris, which was at the center of many of the developments in natural history during the first decades of the 19th century. It was founded in 1793 by an act of the French National Assembly, and was based on an extensive royal collection plus the private collections of aristocrats confiscated during the French revolution, and expanded by material seized in French military conquests during the Napoleonic Wars. The Paris museum was the professional base for Cuvier, and his professional rival Geoffroy Saint-Hilaire. The English anatomists Robert Grant and Richard Owen both spent time studying there. Owen would go on to become the leading British morphologist while working at the museum of the Royal College of Surgeons.
Late 19th century
Evolution
Charles Darwin's publication of the On the Origin of Species in 1859 was a watershed event in all the life sciences, especially paleontology. Fossils had played a role in the development of Darwin's theory. In particular he had been impressed by fossils he had collected in South America during the voyage of the Beagle of giant armadillos, giant sloths, and what at the time he thought were giant llamas that seemed to be related to species still living on the continent in modern times. The scientific debate that started immediately after the publication of Origin led to a concerted effort to look for transitional fossils and other evidence of evolution in the fossil record. There were two areas where early success attracted considerable public attention, the transition between reptiles and birds, and the evolution of the modern single-toed horse. In 1861 the first specimen of Archaeopteryx, an animal with both teeth and feathers and a mix of other reptilian and avian features, was discovered in a limestone quarry in Bavaria and described by Richard Owen. Another would be found in the late 1870s and put on display at the Natural History Museum, Berlin in 1881. Other primitive toothed birds were found by Othniel Marsh in Kansas in 1872. Marsh also discovered fossils of several primitive horses in the Western United States that helped trace the evolution of the horse from the small 5-toed Hyracotherium of the Eocene to the much larger single-toed modern horses of the genus Equus. Thomas Huxley would make extensive use of both the horse and bird fossils in his advocacy of evolution. Acceptance of evolution occurred rapidly in scientific circles, but acceptance of Darwin's proposed mechanism of natural selection as the driving force behind it was much less universal. In particular some paleontologists such as Edward Drinker Cope and Henry Fairfield Osborn preferred alternatives such as neo-Lamarckism, the inheritance of characteristics acquired during life, and orthogenesis, an innate drive to change in a particular direction, to explain what they perceived as linear trends in evolution.
There was also great interest in human evolution. Neanderthal fossils were discovered in 1856, but at the time it was not clear that they represented a different species from modern humans. Eugene Dubois created a sensation with his discovery of Java Man, the first fossil evidence of a species that seemed clearly intermediate between humans and apes, in 1891.
Developments in North America
A major development in the second half of the 19th century was a rapid expansion of paleontology in North America. In 1858 Joseph Leidy described a Hadrosaurus skeleton, which was the first North American dinosaur to be described from good remains. However, it was the massive westward expansion of railroads, military bases, and settlements into Kansas and other parts of the Western United States following the American Civil War that really fueled the expansion of fossil collection. The result was an increased understanding of the natural history of North America, including the discovery of the Western Interior Sea that had covered Kansas and much of the rest of the Midwestern United States during parts of the Cretaceous, the discovery of several important fossils of primitive birds and horses, and the discovery of a number of new dinosaur genera including Allosaurus, Stegosaurus, and Triceratops. Much of this activity was part of a fierce personal and professional rivalry between two men, Othniel Marsh, and Edward Cope, which has become known as the Bone Wars.
Overview of developments in the 20th century
Developments in geology
Two 20th-century developments in geology had a big effect on paleontology. The first was the development of radiometric dating, which allowed absolute dates to be assigned to the geologic timescale. The second was the theory of plate tectonics, which helped make sense of the geographical distribution of ancient life.
Geographical expansion of paleontology
During the 20th century, paleontological exploration intensified everywhere and ceased to be a largely European and North American activity. In the 135 years between Buckland's first discovery and 1969 a total of 170 dinosaur genera were described. In the 25 years after 1969 that number increased to 315. Much of this increase was due to the examination of new rock exposures, particularly in previously little-explored areas in South America and Africa. Near the end of the 20th century the opening of China to systematic exploration for fossils has yielded a wealth of material on dinosaurs and the origin of birds and mammals. Also study of the Chengjiang fauna, a Cambrian fossil site in China, during the 1990s has provided important clues to the origin of vertebrates.
Mass extinctions
The 20th century saw a major renewal of interest in mass extinction events and their effect on the course of the history of life. This was particularly true after 1980 when Luis and Walter Alvarez put forward the Alvarez hypothesis claiming that an impact event caused the Cretaceous–Paleogene extinction event, which killed off the non-avian dinosaurs along with many other living things. Also in the early 1980s Jack Sepkoski and David M. Raup published papers with statistical analysis of the fossil record of marine invertebrates that revealed a pattern (possibly cyclical) of repeated mass extinctions with significant implications for the evolutionary history of life.
Evolutionary paths and theory
Throughout the 20th century new fossil finds continued to contribute to understanding the paths taken by evolution. Examples include major taxonomic transitions such as finds in Greenland, starting in the 1930s (with more major finds in the 1980s), of fossils illustrating the evolution of tetrapods from fish, and fossils in China during the 1990s that shed light on the dinosaur-bird relationship. Other events that have attracted considerable attention have included the discovery of a series of fossils in Pakistan that have shed light on whale evolution, and most famously of all a series of finds throughout the 20th century in Africa (starting with Taung child in 1924) and elsewhere have helped illuminate the course of human evolution. Increasingly, at the end of the 20th century, the results of paleontology and molecular biology were being brought together to reveal detailed phylogenetic trees.
The results of paleontology have also contributed to the development of evolutionary theory. In 1944 George Gaylord Simpson published Tempo and Mode in Evolution, which used quantitative analysis to show that the fossil record was consistent with the branching, non-directional, patterns predicted by the advocates of evolution driven by natural selection and genetic drift rather than the linear trends predicted by earlier advocates of neo-Lamarckism and orthogenesis. This integrated paleontology into the modern evolutionary synthesis. In 1972 Niles Eldredge and Stephen Jay Gould used fossil evidence to advocate the theory of punctuated equilibrium, which maintains that evolution is characterized by long periods of relative stasis and much shorter periods of relatively rapid change.
Cambrian explosion
One area of paleontology that has seen a lot of activity during the 1980s, 1990s, and beyond is the study of the Cambrian explosion during which many of the various phyla of animals with their distinctive body plans first appear. The well-known Burgess Shale Cambrian fossil site was found in 1909 by Charles Doolittle Walcott, and another important site in Chengjiang China was found in 1912. However, new analysis in the 1980s by Harry B. Whittington, Derek Briggs, Simon Conway Morris and others sparked a renewed interest and a burst of activity including discovery of an important new fossil site, Sirius Passet, in Greenland, and the publication of a popular and controversial book, Wonderful Life by Stephen Jay Gould in 1989.
Pre-Cambrian fossils
Prior to 1950 there was no widely accepted fossil evidence of life before the Cambrian period. When Charles Darwin wrote The Origin of Species he acknowledged that the lack of any fossil evidence of life prior to the relatively complex animals of the Cambrian was a potential argument against the theory of evolution, but expressed the hope that such fossils would be found in the future. In the 1860s there were claims of the discovery of pre-Cambrian fossils, but these would later be shown not to have an organic origin. In the late 19th century Charles Doolittle Walcott would discover stromatolites and other fossil evidence of pre-Cambrian life, but at the time the organic origin of those fossils was also disputed. This would start to change in the 1950s with the discovery of more stromatolites along with microfossils of the bacteria that built them, and the publication of a series of papers by the Soviet scientist Boris Vasil'evich Timofeev announcing the discovery of microscopic fossil spores in pre-Cambrian sediments. A key breakthrough would come when Martin Glaessner would show that fossils of soft bodied animals discovered by Reginald Sprigg during the late 1940s in the Ediacaran hills of Australia were in fact pre-Cambrian not early Cambrian as Sprigg had originally believed, making the Ediacaran biota the oldest animals known. By the end of the 20th century, paleobiology had established that the history of life extended back at least 3.5 billion years.
See also
History of biology
History of evolutionary thought
History of geology
History of science
List of fossil sites (with link directory)
List of years in paleontology
Taxonomy of commonly fossilised invertebrates
Timeline of paleontology
Treatise on Invertebrate Paleontology
History of paleontology in the United States
Notes
References
Bowler, Peter J. (2003). Evolution: The History of an Idea. University of California Press. ISBN 978-0-520-23693-6.
Bowler, Peter J. (1992). The Earth Encompassed: A History of the Environmental Sciences. W. W. Norton. ISBN 978-0-393-32080-0.
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Rudwick, Martin J.S. (1985). The Great Devonian Controversy: The Shaping of Scientific Knowledge among Gentlemanly Specialists. The University of Chicago Press. ISBN 978-0-226-73102-5.
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History of paleontology
History of palaeoentomology in Russia |
cueva de las manos | Cueva de las Manos (Spanish for Cave of the Hands or Cave of Hands) is a cave and complex of rock art sites in the province of Santa Cruz, Argentina, 163 km (101 mi) south of the town of Perito Moreno. It is named for the hundreds of paintings of hands stenciled, in multiple collages, on the rock walls. The art was created in several waves between 7,300 BC and 700 AD, during the Archaic period of pre-Columbian South America. The age of the paintings was calculated from the remains of bone pipes used for spraying the paint on the wall of the cave to create the artwork, radiocarbon dating of the artwork, and stratigraphic dating.
The site is considered by some scholars to be the best material evidence of early South American hunter-gatherer groups. Argentine surveyor and archaeologist Carlos J. Gradin and his team conducted the most important research on the site in 1964, when they began excavating sites during a 30-year study of cave art in and around Cueva de las Manos. The site is a National Historic Monument in Argentina and a UNESCO World Heritage Site.
Location
Cueva de las Manos refers to both the main site of the cave and the surrounding complex of rock art sites that includes it. The cave lies at the base of a stepped cliff in the Pinturas River Canyon, in the upper part of the Deseado River basin, in an isolated part of Patagonia. It is about 165 km (103 mi) south of Perito Moreno, a town in northwest Santa Cruz Province, Argentina. It is part of both Perito Moreno National Park and Cueva de las Manos Provincial Park.
Climate
During the time of the Paleoindians, around the late Pleistocene to early Holocene geological periods, the areas between 400 and 500 meters (1,300 and 1,600 ft) above sea level formed a microclimate in the canyon promoting a grassland ecosystem hospitable to many animals. This ecosystem included the Schinus molle plant, which was used to form resins and adhesives and as a source of firewood. It was also home to edible vegetables and plants that could be used for medicine; tubers, such as the rush root; and numerous fruits, such as that of the Berberis plant.The current climate of the cave area can be described as precordilleran steppe (or "grassy foothills"). The climate is cold and dry, with very low humidity. Ian N. M. Wainwright and colleagues state that the area receives a total annual precipitation of less than 20 mm (0.79 in) per year, while Gladys I. Galende and Rocío Vega state that it averages 200 mm (7.9 in) per year. The topography of the canyon blocks the strong westward winds that are common in the region, making winters less severe. The average temperature is 8 °C (46 °F), with extreme highs of around 38 °C (100 °F) and extreme lows of around −10 °C (14 °F). The coldest month is July, and the warmest month is February, which average −3 °C (27 °F) and 21 °C (70 °F), respectively.
Access
In ancient times, people accessed the Pinturas Canyon, and by extension the cave area, through ravines in the east and west, typically from higher elevations around 600 to 700 meters (2,000 to 2,300 ft) above sea level. Currently, there are three gravel roads that lead to the site: a 46 km (29 mi) route from the south, starting near Bajo Caracoles, and two more further north, a 28 km (17 mi) route from Ruta 40 (Route 40) and a 22 km (14 mi) route that ends with a 4 km (2.5 mi) foot trail.
History
When the site was occupied, the Pinturas and Deseado Rivers drained into the Atlantic Ocean and provided water for herds of guanacos, making the area attractive to Paleoindians. As the glacial ice fields melted, the Baker River captured the drainage of the eastward flowing rivers. The resulting reduction in water levels of the Pinturas and Deseado rivers led to a progressive abandonment of the Cueva de las Manos site.Projectile points, a bola stone fragment, side-scrapers, and fire pits have been found alongside the remains of guanaco, puma, fox, birds, and other small animals. Guanacos were the natives' primary food source; hunting methods included bolas, ambushes, and game drives, in which they would drive guanacos into ravines and other confined areas to better collectively hunt them. This technique is recorded in the art of the cave, and shows how the topography of the area influenced the art and how it was created. Dart and spear throwers are also depicted, although there is little archaeological evidence of these types of weapons being used in Patagonia.The Pre-Columbian economy of Patagonia depended on hunting-gathering. Archaeologist Francisco Mena states: "[in the] Middle to Late Holocene Adaptations in Patagonia ... neither agriculture nor fully fledged pastoralism ever emerged." Argentine surveyor and archaeologist Carlos J. Gradin remarks in his writings that all the rock art in the area shows the hunter-gatherer lifestyle of the artists who made it. The presence of obsidian near the cave—which is not natural to the region—implies a broad-ranging network of trade between peoples of the cave area and distant tribal groups.Beginning around 7,500 BC, the site, along with the Cerro Casa de Piedra-7 site near Lake Burmeister, became important landmarks in a nomadic circuit between Pinturas Canyon and its surrounding areas, the western part of the Central High Plateau, and the steppes and forests of the ecotone bordering the steppes and forests of the mountainous-lake environment of the Andes. These regions existed at various elevations. The migratory patterns of this circuit were seasonal, following the abundance of vegetables in each region and the births of guanacos, which varied based on the altitude. The furs of newborn guanacos were highly sought after by the native peoples, increasing the importance of guanaco birth patterns to the timing of the seasonal migrations. The prime time for newborn guanacos near Cueva de las Manos was around November. The groups who inhabited the area included the Toldense people, who lived in the caves until the third or second millennium BC. When occupying the area, temporary camp sites would be made around the cave, where extended families or even large bands of people would gather. The groups that gathered at these camp sites would have enabled the inhabitants to organize group hunting of guanacos.The earliest rock art at the site was created around 7,300 BC. Cueva de las Manos is the only site in the region with rock art of this age, categorized as the A1 and A2 styles of the cave, but after 6,800 BC similar art, particularly hunting scenes of styles A3, A4, and A5, was created at other sites in the region. The site was last inhabited around 700 AD, with the final cave dwellers possibly being ancestors of the Tehuelche tribes.
Modern study and protection
Father Alberto Maria de Agostini, an Italian missionary and explorer, first wrote about the site in 1941. It was then investigated by an expedition of the La Plata Museum in 1949. Argentine surveyor and archaeologist Carlos Gradin and his team began the most substantial research on the site in 1964, initiating a 30-year-long study of the caves and their art. Gradin's work has helped to identify the different stylistic sequences of the cave.Cueva de las Manos is a National Historic Monument in Argentina, and has been since 1993. In 1995, the site became a major subject in a study of Argentina's rock art initiated by the National Institute of Anthropology and Latin American Thought (INAPL). This study led to Cueva de las Manos being listed as a UNESCO World Heritage Site in 1999. In 2015, the land was bought from a private ranch by Rewilding Argentina, an environmental organization. In 2018, the site received its own provincial park, and as of 2020 the land is controlled directly by the state, after being donated by Rewilding Argentina.
Geology
The cave is in the walls of the canyon, which are composed of ignimbrite and other volcanic rocks in the Bahía Laura Group. The rocks were formed about 150 million years ago during the Jurassic period as part of the larger Deseado Massif. The cave and surrounding overhangs were carved out of the rock face through differential erosion, a process by which weaker rocks are eroded away, leaving formations composed of the stronger rocks. This erosion was caused by the Pinturas River, fed by glacial runoff, which cut into the Chon Aike Formation to form the Pinturas Canyon. The cave itself is located at a fissure in the rock face that the river eroded more than the surrounding canyon wall.The site is composed of the cave itself, which is about 20 m (66 ft) deep, two outcroppings, and the walls at either side of the entrance. The entrance faces northeast and is about 15 m (50 ft) in height by 15 m (50 ft) wide. The paintings on the cave's wall span about 60 m × 200 m (200 ft × 650 ft). The initial height of the cave is 10 m (33 ft). The ground inside has an upward slope; as a result, the height is eventually reduced to no more than 2 m (6 ft 7 in).
Artwork
Cueva de las Manos is named for the hundreds of hand paintings stenciled into multiple collages on the rock walls. The art in the Cueva de las Manos is some of the most important art in the New World, and by far the most famous rock art in the Patagonian region. The art dates to between around 7,300 BC to 700 AD, during the Archaic period of Pre-Columbian South America. Scholars Ralph Crane and Lisa Fletcher assert that the rock art at Cueva de las Manos includes the oldest-known cave paintings in South America.The artwork decorates the interior of the cave and the surrounding cliff faces. It can be divided by subject into three basic categories: people, the animals they ate, and the human hand. Inhabitants of the site hunted guanacos for survival, a dependency reflected in their artwork by totemic-like depictions of the creatures.Several waves of people occupied the cave over time. The age of the paintings can be calculated from the remains of bone pipes used for spraying the paint on the wall of the cave to create the stenciled artwork of the hand collages, radiocarbon dating of the artwork itself, and stratigraphic dating, including from a piece of the rock wall that had fallen with art on it. Chemical analysis of the pigments used to create the painting, and analysis of the stylistic aspects and superimposition (overlap) of the different parts of the art has verified that it is authentic. According to scholar Irene Fanning and colleagues, it is "the best material evidence of early hunter gatherer groups in South America."
Forms
Earlier works in the cave were more naturalistic—they looked close to how the subjects of the art would have looked in real life. Over time, depictions became more abstract and different in form from how the subject would normally look.There are over 2,000 handprints in and around the cave. Most of the images are painted as negatives or stenciled, alongside some positive handprints. There are 829 left hands to 31 right hands, suggesting that most painters held the bone spray pipe with their right hand. Some handprints are missing fingers, which could be due to necrosis, amputation, or deformity, but might also indicate the use of sign language or bending fingers to convey meaning.The varying depth of the rock face alters the "canvas" of the artwork, and the different depths from the viewer alter the way the images are seen, based on where the viewer is standing. There is a large amount of superimposition of the handprints in different areas, with some areas containing so many handprints that they form a palimpsest background of layered color. Along with the superimposed masses of images, there are many purposefully placed single hands.
There are also depictions of human beings, guanacos, rheas, felines, south Andean deer, and other animals, as well as geometric shapes, zigzag patterns, representations of the sun, and hunting scenes. The hunting scenes are naturalistic portrayals of a variety of hunting techniques, including the use of game drives and bolas. Similar paintings, though in smaller numbers, can be found in nearby caves. There are also red dots on the ceilings, probably made by submerging hunting bolas in ink and throwing them upwards.The wildlife depicted in the artwork is still found in the area today. Most prominent among the animals are the guanacos, upon which the natives depended for survival. There are repeated scenes of guanacos being surrounded by hunters, suggesting that this was the preferred hunting tactic.
Cultural context
Little is known about the culture of those who made these works aside from the tools they used and what they hunted. Modern research is left to speculate about their culture and what life was like in the societies that created it. However, that so many people contributed to the artwork for thousands of years suggests the cave held great significance for the artists who painted on its walls. The art shows the people of this area had a symbolic element to their culture.Regardless of its purpose, the artwork played a key role in the collective social memories of the peoples who inhabited the area, with earlier groups influencing later ones through a narrative spanning millennia. Important aspects of the culture of the hunter-gatherers are shown in the themes of the art, such as the reproductive cycles of guanacos and collective hunting. The site also bore a deep social and personal connection to the artists, as the same groups returned to the location seasonally and created artwork at the cave, which was a kind of ritual.
Purpose
The exact function or purpose of this art is unknown, although some research has suggested that it may have had a religious or ceremonial purpose as well as a decorative one. Some scholars, such as Merry Wiesner-Hanks, have suggested that handprints are indicative of the human desire to be remembered, or to record that they were there. However, Jean Clottes has challenged this perspective, stating that "the likelihood of such behavior is virtually zero." Instead, Clottes asserts that prehistoric shamanism is the most plausible explanation for the purpose of the artwork, as part of "ceremonies about which we will never know anything", although he acknowledges that this hypothesis does not explain everything, and that much work still needs to be done. Another hypothesis posits that the art served as boundary markers between peoples, showing territoriality and ensuring the cooperation of others by functioning as aggregation sites. There are also hypotheses that the works were part of hunting magic, with Alan Thorne suggesting that they might have been created as part of efforts to influence the number of animals available to be hunted. Regardless, the fact that many people gathered in one place to contribute to the rock art for such a long period shows a large cultural significance, or at least usefulness, to those who participated.
Materials
The binder used in the artwork is unknown, but the mineral pigments include iron oxides, producing reds and purples; kaolin, producing white; natrojarosite, producing yellow; manganese oxide (pyrolusite), producing black; and copper oxide, producing green. Haematite, goethite, green earth, quartz, and calcium oxalate have also been detected. Gypsum was used, which allowed the pigments to better adhere to the surface of the rock faces.
Stylistic groups
Specialists have categorized the art into four stylistic groups, as proposed by Carlos Gradin and adapted and modified by others: A, B, B1, and C, also known as Río Pinturas I, II, III, and IV, respectively. The first two groups were partly conceived to differentiate group A's dynamic depiction of guanacos from group B's static depiction of them.
Stylistic group A
Stylistic group A (also known as Río Pinturas I) is the art of the first hunter-gatherers who lived in the area. It is the oldest style in the cave, and can be traced back to around 7,300 BC. The style is naturalistic and dynamic, and encompasses polychrome, dynamic hunting scenes along with negative human hand motifs. The imagery takes advantage of the grooves and irregularities in the rock face itself to form part of the art. This is especially true in the use of these irregularities to represent the topography of the settings of the images, such as in the depiction of ravines. The hunters depicted in the scenes were likely long distance hunters, and the scenes often depicted ambush or surround tactics being used when hunting guanacos.Since 2010, this stylistic group has been further subdivided into five different sub-styles, or series, categorized by color/material. These series are classified as A1 (Ochre series), which is primarily made up of ochre and some red; A2 (Black series), which is predominantly black but also contains some dark purple; A3 (Red series) which primarily incorporates red; A4 (Purplish/Dark Red series), which uses purplish red and dark red; and A5 (White/Yellow series), which predominately uses the color white but also incorporates yellow-ochre. In terms of layering, A2 generally covers A1; A3 goes over A1 and A2; A4 goes over A3 and A2; and A5 is positioned on top of all other layers. The sub-styles of stylistic group A are numbered chronologically; that is, A1 is the oldest and A5 is the youngest.The Black series in particular introduced several artistic innovations that were carried forward into subsequent artistic styles. These include the introduction of both aerial and hierarchical perspectives, which would be incorporated into later artwork. It also introduced contrasting colors, in the form of black and dark purple, which were used to differentiate between separate representations, a method that would be used throughout the history of the cave art. Many of these influences would carry on in the styles of hunting scenes as late as 5,400 BC.Stylistic group A ended during the H1 eruption of the Hudson volcano, which took place around 4,770/4,675 BC and led to the abandonment of the Rio Pinturas Area. It is very likely that this eruption is what caused the end of this stylistic group.
Stylistic groups B and B1
A new cultural group, lasting from around 5,000 BC until around 1,300 BC, created the art of what is now considered stylistic groups B (Río Pinturas II) and B1 (Río Pinturas III). Static, isolated groups of guanacos with large bellies, possibly pregnant, replace the lively hunting scenes that marked the previous group. These pregnant guanacos and their style and construction were first introduced as part of the Black series of Stylistic group A. Large groups of superimposed handprints, numbering around 2,000, in many colors, are associated with group B, as are some rarer motifs of human and animal footprints.In group B1, a subgroup of B, the forms become more and more schematic, and figures, human and animal, become more stylized; the group includes hand stencils, bola marks, and dotted line patterns.
Stylistic group C
Stylistic group C, Río Pinturas IV, begins around 700 AD and marks the last of the stylistic sequences in the cave. The group focuses around abstract geometric figures, including highly schematic silhouettes of both animal and human figures, alongside circles, zigzag patterns, dots, and more hands superimposed onto larger groups of hands. The primary color is red.
Cultural significance and conservation
Every February the nearby town of Moreno hosts a celebration in honor of the caves called Festival Folklórico Cueva de las Manos.Many tourists visit the cave, which is known worldwide. The number of tourists visiting the site has increased by a factor of four since its inclusion on the UNESCO World Heritage list in 1999. As of 2020, Cueva de las Manos was visited by around 8,000 people per year. This has brought new challenges for preserving the site. Currently, the most significant threat is graffiti, followed by other forms of vandalism, such as visitors taking pieces of painted rock from the walls and touching the paintings.In response, the site has been closed off with chain-link fencing and a boardwalk has been installed to control the movements of visitors. To access the site, visitors must be accompanied by a tour guide. The site also has sanctioned walking trails, a guide lodge, railings, and a parking lot. A team of professionals from the INAPL and the National Scientific and Technical Research Council (CONICET) supervised the construction of these facilities. An awareness program has been undertaken to educate tourists and visitors to the site, including local guides, and to facilitate greater involvement by local communities. The rock art of the site is being recorded and documented in 360° video to make a virtual reality experience involving the site.Despite these measures, the local provincial government, the Argentinian government, and the UNESCO have been criticized for not doing enough to protect the site. The provincial government in particular has been criticized for falling short of the recommendations of the INAPL, including the need for additional staffing and a permanent on-site archaeologist.
See also
Argentine painting
List of Stone Age art
Los Toldos (Santa Cruz) — nearby archaeological site and namesake of the Toldense culture group
Piedra Museo — another archaeological site of the Toldense culture group
Pre-Columbian art
Prehistoric art
Notes
References
Bibliography
Further reading
Gradin, Carlos J (1983). "El arte rupestre de la cuenca del Río Pinturas, Provincia de Santa Cruz, República Argentina". Acta Praehistorica. 2.
Gradin, Carlos J.; Aguerre, Ana M. (1994). Contribución a la Arqueología del Río Pinturas (in Spanish). Búsqueda de Ayllu.
Gradin, Carlos J.; Aschero, Carlos A.; Aguerre, Ana M. (1977). "Investigaciones arqueológicas en la Cueva de las Manos (Alto Río Pinturas, Santa Cruz)". Relaciones de la Sociedad Argentina de Antropología (in Spanish). 10: 201–270. hdl:10915/25285. OCLC 696124191.
External links
Cueva de las Manos Website (in Spanish)
Cueva de las Manos, cave 3D model (Skechfab)
Cueva de las Manos, Perito Moreno, images (in Spanish)
Cave of Hands, Perito Moreno, images
Cueva de las Manos, images
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on the origin of species | On the Origin of Species (or, more completely, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life) is a work of scientific literature by Charles Darwin that is considered to be the foundation of evolutionary biology; it was published on 24 November 1859. Darwin's book introduced the scientific theory that populations evolve over the course of generations through a process of natural selection. The book presented a body of evidence that the diversity of life arose by common descent through a branching pattern of evolution. Darwin included evidence that he had collected on the Beagle expedition in the 1830s and his subsequent findings from research, correspondence, and experimentation.Various evolutionary ideas had already been proposed to explain new findings in biology. There was growing support for such ideas among dissident anatomists and the general public, but during the first half of the 19th century the English scientific establishment was closely tied to the Church of England, while science was part of natural theology. Ideas about the transmutation of species were controversial as they conflicted with the beliefs that species were unchanging parts of a designed hierarchy and that humans were unique, unrelated to other animals. The political and theological implications were intensely debated, but transmutation was not accepted by the scientific mainstream.
The book was written for non-specialist readers and attracted widespread interest upon its publication. Darwin was already highly regarded as a scientist, so his findings were taken seriously and the evidence he presented generated scientific, philosophical, and religious discussion. The debate over the book contributed to the campaign by T. H. Huxley and his fellow members of the X Club to secularise science by promoting scientific naturalism. Within two decades, there was widespread scientific agreement that evolution, with a branching pattern of common descent, had occurred, but scientists were slow to give natural selection the significance that Darwin thought appropriate. During "the eclipse of Darwinism" from the 1880s to the 1930s, various other mechanisms of evolution were given more credit. With the development of the modern evolutionary synthesis in the 1930s and 1940s, Darwin's concept of evolutionary adaptation through natural selection became central to modern evolutionary theory, and it has now become the unifying concept of the life sciences.
Summary of Darwin's theory
Darwin's theory of evolution is based on key facts and the inferences drawn from them, which biologist Ernst Mayr summarised as follows:
Every species is fertile enough that if all offspring survived to reproduce, the population would grow (fact).
Despite periodic fluctuations, populations remain roughly the same size (fact).
Resources such as food are limited and are relatively stable over time (fact).
A struggle for survival ensues (inference).
Individuals in a population vary significantly from one another (fact).
Much of this variation is heritable (fact).
Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their heritable traits to future generations, which produces the process of natural selection (fact).
This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference).
Background
Developments before Darwin's theory
In later editions of the book, Darwin traced evolutionary ideas as far back as Aristotle; the text he cites is a summary by Aristotle of the ideas of the earlier Greek philosopher Empedocles. Early Christian Church Fathers and Medieval European scholars interpreted the Genesis creation narrative allegorically rather than as a literal historical account; organisms were described by their mythological and heraldic significance as well as by their physical form. Nature was widely believed to be unstable and capricious, with monstrous births from union between species, and spontaneous generation of life.
The Protestant Reformation inspired a literal interpretation of the Bible, with concepts of creation that conflicted with the findings of an emerging science seeking explanations congruent with the mechanical philosophy of René Descartes and the empiricism of the Baconian method. After the turmoil of the English Civil War, the Royal Society wanted to show that science did not threaten religious and political stability. John Ray developed an influential natural theology of rational order; in his taxonomy, species were static and fixed, their adaptation and complexity designed by God, and varieties showed minor differences caused by local conditions. In God's benevolent design, carnivores caused mercifully swift death, but the suffering caused by parasitism was a puzzling problem. The biological classification introduced by Carl Linnaeus in 1735 also viewed species as fixed according to the divine plan, but did recognize the hierarchical nature of different taxa. In 1766, Georges Buffon suggested that some similar species, such as horses and asses, or lions, tigers, and leopards, might be varieties descended from a common ancestor. The Ussher chronology of the 1650s had calculated creation at 4004 BC, but by the 1780s geologists assumed a much older world. Wernerians thought strata were deposits from shrinking seas, but James Hutton proposed a self-maintaining infinite cycle, anticipating uniformitarianism.Charles Darwin's grandfather Erasmus Darwin outlined a hypothesis of transmutation of species in the 1790s, and French naturalist Jean-Baptiste Lamarck published a more developed theory in 1809. Both envisaged that spontaneous generation produced simple forms of life that progressively developed greater complexity, adapting to the environment by inheriting changes in adults caused by use or disuse. This process was later called Lamarckism. Lamarck thought there was an inherent progressive tendency driving organisms continuously towards greater complexity, in parallel but separate lineages with no extinction. Geoffroy contended that embryonic development recapitulated transformations of organisms in past eras when the environment acted on embryos, and that animal structures were determined by a constant plan as demonstrated by homologies. Georges Cuvier strongly disputed such ideas, holding that unrelated, fixed species showed similarities that reflected a design for functional needs. His palæontological work in the 1790s had established the reality of extinction, which he explained by local catastrophes, followed by repopulation of the affected areas by other species.In Britain, William Paley's Natural Theology saw adaptation as evidence of beneficial "design" by the Creator acting through natural laws. All naturalists in the two English universities (Oxford and Cambridge) were Church of England clergymen, and science became a search for these laws. Geologists adapted catastrophism to show repeated worldwide annihilation and creation of new fixed species adapted to a changed environment, initially identifying the most recent catastrophe as the biblical flood. Some anatomists such as Robert Grant were influenced by Lamarck and Geoffroy, but most naturalists regarded their ideas of transmutation as a threat to divinely appointed social order.
Inception of Darwin's theory
Darwin went to Edinburgh University in 1825 to study medicine. In his second year he neglected his medical studies for natural history and spent four months assisting Robert Grant's research into marine invertebrates. Grant revealed his enthusiasm for the transmutation of species, but Darwin rejected it. Starting in 1827, at Cambridge University, Darwin learnt science as natural theology from botanist John Stevens Henslow, and read Paley, John Herschel and Alexander von Humboldt. Filled with zeal for science, he studied catastrophist geology with Adam Sedgwick.
In December 1831, he joined the Beagle expedition as a gentleman naturalist and geologist. He read Charles Lyell's Principles of Geology and from the first stop ashore, at St. Jago, found Lyell's uniformitarianism a key to the geological history of landscapes. Darwin discovered fossils resembling huge armadillos, and noted the geographical distribution of modern species in hope of finding their "centre of creation". The three Fuegian missionaries the expedition returned to Tierra del Fuego were friendly and civilised, yet to Darwin their relatives on the island seemed "miserable, degraded savages", and he no longer saw an unbridgeable gap between humans and animals. As the Beagle neared England in 1836, he noted that species might not be fixed.Richard Owen showed that fossils of extinct species Darwin found in South America were allied to living species on the same continent. In March 1837, ornithologist John Gould announced that Darwin's rhea was a separate species from the previously described rhea (though their territories overlapped), that mockingbirds collected on the Galápagos Islands represented three separate species each unique to a particular island, and that several distinct birds from those islands were all classified as finches. Darwin began speculating, in a series of notebooks, on the possibility that "one species does change into another" to explain these findings, and around July sketched a genealogical branching of a single evolutionary tree, discarding Lamarck's independent lineages progressing to higher forms. Unconventionally, Darwin asked questions of fancy pigeon and animal breeders as well as established scientists. At the zoo he had his first sight of an ape, and was profoundly impressed by how human the orangutan seemed.In late September 1838, he started reading Thomas Malthus's An Essay on the Principle of Population with its statistical argument that human populations, if unrestrained, breed beyond their means and struggle to survive. Darwin related this to the struggle for existence among wildlife and botanist de Candolle's "warring of the species" in plants; he immediately envisioned "a force like a hundred thousand wedges" pushing well-adapted variations into "gaps in the economy of nature", so that the survivors would pass on their form and abilities, and unfavourable variations would be destroyed. By December 1838, he had noted a similarity between the act of breeders selecting traits and a Malthusian Nature selecting among variants thrown up by "chance" so that "every part of newly acquired structure is fully practical and perfected".Darwin now had the basic framework of his theory of natural selection, but he was fully occupied with his career as a geologist and held back from compiling it until his book on The Structure and Distribution of Coral Reefs was completed. As he recalled in his autobiography, he had "at last got a theory by which to work", but it was only in June 1842 that he allowed himself "the satisfaction of writing a very brief abstract of my theory in pencil".
Further development
Darwin continued to research and extensively revise his theory while focusing on his main work of publishing the scientific results of the Beagle voyage. He tentatively wrote of his ideas to Lyell in January 1842; then in June he roughed out a 35-page "Pencil Sketch" of his theory. Darwin began correspondence about his theorising with the botanist Joseph Dalton Hooker in January 1844, and by July had rounded out his "sketch" into a 230-page "Essay", to be expanded with his research results and published if he died prematurely.
In November 1844, the anonymously published popular science book Vestiges of the Natural History of Creation, written by Scottish journalist Robert Chambers, widened public interest in the concept of transmutation of species. Vestiges used evidence from the fossil record and embryology to support the claim that living things had progressed from the simple to the more complex over time. But it proposed a linear progression rather than the branching common descent theory behind Darwin's work in progress, and it ignored adaptation. Darwin read it soon after publication, and scorned its amateurish geology and zoology, but he carefully reviewed his own arguments after leading scientists, including Adam Sedgwick, attacked its morality and scientific errors. Vestiges had significant influence on public opinion, and the intense debate helped to pave the way for the acceptance of the more scientifically sophisticated Origin by moving evolutionary speculation into the mainstream. While few naturalists were willing to consider transmutation, Herbert Spencer became an active proponent of Lamarckism and progressive development in the 1850s.Hooker was persuaded to take away a copy of the "Essay" in January 1847, and eventually sent a page of notes giving Darwin much-needed feedback. Reminded of his lack of expertise in taxonomy, Darwin began an eight-year study of barnacles, becoming the leading expert on their classification. Using his theory, he discovered homologies showing that slightly changed body parts served different functions to meet new conditions, and he found an intermediate stage in the evolution of distinct sexes.Darwin's barnacle studies convinced him that variation arose constantly and not just in response to changed circumstances. In 1854, he completed the last part of his Beagle-related writing and began working full-time on evolution. He now realised that the branching pattern of evolutionary divergence was explained by natural selection working constantly to improve adaptation. His thinking changed from the view that species formed in isolated populations only, as on islands, to an emphasis on speciation without isolation; that is, he saw increasing specialisation within large stable populations as continuously exploiting new ecological niches. He conducted empirical research focusing on difficulties with his theory. He studied the developmental and anatomical differences between different breeds of many domestic animals, became actively involved in fancy pigeon breeding, and experimented (with the help of his young son Francis) on ways that plant seeds and animals might disperse across oceans to colonise distant islands. By 1856, his theory was much more sophisticated, with a mass of supporting evidence.
Publication
Time taken to publish
In his autobiography, Darwin said he had "gained much by my delay in publishing from about 1839, when the theory was clearly conceived, to 1859; and I lost nothing by it". On the first page of his 1859 book he noted that, having begun work on the topic in 1837, he had drawn up "some short notes" after five years, had enlarged these into a sketch in 1844, and "from that period to the present day I have steadily pursued the same object."Various biographers have proposed that Darwin avoided or delayed making his ideas public for personal reasons. Reasons suggested have included fear of religious persecution or social disgrace if his views were revealed, and concern about upsetting his clergymen naturalist friends or his pious wife Emma. Charles Darwin's illness caused repeated delays. His paper on Glen Roy had proved embarrassingly wrong, and he may have wanted to be sure he was correct. David Quammen has suggested all these factors may have contributed, and notes Darwin's large output of books and busy family life during that time.A more recent study by science historian John van Wyhe has determined that the idea that Darwin delayed publication only dates back to the 1940s, and Darwin's contemporaries thought the time he took was reasonable. Darwin always finished one book before starting another. While he was researching, he told many people about his interest in transmutation without causing outrage. He firmly intended to publish, but it was not until September 1854 that he could work on it full-time. His 1846 estimate that writing his "big book" would take five years proved optimistic.
Events leading to publication: "big book" manuscript
An 1855 paper on the "introduction" of species, written by Alfred Russel Wallace, claimed that patterns in the geographical distribution of living and fossil species could be explained if every new species always came into existence near an already existing, closely related species. Charles Lyell recognised the implications of Wallace's paper and its possible connection to Darwin's work, although Darwin did not, and in a letter written on 1–2 May 1856 Lyell urged Darwin to publish his theory to establish priority. Darwin was torn between the desire to set out a full and convincing account and the pressure to quickly produce a short paper. He met Lyell, and in correspondence with Joseph Dalton Hooker affirmed that he did not want to expose his ideas to review by an editor as would have been required to publish in an academic journal. He began a "sketch" account on 14 May 1856, and by July had decided to produce a full technical treatise on species as his "big book" on Natural Selection. His theory including the principle of divergence was complete by 5 September 1857 when he sent Asa Gray a brief but detailed abstract of his ideas.
Joint publication of papers by Wallace and Darwin
Darwin was hard at work on the manuscript for his "big book" on Natural Selection, when on 18 June 1858 he received a parcel from Wallace, who stayed on the Maluku Islands (Ternate and Gilolo). It enclosed twenty pages describing an evolutionary mechanism, a response to Darwin's recent encouragement, with a request to send it on to Lyell if Darwin thought it worthwhile. The mechanism was similar to Darwin's own theory. Darwin wrote to Lyell that "your words have come true with a vengeance, ... forestalled" and he would "of course, at once write and offer to send [it] to any journal" that Wallace chose, adding that "all my originality, whatever it may amount to, will be smashed". Lyell and Hooker agreed that a joint publication putting together Wallace's pages with extracts from Darwin's 1844 Essay and his 1857 letter to Gray should be presented at the Linnean Society, and on 1 July 1858, the papers entitled On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection, by Wallace and Darwin respectively, were read out but drew little reaction. While Darwin considered Wallace's idea to be identical to his concept of natural selection, historians have pointed out differences. Darwin described natural selection as being analogous to the artificial selection practised by animal breeders, and emphasised competition between individuals; Wallace drew no comparison to selective breeding, and focused on ecological pressures that kept different varieties adapted to local conditions. Some historians have suggested that Wallace was actually discussing group selection rather than selection acting on individual variation.
Abstract of Species book
Soon after the meeting, Darwin decided to write "an abstract of my whole work" in the form of one or more papers to be published by the Linnean Society, but was concerned about "how it can be made scientific for a Journal, without giving facts, which would be impossible." He asked Hooker how many pages would be available, but "If the Referees were to reject it as not strictly scientific I would, perhaps publish it as pamphlet." He began his "abstract of Species book" on 20 July 1858, while on holiday at Sandown, and wrote parts of it from memory, while sending the manuscripts to his friends for checking.By early October, he began to "expect my abstract will run into a small volume, which will have to be published separately." Over the same period, he continued to collect information and write large fully detailed sections of the manuscript for his "big book" on Species, Natural Selection.
Murray as publisher; choice of title
By mid-March 1859 Darwin's abstract had reached the stage where he was thinking of early publication; Lyell suggested the publisher John Murray, and met with him to find if he would be willing to publish. On 28 March Darwin wrote to Lyell asking about progress, and offering to give Murray assurances "that my Book is not more un-orthodox, than the subject makes inevitable." He enclosed a draft title sheet proposing An abstract of an Essay on the Origin of Species and Varieties Through natural selection, with the year shown as "1859".Murray's response was favourable, and a very pleased Darwin told Lyell on 30 March that he would "send shortly a large bundle of M.S. but unfortunately I cannot for a week, as the three first chapters are in three copyists' hands". He bowed to Murray's objection to "abstract" in the title, though he felt it excused the lack of references, but wanted to keep "natural selection" which was "constantly used in all works on Breeding", and hoped "to retain it with Explanation, somewhat as thus",— Through Natural Selection or the preservation of favoured races.
On 31 March Darwin wrote to Murray in confirmation, and listed headings of the 12 chapters in progress: he had drafted all except "XII. Recapitulation & Conclusion". Murray responded immediately with an agreement to publish the book on the same terms as he published Lyell, without even seeing the manuscript: he offered Darwin ⅔ of the profits. Darwin promptly accepted with pleasure, insisting that Murray would be free to withdraw the offer if, having read the chapter manuscripts, he felt the book would not sell well (eventually Murray paid £180 to Darwin for the first edition and by Darwin's death in 1882 the book was in its sixth edition, earning Darwin nearly £3000).
On 5 April, Darwin sent Murray the first three chapters, and a proposal for the book's title. An early draft title page suggests On the Mutability of Species. Murray cautiously asked Whitwell Elwin to review the chapters. At Lyell's suggestion, Elwin recommended that, rather than "put forth the theory without the evidence", the book should focus on observations upon pigeons, briefly stating how these illustrated Darwin's general principles and preparing the way for the larger work expected shortly: "Every body is interested in pigeons." Darwin responded that this was impractical: he had only the last chapter still to write. In September the main title still included "An essay on the origin of species and varieties", but Darwin now proposed dropping "varieties".With Murray's persuasion, the title was eventually agreed as On the Origin of Species, with the title page adding by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. In this extended title (and elsewhere in the book) Darwin used the biological term "races" interchangeably with "varieties", meaning varieties within a species. He used the term broadly, and as well as discussions of "the several races, for instance, of the cabbage" and "the hereditary varieties or races of our domestic animals and plants", there are three instances in the book where the phrase "races of man" is used, referring to races of humans.
Publication and subsequent editions
On the Origin of Species was first published on Thursday 24 November 1859, priced at fifteen shillings with a first printing of 1250 copies. The book had been offered to booksellers at Murray's autumn sale on Tuesday 22 November, and all available copies had been taken up immediately. In total, 1,250 copies were printed but after deducting presentation and review copies, and five for Stationers' Hall copyright, around 1,170 copies were available for sale. Significantly, 500 were taken by Mudie's Library, ensuring that the book promptly reached a large number of subscribers to the library. The second edition of 3,000 copies was quickly brought out on 7 January 1860, and incorporated numerous corrections as well as a response to religious objections by the addition of a new epigraph on page ii, a quotation from Charles Kingsley, and the phrase "by the Creator" added to the closing sentence. During Darwin's lifetime the book went through six editions, with cumulative changes and revisions to deal with counter-arguments raised. The third edition came out in 1861, with a number of sentences rewritten or added and an introductory appendix, An Historical Sketch of the Recent Progress of Opinion on the Origin of Species. In response to objections that the origin of life was unexplained, Darwin pointed to acceptance of Newton's law even though the cause of gravity was unknown, and Leibnitz had accused Newton of introducing "occult qualities & miracles". The fourth edition in 1866 had further revisions. The fifth edition, published on 10 February 1869, incorporated more changes and for the first time included the phrase "survival of the fittest", which had been coined by the philosopher Herbert Spencer in his Principles of Biology (1864).In January 1871, George Jackson Mivart's On the Genesis of Species listed detailed arguments against natural selection, and claimed it included false metaphysics. Darwin made extensive revisions to the sixth edition of the Origin (this was the first edition in which he used the word "evolution" which had commonly been associated with embryological development, though all editions concluded with the word "evolved"), and added a new chapter VII, Miscellaneous objections, to address Mivart's arguments.The sixth edition was published by Murray on 19 February 1872 as The Origin of Species, with "On" dropped from the title. Darwin had told Murray of working men in Lancashire clubbing together to buy the fifth edition at 15 shillings and wanted it made more widely available; the price was halved to 7s 6d by printing in a smaller font. It includes a glossary compiled by W.S. Dallas. Book sales increased from 60 to 250 per month.
Publication outside Great Britain
In the United States, botanist Asa Gray, an American colleague of Darwin, negotiated with a Boston publisher for publication of an authorised American version, but learnt that two New York publishing firms were already planning to exploit the absence of international copyright to print Origin. Darwin was delighted by the popularity of the book, and asked Gray to keep any profits. Gray managed to negotiate a 5% royalty with Appleton's of New York, who got their edition out in mid-January 1860, and the other two withdrew. In a May letter, Darwin mentioned a print run of 2,500 copies, but it is not clear if this referred to the first printing only, as there were four that year.The book was widely translated in Darwin's lifetime, but problems arose with translating concepts and metaphors, and some translations were biased by the translator's own agenda. Darwin distributed presentation copies in France and Germany, hoping that suitable applicants would come forward, as translators were expected to make their own arrangements with a local publisher. He welcomed the distinguished elderly naturalist and geologist Heinrich Georg Bronn, but the German translation published in 1860 imposed Bronn's own ideas, adding controversial themes that Darwin had deliberately omitted. Bronn translated "favoured races" as "perfected races", and added essays on issues including the origin of life, as well as a final chapter on religious implications partly inspired by Bronn's adherence to Naturphilosophie. In 1862, Bronn produced a second edition based on the third English edition and Darwin's suggested additions, but then died of a heart attack. Darwin corresponded closely with Julius Victor Carus, who published an improved translation in 1867. Darwin's attempts to find a translator in France fell through, and the translation by Clémence Royer published in 1862 added an introduction praising Darwin's ideas as an alternative to religious revelation and promoting ideas anticipating social Darwinism and eugenics, as well as numerous explanatory notes giving her own answers to doubts that Darwin expressed. Darwin corresponded with Royer about a second edition published in 1866 and a third in 1870, but he had difficulty getting her to remove her notes and was troubled by these editions. He remained unsatisfied until a translation by Edmond Barbier was published in 1876. A Dutch translation by Tiberius Cornelis Winkler was published in 1860. By 1864, additional translations had appeared in Italian and Russian. In Darwin's lifetime, Origin was published in Swedish in 1871, Danish in 1872, Polish in 1873, Hungarian in 1873–1874, Spanish in 1877 and Serbian in 1878. By 1977, Origin had appeared in an additional 18 languages, including Chinese by Ma Chün-wu who added non-Darwinian ideas; he published the preliminaries and chapters 1–5 in 1902–1904, and his complete translation in 1920.
Content
Title pages and introduction
Page ii contains quotations by William Whewell and Francis Bacon on the theology of natural laws, harmonising science and religion in accordance with Isaac Newton's belief in a rational God who established a law-abiding cosmos. In the second edition, Darwin added an epigraph from Joseph Butler affirming that God could work through scientific laws as much as through miracles, in a nod to the religious concerns of his oldest friends. The Introduction establishes Darwin's credentials as a naturalist and author, then refers to John Herschel's letter suggesting that the origin of species "would be found to be a natural in contradistinction to a miraculous process":
WHEN on board HMS Beagle, as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species—that mystery of mysteries, as it has been called by one of our greatest philosophers.
Darwin refers specifically to the distribution of the species rheas, and to that of the Galápagos tortoises and mockingbirds. He mentions his years of work on his theory, and the arrival of Wallace at the same conclusion, which led him to "publish this Abstract" of his incomplete work. He outlines his ideas, and sets out the essence of his theory:
As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.
Starting with the third edition, Darwin prefaced the introduction with a sketch of the historical development of evolutionary ideas. In that sketch he acknowledged that Patrick Matthew had, unknown to Wallace or himself, anticipated the concept of natural selection in an appendix to a book published in 1831; in the fourth edition he mentioned that William Charles Wells had done so as early as 1813.
Variation under domestication and under nature
Chapter I covers animal husbandry and plant breeding, going back to ancient Egypt. Darwin discusses contemporary opinions on the origins of different breeds under cultivation to argue that many have been produced from common ancestors by selective breeding. As an illustration of artificial selection, he describes fancy pigeon breeding, noting that "[t]he diversity of the breeds is something astonishing", yet all were descended from one species of rock pigeon. Darwin saw two distinct kinds of variation: (1) rare abrupt changes he called "sports" or "monstrosities" (example: Ancon sheep with short legs), and (2) ubiquitous small differences (example: slightly shorter or longer bill of pigeons). Both types of hereditary changes can be used by breeders. However, for Darwin the small changes were most important in evolution. In this chapter Darwin expresses his erroneous belief that environmental change is necessary to generate variation.In Chapter II, Darwin specifies that the distinction between species and varieties is arbitrary, with experts disagreeing and changing their decisions when new forms were found. He concludes that "a well-marked variety may be justly called an incipient species" and that "species are only strongly marked and permanent varieties". He argues for the ubiquity of variation in nature. Historians have noted that naturalists had long been aware that the individuals of a species differed from one another, but had generally considered such variations to be limited and unimportant deviations from the archetype of each species, that archetype being a fixed ideal in the mind of God. Darwin and Wallace made variation among individuals of the same species central to understanding the natural world.
Struggle for existence, natural selection, and divergence
In Chapter III, Darwin asks how varieties "which I have called incipient species" become distinct species, and in answer introduces the key concept he calls "natural selection"; in the fifth edition he adds, "But the expression often used by Mr. Herbert Spencer, of the Survival of the Fittest, is more accurate, and is sometimes equally convenient."
Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring ... I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's power of selection.
He notes that both A. P. de Candolle and Charles Lyell had stated that all organisms are exposed to severe competition. Darwin emphasizes that he used the phrase "struggle for existence" in "a large and metaphorical sense, including dependence of one being on another"; he gives examples ranging from plants struggling against drought to plants competing for birds to eat their fruit and disseminate their seeds. He describes the struggle resulting from population growth: "It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms." He discusses checks to such increase including complex ecological interdependencies, and notes that competition is most severe between closely related forms "which fill nearly the same place in the economy of nature".Chapter IV details natural selection under the "infinitely complex and close-fitting ... mutual relations of all organic beings to each other and to their physical conditions of life". Darwin takes as an example a country where a change in conditions led to extinction of some species, immigration of others and, where suitable variations occurred, descendants of some species became adapted to new conditions. He remarks that the artificial selection practised by animal breeders frequently produced sharp divergence in character between breeds, and suggests that natural selection might do the same, saying:
But how, it may be asked, can any analogous principle apply in nature? I believe it can and does apply most efficiently, from the simple circumstance that the more diversified the descendants from any one species become in structure, constitution, and habits, by so much will they be better enabled to seize on many and widely diversified places in the polity of nature, and so be enabled to increase in numbers.
Historians have remarked that here Darwin anticipated the modern concept of an ecological niche. He did not suggest that every favourable variation must be selected, nor that the favoured animals were better or higher, but merely more adapted to their surroundings.
Darwin proposes sexual selection, driven by competition between males for mates, to explain sexually dimorphic features such as lion manes, deer antlers, peacock tails, bird songs, and the bright plumage of some male birds. He analysed sexual selection more fully in The Descent of Man, and Selection in Relation to Sex (1871). Natural selection was expected to work very slowly in forming new species, but given the effectiveness of artificial selection, he could "see no limit to the amount of change, to the beauty and infinite complexity of the coadaptations between all organic beings, one with another and with their physical conditions of life, which may be effected in the long course of time by nature's power of selection". Using a tree diagram and calculations, he indicates the "divergence of character" from original species into new species and genera. He describes branches falling off as extinction occurred, while new branches formed in "the great Tree of life ... with its ever branching and beautiful ramifications".
Variation and heredity
In Darwin's time there was no agreed-upon model of heredity; in Chapter I Darwin admitted, "The laws governing inheritance are quite unknown." He accepted a version of the inheritance of acquired characteristics (which after Darwin's death came to be called Lamarckism), and Chapter V discusses what he called the effects of use and disuse; he wrote that he thought "there can be little doubt that use in our domestic animals strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited", and that this also applied in nature. Darwin stated that some changes that were commonly attributed to use and disuse, such as the loss of functional wings in some island-dwelling insects, might be produced by natural selection. In later editions of Origin, Darwin expanded the role attributed to the inheritance of acquired characteristics. Darwin also admitted ignorance of the source of inheritable variations, but speculated they might be produced by environmental factors. However, one thing was clear: whatever the exact nature and causes of new variations, Darwin knew from observation and experiment that breeders were able to select such variations and produce huge differences in many generations of selection. The observation that selection works in domestic animals is not destroyed by lack of understanding of the underlying hereditary mechanism.
Breeding of animals and plants showed related varieties varying in similar ways, or tending to revert to an ancestral form, and similar patterns of variation in distinct species were explained by Darwin as demonstrating common descent. He recounted how Lord Morton's mare apparently demonstrated telegony, offspring inheriting characteristics of a previous mate of the female parent, and accepted this process as increasing the variation available for natural selection.More detail was given in Darwin's 1868 book on The Variation of Animals and Plants Under Domestication, which tried to explain heredity through his hypothesis of pangenesis. Although Darwin had privately questioned blending inheritance, he struggled with the theoretical difficulty that novel individual variations would tend to blend into a population. However, inherited variation could be seen, and Darwin's concept of selection working on a population with a range of small variations was workable. It was not until the modern evolutionary synthesis in the 1930s and 1940s that a model of heredity became completely integrated with a model of variation. This modern evolutionary synthesis had been dubbed Neo Darwinian Evolution because it encompasses Charles Darwin's theories of evolution with Gregor Mendel's theories of genetic inheritance.
Difficulties for the theory
Chapter VI begins by saying the next three chapters will address possible objections to the theory, the first being that often no intermediate forms between closely related species are found, though the theory implies such forms must have existed. As Darwin noted, "Firstly, why, if species have descended from other species by insensibly fine gradations, do we not everywhere see innumerable transitional forms? Why is not all nature in confusion, instead of the species being, as we see them, well defined?" Darwin attributed this to the competition between different forms, combined with the small number of individuals of intermediate forms, often leading to extinction of such forms.Another difficulty, related to the first one, is the absence or rarity of transitional varieties in time. Darwin commented that by the theory of natural selection "innumerable transitional forms must have existed," and wondered "why do we not find them embedded in countless numbers in the crust of the earth?" (For further discussion of these difficulties, see Speciation#Darwin's dilemma: Why do species exist? and Bernstein et al. and Michod.)
The chapter then deals with whether natural selection could produce complex specialised structures, and the behaviours to use them, when it would be difficult to imagine how intermediate forms could be functional. Darwin said:
Secondly, is it possible that an animal having, for instance, the structure and habits of a bat, could have been formed by the modification of some animal with wholly different habits? Can we believe that natural selection could produce, on the one hand, organs of trifling importance, such as the tail of a giraffe, which serves as a fly-flapper, and, on the other hand, organs of such wonderful structure, as the eye, of which we hardly as yet fully understand the inimitable perfection?
His answer was that in many cases animals exist with intermediate structures that are functional. He presented flying squirrels, and flying lemurs as examples of how bats might have evolved from non-flying ancestors. He discussed various simple eyes found in invertebrates, starting with nothing more than an optic nerve coated with pigment, as examples of how the vertebrate eye could have evolved. Darwin concludes: "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case."In a section on "organs of little apparent importance", Darwin discusses the difficulty of explaining various seemingly trivial traits with no evident adaptive function, and outlines some possibilities such as correlation with useful features. He accepts that we "are profoundly ignorant of the causes producing slight and unimportant variations" which distinguish domesticated breeds of animals, and human races. He suggests that sexual selection might explain these variations:
I might have adduced for this same purpose the differences between the races of man, which are so strongly marked; I may add that some little light can apparently be thrown on the origin of these differences, chiefly through sexual selection of a particular kind, but without here entering on copious details my reasoning would appear frivolous.
Chapter VII (of the first edition) addresses the evolution of instincts. His examples included two he had investigated experimentally: slave-making ants and the construction of hexagonal cells by honey bees. Darwin noted that some species of slave-making ants were more dependent on slaves than others, and he observed that many ant species will collect and store the pupae of other species as food. He thought it reasonable that species with an extreme dependency on slave workers had evolved in incremental steps. He suggested that bees that make hexagonal cells evolved in steps from bees that made round cells, under pressure from natural selection to economise wax. Darwin concluded:
Finally, it may not be a logical deduction, but to my imagination it is far more satisfactory to look at such instincts as the young cuckoo ejecting its foster-brothers, —ants making slaves, —the larvæ of ichneumonidæ feeding within the live bodies of caterpillars, —not as specially endowed or created instincts, but as small consequences of one general law, leading to the advancement of all organic beings, namely, multiply, vary, let the strongest live and the weakest die.
Chapter VIII addresses the idea that species had special characteristics that prevented hybrids from being fertile in order to preserve separately created species. Darwin said that, far from being constant, the difficulty in producing hybrids of related species, and the viability and fertility of the hybrids, varied greatly, especially among plants. Sometimes what were widely considered to be separate species produced fertile hybrid offspring freely, and in other cases what were considered to be mere varieties of the same species could only be crossed with difficulty. Darwin concluded: "Finally, then, the facts briefly given in this chapter do not seem to me opposed to, but even rather to support the view, that there is no fundamental distinction between species and varieties."In the sixth edition Darwin inserted a new chapter VII (renumbering the subsequent chapters) to respond to criticisms of earlier editions, including the objection that many features of organisms were not adaptive and could not have been produced by natural selection. He said some such features could have been by-products of adaptive changes to other features, and that often features seemed non-adaptive because their function was unknown, as shown by his book on Fertilisation of Orchids that explained how their elaborate structures facilitated pollination by insects. Much of the chapter responds to George Jackson Mivart's criticisms, including his claim that features such as baleen filters in whales, flatfish with both eyes on one side and the camouflage of stick insects could not have evolved through natural selection because intermediate stages would not have been adaptive. Darwin proposed scenarios for the incremental evolution of each feature.
Geological record
Chapter IX deals with the fact that the geological record appears to show forms of life suddenly arising, without the innumerable transitional fossils expected from gradual changes. Darwin borrowed Charles Lyell's argument in Principles of Geology that the record is extremely imperfect as fossilisation is a very rare occurrence, spread over vast periods of time; since few areas had been geologically explored, there could only be fragmentary knowledge of geological formations, and fossil collections were very poor. Evolved local varieties which migrated into a wider area would seem to be the sudden appearance of a new species. Darwin did not expect to be able to reconstruct evolutionary history, but continuing discoveries gave him well-founded hope that new finds would occasionally reveal transitional forms. To show that there had been enough time for natural selection to work slowly, he cited the example of The Weald as discussed in Principles of Geology together with other observations from Hugh Miller, James Smith of Jordanhill and Andrew Ramsay. Combining this with an estimate of recent rates of sedimentation and erosion, Darwin calculated that erosion of The Weald had taken around 300 million years. The initial appearance of entire groups of well-developed organisms in the oldest fossil-bearing layers, now known as the Cambrian explosion, posed a problem. Darwin had no doubt that earlier seas had swarmed with living creatures, but stated that he had no satisfactory explanation for the lack of fossils. Fossil evidence of pre-Cambrian life has since been found, extending the history of life back for billions of years.Chapter X examines whether patterns in the fossil record are better explained by common descent and branching evolution through natural selection, than by the individual creation of fixed species. Darwin expected species to change slowly, but not at the same rate – some organisms such as Lingula were unchanged since the earliest fossils. The pace of natural selection would depend on variability and change in the environment. This distanced his theory from Lamarckian laws of inevitable progress. It has been argued that this anticipated the punctuated equilibrium hypothesis, but other scholars have preferred to emphasise Darwin's commitment to gradualism. He cited Richard Owen's findings that the earliest members of a class were a few simple and generalised species with characteristics intermediate between modern forms, and were followed by increasingly diverse and specialised forms, matching the branching of common descent from an ancestor. Patterns of extinction matched his theory, with related groups of species having a continued existence until extinction, then not reappearing. Recently extinct species were more similar to living species than those from earlier eras, and as he had seen in South America, and William Clift had shown in Australia, fossils from recent geological periods resembled species still living in the same area.
Geographic distribution
Chapter XI deals with evidence from biogeography, starting with the observation that differences in flora and fauna from separate regions cannot be explained by environmental differences alone; South America, Africa, and Australia all have regions with similar climates at similar latitudes, but those regions have very different plants and animals. The species found in one area of a continent are more closely allied with species found in other regions of that same continent than to species found on other continents. Darwin noted that barriers to migration played an important role in the differences between the species of different regions. The coastal sea life of the Atlantic and Pacific sides of Central America had almost no species in common even though the Isthmus of Panama was only a few miles wide. His explanation was a combination of migration and descent with modification. He went on to say: "On this principle of inheritance with modification, we can understand how it is that sections of genera, whole genera, and even families are confined to the same areas, as is so commonly and notoriously the case." Darwin explained how a volcanic island formed a few hundred miles from a continent might be colonised by a few species from that continent. These species would become modified over time, but would still be related to species found on the continent, and Darwin observed that this was a common pattern. Darwin discussed ways that species could be dispersed across oceans to colonise islands, many of which he had investigated experimentally.Chapter XII continues the discussion of biogeography. After a brief discussion of freshwater species, it returns to oceanic islands and their peculiarities; for example on some islands roles played by mammals on continents were played by other animals such as flightless birds or reptiles. The summary of both chapters says:
... I think all the grand leading facts of geographical distribution are explicable on the theory of migration (generally of the more dominant forms of life), together with subsequent modification and the multiplication of new forms. We can thus understand the high importance of barriers, whether of land or water, which separate our several zoological and botanical provinces. We can thus understand the localisation of sub-genera, genera, and families; and how it is that under different latitudes, for instance in South America, the inhabitants of the plains and mountains, of the forests, marshes, and deserts, are in so mysterious a manner linked together by affinity, and are likewise linked to the extinct beings which formerly inhabited the same continent ... On these same principles, we can understand, as I have endeavoured to show, why oceanic islands should have few inhabitants, but of these a great number should be endemic or peculiar; ...
Classification, morphology, embryology, rudimentary organs
Chapter XIII starts by observing that classification depends on species being grouped together in a Taxonomy, a multilevel system of groups and sub-groups based on varying degrees of resemblance. After discussing classification issues, Darwin concludes:
All the foregoing rules and aids and difficulties in classification are explained, if I do not greatly deceive myself, on the view that the natural system is founded on descent with modification; that the characters which naturalists consider as showing true affinity between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical; that community of descent is the hidden bond which naturalists have been unconsciously seeking, ...
Darwin discusses morphology, including the importance of homologous structures. He says, "What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?" This made no sense under doctrines of independent creation of species, as even Richard Owen had admitted, but the "explanation is manifest on the theory of the natural selection of successive slight modifications" showing common descent. He notes that animals of the same class often have extremely similar embryos. Darwin discusses rudimentary organs, such as the wings of flightless birds and the rudiments of pelvis and leg bones found in some snakes. He remarks that some rudimentary organs, such as teeth in baleen whales, are found only in embryonic stages. These factors also supported his theory of descent with modification.
Concluding remarks
The final chapter, "Recapitulation and Conclusion", reviews points from earlier chapters, and Darwin concludes by hoping that his theory might produce revolutionary changes in many fields of natural history. He suggests that psychology will be put on a new foundation and implies the relevance of his theory to the first appearance of humanity with the sentence that "Light will be thrown on the origin of man and his history." Darwin ends with a passage that became well known and much quoted:
It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us ... Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
Darwin added the phrase "by the Creator" from the 1860 second edition onwards, so that the ultimate sentence begins "There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one".
Structure, style, and themes
Nature and structure of Darwin's argument
Darwin's aims were twofold: to show that species had not been separately created, and to show that natural selection had been the chief agent of change. He knew that his readers were already familiar with the concept of transmutation of species from Vestiges, and his introduction ridicules that work as failing to provide a viable mechanism. Therefore, the first four chapters lay out his case that selection in nature, caused by the struggle for existence, is analogous to the selection of variations under domestication, and that the accumulation of adaptive variations provides a scientifically testable mechanism for evolutionary speciation.Later chapters provide evidence that evolution has occurred, supporting the idea of branching, adaptive evolution without directly proving that selection is the mechanism. Darwin presents supporting facts drawn from many disciplines, showing that his theory could explain a myriad of observations from many fields of natural history that were inexplicable under the alternative concept that species had been individually created. The structure of Darwin's argument showed the influence of John Herschel, whose philosophy of science maintained that a mechanism could be called a vera causa (true cause) if three things could be demonstrated: its existence in nature, its ability to produce the effects of interest, and its ability to explain a wide range of observations. This reflected the influence of William Whewell's idea of a consilience of inductions, as explained in his work Philosophy of the Inductive Sciences, where if you could argue that a proposed mechanism successfully explained various phenomena you could then use those arguments as evidence for that mechanism.
Literary style
The Examiner review of 3 December 1859 commented, "Much of Mr. Darwin's volume is what ordinary readers would call 'tough reading;' that is, writing which to comprehend requires concentrated attention and some preparation for the task. All, however, is by no means of this description, and many parts of the book abound in information, easy to comprehend and both instructive and entertaining."While the book was readable enough to sell, its dryness ensured that it was seen as aimed at specialist scientists and could not be dismissed as mere journalism or imaginative fiction. Though Richard Owen did complain in the Quarterly Review that the style was too easy for a serious work of science. Unlike the still-popular Vestiges, it avoided the narrative style of the historical novel and cosmological speculation, though the closing sentence clearly hinted at cosmic progression. Darwin had long been immersed in the literary forms and practices of specialist science, and made effective use of his skills in structuring arguments. David Quammen has described the book as written in everyday language for a wide audience, but noted that Darwin's literary style was uneven: in some places he used convoluted sentences that are difficult to read, while in other places his writing was beautiful. Quammen advised that later editions were weakened by Darwin making concessions and adding details to address his critics, and recommended the first edition. James T. Costa said that because the book was an abstract produced in haste in response to Wallace's essay, it was more approachable than the big book on natural selection Darwin had been working on, which would have been encumbered by scholarly footnotes and much more technical detail. He added that some parts of Origin are dense, but other parts are almost lyrical, and the case studies and observations are presented in a narrative style unusual in serious scientific books, which broadened its audience.
Human evolution
From his early transmutation notebooks in the late 1830s onwards, Darwin considered human evolution as part of the natural processes he was investigating, and rejected divine intervention. In 1856, his "big book on species" titled Natural Selection was to include a "note on Man", but when Wallace enquired in December 1857, Darwin replied; "You ask whether I shall discuss 'man';—I think I shall avoid whole subject, as so surrounded with prejudices, though I fully admit that it is the highest & most interesting problem for the naturalist."
On 28 March 1859, with his manuscript for the book well under way, Darwin wrote to Lyell offering the suggested publisher John Murray assurances "That I do not discuss origin of man".In the final chapter of On the Origin of Species, "Recapitulation and Conclusion", Darwin briefly highlights the human implications of his theory:
"In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history."
Discussing this in January 1860, Darwin assured Lyell that "by the sentence [Light will be thrown on the origin of man and his history] I show that I believe man is in same predicament with other animals. Many modern writers have seen this sentence as Darwin’s only reference to humans in the book; Janet Browne describes it as his only discussion there of human origins, while noting that the book makes other references to humanity.Some other statements in the book are quietly effective at pointing out the implication that humans are simply another species, evolving through the same processes and principles affecting other organisms. For example, in Chapter III: "Struggle for Existence" Darwin includes "slow-breeding man" among other examples of Malthusian population growth. In his discussions on morphology, Darwin compares and comments on bone structures that are homologous between humans and other mammals.Darwin's early notebooks discussed how non-adaptive characteristics could be selected when animals or humans chose mates, with races of humans differing over ideas of beauty. In his 1856 notes responding to Robert Knox's The Races of Man: A Fragment, he called this effect sexual selection. He added notes on sexual selection to his "big book on species", and in mid-1857 he added a section heading "Theory applied to Races of Man", but did not add text on this topic.In On the Origin of Species, Chapter VI: "Difficulties on Theory", Darwin mentions this in the context of "slight and unimportant variations":
I might have adduced for this same purpose the differences between the races of man, which are so strongly marked; I may add that some little light can apparently be thrown on the origin of these differences, chiefly through sexual selection of a particular kind, but without here entering on copious details my reasoning would appear frivolous."
When Darwin published The Descent of Man, and Selection in Relation to Sex twelve years later, he said that he had not gone into detail on human evolution in the Origin as he thought that would "only add to the prejudices against my views". He had not completely avoided the topic:
It seemed to me sufficient to indicate, in the first edition of my 'Origin of Species,' that by this work 'light would be thrown on the origin of man and his history;' and this implies that man must be included with other organic beings in any general conclusion respecting his manner of appearance on this earth.
He also said that he had "merely alluded" in that book to sexual selection differentiating human races.
Reception
The book aroused international interest and a widespread debate, with no sharp line between scientific issues and ideological, social and religious implications. Much of the initial reaction was hostile, in a large part because very few reviewers actually understood his theory, but Darwin had to be taken seriously as a prominent and respected name in science. Bishop Samuel Wilberforce wrote a review in Quarterly Review in 1860 where he disagreed with Darwin's 'argument'. There was much less controversy than had greeted the 1844 publication Vestiges of Creation, which had been rejected by scientists, but had influenced a wide public readership into believing that nature and human society were governed by natural laws. The Origin of Species as a book of wide general interest became associated with ideas of social reform. Its proponents made full use of a surge in the publication of review journals, and it was given more popular attention than almost any other scientific work, though it failed to match the continuing sales of Vestiges. Darwin's book legitimised scientific discussion of evolutionary mechanisms, and the newly coined term 'Darwinism' was used to cover the whole range of evolutionism, not just his own ideas. By the mid-1870s, evolutionism was triumphant.While Darwin had been somewhat coy about human origins, not identifying any explicit conclusion on the matter in his book, he had dropped enough hints about human's animal ancestry for the inference to be made, and the first review claimed it made a creed of the "men from monkeys" idea from Vestiges. Human evolution became central to the debate and was strongly argued by Huxley who featured it in his popular "working-men's lectures". Darwin did not publish his own views on this until 1871.The naturalism of natural selection conflicted with presumptions of purpose in nature and while this could be reconciled by theistic evolution, other mechanisms implying more progress or purpose were more acceptable. Herbert Spencer had already incorporated Lamarckism into his popular philosophy of progressive free market human society. He popularised the terms 'evolution' and 'survival of the fittest', and many thought Spencer was central to evolutionary thinking.
Impact on the scientific community
Scientific readers were already aware of arguments that species changed through processes that were subject to laws of nature, but the transmutational ideas of Lamarck and the vague "law of development" of Vestiges had not found scientific favour. Darwin presented natural selection as a scientifically testable mechanism while accepting that other mechanisms such as inheritance of acquired characters were possible. His strategy established that evolution through natural laws was worthy of scientific study, and by 1875, most scientists accepted that evolution occurred but few thought natural selection was significant. Darwin's scientific method was also disputed, with his proponents favouring the empiricism of John Stuart Mill's A System of Logic, while opponents held to the idealist school of William Whewell's Philosophy of the Inductive Sciences, in which investigation could begin with the intuitive idea that species were fixed objects created by design. Early support for Darwin's ideas came from the findings of field naturalists studying biogeography and ecology, including Joseph Dalton Hooker in 1860, and Asa Gray in 1862. Henry Walter Bates presented research in 1861 that explained insect mimicry using natural selection. Alfred Russel Wallace discussed evidence from his Malay archipelago research, including an 1864 paper with an evolutionary explanation for the Wallace line.
Evolution had less obvious applications to anatomy and morphology, and at first had little impact on the research of the anatomist Thomas Henry Huxley. Despite this, Huxley strongly supported Darwin on evolution; though he called for experiments to show whether natural selection could form new species, and questioned if Darwin's gradualism was sufficient without sudden leaps to cause speciation. Huxley wanted science to be secular, without religious interference, and his article in the April 1860 Westminster Review promoted scientific naturalism over natural theology, praising Darwin for "extending the domination of Science over regions of thought into which she has, as yet, hardly penetrated" and coining the term "Darwinism" as part of his efforts to secularise and professionalise science. Huxley gained influence, and initiated the X Club, which used the journal Nature to promote evolution and naturalism, shaping much of late-Victorian science. Later, the German morphologist Ernst Haeckel would convince Huxley that comparative anatomy and palaeontology could be used to reconstruct evolutionary genealogies.The leading naturalist in Britain was the anatomist Richard Owen, an idealist who had shifted to the view in the 1850s that the history of life was the gradual unfolding of a divine plan. Owen's review of the Origin in the April 1860 Edinburgh Review bitterly attacked Huxley, Hooker and Darwin, but also signalled acceptance of a kind of evolution as a teleological plan in a continuous "ordained becoming", with new species appearing by natural birth. Others that rejected natural selection, but supported "creation by birth", included the Duke of Argyll who explained beauty in plumage by design. Since 1858, Huxley had emphasised anatomical similarities between apes and humans, contesting Owen's view that humans were a separate sub-class. Their disagreement over human origins came to the fore at the British Association for the Advancement of Science meeting featuring the legendary 1860 Oxford evolution debate. In two years of acrimonious public dispute that Charles Kingsley satirised as the "Great Hippocampus Question" and parodied in The Water-Babies as the "great hippopotamus test", Huxley showed that Owen was incorrect in asserting that ape brains lacked a structure present in human brains. Others, including Charles Lyell and Alfred Russel Wallace, thought that humans shared a common ancestor with apes, but higher mental faculties could not have evolved through a purely material process. Darwin published his own explanation in the Descent of Man (1871).
Impact outside Great Britain
The German physiologist Emil du Bois-Reymond converted to Darwinism after reading an English copy of On the Origin of Species in the spring of 1860. Du Bois-Reymond was a committed supporter, securing Darwin an honorary degree from the University of Breslau, teaching his theory to students at the University of Berlin, and defending his name to paying audiences across Germany and The Netherlands. Du Bois-Reymond's exposition resembled Darwin's: he endorsed natural selection, rejected the inheritance of acquired characters, remained silent on the origin of variation, and identified "the altruism of bees, the regeneration of tissue, the effects of exercise, and the inheritance of disadvantageous traits" as puzzles presented by the theory.Evolutionary ideas, although not natural selection, were accepted by other German biologists accustomed to ideas of homology in morphology from Goethe's Metamorphosis of Plants and from their long tradition of comparative anatomy. Bronn's alterations in his German translation added to the misgivings of conservatives but encouraged political radicals. Ernst Haeckel was particularly ardent, aiming to synthesise Darwin's ideas with those of Lamarck and Goethe while still reflecting the spirit of Naturphilosophie. His ambitious programme to reconstruct the evolutionary history of life was joined by Huxley and supported by discoveries in palaeontology. Haeckel used embryology extensively in his recapitulation theory, which embodied a progressive, almost linear model of evolution. Darwin was cautious about such histories, and had already noted that von Baer's laws of embryology supported his idea of complex branching.Asa Gray promoted and defended Origin against those American naturalists with an idealist approach, notably Louis Agassiz, who viewed every species as a distinct fixed unit in the mind of the Creator, classifying as species what others considered merely varieties. Edward Drinker Cope and Alpheus Hyatt reconciled this view with evolutionism in a form of neo-Lamarckism involving recapitulation theory.French-speaking naturalists in several countries showed appreciation of the much-modified French translation by Clémence Royer, but Darwin's ideas had little impact in France, where any scientists supporting evolutionary ideas opted for a form of Lamarckism. The intelligentsia in Russia had accepted the general phenomenon of evolution for several years before Darwin had published his theory, and scientists were quick to take it into account, although the Malthusian aspects were felt to be relatively unimportant. The political economy of struggle was criticised as a British stereotype by Karl Marx and by Leo Tolstoy, who had the character Levin in his novel Anna Karenina voice sharp criticism of the morality of Darwin's views.
Challenges to natural selection
There were serious scientific objections to the process of natural selection as the key mechanism of evolution, including Carl Nägeli's insistence that a trivial characteristic with no adaptive advantage could not be developed by selection. Darwin conceded that these could be linked to adaptive characteristics. His estimate that the age of the Earth allowed gradual evolution was disputed by William Thomson (later awarded the title Lord Kelvin), who calculated that it had cooled in less than 100 million years. Darwin accepted blending inheritance, but Fleeming Jenkin calculated that as it mixed traits, natural selection could not accumulate useful traits. Darwin tried to meet these objections in the fifth edition. Mivart supported directed evolution, and compiled scientific and religious objections to natural selection. In response, Darwin made considerable changes to the sixth edition. The problems of the age of the Earth and heredity were only resolved in the 20th century.By the mid-1870s, most scientists accepted evolution, but relegated natural selection to a minor role as they believed evolution was purposeful and progressive. The range of evolutionary theories during "the eclipse of Darwinism" included forms of "saltationism" in which new species were thought to arise through "jumps" rather than gradual adaptation, forms of orthogenesis claiming that species had an inherent tendency to change in a particular direction, and forms of neo-Lamarckism in which inheritance of acquired characteristics led to progress. The minority view of August Weismann, that natural selection was the only mechanism, was called neo-Darwinism. It was thought that the rediscovery of Mendelian inheritance invalidated Darwin's views.
Impact on economic and political debates
While some, like Spencer, used analogy from natural selection as an argument against government intervention in the economy to benefit the poor, others, including Alfred Russel Wallace, argued that action was needed to correct social and economic inequities to level the playing field before natural selection could improve humanity further. Some political commentaries, including Walter Bagehot's Physics and Politics (1872), attempted to extend the idea of natural selection to competition between nations and between human races. Such ideas were incorporated into what was already an ongoing effort by some working in anthropology to provide scientific evidence for the superiority of Caucasians over non-white races and justify European imperialism. Historians write that most such political and economic commentators had only a superficial understanding of Darwin's scientific theory, and were as strongly influenced by other concepts about social progress and evolution, such as the Lamarckian ideas of Spencer and Haeckel, as they were by Darwin's work. Darwin objected to his ideas being used to justify military aggression and unethical business practices as he believed morality was part of fitness in humans, and he opposed polygenism, the idea that human races were fundamentally distinct and did not share a recent common ancestry.
Religious attitudes
The book produced a wide range of religious responses at a time of changing ideas and increasing secularisation. The issues raised were complex and there was a large middle ground. Developments in geology meant that there was little opposition based on a literal reading of Genesis, but defence of the argument from design and natural theology was central to debates over the book in the English-speaking world.
Natural theology was not a unified doctrine, and while some such as Louis Agassiz were strongly opposed to the ideas in the book, others sought a reconciliation in which evolution was seen as purposeful. In the Church of England, some liberal clergymen interpreted natural selection as an instrument of God's design, with the cleric Charles Kingsley seeing it as "just as noble a conception of Deity". In the second edition of January 1860, Darwin quoted Kingsley as "a celebrated cleric", and added the phrase "by the Creator" to the closing sentence, which from then on read "life, with its several powers, having been originally breathed by the Creator into a few forms or into one". While some commentators have taken this as a concession to religion that Darwin later regretted, Darwin's view at the time was of God creating life through the laws of nature, and even in the first edition there are several references to "creation".Baden Powell praised "Mr Darwin's masterly volume [supporting] the grand principle of the self-evolving powers of nature". In America, Asa Gray argued that evolution is the secondary effect, or modus operandi, of the first cause, design, and published a pamphlet defending the book in terms of theistic evolution, Natural Selection is not inconsistent with Natural Theology. Theistic evolution became a popular compromise, and St. George Jackson Mivart was among those accepting evolution but attacking Darwin's naturalistic mechanism. Eventually it was realised that supernatural intervention could not be a scientific explanation, and naturalistic mechanisms such as neo-Lamarckism were favoured over natural selection as being more compatible with purpose.Even though the book did not explicitly spell out Darwin's beliefs about human origins, it had dropped a number of hints about human's animal ancestry and quickly became central to the debate, as mental and moral qualities were seen as spiritual aspects of the immaterial soul, and it was believed that animals did not have spiritual qualities. This conflict could be reconciled by supposing there was some supernatural intervention on the path leading to humans, or viewing evolution as a purposeful and progressive ascent to mankind's position at the head of nature. While many conservative theologians accepted evolution, Charles Hodge argued in his 1874 critique "What is Darwinism?" that "Darwinism", defined narrowly as including rejection of design, was atheism though he accepted that Asa Gray did not reject design. Asa Gray responded that this charge misrepresented Darwin's text. By the early 20th century, four noted authors of The Fundamentals were explicitly open to the possibility that God created through evolution, but fundamentalism inspired the American creation–evolution controversy that began in the 1920s. Some conservative Roman Catholic writers and influential Jesuits opposed evolution in the late 19th and early 20th century, but other Catholic writers, starting with Mivart, pointed out that early Church Fathers had not interpreted Genesis literally in this area. The Vatican stated its official position in a 1950 papal encyclical, which held that evolution was not inconsistent with Catholic teaching.
Modern influence
Various alternative evolutionary mechanisms favoured during "the eclipse of Darwinism" became untenable as more was learned about inheritance and mutation. The full significance of natural selection was at last accepted in the 1930s and 1940s as part of the modern evolutionary synthesis. During that synthesis biologists and statisticians, including R. A. Fisher, Sewall Wright and J. B. S. Haldane, merged Darwinian selection with a statistical understanding of Mendelian genetics.Modern evolutionary theory continues to develop. Darwin's theory of evolution by natural selection, with its tree-like model of branching common descent, has become the unifying theory of the life sciences. The theory explains the diversity of living organisms and their adaptation to the environment. It makes sense of the geological record, biogeography, parallels in embryonic development, biological homologies, vestigiality, cladistics, phylogenetics and other fields, with unrivalled explanatory power; it has also become essential to applied sciences such as medicine and agriculture. Despite the scientific consensus, a religion-based political controversy has developed over how evolution is taught in schools, especially in the United States.Interest in Darwin's writings continues, and scholars have generated an extensive literature, the Darwin Industry, about his life and work. The text of Origin itself has been subject to much analysis including a variorum, detailing the changes made in every edition, first published in 1959, and a concordance, an exhaustive external index published in 1981. Worldwide commemorations of the 150th anniversary of the publication of On the Origin of Species and the bicentenary of Darwin's birth were scheduled for 2009. They celebrated the ideas which "over the last 150 years have revolutionised our understanding of nature and our place within it".In a survey conducted by a group of academic booksellers, publishers and librarians in advance of Academic Book Week in the United Kingdom, On the Origin of Species was voted the most influential academic book ever written. It was hailed as "the supreme demonstration of why academic books matter" and "a book which has changed the way we think about everything".
See also
On the Origin of Species – full text at Wikisource of the first edition, 1859
The Origin of Species – full text at Wikisource of the 6th edition, 1872
Charles Darwin bibliography
History of biology
History of evolutionary thought
History of speciation
Modern evolutionary synthesis
The Complete Works of Charles Darwin Online
The Descent of Man, and Selection in Relation to Sex, published in 1871; his second major book on evolutionary theory.
Transmutation of species
References
Works cited
Further reading
Browne, Janet (2007), Darwin's Origin of Species: A Biography, Grove Press, ISBN 978-0-87113-953-5
Malthus, Thomas Robert (1826), An Essay on the Principle of Population: A View of its Past and Present Effects on Human Happiness; with an Inquiry into Our Prospects Respecting the Future Removal or Mitigation of the Evils which It Occasions, vol. 1 (6th ed.), London: John Murray, retrieved 13 November 2017 (Vol. 2)
Reznick, David N. (2009), The Origin Then and Now: An Interpretive Guide to the Origin of Species, Princeton University Press, ISBN 978-0-691-12978-5
Schopf, J. William; Scheibel, Arnold B. (1997), The Origin and Evolution of Intelligence, Boston: Jones and Bartlett, ISBN 0-7637-0365-6
van Hoorn, Marijn (2009), Teyler, Winkler, Darwin (Lecture given at the Congress of the European Botanical and Horticultural Libraries Group, Prague, 23 April 2009), Teyler Net (Weblog of the Teylers Museum, Haarlem), archived from the original on 2 December 2011, retrieved 27 April 2010
Pechenik, Jan A. (2023), The Readable Darwin: The Origin of Species Edited for Modern Readers (2 ed.), Oxford University Press, ISBN 978-0-19757-526-0
Contemporary reviews
Carpenter, William Benjamin (1859), "Darwin on the Origin of Species", National Review, vol. 10, no. December 1859, pp. 188–214. Published anonymously.
Gray, Asa (1860), "(Review of) The Origin of Species", Athenaeum (1710: 4 August 1860): 161. Extract from Proceedings of the American Academy of Arts and Sciences 4 (1860): 411–415.
Huxley, Thomas Henry (1859), "Time and Life: Mr Darwin's Origin of Species", Macmillan's Magazine, 1: 142–148.
Huxley, Thomas Henry (1859), "Darwin on the Origin of Species", The Times (26 December 1859): 8–9. Published anonymously.
Jenkin, Fleeming (1867), "(Review of) The Origin of Species", North British Review, 46 (June 1867): 277–318. Published anonymously.
Murray, Andrew (1860), "On Mr Darwin's Theory of the Origin of Species", Proceedings of the Royal Society of Edinburgh, 4: 274–291, doi:10.1017/S0370164600034246.
Owen, Richard (1860), "Review of Darwin's Origin of Species", Edinburgh Review, 3 (April 1860): 487–532. Published anonymously.
Wilberforce, Samuel (1860), "(Review of) On the Origin of Species, by means of Natural Selection; or the Preservation of Favoured Races in the Struggle for Life", Quarterly Review, 108 (215: July 1860): 225–264. Published anonymously.For further reviews, see Darwin Online: Reviews & Responses to Darwin, Darwin Online, 10 March 2009, retrieved 18 June 2009
External links
The Complete Works of Charles Darwin Online:
Table of contents, bibliography of On the Origin of Species – links to text and images of all six British editions of The Origin of Species, the 6th edition with additions and corrections (final text), the first American edition, and translations into Danish, Dutch, French, German, Polish, Russian and Spanish
Online Variorum, showing every change between the six British editions
On the Origin of Species at Standard Ebooks
On the Origin of Species eBook provided by Project Gutenberg
On the Origin of Species public domain audiobook at LibriVox
On the Origin of Species on In Our Time at the BBC
On the Origin of Species, full text with embedded audio
A collection of Victorian Science Texts
Darwin Correspondence Project Home Page, University Library, Cambridge
View online at the Biodiversity Heritage Library On the Origin of Species 1860 American edition, D Appleton and Company, New York, with front insert by H. E. Barker, Lincolniana
Darwin's notes on the creation of On the Origin of Species digitised in Cambridge Digital Library |
challenger expedition | The Challenger expedition of 1872–1876 was a scientific programme that made many discoveries to lay the foundation of oceanography. The expedition was named after the naval vessel that undertook the trip, HMS Challenger.
The expedition, initiated by William Benjamin Carpenter, was placed under the scientific supervision of Sir Charles Wyville Thomson—of the University of Edinburgh and Merchiston Castle School—assisted by five other scientists, including Sir John Murray, a secretary-artist and a photographer. The Royal Society of London obtained the use of Challenger from the Royal Navy and in 1872 modified the ship for scientific tasks, equipping it with separate laboratories for natural history and chemistry. The expedition, led by Captain George Nares, sailed from Portsmouth, England, on 21 December 1872. Other naval officers included Commander John Maclear.Under the scientific supervision of Thomson himself, the ship traveled approximately 68,890 nautical miles (79,280 miles; 127,580 kilometres) surveying and exploring. The result was the Report of the Scientific Results of the Exploring Voyage of H.M.S. Challenger during the years 1873–76 which, among many other discoveries, catalogued over 4,000 previously unknown species. John Murray, who supervised the publication, described the report as "the greatest advance in the knowledge of our planet since the celebrated discoveries of the fifteenth and sixteenth centuries". The report is available online as the Report of the Voyage of HMS Challenger. Challenger sailed close to Antarctica, but not within sight of it. However, it was the first scientific expedition to take pictures of icebergs.
Preparations
To enable it to probe the depths, 15 of Challenger's 17 guns were removed and its spars reduced to make more space available. Laboratories, extra cabins and a special dredging platform were installed. Challenger used mainly sail power during the expedition; the steam engine was used only for dragging the dredge, station-keeping while taking soundings, and entering and leaving ports. It was loaded with specimen jars, filled with alcohol for preservation of samples, microscopes and chemical apparatus, trawls and dredges, thermometers, barometers, water sampling bottles, sounding leads, devices to collect sediment from the sea bed and great lengths of rope with which to suspend the equipment into the ocean depths.Because of the novelty of the expedition, some of the equipment was invented or specially modified for the occasion. It carried 181 miles (291 km) of Italian hemp rope for sounding.
Expedition
On its landmark journey circumnavigating the globe, 492 deep sea soundings, 133 bottom dredges, 151 open water trawls and 263 serial water temperature observations were taken. About 4,700 new species of marine life were discovered.
The scientific work was conducted by Wyville Thomson, John Murray, John Young Buchanan, Henry Nottidge Moseley, and Rudolf von Willemoes-Suhm. Frank Evers Bed was appointed prosector. The official expedition artist was John James Wild. As well as Nares and Maclear, others that were part of the naval crew included Pelham Aldrich, George Granville Campbell, and Andrew Francis Balfour (one of the sons of Scottish botanist John Hutton Balfour). Also among the officers was Thomas Henry Tizard, who had carried out important hydrographic observations on previous voyages. Though he was not among the civilian scientific staff, Tizard would later help write the official account of the expedition, and also become a Fellow of the Royal Society.
The original ship's complement included 21 officers and around 216 crew members. By the end of the voyage, this had been reduced to 144 due to deaths, desertions, personnel being left ashore due to illness, and planned departures.Challenger reached Hong Kong in December 1874, at which point Nares and Aldrich left the ship to take part in the British Arctic Expedition. The new captain was Frank Tourle Thomson. The second-in-command, and the most senior officer present throughout the entire expedition, was Commander John Maclear. Willemoes-Suhm died and was buried at sea on the voyage to Tahiti. Lords Campbell and Balfour left the ship in Valparaiso, Chile, after being promoted.
The first leg of the expedition took the ship from Portsmouth (December 1872) south to Lisbon (January 1873) and then on to Gibraltar. The next stops were Madeira and the Canary Islands (both February 1873). The period from February to July 1873 was spent crossing the Atlantic westwards from the Canary Islands to the Virgin Islands, then heading north to the North Atlantic archipelago and Imperial fortress colony of Bermuda (home base of the North America and West Indies Station), east to the Azores, back to Madeira, and then south to the Cape Verde Islands. During this period, there was a detour in April and May 1873, sailing from Bermuda north to Halifax and back, crossing the Gulf Stream twice with the reverse journey crossing further to the east.After leaving the Cape Verde Islands in August 1873, the expedition initially sailed south-east and then headed west to reach St Paul's Rocks. From here, the route went south across the equator to Fernando de Noronha during September 1873, and onwards that same month to Bahia (now called Salvador) in Brazil. The period from September to October 1873 was spent crossing the Atlantic from Bahia to the Cape of Good Hope, touching at Tristan da Cunha on the way.
December 1873 to February 1874 was spent sailing on a roughly south-eastern track from the Cape of Good Hope to the parallel of 60 degrees south. The islands visited during this period were the Prince Edward Islands, the Crozet Islands, the Kerguelen Islands, and Heard Island. February 1874 was spent travelling south and then generally eastwards in the vicinity of the Antarctic Circle, with sightings of icebergs, pack ice and whales. The route then took the ship north-eastward and away from the ice regions in March 1874, with the expedition reaching Melbourne in Australia later that month. The journey eastward along the coast from Melbourne to Sydney took place in April 1874, passing by Wilsons Promontory and Cape Howe.
When the voyage resumed in June 1874, the route went east from Sydney to Wellington in New Zealand, followed by a large loop north into the Pacific calling at Tonga and Fiji, and then back westward to Cape York in Australia by the end of August. The ship arrived in New Zealand in late June and left in early July. Before reaching Wellington (on New Zealand's North Island), brief stops were made at Port Hardy (on d'Urville Island) and Queen Charlotte Sound and Challenger passed through the Cook Strait to reach Wellington.
The route from Wellington to Tonga went along the east coast of New Zealand's North Island, and then north and east into the open Pacific, passing by the Kermadec Islands en route to Tongatabu, the main island of the Tonga archipelago (then known as the Friendly Islands). The waters around the Fijian islands, a short distance to the north-west of Tonga, were surveyed during late July and early August 1874. The ship's course was then set westward, reaching Raine Island—on the outer edge of the Great Barrier Reef—at the end of August and thence arriving at Cape York, at the tip of Australia's Cape York Peninsula.Over the following three months, from September to November 1874, the expedition visited several islands and island groups while sailing from Cape York to China and Hong Kong (then a British colony). The first part of the route passed north and west over the Arafura Sea, with New Guinea to the north-east and the Australian mainland to the south-west. The first islands visited were the Aru Islands, followed by the nearby Kai Islands. The ship then crossed the Banda Sea touching at the Banda Islands, to reach Amboina (Ambon Island) in October 1874, and then continuing to Ternate Island. At the time, all these islands were part of Netherlands East-Indies and are since 1949 part of Indonesia.
From Ternate, the route went north-westward towards the Philippines, passing east of Celebes (Sulawesi) into the Celebes Sea. The expedition called at Samboangan (Zamboanga) on Mindanao, and then Iloilo on the island of Panay, before navigating within the interior of the archipelago en route to the bay and harbour of Manila on the island of Luzon. The crossing north-westward from Manila to Hong Kong took place in November 1874.After several weeks in Hong Kong, the expedition departed in early January 1875 to retrace their route south-east towards New Guinea. The first stop on this outward leg of the journey was Manila. From there, they continued on to Samboangan, but took a different route through the interior of the Philippines, this time touching at the island of Zebu. From Samboangan the ship diverged from the inward route, this time passing south of Mindanao—in early-February 1875.
Challenger then headed east into the open sea, before turning to the south-east and making landfall at Humboldt Bay (now Yos Sudarso Bay) on the north coast of New Guinea. By March 1875, the expedition had reached the Admiralty Islands north-east of New Guinea. The final stage of the voyage on this side of the Pacific was a long journey across the open ocean to the north, passing mostly west of the Caroline Islands and the Mariana Islands, reaching port in Yokohama, Japan, in April 1875.
Challenger departed Japan in mid-June 1875, heading east across the Pacific to a point due north of the Sandwich Islands (Hawaii), and then turning south, making landfall at the end of July at Honolulu on the Hawaiian island of Oahu. A couple of weeks later, in mid-August, the ship departed south-eastward, anchoring at Hilo Bay off Hawaii's Big Island, before continuing to the south and reaching Tahiti in mid-September.
The expedition left Tahiti in early October, swinging to the west and south of the Tubuai Islands and then heading to the south-east before turning east towards the South American coast. The route touched at the Juan Fernández Islands in mid-November 1875, with Challenger reaching the port of Valparaiso in Chile a few days later. The next stage of the journey commenced the following month, with the route taking the ship south-westward back out into the Pacific, past the Juan Fernández Islands, before turning to the south-east and back towards South America, reaching Port Otway in the Gulf of Penas on 31 December 1875.Most of January 1876 was spent navigating around the southern tip of South America, surveying and touching at many of the bays and islands of the Patagonian archipelago, the Strait of Magellan, and Tierra del Fuego. Locations visited here include Hale Cove, Gray Harbour, Port Grappler, Tom Bay, all in the vicinity of Wellington Island; Puerta Bueno, near Hanover Island; Isthmus Bay, near the Queen Adelaide Archipelago; and Port Churruca, near Santa Ines Island.
The final stops, before heading out into the Atlantic, were Port Famine, Sandy Point, and Elizabeth Island. Challenger reached the Falkland Islands towards the end of January, calling at Port Stanley and then continuing northward, reaching Montevideo in Uruguay in mid-February 1876. The ship left Montevideo at the end of February, heading first due east and then due north, arriving at Ascension Island at the end of March 1876.
The period from early- to mid-April was spent sailing from Ascension Island to the Cape Verde Islands. From here, the route taken in late April and early May 1876 was a westward loop to the north out into the mid-Atlantic, eventually turning due east towards Europe to touch land at Vigo in Spain towards the end of May. The final stage of the voyage took the ship and its crew north-eastward from Vigo, skirting the Bay of Biscay to make landfall in England. Challenger returned to Spithead, Hampshire, on 24 May 1876, having spent 713 days out of the intervening 1,250 at sea.
Scientific objectives
The Royal Society stated the voyage's scientific goals were:
To investigate the physical conditions of the deep sea in the great ocean basins—as far as the neighborhood of the Great Southern Ice Barrier—in regard to depth, temperature, circulation, specific gravity and penetration of light.
To determine the chemical composition of seawater at various depths from the surface to the bottom, the organic matter in solution and the particles in suspension.
To ascertain the physical and chemical character of deep-sea deposits and the sources of these deposits.
To investigate the distribution of organic life at different depths and on the deep seafloor.One of the goals of the physical measurements for HMS Challenger was to be able to verify the hypothesis put forward by Carpenter on the link between temperature mapping and global ocean circulation in order to provide some answers on the phenomena involved in the major oceanic mixing. This study is a continuation of the preliminary exploratory missions of HMS Lightning (1823) and HMS Porcupine (1844). These results are important for Carpenter because his explanation differed from that of another renowned oceanographer at the time, the American Matthew Fontaine Maury. All these results of physical measurements were synthesized by John James Wild (i.e. the expedition's secretary-artist) in his doctoral thesis at the University of Zurich.A second important issue concerning the collection of different kinds of physical data on the ocean floor was the laying of submarine telegraph cables. Many transoceanic cables were being laid in the 1860s and 1870s and their efficient laying and operation were matters of great strategic and commercial importance.At each of the 360 stations the crew measured the bottom depth and temperature at different depths, observed weather and surface ocean conditions, and collected seafloor, water, and biota samples. Challenger's crew used methods that were developed in prior small-scale expeditions to make observations. To measure depth, they would lower a line with a weight attached to it until it reached the sea floor. The line was marked in 25-fathom (150 ft; 46 m) intervals with flags denoting depth. Because of this, the depth measurements from Challenger were, at best, accurate to the nearest 25-fathom (150 ft; 46 m) demarcation. The sinker often had a small container attached to it that would allow for the collection of bottom sediment samples.The crew used a variety of dredges and trawls to collect biological samples. The dredges consisted of metal nets attached to a wooden plank and dragged across the sea floor. Mop heads attached to the wooden plank would sweep across the sea floor and release organisms from the ocean bottom to be caught in the nets. Trawls were large metal nets towed behind the ship to collect organisms at different depths of water. Upon the retrieval of a dredge or trawl, Challenger crew would sort, rinse, and store the specimens for examination upon return. The specimens were often preserved in either brine or alcohol.The primary thermometer used throughout the Challenger expedition was the Miller–Casella thermometer, which contained two markers within a curved mercury tube to record the maximum and minimum temperature through which the instrument traveled. Several of these thermometers would be lowered at various depths for recording. However, this design assumed that the water closer to the surface of the ocean was always warmer than that below. During the voyage, Challenger's crew tested the reversing thermometer, which could measure temperature at specified depths. Afterwards, this type of thermometer was used extensively until the second half of the 20th century. After the return of the Challenger, C.W. Thomson asked Peter Tait to solve a thorny and important question: to evaluate the error in the measurement of the temperature of deep waters caused by the high pressures to which the thermometers were subjected. Tait solved this question and continued his work with a more fundamental study on the compressibility of liquids leading to his famous Tait equation. William Dittmar of Glasgow University established the composition of seawater. Murray and Alphonse François Renard mapped oceanic sediments.
Thomson believed, as did many adherents of the then-recent theory of evolution, that the deep sea would be home to "living fossils" long extinct in shallower waters, examples of "missing links". They believed that the conditions of constant cold temperature, darkness, and lack of currents, waves, or seismic events provided such a stable environment that evolution would slow or stop entirely. Louis Agassiz believed that in the deeps "we should expect to find representatives of earlier geological periods." Thomas Huxley stated that he expected to see "zoological antiquities which in the tranquil and little changed depths of the ocean have escaped the causes of destruction at work in the shallows and represent the predominant population of a past age." Nothing of the sort came to pass, however; though a few organisms previously regarded as extinct were found and cataloged among the many new discoveries, the harvest was typical of what might be found in exploring any equivalent extent of new territory. Furthermore, in the process of preserving specimens in alcohol, Thomson and chemist John Young Buchanan realized that he had inadvertently debunked Huxley's prior report of Bathybius haeckelii, an acellular protoplasm covering the sea bottoms, which was purported to be the link between non-living matter and living cells. The net effect was a setback for the proponents of evolution.
Challenger Deep
On 23 March 1875, at sample station number 225 located in the southwest Pacific Ocean between Guam and Palau, the crew recorded a sounding of 4,475 fathoms (26,850 ft; 8,184 m) deep, which was confirmed by an additional sounding. As shown by later expeditions using modern equipment, this area represents the southern end of the Mariana Trench and is one of the deepest known places on the ocean floor.
Modern soundings to 6,012 fathoms (36,070 ft; 10,994 m) have since been found near the site of the Challenger's original sounding. Challenger's discovery of this depth was a key finding of the expedition in broadening oceanographic knowledge about the ocean's depth and extent; the depression, the Challenger Deep, now bears the name of the vessel and its successor, HMS Challenger II, which in 1951 identified a depth of 5,944 fathoms nearby. Thomas Gaskell, the Chief Scientist on HMS Challenger II, observed that the later measurementwas not more than 50 miles from the spot where the nineteenth-century Challenger found her deepest depth [...] and it may be thought fitting that a ship with the name Challenger should put the seal on the work of that great pioneering expedition of oceanography.The expedition also verified the existence of the Mid-Atlantic Ridge extending from the southern hemisphere to the northern one.
Legacy
Findings from the Challenger expedition continued to be published until 1895, 19 years after the completion of its journey, by the Challenger Office, Edinburgh, established for that purpose. The report contained 50 volumes and was over 29,500 pages in length. Specimens brought back by Challenger were distributed to the world's foremost experts for examination, which greatly increased the expenses and time required to finalize the report. The report and specimens were displayed at the British Natural History Museum from January to July, 2023. Some specimens, many of which were the first discovered of their kind, are still examined by scientists today.A large number of scientists worked on categorizing the material brought back from the expedition including the paleontologist Gabriel Warton Lee. George Albert Boulenger, herpetologist at the Natural History Museum, named a species of lizard, Saproscincus challengeri, after Challenger.Before the Challenger expedition, oceanography had been mainly speculative. As the first true oceanographic cruise, the Challenger expedition laid the groundwork for an entire academic and research discipline. "Challenger" was applied to such varied phenomena as the Challenger Society for Marine Science, the oceanographic and marine geological survey ship Glomar Challenger, and the Space Shuttle Challenger.
References
Further reading
General
"HMS Challenger expedition". Natural History Museum. Archived from the original on 2 November 2014.
"Challenger Expedition (1872–1876)". University of Kansas Natural History Museum. Archived from the original on 14 December 2012.
"The letters of Joseph Matkin from HMS Challenger". Birch Aquarium at Scripps Institute of Oceanography. Archived from the original on 23 July 2008.
"Map of the route taken by HMS Challenger". Birch Aquarium at Scripps Institute of Oceanography. Archived from the original on 22 March 2012.
"The Challenger Medal Roll (1895)". Library of 19th Century Science. Archived from the original on 13 March 2009.Primary reports, accounts, and letters
"Report Of The Scientific Results of the Exploring Voyage of H.M.S. Challenger during the years 1873–76". Library of 19th Century Science. Archived from the original on 7 July 2005.
Philip F. Rehbock, ed. (1992). At Sea with the Scientifics: The Challenger Letters of Joseph Matkin. University of Hawaii Press. ISBN 082481424X.
Robert Wynn Jones and Henry Bowman Brady (1884). The Challenger Foraminifera (1994 reprint ed.). Oxford University Press and Natural History Museum. ISBN 0198540965.
Lord George Granville Campbell (1876). Log-letters from "The Challenger". Macmillan.
William James Joseph Spry (1877). The Cruise of Her Majesty's ship "Challenger". Harper & Brothers – via archive.org.
Henry Nottidge Moseley (1879). Notes by a Naturalist on the "Challenger". Macmillan.
"Archive entry for journals of Andrew F. Balfour, including three from HMS Challenger voyage". AIM25 archives. Archived from the original on 9 June 2012.Secondary literature
Antony Adler (2019). Neptune's Laboratory: Fantasy, Fear, and Science at Sea. Harvard University Press. ISBN 9780674972018.
Helen M. Rozwadowski (2005). Fathoming the Ocean. Harvard University Press. ISBN 0674027566.
R. M. Corfield (2003). The Silent Landscape: the Scientific Voyage of HMS Challenger. Joseph Henry Press. ISBN 0309089042.
Eileen V. Brunton (1994). The Challenger Expedition, 1872–1876: A Visual Index. Natural History Museum. ISBN 0565011391.
Eric Linklater (1974). The Voyage of the 'Challenger'. Cardinal. ISBN 0351172238.
John B. Tait (1972). "Centenary of the Challenger Expedition, 1872–1876". Scottish Geographical Magazine. 88 (3): 221. doi:10.1080/00369227208736231.
George Watson Cole (1901). Bermuda and the Challenger Expedition (2010 reprint ed.). Kessinger Publishing. ISBN 116639994X.
David M. Lawrence (2002). Upheaval From the Abyss: Ocean Floor Mapping and the Earth Science Revolution. Rutgers University Press. ISBN 9780813530284.Collections and archives
"HMS Challenger collection". Natural History Museum. Archived from the original on 2 November 2014.
"Foraminifera in Brady HMS Challenger Collection". Foraminifera.eu-Project.
"HMS Challenger Papers, 1872–1876". Edinburgh University Library (Archives Hub). Archived from the original on 14 January 2012.
External links
Media related to Challenger expedition at Wikimedia Commons |
microfossil | A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, such as a hand lens, is referred to as a macrofossil.
Microfossils are a common feature of the geological record, from the Precambrian to the Holocene. They are most common in deposits of marine environments, but also occur in brackish water, fresh water and terrestrial sedimentary deposits. While every kingdom of life is represented in the microfossil record, the most abundant forms are protist skeletons or microbial cysts from the Chrysophyta, Pyrrhophyta, Sarcodina, acritarchs and chitinozoans, together with pollen and spores from the vascular plants.
Overview
A microfossil is a descriptive term applied to fossilized plants and animals whose size is just at or below the level at which the fossil can be analyzed by the naked eye. A commonly applied cutoff point between "micro" and "macro" fossils is 1 mm. Microfossils may either be complete (or near-complete) organisms in themselves (such as the marine plankters foraminifera and coccolithophores) or component parts (such as small teeth or spores) of larger animals or plants. Microfossils are of critical importance as a reservoir of paleoclimate information, and are also commonly used by biostratigraphers to assist in the correlation of rock units.
Microfossils are found in rocks and sediments as the microscopic remains of what were once life forms such as plants, animals, fungus, protists, bacteria and archaea. Terrestrial microfossils include pollen and spores. Marine microfossils found in marine sediments are the most common microfossils. Everywhere in the oceans, microscopic protist organisms multiply prolifically, and many grow tiny skeletons which readily fossilise. These include foraminifera, dinoflagellates and radiolarians. Palaeontologists (geologists who study fossils) are interested in these microfossils because they can use them to determine how environments and climates have changed in the past, and where oil and gas can be found today.Some microfossils are formed by colonial organisms such as Bryozoa (especially the Cheilostomata), which have relatively large colonies but are classified by fine skeletal details of the small individuals of the colony. As another example, many fossil genera of Foraminifera, which are protists are known from shells (called tests) that were as big as coins, such as the genus Nummulites.
In 2017, fossilized microorganisms, or microfossils, were discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada that may be as old as 4.28 billion years old, the oldest record of life on Earth, suggesting "an almost instantaneous emergence of life" (in a geological time-scale), after ocean formation 4.41 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. Nonetheless, life may have started even earlier, at nearly 4.5 billion years ago, as claimed by some researchers.
Index fossils
Index fossils, also known as guide fossils, indicator fossils or dating fossils, are the fossilized remains or traces of particular plants or animals that are characteristic of a particular span of geologic time or environment, and can be used to identify and date the containing rocks. To be practical, index fossils must have a limited vertical time range, wide geographic distribution, and rapid evolutionary trends. Rock formations separated by great distances but containing the same index fossil species are thereby known to have both formed during the limited time that the species lived.
Index fossils were originally used to define and identify geologic units, then became a basis for defining geologic periods, and then for faunal stages and zones.
Species of microfossils such as acritarchs, chitinozoans, conodonts, dinoflagellate cysts, ostracods, pollen, spores and foraminiferans are amongst the many species have been identified as index fossils that are widely used in biostratigraphy. Different fossils work well for sediments of different ages. To work well, the fossils used must be widespread geographically, so that they can be found in many different places. They must also be short lived as a species, so that the period of time during which they could be incorporated in the sediment is relatively narrow. The longer lived the species, the poorer the stratigraphic precision, so fossils that evolve rapidly.
Often biostratigraphic correlations are based on a faunal assemblage, rather than an individual species — this allows greater precision as the time spawn in which all of the species in the assemblage existed together is narrower than the time spans of any of the members. Further, if only one species is present in a sample, it can mean either that (1) the strata were formed in the known fossil range of that organism; or (2) that the fossil range of the organism was incompletely known, and the strata extend the known fossil range. If the fossil is easy to preserve and easy to identify, more precise time estimating of the stratigraphic layers is possible.
Composition
Microfossil can be classification by their composition as: (a) siliceous, as in diatoms and radiolaria, (b) calcareous, as in coccoliths and foraminifera, (c) phosphatic, as in the study of some vertebrates, or (d) organic, as in the pollen and spores studied in palynology. This division focuses on differences in the mineralogical and chemical composition of microfossil remains rather than on taxonomic or ecological distinctions.
Siliceous microfossils: Siliceous microfossils include diatoms, radiolarians, silicoflagellates, ebridians, phytoliths, some scolecodonts (worm jaws), and sponge spicules.
Calcareous microfossils: Calcareous (CaCO3) microfossils include coccoliths, foraminifera, calcareous dinoflagellate cysts, and ostracods (seed shrimp).
Phosphatic microfossils: Phosphatic microfossils include conodonts (tiny oral structures of an extinct chordate group), some scolecodonts (worm jaws), shark spines and teeth and other fish remains (collectively called ichthyoliths).
Organic microfossils: The study of organic microfossils is called palynology. Organic microfossils include pollen, spores, chitinozoans (thought to be the egg cases of marine invertebrates), scolecodonts (worm jaws), acritarchs, dinoflagellate cysts, and fungal remains.
Organic-walled
Palynomorphs
Pollen grain
Pollen has an outer sheath, called a sporopollenin, which affords it some resistance to the rigours of the fossilisation process that destroy weaker objects. It is produced in huge quantities. There is an extensive fossil record of pollen grains, often disassociated from their parent plant. The discipline of palynology is devoted to the study of pollen, which can be used both for biostratigraphy and to gain information about the abundance and variety of plants alive — which can itself yield important information about paleoclimates. Also, pollen analysis has been widely used for reconstructing past changes in vegetation and their associated drivers.
Pollen is first found in the fossil record in the late Devonian period, but at that time it is indistinguishable from spores. It increases in abundance until the present day.
Plant spores
A spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, fungi and protozoa. Bacterial spores are not part of a sexual cycle but are resistant structures used for survival under unfavourable conditions.
Fungal spores
Chitinozoa
Chitinozoa are a taxon of flask-shaped, organic walled marine microfossils produced by an as yet unknown organism.Common from the Ordovician to Devonian periods (i.e. the mid-Paleozoic), the millimetre-scale organisms are abundant in almost all types of marine sediment across the globe. This wide distribution, and their rapid pace of evolution, makes them valuable biostratigraphic markers.
Their bizarre form has made classification and ecological reconstruction difficult. Since their discovery in 1931, suggestions of protist, plant, and fungal affinities have all been entertained. The organisms have been better understood as improvements in microscopy facilitated the study of their fine structure, and it has been suggested that they represent either the eggs or juvenile stage of a marine animal. However, recent research has suggested that they represent the test of a group of protists with uncertain affinities.The ecology of chitinozoa is also open to speculation; some may have floated in the water column, where others may have attached themselves to other organisms. Most species were particular about their living conditions, and tend to be most common in specific paleoenvironments. Their abundance also varied with the seasons.
Acritarchs
Acritarchs, Greek for confused origins, are organic-walled microfossils, known from about 2,000 million years ago to the present. Acritarchs are not a specific biological taxon, but rather a group with uncertain or unknown affinities. Most commonly they are composed of thermally altered acid insoluble carbon compounds (kerogen). While the classification of acritarchs into form genera is entirely artificial, it is not without merit, as the form taxa show traits similar to those of genuine taxa — for example the 'explosion' in the Cambrian and the mass extinction at the end of the Permian.
Acritarch diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion. Precambrian marine diversity was dominated by acritarchs. They underwent a boom around 1,000 million years ago, increasing in abundance, diversity, size, complexity of shape, and especially size and number of spines. Their increasingly spiny forms in the last 1 billion years may indicate an increased need for defence against predation.Acritarchs may include the remains of a wide range of quite different kinds of organisms—ranging from the egg cases of small metazoans to resting cysts of many kinds of chlorophyta (green algae). It is likely that most acritarch species from the Paleozoic represent various stages of the life cycle of algae that were ancestral to the dinoflagellates. The nature of the organisms associated with older acritarchs is generally not well understood, though many are probably related to unicellular marine algae. In theory, when the biological source (taxon) of an acritarch does become known, that particular microfossil is removed from the acritarchs and classified with its proper group.
Acritarchs were most likely eukaryotes. While archaea, bacteria and cyanobacteria (prokaryotes) usually produce simple fossils of a very small size, eukaryotic unicellular fossils are usually larger and more complex, with external morphological projections and ornamentation such as spines and hairs that only eukaryotes can produce; as most acritarchs have external projections (e.g., hair, spines, thick cell membranes, etc.), they are predominantly eukaryotes, although simple eukaryote acritarchs also exist.Acritarchs are found in sedimentary rocks from the present back into the Archean. They are typically isolated from siliciclastic sedimentary rocks using hydrofluoric acid but are occasionally extracted from carbonate-rich rocks. They are excellent candidates for index fossils used for dating rock formations in the Paleozoic Era and when other fossils are not available. Because most acritarchs are thought to be marine (pre-Triassic), they are also useful for palaeoenvironmental interpretation. The Archean and earliest Proterozoic microfossils termed "acritarchs" may actually be prokaryotes. The earliest eukaryotic acritarchs known (as of 2020) are from between 1950 and 2150 million years ago.Recent application of atomic force microscopy, confocal microscopy, Raman spectroscopy, and other analytic techniques to the study of the ultrastructure, life history, and systematic affinities of mineralized, but originally organic-walled microfossils, have shown some acritarchs are fossilized microalgae. In the end, it may well be, as Moczydłowska et al. suggested in 2011, that many acritarchs will, in fact, turn out to be algae.
Archean cells
Cells can be preserved in the rock record because their cell walls are made of proteins which convert to the organic material kerogen as the cell breaks down after death. Kerogen is insoluble in mineral acids, bases, and organic solvents. Over time, it is mineralised into graphite or graphite-like carbon, or degrades into oil and gas hydrocarbons. There are three main types of cell morphologies. Though there is no established range of sizes for each type, spheroid microfossils can be as small as about 8 micrometres, filamentous microfossils have diameters typically less than 5 micrometres and have a length that can range from tens of micrometres to 100 micrometres, and spindle-like microfossils can be as long as 50 micrometres.
Mineralised
Siliceous
Siliceous ooze is a type of biogenic pelagic sediment located on the deep ocean floor. Siliceous oozes are the least common of the deep sea sediments, and make up approximately 15% of the ocean floor. Oozes are defined as sediments which contain at least 30% skeletal remains of pelagic microorganisms. Siliceous oozes are largely composed of the silica based skeletons of microscopic marine organisms such as diatoms and radiolarians. Other components of siliceous oozes near continental margins may include terrestrially derived silica particles and sponge spicules. Siliceous oozes are composed of skeletons made from opal silica Si(O2), as opposed to calcareous oozes, which are made from skeletons of calcium carbonate organisms (i.e. coccolithophores). Silica (Si) is a bioessential element and is efficiently recycled in the marine environment through the silica cycle. Distance from land masses, water depth and ocean fertility are all factors that affect the opal silica content in seawater and the presence of siliceous oozes.
Phytoliths (Greek for plant stones) are rigid, microscopic structures made of silica, found in some plant tissues and persisting after the decay of the plant. These plants take up silica from the soil, whereupon it is deposited within different intracellular and extracellular structures of the plant. Phytoliths come in varying shapes and sizes. The term "phytolith" is sometimes used to refer to all mineral secretions by plants, but more commonly refers to siliceous plant remains.
Calcareous
The term calcareous can be applied to a fossil, sediment, or sedimentary rock which is formed from, or contains a high proportion of, calcium carbonate in the form of calcite or aragonite. Calcareous sediments (limestone) are usually deposited in shallow water near land, since the carbonate is precipitated by marine organisms that need land-derived nutrients. Generally speaking, the farther from land sediments fall, the less calcareous they are. Some areas can have interbedded calcareous sediments due to storms, or changes in ocean currents. Calcareous ooze is a form of calcium carbonate derived from planktonic organisms that accumulates on the sea floor. This can only occur if the ocean is shallower than the carbonate compensation depth. Below this depth, calcium carbonate begins to dissolve in the ocean, and only non-calcareous sediments are stable, such as siliceous ooze or pelagic red clay.
Ostracods
Ostracods are widespread crustaceans, generally small, sometimes known as seed shrimps. They are flattened from side to side and protected with a calcareous or chitinous bivalve-like shell. There are about 70,000 known species, 13,000 of which are extant. Ostracods are typically about 1 mm (0.039 in) in size, though they can range from 0.2 to 30 mm (0.008 to 1.181 in), with some species such as Gigantocypris being too large to be regarded as microfossils.
Conodonts
Conodonts (cone tooth in Greek) are tiny, extinct jawless fish that resemble eels. For many years, they were known only from tooth-like microfossils found in isolation and now called conodont elements. The evolution of mineralized tissues has been a puzzle for more than a century. It has been hypothesized that the first mechanism of chordate tissue mineralization began either in the oral skeleton of conodont or the dermal skeleton of early agnathans. Conodont elements are made of a phosphatic mineral, hydroxylapatite.The element array constituted a feeding apparatus that is radically different from the jaws of modern animals. They are now termed "conodont elements" to avoid confusion. The three forms of teeth (i.e., coniform cones, ramiform bars, and pectiniform platforms) probably performed different functions. For many years, conodonts were known only from enigmatic tooth-like microfossils (200 micrometres to 5 millimetres in length) which occur commonly, but not always in isolation, and were not associated with any other fossil.Conodonts are globally widespread in sediments.Their many forms are considered index fossils, fossils used to define and identify geological periods and date strata. Conodonts elements can be used to estimate the temperatures rocks have been exposed to, which allows the thermal maturation levels of sedimentary rocks to be determined, which is important for hydrocarbon exploration. Conodont teeth are the earliest vertebrate teeth found in the fossil record, and some conodont teeth are the sharpest that have ever been recorded.
Scolecodonts
Scolecodonts (worm jaws in Latin) are tiny jaws of polychaete annelids of the order Eunicida - a diverse and abundant group of worms which has been inhabiting different marine environments in the past 500 million years. Composed of highly resistant organic substance, the scolecodonts are frequently found as fossils from the rocks as old as the late Cambrian. Since the worms themselves were soft-bodied and hence extremely rarely preserved in the fossil record, their jaws constitute the main evidence of polychaetes in the geological past, and the only way to restore the evolution of this important group of animals. Small size of scolecodonts, usually less than 1 mm, puts them into a microfossil category. They are common by-product of conodont, chitinozoan and acritarch samples, but sometimes they occur in the sediments where other fossils are very rare or absent.
Cloudinids
The cloudinids were an early metazoan family that lived in the late Ediacaran period about 550 million years ago, and became extinct at the base of the Cambrian. They formed small millimetre size conical fossils consisting of calcareous cones nested within one another; the appearance of the organism itself remains unknown. The name Cloudina honors Preston Cloud. Fossils consist of a series of stacked vase-like calcite tubes, whose original mineral composition is unknown, Cloudinids comprise two genera: Cloudina itself is mineralized, whereas Conotubus is at best weakly mineralized, whilst sharing the same "funnel-in-funnel" construction.Cloudinids had a wide geographic range, reflected in the present distribution of localities in which their fossils are found, and are an abundant component of some deposits. Cloudina is usually found in association with microbial stromatolites, which are limited to shallow water, and it has been suggested that cloudinids lived embedded in the microbial mats, growing new cones to avoid being buried by silt. However no specimens have been found embedded in mats, and their mode of life is still an unresolved question.
The classification of the cloudinids has proved difficult: they were initially regarded as polychaete worms, and then as coral-like cnidarians on the basis of what look like buds on some specimens. Current scientific opinion is divided between classifying them as polychaetes and regarding it as unsafe to classify them as members of any broader grouping. In 2020, a new study showed the presence of Nephrozoan type guts, the oldest on record, supporting the bilaterian interpretation.Cloudinids are important in the history of animal evolution for two reasons. They are among the earliest and most abundant of the small shelly fossils with mineralized skeletons, and therefore feature in the debate about why such skeletons first appeared in the Late Ediacaran. The most widely supported answer is that their shells are a defense against predators, as some Cloudina specimens from China bear the marks of multiple attacks, which suggests they survived at least a few of them. The holes made by predators are approximately proportional to the size of the Cloudina specimens, and Sinotubulites fossils, which are often found in the same beds, have so far shown no such holes. These two points suggest that predators attacked in a selective manner, and the evolutionary arms race which this indicates is commonly cited as a cause of the Cambrian explosion of animal diversity and complexity.
Dinoflagellate cysts
Some dinoflagellates produce resting stages, called dinoflagellate cysts or dinocysts, as part of their lifecycles. Dinoflagellates are mainly represented in the fossil record by these dinocysts, typically 15 to 100 micrometres in diameter, which accumulate in sediments as microfossils. Organic-walled dinocysts have resistant cell walls made out of dinosporin. There are also calcareous dinoflagellate cysts and siliceous dinoflagellate cysts.
Dinocysts are produced by a proportion of dinoflagellates as a dormant, zygotic stage of their lifecycle. These dinocyst stages are known to occur in 84 of the 350 described freshwater dinoflagellate species, and in about 10% of the known marine species. Dinocysts have a long geological record with geochemical markers suggest a presence that goes back to the Early Cambrian.
Sponge spicules
Spicules are structural elements found in most sponges. They provide structural support and deter predators. The meshing of many spicules serves as the sponge’s skeleton, providing structural support and defense against predators.
Smaller, microscopic spicules can become microfossils, and are referred to as microscleres. Larger spicules visible to the naked eye are called megascleres. Spicule can be calcareous, siliceous, or composed of spongin. They are found in a range of symmetry types.
Freshwater sediments
Marine sediments
Sediments at the bottom of the ocean have two main origins, terrigenous and biogenous.
Terrigenous sediments account for about 45% of the total marine sediment, and originate in the erosion of rocks on land, transported by rivers and land runoff, windborne dust, volcanoes, or grinding by glaciers.
Biogenous
Biogenous sediments account for the other 55% of the total sediment, and originate in the skeletal remains of marine protists (single-celled plankton and benthos microorganisms). Much smaller amounts of precipitated minerals and meteoric dust can also be present. Ooze, in the context of a marine sediment, does not refer to the consistency of the sediment but to its biological origin. The term ooze was originally used by John Murray, the "father of modern oceanography", who proposed the term radiolarian ooze for the silica deposits of radiolarian shells brought to the surface during the Challenger expedition. A biogenic ooze is a pelagic sediment containing at least 30 per cent from the skeletal remains of marine organisms.
Diatomaceous earth
Siliceous ooze
Kerogen
Alginite
Lithified
Micropaleontology
The study of microfossils is called micropaleontology. In micropaleontology, what would otherwise be distinct categories are grouped together based solely on their size, including microscopic organisms and minute parts of larger organisms. Numerous sediments have microfossils, which serve as significant biostratigraphic, paleoenvironmental, and paleoceanographic markers. Their widespread presence around the world and physical toughness makes microfossils important for biostratigraphy, while the manner in which they have reacted to environmental changes makes them helpful when reconstructing past environments.
See also
References
Other sources
De Wever, Patrick (2020). Marvelous microfossils : creators, timekeepers, architects. Baltimore. ISBN 978-1-4214-3674-6. OCLC 1148175375.{{cite book}}: CS1 maint: location missing publisher (link) |
kallakurichi district | Kallakurichi is one of the 38 districts in the state of Tamil Nadu in India. The district headquarter is Kallakurichi. Kallakurichi District was announced on 8 January 2019 and it came into existence on 26 November 2019.
History
During Ancient times, the region was under the rules of Cholas, Pallavas and various Local Chieftains like Tirukoilur king Malaiyaman. Due to its location between Chola naadu and Thondai naadu, the region was aptly called Nadu naadu (Mid-land). In later times, it passed between the hands of Gingee Nayaks, Arcot Nawabs. During the British Rule, the whole region was a part of the South Arcot District of Madras Presidency.
Prior to 1960, the town of Kallakurichi was considered a village. In 1960, Kallakurichi became a town panchayat, and then was subsequently upgraded to special-grade town panchayat. On 20 October 2004, it was further upgraded to the third-grade municipality. On 7 September 2010, the municipality was upgraded to first-grade municipality. On 8 January 2019, the region surrounding the municipality of Kallakurichi was announced as the 33rd district of Tamil Nadu by bifurcating Villupuram. The area of this municipality is 11.69 km2 divided into 21 wards.
Geography
Kallakurichi District is bounded by Thiruvannamalai district in the north, Villupuram district in the east, Dharmapuri and Salem districts in the west, Perambalur and Cuddalore districts in the south. The greater part of the district is covered by the metamorphic rocks belonging to gneiss family. There are also three great groups of sedimentary rocks belonging to different geological periods. The Kalrayan Hills in the North represents a continuous range of hills covered with some thorny forests and vegetation, which are part of Eastern Ghats. Major rivers in the district include the Thenpennai, Manimukthar, Gomukhi, and Gadilam. Major source of irrigation is through lakes, canals and wells.
Kalvarayan Hills
The Kalvarayan Hills are a major range of hills situated in the Eastern Ghats. Along with the Pachaimalai, Alavaimalai, Javadi, and Shevaroy hills, they separate the Kaveri River basin to the south from the Palar River basin to the north. The hills range in height from 2000 feet to 3000 feet and extend over an area of 1,095 square kilometres.
Climate
The climate is moderate to hot, with the maximum temperature being 38 °C and the minimum at 21 °C. The District gets its rainfall from the northeast monsoon during the winter months and the southwest monsoon during the summer months. The average annual rainfall is 1,070 mm.
Politics
Divisions
The district is divided into the 6 taluks of Kallakkurichi, Sankarapuram, Chinnasalem, Ulundurpet, Tirukkovilur and Kalvarayan Hills.Administrative Divisions
Municipalities
1) Kallakurichi
2) Thirukovilur
3) Ulundurpet
Town Panchayats
1) Sankarapuram
2) Chinnasalem
3) Thiyagadurugam
4) Vadakkanandal
5) Manalurpet
Unions
1) Kallakurichi
2) Sankarapuram
3) Thirukovilur
4) Rishivandiyam
5) Thiyagadurugam
6) Ulundurpet
7) Chinnasalem
8) Thirunavalur
9) Kalvarayanmalai
Demographics
At the time of the 2011 census, Kallakurichi district had a population of 13,47,204. Kallakurichi district had a sex ratio of 981 females per 1000 males. 197,385 (14.65%) lived in urban areas. Scheduled Castes and Scheduled Tribes made up 30.56% and 3.74% of the population respectively. Most tribals are Malayalis who live in the Kalavarayan Hills.
Hindus are the majority religion with 91.03% of the population. Christians, who are mostly Dalits and live in rural areas, are 4.45% of the population. Muslims are 4.24% of the population, living predominantly in urban areas.
Tamil is the predominant language, spoken by 95.97% of the population as their mother tongue. 2.48% of the population speaks Urdu and 1.38% Telugu as their first language.
Economy
Kallakurichi is an emerging agricultural district. It is also known as "Home of Agriculture". There are numerous rice-processing units or modern rice mills, both small and big throughout the district. Textiles, jewellery and agricultural feeds are major businesses. The District has two government co-operative sugar mills and one private sugar mill, and one solvent extraction plant. There are many poultry farms in and around Kallakurichi. The name is derived due to the green nature of this town along the banks of the river Gomuki which nourishes the town by its water.
Education
The District has numerous colleges and schools, both government and private. Notable colleges are Government Kallakurichi Medical College,Government arts college, Polytechnic college in Sankarapuram, A.K.T Engineering College. There was an announcement by the Chief Minister of Tamil Nadu in March 2020 to build a medical college with the initial funding of 370 crores near Pumputhottam, in Siruvangur village, which is 3.5 kilometers from Kallakurichi town and 1st batch of 150 students have started from the academic year 2021/2022.
Transport
The District is connected by roads and railways to major cities and to the rest of the state.
The major roads are, National Highway, NH – 79 connecting Salem to Ulundurpet, The District is connected by Railway through Chinnasalem Railway Station on Salem – Vridhachalam Railway Line.
NH-79 Salem-Kallakurichi-Ulundurpet
NH-534 Chinnasalem-Veppur-Vridhachalam
SH-9 Cuddalore-Panruti-Tirukoilur-Tiruvannamalai-Vellore
SH-9A Tiruvannamalai-Thiyagadurugam
SH-6 Kallakurichi-Sankarapuram-Tiruvannamalai
SH-68 Cuddalore-Thirukovilur-Sankarapuram
SH-69 Vridhachalam-Ulundurpet-Villupuram
SH-7 Thirukoilur-Villupuram
SH-204 Kallakurichi-Koothakudi-Trichy
SH-211 Thirukovilur Byepass Road -Kandachipuram
SH-245 Kallakurichi-Kachirayapalayam-Sankarapuram
SH-137 Thirukoilur-Asanur
SH-246 Tirukkovilur- Thiyagadurgam
See also
List of districts of Tamil Nadu
Vilandai
References
External links
Official website |
carbonado | Carbonado, commonly known as black diamond, is one of the toughest forms of natural diamond. It is an impure, high-density, micro-porous form of polycrystalline diamond consisting of diamond, graphite, and amorphous carbon, with minor crystalline precipitates filling pores and occasional reduced metal inclusions. Titanium nitride (TiN, osbornite) has been found in carbonado. It is found primarily in alluvial deposits where it is most prominent in mid-elevation equatorial regions such as Central African Republic and in Brazil, where the vast majority of carbonado diamondites have been found. Its natural colour is black or dark grey, and it is more porous than other diamonds.
Unusual properties
Carbonado diamonds are typically pea-sized or larger porous aggregates of many tiny black crystals. The most characteristic carbonados are mined in the Central African Republic and in Brazil, in neither place associated with kimberlite, the source of typical gem diamonds. Lead isotope analyses have been interpreted as documenting crystallization of carbonados about 3 billion years ago; yet carbonado is found in younger sedimentary rocks.Mineral grains included within diamonds have been studied extensively for clues to diamond origin. Some typical diamonds contain inclusions of common mantle minerals such as pyrope and forsterite, but such mantle minerals have not been observed in carbonado. In contrast, some carbonados contain authigenic inclusions of minerals characteristic of the Earth's crust; the inclusions do not necessarily establish formation of the diamonds in the crust, because while the obvious crystal inclusions occur in the pores that are common in carbonados, they may have been introduced after carbonado formation. Inclusions of other minerals, rare or nearly absent in the Earth's crust, are found at least partly incorporated in diamond, not just in pores: among such other minerals are those with compositions of Si, SiC, and Fe‑Ni. No distinctive high-pressure minerals, including the hexagonal carbon polymorph, lonsdaleite, have been found as inclusions in carbonados although such inclusions might be expected if carbonados formed by meteorite impact.Isotope studies have yielded further clues to carbonado origin. The carbon isotope value is very low (little carbon‑13 compared to carbon‑12, relative to typical diamonds).Carbonado exhibits strong luminescence (photoluminescence and cathodoluminescence) induced by nitrogen and by vacancies existing in the crystal lattice. Luminescence halos are present around radioactive inclusions, and it is suggested that the radiation damage occurred after formation of the carbonados, an observation perhaps pertinent to the radiation hypothesis listed below.
Toughness vs. hardness
Carbonado’s polycrystalline texture makes it more durable than a monocrystalline diamond. It is the same hardness as other types of diamond, but it is much tougher. Its polycrystalline texture allows a single abrasive granule to present multiple crystallographic orientations of the diamond crystal at the cutting surface and the hardest orientation does the most aggressive cutting.
Cutting tools made with carbonado last longer and require less maintenance. Carbonado was recognized as an abrasive in the 1800s and was more highly valued for its cutting and grinding effectiveness over other varieties of diamond. The problem with carbonado is its rarity. It is only found in two countries, and total worldwide production has only been a few tons. Carbonado is not an important commodity in today's abrasive market.
In the late 1800s, when De Beers was developing their diamond mines in South Africa, they preferred carbonado over their own diamonds for diamond drilling. Gardner F. Williams, General Manager of De Beers Consolidated Mines, Ltd. lamented: "Round or shot boart is found in the mines at Kimberley and is very valuable for use in diamond drilling since the Brazilian carbonado has become so scarce."
Hypotheses for origin
The origin of carbonado is controversial, and some proposed hypotheses are as follows:
Direct conversion of organic carbon under high-pressure conditions in the Earth's interior, the most common hypothesis for diamond formation
Shock metamorphism induced by meteoritic impact at the Earth's surface
Radiation-induced diamond formation by spontaneous fission of uranium and thorium
Accumulated local formation in reduced organic-rich sediment over long geologic periods due to pyrometamorphic-rapid processes associated with long-duration superbolt lightning strikes, known to have similar global distribution as carbonado diamondite deposits at similar elevations.
Formation inside an earlier-generation giant star in our area, that long ago exploded in a supernova.
An origin in interstellar space, due to the impact of an asteroid, rather than being thrown from within an exploding star.The origin of carbonado is still under debate.
Extraterrestrial origin hypothesis
Supporters of an extraterrestrial origin of carbonados such as Stephen Haggerty propose that their material source was a supernova which occurred at least 3.8 billion years ago. After coalescing and drifting through outer space for about one and a half billion years, a large mass fell to earth as a meteorite approximately 2.3 billion years ago. It possibly fragmented during entry into the Earth's atmosphere and impacted in a region which would much later split into Brazil and the Central African Republic, assumed to be the only two known locations of carbonado-diamond deposits.
The presence of osbornite, which only forms under very reducing conditions and at very high temperatures, argues for an extraterrestrial origin.
Largest cut diamond
The largest cut black diamond in the world is a carbonado named 'The Enigma', weighing 555.55 carats (111 g).
See also
Amsterdam Diamond – 6.748 g carbonado diamond, with 145 facets, in a pear shape, cut from a 11.17 g roughPages displaying wikidata descriptions as a fallback
Bort – Shards of non-gem-quality diamonds
Korloff Noir – Black diamond
Material properties of diamond
Popigai diamonds – Impact crater in Siberia, Russia
Sergio (carbonado) – Largest known rough diamond
Spirit of de Grisogono Diamond – World's largest cut black diamond
Superhard material – Material with Vickers hardness exceeding 40 gigapascals
List of diamonds
References
External links
Photo of porous carbonado at National Science Foundation
Photo of glossy carbonado and article on possible extraterrestrial origins at PBS Nova
Mystery Diamonds: Geoscientists Investigate Rare Carbon Formation ScienceDaily (June 1, 2007) Story
Diamonds From Outer Space: Geologists Discover Origin Of Earth's Mysterious Black Diamonds ScienceDaily (January 9, 2007) Story. |
clathrate gun hypothesis | The clathrate gun hypothesis is a proposed explanation for the periods of rapid warming during the Quaternary. The hypothesis is that changes in fluxes in upper intermediate waters in the ocean caused temperature fluctuations that alternately accumulated and occasionally released methane clathrate on upper continental slopes. This would have had an immediate impact on the global temperature, as methane is a much more powerful greenhouse gas than carbon dioxide. Despite its atmospheric lifetime of around 12 years, methane's global warming potential is 72 times greater than that of carbon dioxide over 20 years, and 25 times over 100 years (33 when accounting for aerosol interactions). It is further proposed that these warming events caused the Bond Cycles and individual interstadial events, such as the Dansgaard–Oeschger interstadials.The hypothesis was supported for the Bølling-Allerød and Preboreal period, but not for Dansgaard–Oeschger interstadials, although there are still debates on the topic. While it may be important on the millennial timescales, it is no longer considered relevant for the near future climate change: the IPCC Sixth Assessment Report states "It is very unlikely that gas clathrates (mostly methane) in deeper terrestrial permafrost and subsea clathrates will lead to a detectable departure from the emissions trajectory during this century".
Mechanism
Methane clathrate, also known commonly as methane hydrate, is a form of water ice that contains a large amount of methane within its crystal structure. Potentially large deposits of methane clathrate have been found under sediments on the ocean floors of the Earth, although the estimates of total resource size given by various experts differ by many orders of magnitude, leaving doubt as to the size of methane clathrate deposits (particularly in the viability of extracting them as a fuel resource). Indeed, cores of greater than 10 centimeters' contiguous depth had only been found in three sites as of 2000, and some resource reserve size estimates for specific deposits/locations have been based primarily on seismology. The sudden release of large amounts of natural gas from methane clathrate deposits in runaway climate change could be a cause of past, future, and present climate changes.
In the Arctic ocean, clathrates can exist in shallower water stabilized by lower temperatures rather than higher pressures; these may potentially be marginally stable much closer to the surface of the sea-bed, stabilized by a frozen 'lid' of permafrost preventing methane escape. The so-called self-preservation phenomenon has been studied by Russian geologists starting in the late 1980s. This metastable clathrate state can be a basis for release events of methane excursions, such as during the interval of the Last Glacial Maximum. A study from 2010 concluded with the possibility for a trigger of abrupt climate warming based on metastable methane clathrates in the East Siberian Arctic Shelf (ESAS) region.
Possible past releases
Studies published in 2000 considered this hypothetical effect to be responsible for warming events in and at the end of the Last Glacial Maximum. Although periods of increased atmospheric methane match periods of continental-slope failure, later work found that the distinct deuterium/hydrogen (D/H) isotope ratio indicated that wetland methane emissions was the main contributor to atmospheric methane concentrations. While there were major dissociation events during the last deglaciation, with Bølling-Allerød warming triggering the disappearance of the entire methane hydrate deposit in the Barents Sea within 5000 years, those events failed to counteract the onset of a major Younger Dryas cooling period, suggesting that most of the methane stayed within the seawater after being liberated from the seafloor deposits, with very little entering the atmosphere.In 2008, it was suggested that equatorial permafrost methane clathrate may have had a role in the sudden warm-up of "Snowball Earth", 630 million years ago.Other events potentially linked to methane hydrate excursions are the Permian–Triassic extinction event and the Paleocene–Eocene Thermal Maximum.
Paleocene–Eocene Thermal Maximum
Permian–Triassic extinction event
Climate change feedback
Modern deposits
Most deposits of methane clathrate are in sediments too deep to respond rapidly, and 2007 modelling by Archer suggests that the methane forcing derived from them should remain a minor component of the overall greenhouse effect. Clathrate deposits destabilize from the deepest part of their stability zone, which is typically hundreds of metres below the seabed. A sustained increase in sea temperature will warm its way through the sediment eventually, and cause the shallowest, most marginal clathrate to start to break down; but it will typically take on the order of a thousand years or more for the temperature change to get that far into the seabed. Further, subsequent research on midlatitude deposits in the Atlantic and Pacific Ocean found that any methane released from the seafloor, no matter the source, fails to reach the atmosphere once the depth exceeds 430 m (1,411 ft), while geological characteristics of the area make it impossible for hydrates to exist at depths shallower than 550 m (1,804 ft).
However, some methane clathrates deposits in the Arctic are much shallower than the rest, which could make them far more vulnerable to warming. A trapped gas deposit on the continental slope off Canada in the Beaufort Sea, located in an area of small conical hills on the ocean floor is just 290 m (951 ft) below sea level and considered the shallowest known deposit of methane hydrate. However, the East Siberian Arctic Shelf averages 45 meters in depth, and it is assumed that below the seafloor, sealed by sub-sea permafrost layers, hydrates deposits are located. This would mean that when the warming potentially talik or pingo-like features within the shelf, they would also serve as gas migration pathways for the formerly frozen methane, and a lot of attention has been paid to that possibility. Shakhova et al. (2008) estimate that not less than 1,400 gigatonnes of carbon is presently locked up as methane and methane hydrates under the Arctic submarine permafrost, and 5–10% of that area is subject to puncturing by open talik. Their paper initially included the line that the "release of up to 50 gigatonnes of predicted amount of hydrate storage [is] highly possible for abrupt release at any time". A release on this scale would increase the methane content of the planet's atmosphere by a factor of twelve, equivalent in greenhouse effect to a doubling in the 2008 level of CO2.
This is what led to the original Clathrate gun hypothesis, and in 2008 the United States Department of Energy National Laboratory system and the United States Geological Survey's Climate Change Science Program both identified potential clathrate destabilization in the Arctic as one of four most serious scenarios for abrupt climate change, which have been singled out for priority research. The USCCSP released a report in late December 2008 estimating the gravity of this risk. A 2012 study of the effects for the original hypothesis, based on a coupled climate–carbon cycle model (GCM) assessed a 1000-fold (from <1 to 1000 ppmv) methane increase—within a single pulse, from methane hydrates (based on carbon amount estimates for the PETM, with ~2000 GtC), and concluded it would increase atmospheric temperatures by more than 6 °C within 80 years. Further, carbon stored in the land biosphere would decrease by less than 25%, suggesting a critical situation for ecosystems and farming, especially in the tropics. Another 2012 assessment of the literature identifies methane hydrates on the Shelf of East Arctic Seas as a potential trigger.A risk of seismic activity being potentially responsible for mass methane releases has been considered as well. In 2012, seismic observations destabilizing methane hydrate along the continental slope of the eastern United States, following the intrusion of warmer ocean currents, suggests that underwater landslides could release methane. The estimated amount of methane hydrate in this slope is 2.5 gigatonnes (about 0.2% of the amount required to cause the PETM), and it is unclear if the methane could reach the atmosphere. However, the authors of the study caution: "It is unlikely that the western North Atlantic margin is the only area experiencing changing ocean currents; our estimate of 2.5 gigatonnes of destabilizing methane hydrate may therefore represent only a fraction of the methane hydrate currently destabilizing globally." Bill McGuire notes, "There may be a threat of submarine landslides around the margins of Greenland, which are less well explored. Greenland is already uplifting, reducing the pressure on the crust beneath and also on submarine methane hydrates in the sediment around its margins, and increased seismic activity may be apparent within decades as active faults beneath the ice sheet are unloaded. This could provide the potential for the earthquake or methane hydrate destabilisation of submarine sediment, leading to the formation of submarine slides and, perhaps, tsunamis in the North Atlantic."
Observed emissions
East Siberian Arctic Shelf
Research carried out in 2008 in the Siberian Arctic showed methane releases on the annual scale of millions of tonnes, which was a substantial increase on the previous estimate of 0.5 millions of tonnes per year. apparently through perforations in the seabed permafrost, with concentrations in some regions reaching up to 100 times normal levels. The excess methane has been detected in localized hotspots in the outfall of the Lena River and the border between the Laptev Sea and the East Siberian Sea. At the time, some of the melting was thought to be the result of geological heating, but more thawing was believed to be due to the greatly increased volumes of meltwater being discharged from the Siberian rivers flowing north.By 2013, the same team of researchers used multiple sonar observations to quantify the density of bubbles emanating from subsea permafrost into the ocean (a process called ebullition), and found that 100–630 mg methane per square meter is emitted daily along the East Siberian Arctic Shelf (ESAS), into the water column. They also found that during storms, when wind accelerates air-sea gas exchange, methane levels in the water column drop dramatically. Observations suggest that methane release from seabed permafrost will progress slowly, rather than abruptly. However, Arctic cyclones, fueled by global warming, and further accumulation of greenhouse gases in the atmosphere could contribute to more rapid methane release from this source. Altogether, their updated estimate had now amounted to 17 millions of tonnes per year.However, these findings were soon questioned, as this rate of annual release would mean that the ESAS alone would account for between 28% and 75% of the observed Arctic methane emissions, which contradicts many other studies. In January 2020, it was found that the rate at which methane enters the atmosphere after it had been released from the shelf deposits into the water column had been greatly overestimated, and observations of atmospheric methane fluxes taken from multiple ship cruises in the Arctic instead indicate that only around 3.02 million tonnes of methane are emitted annually from the ESAS. A modelling study published in 2020 suggested that under the present-day conditions, annual methane release from the ESAS may be as low as 1000 tonnes, with 2.6 – 4.5 million tonnes representing the peak potential of turbulent emissions from the shelf.
Beaufort Sea continental slope
A radiocarbon dating study in 2018 found that after the 30-meter isobath, only around 10% of the methane in surface waters can be attributed to ancient permafrost or methane hydrates. The authors suggested that even a significantly accelerated methane release would still largely fail to reach the atmosphere.
Svalbard
Hong et al. 2017 studied methane seepage in the shallow arctic seas at the Barents Sea close to Svalbard. Temperature at the seabed has fluctuated seasonally over the last century, between −1.8 °C (28.8 °F) and 4.8 °C (40.6 °F), it has only affected release of methane to a depth of about 1.6 meters at the sediment-water interface. Hydrates can be stable through the top 60 meters of the sediments and the current observed releases originate from deeper below the sea floor. They conclude that the increased methane flux started hundreds to thousands of years ago, noted about it, "..episodic ventilation of deep reservoirs rather than warming-induced gas hydrate dissociation." Summarizing his research, Hong stated:
The results of our study indicate that the immense seeping found in this area is a result of natural state of the system. Understanding how methane interacts with other important geological, chemical and biological processes in the Earth system is essential and should be the emphasis of our scientific community.
Research by Klaus Wallmann et al. 2018 concluded that hydrate dissociation at Svalbard 8,000 years ago was due to isostatic rebound (continental uplift following deglaciation). As a result, the water depth got shallower with less hydrostatic pressure, without further warming. The study, also found that today's deposits at the site become unstable at a depth of ~ 400 meters, due to seasonal bottom water warming, and it remains unclear if this is due to natural variability or anthropogenic warming. Moreover, another paper published in 2017 found that only 0.07% of the methane released from the gas hydrate dissociation at Svalbard appears to reach the atmosphere, and usually only when the wind speeds were low. In 2020, a subsequent study confirmed that only a small fraction of methane from the Svalbard seeps reaches the atmosphere, and that the wind speed holds a greater influence on the rate of release than dissolved methane concentration on site.Finally, a paper published in 2017 indicated that the methane emissions from at least one seep field at Svalbard were more than compensated for by the enhanced carbon dioxide uptake due to the greatly increased phytoplankton activity in this nutrient-rich water. The daily amount of carbon dioxide absorbed by the phytoplankton was 1,900 greater than the amount of methane emitted, and the negative (i.e. indirectly cooling) radiative forcing from the CO2 uptake was up to 251 times greater than the warming from the methane release.
Current outlook
In 2014 based on their research on the northern United States Atlantic marine continental margins from Cape Hatteras to Georges Bank, a group of scientists from the US Geological Survey, the Department of Geosciences, Mississippi State University, Department of Geological Sciences, Brown University and Earth Resources Technology, found widespread leakage of methane from the seafloor, but they did not assign specific dates, beyond suggesting that some of the seeps were more than 1000 years old. In March 2017, a meta-analysis by the USGS Gas Hydrates Project concluded:
Our review is the culmination of nearly a decade of original research by the USGS, my coauthor Professor John Kessler at the University of Rochester, and many other groups in the community," said USGS geophysicist Carolyn Ruppel, who is the paper's lead author and oversees the USGS Gas Hydrates Project. "After so many years spent determining where gas hydrates are breaking down and measuring methane flux at the sea-air interface, we suggest that conclusive evidence for release of hydrate-related methane to the atmosphere is lacking. In June 2017, scientists from the Center for Arctic Gas Hydrate (CAGE), Environment and Climate at the University of Tromsø, published a study describing over a hundred ocean sediment craters, some 300 meters wide and up to 30 meters deep, formed due to explosive eruptions, attributed to destabilizing methane hydrates, following ice-sheet retreat during the last glacial period, around 15,000 years ago, a few centuries after the Bølling-Allerød warming. These areas around the Barents Sea, still seep methane today, and still existing bulges with methane reservoirs could eventually have the same fate. Later that same year, the Arctic Council published SWIPA 2017 report, where it cautioned "Arctic sources and sinks of greenhouse gases are still hampered by data and knowledge gaps."In 2018, a perspective piece devoted to tipping points in the climate system suggested that the climate change contribution from methane hydrates would be "negligible" by the end of the century, but could amount to 0.4–0.5 °C (0.72–0.90 °F) on the millennial timescales. In 2021, the IPCC Sixth Assessment Report no longer included methane hydrates in the list of potential tipping points, and says that "it is very unlikely that CH4 emissions from clathrates will substantially warm the climate system over the next few centuries." The report had also linked terrestrial hydrate deposites to gas emission craters discovered in the Yamal Peninsula in Siberia, Russia beginning in July 2014, but noted that since terrestrial gas hydrates predominantly from at a depth below 200 metres, a substantial response within the next few centuries can be ruled out. Likewise, a 2022 assessment of tipping points described methane hydrates as a "threshold-free feedback" rather than a tipping point.
In fiction
The science fiction novel Mother of Storms by John Barnes offers a fictional example of catastrophic climate change caused by methane clathrate release.
In The Life Lottery by Ian Irvine unprecedented seismic activity triggers a release of methane hydrate, reversing global cooling.
The hypothesis is the basis of an experiment in the PlayStation 2 game Death By Degrees.
In Transcendent by Stephen Baxter, averting such a crisis is a major plotline.
The novel The Black Silent by author David Dun features this idea as a key scientific point.
In the anime Ergo Proxy, a string of explosions in the methane hydrate reserves wipes out 85% of species on Earth.
The novel The Far Shore of Time by Frederik Pohl features an alien race attempting to destroy humanity by bombing the methane clathrate reserves, thus releasing the gas into the atmosphere.
The novel The Swarm by Frank Schätzing features what first appear to be freak events related to the world's oceans.
In Charles Stross' Laundry Files universe, an intentionally triggered clathrate gun scenario is viewed as a possible retaliatory strategy that could be utilized by Blue Hades in response to terminal violation of the Benthic Treaty.
See also
References
Further reading
Benton, Michael J.; Twitchett, Richard J. (July 2003). "How to kill (almost) all life: the end-Permian extinction event" (PDF). Trends in Ecology and Evolution. 18 (7): 358–365. doi:10.1016/S0169-5347(03)00093-4. Archived from the original (PDF) on 2007-04-18. Retrieved 2006-11-26., cited by 21 other articles.
Svensen, Henrik; Planke, Sverre; Malthe-Sørenssen, Anders; Jamtveit, Bjørn; Myklebust, Reidun Rasmussen; Eidem, Torfinn; Rey, Sebastian S. (2004). "Release of methane from a volcanic basin as a mechanism for initial Eocene global warming". Nature. 429 (6991): 542–545. Bibcode:2004Natur.429..542S. doi:10.1038/nature02566. PMID 15175747. S2CID 4419088.
Thomas, Deborah J.; Zachos, James C.; Thomas, Ellen; Bohaty, Steven (2002). "Warming the fuel for the fire: Evidence for the thermal dissociation of methane hydrate during the Paleocene-Eocene thermal maximum" (PDF). Geology. 30 (12): 1067–70. Bibcode:2002Geo....30.1067T. doi:10.1130/0091-7613(2002)030<1067:WTFFTF>2.0.CO;2. ISSN 0091-7613.
Archer, D.; Buffett, B. (2004). "Temperature sensitivity and time dependence of the global ocean clathrate reservoir". American Geophysical Union, Fall Meeting. Bibcode:2004AGUFMGC51D1069A.
External links
Kennett, James P. (20 May 2005). "Abstract: Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis". Paul A. Witherspoon Distinguished Seminar Series. Earth Sciences Division, Lawrence Berkeley National Laboratory. Archived from the original on 22 July 2012. Retrieved 17 March 2013.
Hudson, Geoff (24 May 2009). "The trigger for the clathrate gun". Ockham's Razor. Radio National, Australian Broadcasting Corporation.
Chakoumakos, Bryan C. (2004). "Preface to the Clathrate Hydrates special issue" (PDF). American Mineralogist. 89: 1153–4.
Adam, David (14 January 2010). "Arctic permafrost leaking methane at record levels, figures show". Guardian.
Harris, Richard (26 January 2010). "Methane Causes Vicious Cycle In Global Warming". NPR.org. NPR.
Methane: A Scientific Journey from Obscurity to Climate Super-Stardom Good Sept. 2004 background report from NASA GISS
Wakening the Kraken |
pachycephalosaurus | Pachycephalosaurus (; meaning "thick-headed lizard", from Greek pachys-/παχύς- "thick", kephale/κεφαλή "head" and sauros/σαῦρος "lizard") is a genus of pachycephalosaurid ornithischian dinosaur. The type species, P. wyomingensis, is the only known species, but some researchers argue that the genus Stygimoloch might be a second species, P. spinifer or a juvenile specimen of P. wyomingensis. It lived during the Maastrichtian age of the Late Cretaceous period in what is now western North America. Remains have been excavated in Montana, South Dakota, Wyoming, and Alberta. The species is known mainly from a single skull, plus a few extremely thick skull roofs (at 22 cm/9” thick). More complete fossils would come to be found in the following years.
Pachycephalosaurus was among the last species of non-avian dinosaurs on Earth before the Cretaceous–Paleogene extinction event. The genus Tylosteus has been synonymized with Pachycephalosaurus, as have the genera Stygimoloch and Dracorex, in recent studies.Like other pachycephalosaurids, Pachycephalosaurus was a bipedal herbivore, possessing long, strong legs and somewhat small arms with five-fingered hands. Pachycephalosaurus is the largest-known pachycephalosaur, known for having an extremely thick, slightly domed skull roof; visually, the structure of the skull suggests a ‘battering ram’ function in life, evolved for use as a defensive mechanism or intra-species combat, similar to what is seen with today’s bighorn sheep or muskoxen (with male animals routinely charging and head-butting each other for dominance). This hypothesis has actually been highly disputed in recent years.
History of discovery
Remains attributable to Pachycephalosaurus may have been found as early as the 1850s. As determined by Donald Baird, in 1859 or 1860, Ferdinand Vandeveer Hayden, an early fossil collector in the American West, collected a bone fragment in the vicinity of the head of the Missouri River, from what is now known to be the Lance Formation of southeastern Montana. This specimen, ANSP 8568, was described by Joseph Leidy in 1872 as belonging to the dermal armor of a reptile or an armadillo-like animal. It became known as Tylosteus. Its actual nature was not revealed until Baird studied it again over a century later and identified it as a squamosal (bone from the back of the skull) of Pachycephalosaurus, including a set of bony knobs corresponding to those found on other specimens of Pachycephalosaurus. Because the name Tylosteus predates Pachycephalosaurus, according to the International Code of Zoological Nomenclature Tylosteus would normally be preferred. In 1985, Baird successfully petitioned to have Pachycephalosaurus used instead of Tylosteus because the latter name had not been used for over fifty years, was based on undiagnostic materials, and had poor geographic and stratigraphic information. This may not be the end of the story, however. Robert Sullivan suggested in 2006 that ANSP 8568 is more like the corresponding bone of Dracorex than that of Pachycephalosaurus. The issue is of uncertain importance, though, if Dracorex actually represents a juvenile Pachycephalosaurus, as has been recently proposed.In 1890, during the Bone Wars between Othniel Charles Marsh and Edward Drinker Cope, one of Marsh's collectors, John Bell Hatcher, collected a partial left squamosal (YPM VP 335) later referred to Stygimoloch spinifer near Lance Creek, Wyoming in the Lance Formation. Marsh described the squamosal along with the dermal armor of Denversaurus as the body armor of Triceratops in 1892, believing that the squamosal was a spike akin to the plates on Stegosaurus. The squamosal spike was even featured in Charles Knight’s painting of Cope’s ceratopsid Agathaumas, likely based on Marsh’s hypothesis. Marsh also named a species of now-dubious ankylosaur Palaeoscincus in 1892 based on a single tooth (YPM 4810), also collected by Hatcher from the Lance. The tooth was named Palaeoscinus latus, but in 1990, Coombs found the tooth to be from a pachycephalosaurid, possibly even Pachycephalosaurus itself. Hatcher also collected several additional teeth and skull fragments while working for Marsh, though these have yet to be described.P. wyomingensis, the type and currently only valid species of Pachycephalosaurus, was named by Charles W. Gilmore in 1931. He coined it for the partial skull USNM 12031, from the Lance Formation of Niobrara County, Wyoming. Gilmore assigned his new species to Troodon as T. wyomingensis. At the time, paleontologists thought that Troodon, then known only from teeth, was the same as Stegoceras, which had similar teeth. Accordingly, what are now known as pachycephalosaurids were assigned to the family Troodontidae, a misconception which was not corrected until 1945 by Charles M. Sternberg.
In 1943, Barnum Brown and Erich Maren Schlaikjer, with newer, more complete material, established the genus Pachycephalosaurus. They named two species: Pachycephalosaurus grangeri, the type species of their new genus, and Pachycephalosaurus reinheimeri. P. grangeri was based on AMNH 1696, a nearly complete skull from the Hell Creek Formation of Ekalaka, Carter County, Montana. P. reinheimeri was based on what is now DMNS 469, a dome and a few associated elements from the Lance Formation of Corson County, South Dakota. They also referred the older species "Troodon" wyomingensis to their new genus. Their two newer species have been considered synonymous with P. wyomingensis since 1983.In 2015, some pachycephalosaurid material and a domed parietal attributable to Pachycephalosaurus were discovered in the Scollard Formation of Alberta, implying that the dinosaurs of this era were cosmopolitan and didn't have discrete faunal provinces.
Description
The anatomy of Pachycephalosaurus itself is poorly known, as only skull remains have been described. Pachycephalosaurus is famous for having a large, bony dome on top of its skull, up to 25 cm (10 in) thick, which safely cushioned its brain. The dome's rear aspect was edged with bony knobs and short bony spikes projected upwards from the snout. However, the spikes were probably blunted, not sharp.The skull was short and possessed large, rounded eye sockets that faced forward, suggesting that the animal had binocular vision. Pachycephalosaurus had a small muzzle that ended in a pointed beak. The teeth were tiny, with leaf-shaped crowns. The head was supported by an "S"- or "U"-shaped neck. Younger individuals of Pachycephalosaurus might have had flatter skulls and larger horns projecting from the back of the skull. As the animal grew, the horns shrunk and rounded out as the dome grew.
Pachycephalosaurus was bipedal and possibly the largest of all pachycephalosaurids. It has been estimated that Pachycephalosaurus was about 4.5 metres (14.8 ft) long and weighed about 370–450 kilograms (820–990 lb). Based on other pachycephalosaurids, it probably had a fairly short, thick neck, short arms, a bulky body, long legs, and a heavy tail that was likely held rigid by ossified tendons.
Classification
Pachycephalosaurus gives its name to Pachycephalosauria, a clade of herbivorous ornithischian dinosaurs that lived during the Late Cretaceous period in North America and Asia. Despite their bipedal stance, they were a part of Marginocephalia, thus being likely more closely related to the ceratopsians than the ornithopods.Pachycephalosaurus is the most famous member of Pachycephalosauria, even if it is not the best-preserved member. The clade also includes Stenopelix, Wannanosaurus, Goyocephale, Stegoceras, Homalocephale, Tylocephale, Sphaerotholus, and Prenocephale. Within the tribe Pachycephalosaurini, Pachycephalosaurus is most closely related to Alaskacephale. Dracorex and Stygimoloch have also been synonymized with Pachycephalosaurus.
In 2010, Gregory S. Paul proposed that, while Stygimoloch and Dracorex possibly represent different growth stages of Pachycephalosaurus, Stygimoloch might represent a different species, P. spinifer. This idea has been regarded as a way of interpretation by Mark Witton and Thomas Holtz. A phylogenetic analysis from 2021 by Evans and colleagues accepted the validity of the genus Stygimoloch on the basis of it being found in later rock layers than Pachycephalosaurus, but agreed with the consensus that Dracorex represents an ontogimorph instead of a distinct taxon. However, David Evans himself noted in a Twitter post that he and his colleagues would also consider Stygimoloch as P. spinifer.Below is a cladogram modified from Evans et al., 2013.
Below is a cladogram from Evans et al., 2021.
Paleobiology
Growth
Aside from Pachycephalosaurus itself, two other pachycephalosaurs were described from the latest Cretaceous of the northwestern United States: Stygimoloch spinifer ("thorny Moloch of the Styx") and Dracorex hogwartsia ("dragon king of Hogwarts"). The former is only known from a juvenile skull with a reduced dome and large spikes, while the latter, also known from only a juvenile skull, had a seemingly flat head with short horns. Due to their unique head ornamentation, they were seen as separate species for a number of years. However, in 2007, they were proposed to be juvenile or female morphologies of Pachycephalosaurus. At that year's meeting of the Society of Vertebrate Paleontology, Jack Horner of Montana State University presented evidence, from analysis of the skull of the Dracorex specimen, that it may be a juvenile form of Stygimoloch. In addition to this, he presented data that indicates that both Stygimoloch and Dracorex may be juvenile forms of Pachycephalosaurus. Horner and M.B. Goodwin published their findings in 2009, showing that the spike and skull dome bones of all three "species" exhibit extreme plasticity and that both Dracorex and Stygimoloch are known only from juvenile specimens, while Pachycephalosaurus is known only from adult specimens. These observations, in addition to the fact that all three forms lived in the same time and place, led them to conclude that Dracorex and Stygimoloch were simply juvenile Pachycephalosaurus, which lost spikes and grew domes as they aged. A 2010 study by Nick Longrich and colleagues also supported the hypothesis that all flat-skulled pachycephalosaur species were juveniles of the dome-headed adults, such as Goyocephale and Homalocephale.The discovery of baby skulls assigned to Pachycephalosaurus that were described in 2016 from two different bone beds in the Hell Creek Formation has been presented as further evidence for this hypothesis. The fossils, as described by David Evans and Mark Goodwin et al are identical to all three supposed genera in the placement of the rugose knobs on their skulls, and the unique features of Stygimoloch and Dracorex are thus instead morphologically consistent features on a Pachycephalosaurus growth curve.It has been noted that morphological differences between Stygimoloch and Pachycephalosaurus may also partly be due to slight stratigraphic differences. The few Stygimoloch specimens that have reliable stratigraphic data were all collected from the upper part of the Hell Creek Formation, whereas Pachycephalosaurus morphs were all collected from the lower part. This has also led to suggestions that Stygimoloch might represent its own species, P. spinifer. In their 2021 redescription of Sinocephale bexelli, Evans and his colleageues treated Stygimoloch (but not Dracorex) as a separate taxon based on their phylogenetic analysis. However, Evans himself has noted that he and his colleagues support the idea of P. spinifer.
Dome function
It has been widely hypothesized for decades that Pachycephalosaurus and its relatives were the ancient, bipedal equivalents of bighorn sheep or musk oxen, where male individuals would ram each other headlong and that they would horizontally straighten their head, neck, and body in order to transmit stress during ramming. However, there have also been alternative suggestions that the pachycephalosaurs could not have used their domes in this way.
The primary argument that has been raised against head-butting is that the skull roof may not have adequately sustained impact associated with ramming, as well as a lack of definitive evidence of scars or other damage on fossilized Pachycephalosaurus skulls. However, more recent analyses have uncovered such damage (see below). Furthermore, the cervical and anterior dorsal vertebrae show that the neck was carried in an "S"- or "U"-shaped curve, rather than a straight orientation and that it might have been unfit for transmitting stress from direct head-butting. Lastly, the rounded shape of the skull would lessen the contacted surface area during head-butting, resulting in glancing blows.
Alternatively, Pachycephalosaurus and other pachycephalosaurids may have engaged in flank-butting during intraspecific combat. In this scenario, an individual may have stood roughly parallel or faced a rival directly, using intimidation displays to cow its rival. If intimidation failed, the Pachycephalosaurus would bend its head downward and to the side, striking the rival on its flank. This hypothesis is supported by the relatively broad torso of most pachycephalosaurs, which would have protected vital organs from trauma. The flank-butting theory was first proposed by Sues in 1978 and expanded upon by Ken Carpenter in 1997.
In 2012, a study showed that cranial pathologies in a P. wyomingensis specimen were likely due to agonistic behavior. It was also proposed that similar damage in other pachycephalosaur specimens (previously explained as taphonomic artifacts and bone absorptions) may instead have been due to such behavior. Peterson et al. (2013) studied cranial pathologies among Pachycephalosauridae and found that 22% of all domes examined had lesions that are consistent with osteomyelitis, an infection of the bone resulting from penetrating trauma or trauma to the tissue overlying the skull that lead to an infection of the bone tissue. This high rate of pathology lends more support to the hypothesis that pachycephalosaurid domes were employed in intra-specific combat. Pachycephalosaurus wyomingensis specimen BMR P2001.4.5 was observed to have 23 lesions in its frontal bone and P. wyomingensis specimen DMNS 469 was observed to have 5 lesions. The frequency of trauma was comparable across the different genera in the pachycephalosaurid family, despite the fact that these genera vary with respect to the size and architecture of their domes and the fact that they existed during varying geologic periods. These findings were in stark contrast with the results from analysis of the relatively flat-headed pachycephalosaurids, where there was an absence of pathology. This would support the hypothesis that these individuals represent either females or juveniles, where intra-specific combat behavior is not expected.
Histological examination reveals that pachycephalosaurid domes are composed of a unique form of fibrolamellar bone that contains fibroblasts, which play a critical role in wound healing and are capable of rapidly depositing bone during remodeling. Peterson et al. (2013) concluded that, taken together, the frequency of lesion distribution and the bone structure of frontoparietal domes lends strong support to the hypothesis that pachycephalosaurids used their unique cranial structures for agonistic behavior. CT scan comparisons of the skulls of Stegoceras validum, Prenocephale prenes, and several head-striking artiodactyls have also supported pachycephalosaurids as being well-equipped for head-butting.
Diet
Scientists do not yet know what these dinosaurs ate. Having very small, ridged teeth, they could not have chewed tough, fibrous plants like flowering shrubs as effectively as other dinosaurs of the same period. It is assumed that pachycephalosaurs lived on a mixed diet of leaves, seeds, and fruits. The sharp, serrated teeth would have been very effective for shredding plants. It has also been suspected to a degree that it may have included meat in its diet. The most complete fossil jaw shows that it had serrated blade-like front teeth, reminiscent of those of carnivorous theropods.
Paleoecology
Nearly all Pachycephalosaurus fossils have been recovered from the Lance Formation and Hell Creek Formation of the northwestern United States. Pachycephalosaurus possibly coexisted alongside additional pachycephalosaur species of the genera Sphaerotholus, as well as Dracorex and Stygimoloch, though these last two genera may represent different growth stages of Pachycephalosaurus itself. Other dinosaurs that shared its time and place include Thescelosaurus, the hadrosaurid Edmontosaurus and a possible species of Parasaurolophus, ceratopsians like Triceratops, Torosaurus, Nedoceratops, Tatankaceratops, and Leptoceratops, the ankylosaurid Ankylosaurus, the nodosaurids Denversaurus and Edmontonia, and the theropods Acheroraptor, Dakotaraptor, Ornithomimus, Struthiomimus, Anzu, Leptorhynchos, Pectinodon, Paronychodon, Richardoestesia, and Tyrannosaurus.
See also
Timeline of pachycephalosaur research
References
External links
Pachycephalosaurus in the Dinodictionary Archived May 10, 2012, at the Wayback Machine
Pachycephalosaurus wyomingensis from National Geographic Online
TEDx talk by Jack Horner on shape-shifting dinosaur skulls and dinosaur misclassification.
Data related to Pachycephalosaurus at Wikispecies
Media related to Pachycephalosaurus at Wikimedia Commons |
cenote | A cenote (English: or ; Latin American Spanish: [seˈnote]) is a natural pit, or sinkhole, resulting from the collapse of limestone bedrock that exposes groundwater. The term originated on the Yucatán Peninsula of Mexico, where cenotes were commonly used for water supplies by the ancient Maya, and occasionally for sacrificial offerings. The term derives from a word used by the lowland Yucatec Maya—tsʼonoʼot—to refer to any location with accessible groundwater.The Yucatán Peninsula alone has an estimated 10,000 cenotes, water-filled sinkholes naturally formed by the collapse of limestone, located across the Yucatán Peninsula, in Mexico. Some of these cenotes are at risk from the construction of the new tourist Maya Train.Cenotes are common geological forms in low-altitude regions, particularly on islands, coastlines, and platforms with young post-Paleozoic limestone with little soil development. The term cenote, originally used only to describe the features in Yucatán, has since been applied to similar karst features in other countries such as Cuba, Australia, and the United States.
Definition and description
Cenotes are surface connections to subterranean water bodies. While the best-known cenotes are large open-water pools measuring tens of meters in diameter, such as those at Chichen Itza in Mexico, the greatest number of cenotes are smaller sheltered sites and do not necessarily have any surface exposed water. Some cenotes are only found through small <1 m (3 ft) diameter holes created by tree roots, with human access through enlarged holes, such as the cenotes Cenote Choo-Ha, Tamcach-Ha, and Multum-Ha near Tulum. There are at least 6,000 cenotes in the Yucatán Peninsula of Mexico. Cenote water is often very clear, as the water comes from rain water filtering slowly through the ground, and therefore contains very little suspended particulate matter. The groundwater flow rate within a cenote may be very slow. In many cases, cenotes are areas where sections of the cave roof have collapsed revealing an underlying cave system, and the water flow rates may be much faster: up to 10 kilometers (6 mi) per day.The Yucatan cenotes attract cavern and cave divers who have documented extensive flooded cave systems, some of which have been explored for lengths of 376 km (234 mi) or more.
Geology and hydrology
Cenotes are formed by the dissolution of rock and the resulting subsurface void, which may or may not be linked to an active cave system, and the subsequent structural collapse. Rock that falls into the water below is slowly removed by further dissolution, creating space for more collapse blocks. Likely, the rate of collapse increases during periods when the water table is below the ceiling of the void since the rock ceiling is no longer buoyantly supported by the water in the void.
Cenotes may be fully collapsed, creating an open water pool, or partially collapsed with some portion of a rock overhanging above the water. The stereotypical cenotes often resemble small circular ponds, measuring some tens of meters in diameter with sheer rock walls. Most cenotes, however, require some degree of stooping or crawling to access the water.
Penetration and extent
In the north and northwest of the Yucatán Peninsula in Mexico, the cenotes generally overlie vertical voids penetrating 50 to 100 m (160 to 330 ft) below the modern water table. However, very few of these cenotes appear to be connected with horizontally extensive underground river systems, with water flow through them being more likely dominated by aquifer matrix and fracture flows.In contrast, the cenotes along the Caribbean coast of the Yucatán Peninsula (within the state of Quintana Roo) often provide access to extensive underwater cave systems, such as Sistema Ox Bel Ha, Sistema Sac Actun/Sistema Nohoch Nah Chich and Sistema Dos Ojos.
Freshwater/seawater interface
The Yucatán Peninsula contains a vast coastal aquifer system, which is typically density-stratified. The infiltrating meteoric water (i.e., rainwater) floats on top of higher-density saline water intruding from the coastal margins. The whole aquifer is therefore an anchialine system (one that is land-locked but connected to an ocean). Where a cenote, or the flooded cave to which it is an opening, provides deep enough access into the aquifer, the interface between the fresh and saline water may be reached. The density interface between the fresh and saline waters is a halocline, which means a sharp change in salt concentration over a small change in depth. Mixing of the fresh and saline water results in a blurry swirling effect caused by refraction between the different densities of fresh and saline waters.
The depth of the halocline is a function of several factors: climate and specifically how much meteoric water recharges the aquifer, hydraulic conductivity of the host rock, distribution and connectivity of existing cave systems, and how effective these are at draining water to the coast, and the distance from the coast. In general, the halocline is deeper further from the coast, and in the Yucatán Peninsula this depth is 10 to 20 m (33 to 66 ft) below the water table at the coast, and 50 to 100 m (160 to 330 ft) below the water table in the middle of the peninsula, with saline water underlying the whole of the peninsula.
Types
In 1936, a simple morphometry-based classification system for cenotes was presented.
Cenotes-cántaro (Jug or pit cenotes) are those with a surface connection narrower than the diameter of the water body;
Cenotes-cilíndricos (Cylinder cenotes) are those with strictly vertical walls;
Cenotes-aguadas (Basin cenotes) are those with shallow water basins; and
Grutas (Cave cenotes) are those having a horizontal entrance with dry sections.The classification scheme was based on morphometric observations above the water table, and therefore incompletely reflects the processes by which the cenotes formed and the inherent hydrogeochemical relationship with the underlying flooded cave networks, which were only discovered in the 1980s and later with the initiation of cave diving exploration.
Flora and fauna
Flora and fauna are generally scarcer than in the open ocean; however, marine animals do thrive in caves. In caverns, one can spot mojarras, mollies, guppies, catfish, small eels and frogs. In the most secluded and darker cenotes, the fauna has evolved to resemble those of many cave-dwelling species. For example, many animals don't have pigmentation and are often blind, so they are equipped with long feelers to find food and make their way around in the dark.
Chicxulub crater
Although cenotes are found widely throughout much of the Yucatán Peninsula, a higher-density circular alignment of cenotes overlies the measured rim of the Chicxulub crater. This crater structure, identified from the alignment of cenotes, but also subsequently mapped using geophysical methods (including gravity mapping) and also drilled into with core recovery, has been dated to the boundary between the Cretaceous and Paleogene geologic periods, 66 million years ago. This meteorite impact at the Cretaceous–Paleogene boundary is therefore associated with the mass extinction of the dinosaurs and is also known as the Cretaceous–Paleogene extinction event.
Archaeology and anthropology
In 2001–2002 expeditions led by Arturo H. González and Carmen Rojas Sandoval in the Yucatán discovered three human skeletons; one of them, Eve of Naharon, was carbon-dated to be 13,600 years old. In March 2008, three members of the Proyecto Espeleológico de Tulum and Global Underwater Explorers dive team, Alex Alvarez, Franco Attolini, and Alberto Nava, explored a section of Sistema Aktun Hu (part of Sistema Sac Actun) known as the pit Hoyo Negro. At a depth of 57 m (187 ft) the divers located the remains of a mastodon and a human skull (at 43 m [141 ft]) that might be the oldest evidence of human habitation in the region.The Yucatán Peninsula has almost no rivers and only a few lakes, and those are often marshy. The widely distributed cenotes are the only perennial source of potable water and have long been the principal source of water in much of the region. Major Maya settlements required access to adequate water supplies, and therefore cities, including the famous Chichen Itza, were built around these natural wells. Many cenotes like the Sacred Cenote in Chichen Itza played an important role in Maya rites. The Maya believed that cenotes were portals to Xibalba or the afterlife, and home to the rain god, Chac. The Maya often deposited human remains as well as ceremonial artifacts in these cenotes.
The discovery of golden sacrificial artifacts in some cenotes led to the archaeological exploration of most cenotes in the first part of the 20th century. Edward Herbert Thompson (1857–1935), an American diplomat who had bought the Chichen Itza site, began dredging the Sacred Cenote there in 1904. He discovered human skeletons and sacrificial objects confirming a local legend, the Cult of the Cenote, involving human sacrifice to the rain god Chaac by the ritual casting of victims and objects into the cenote. However, not all cenotes were sites of human sacrifice. The cenote at Punta Laguna has been extensively studied and none of the approximately 120 individuals show signs of sacrifice.
The remains of this cultural heritage are protected by the UNESCO Convention on the Protection of the Underwater Cultural Heritage.
Scuba diving
Cenotes have attracted cavern and cave divers, and there are organized efforts to explore and map these underwater systems. They are public or private and sometimes considered "National Natural Parks". Great care should be taken to avoid spoiling this fragile ecosystem when diving. In Mexico, the Quintana Roo Speleological Survey maintains a list of the longest and deepest water-filled and dry caves within the state boundaries. When cavern diving, one must be able to see natural light the entire time that one is exploring the cavern (e.g., Kukulkan cenote near Tulum, Mexico). During a cave dive, one passes the point where daylight can penetrate, and one follows a safety guideline to exit the cave. Things change quite dramatically once moving from a cavern dive into a cave dive. Too many divers, even experienced ones, have died for ignoring safety recommendations.Contrary to cenote cavern diving, cenote cave diving requires special equipment and training (certification for cave diving). However, both cavern and cave diving require detailed briefings, diving experience, and weight adjustment to freshwater buoyancy. The cenotes are usually filled with rather cool fresh water. Cenote divers must be wary of possible halocline; this produces blurred vision until they reach a more homogeneous area.
Notable cenotes
Australia
Ewens Ponds, near Mount Gambier, South Australia
Kilsby Sinkhole, near Mount Gambier, South Australia
Little Blue Lake, near Mount Schank, South Australia
Bahamas
Thunderball Grotto, on Staniel Cay
Belize
Great Blue Hole
Canada
Devil's Bath is the largest cenote in Canada at a size of 1178 ft (359m) in diameter and 144 ft (44m) in depth. It is located near the village of Port Alice, British Columbia on the northwest coastline of Vancouver Island. Devil's Bath is continuously fed by an underground spring and is connected by underwater tunnel to the Benson River Cave.
Dominican Republic
Hoyo Azul (Punta Cana)
Los Tres Ojos
Ojos Indigenas (Punta Cana)
Greece
Melissani Cave, Kefalonia
Jamaica
Blue Hole (Ocho Rios)
Mexico
Yucatán Peninsula
Dos Ojos, Municipality of Tulum
Dzibilchaltun, Yucatán
Ik Kil, Yucatan
Gran Cenote, Municipality of Tulum
Hubiku, Yucatan
Sacred Cenote, Chichen Itza
Xtacunbilxunan, Bolonchén
Cenote Azul, Playa del Carmen
Jardin Del Eden, Bacalar
Choo-Ha, Coba
Zaci, Valladolid
El Zapote, the site of the Hells Bells bell-like rock formation
United States
Blue Hole, Santa Rosa, New Mexico
Blue Hole, Castalia, Ohio
Bottomless Lakes, near Roswell, New Mexico
Montezuma Well, Verde Valley, Arizona
Hamilton Pool, Austin, Texas
Zimbabwe
Chinhoyi Caves in Zimbabwe
See also
Aquifer – Underground layer of water-bearing permeable rock
Blue hole – Marine cavern or sinkhole, open to the surface, in carbonate bedrock
Karst – Topography from dissolved soluble rocks
Quintana Roo Speleological Survey – Data repository for explored sites within the state of Quintana Roo
Saltwater intrusion – Movement of saline water into freshwater aquifers
Sinkhole – Geologically-formed topological depression
List of sinkholes – Links to Wikipedia articles on sinkholes, blue holes, dolines, cenotes, and pit caves
References
Citations
Other sources
RAE [Real Academia Española] (2001). Diccionario de la lengua española (in Spanish) (22nd ed.). Madrid: Editorial Espasa Calpe. ISBN 84-239-6814-6. OCLC 48657242. Archived from the original on 2010-02-06.
Sharer, Robert J.; Loa P. Traxler (2006). The Ancient Maya (6th, fully revised ed.). Stanford, CA: Stanford University Press. ISBN 0-8047-4816-0. OCLC 28067148.
External links
Cenotes of Chichén Itzá
Doline, Sinkhole, Cenote
Sistema Zacatón
Stages in the Formation of a Cenote
Volcanic karstification of Sistema Zacaton, Mexico (Gary, Sharp, 2006)
Year 1999 Cenotes Conference in Perugia, Italy |
badab-e surt | Badab Soort (Persian: باداب سورت) is a natural site in Mazandaran Province in northern Iran, 95 kilometres (59 mi) south-east of the city of Sari, and 7 kilometres (4.3 mi) east of Orost village. It comprises a range of stepped travertine terrace formations that have been created over thousands of years as flowing water from two mineral hot springs cooled and deposited carbonate minerals on the mountainside.
Etymology
Badab is a Persian compound of Bād "gas" + āb "water", translating to "gassed water", referring to the springs' waters being carbonated mineral waters. Soort is an old name for the Orost village and a Persian word meaning intensity.
Geology
Badab Soort's springs are two distinct mineral springs with different natural characteristics, located at 1,840 metres (6,040 ft) above sea level. The first spring contains very salty water that gathers in a small natural pool; its water is considered to have medicinal properties, especially as a cure for rheumatism and some types of skin diseases and skin conditions. The second spring has a sour taste and is predominantly orange mainly due to the large iron oxide sediments at its outlet.Badab Soort's terraces are made of travertine, a sedimentary rock deposited by flowing water from the two distinct mineral springs; they were formed during Pleistocene and Pliocene geological periods. When the water, supersaturated with calcium carbonate and iron carbonate, reaches the surface, carbon dioxide degases from it, and mineral carbonates are deposited. The depositing continues until the carbon dioxide in the water balances the carbon dioxide in the air. Iron carbonate and calcium carbonate are deposited by the water as soft jellies, but they eventually harden into travertine.As a result, over the course of thousands of years the water from these two springs emanating from the mountain range have combined and resulted in a number of orange-, red- and yellow-colored pools shaped as a naturally formed staircase. The surrounding vegetation to the north consists of pine forests while to the east it mainly consists of short trees and shrubs; and rock quarries can be seen to the west of the site.
Panoramic view
Similar places
Mammoth Hot Springs in the USA
Pamukkale in Turkey
Huanglong Scenic and Historic Interest Area in China
References
External links
Wikimapia
Samaee Gallery
Badab Soort pictures by Bamdadan
Short video of Badab-e Surt on YouTube |
period | Period may refer to:
Common uses
Period (punctuation)
Era, a length or span of time
Menstruation, commonly referred to as a "period"
Arts, entertainment, and media
Period (music), a concept in musical composition
Periodic sentence (or rhetorical period), a concept in grammar and literary style.
Period, a descriptor for a historical or period drama
Period, a timeframe in which a particular style of antique furniture or some other work of art was produced, such as the "Edwardian period"
Period (Another American Lie), a 1987 album by B.A.L.L.
Period (mixtape), a 2018 mixtape by City Girls
Period, the final book in Dennis Cooper's George Miles cycle of novels
Periods., a comedy film series
Mathematics
In a repeating decimal, the length of the repetend
Period of a function, length or duration after which a function repeats itself
Period (algebraic geometry), numbers that can be expressed as integrals of algebraic differential forms over algebraically defined domains, forming a ring
Science
Period (gene), a gene in Drosophila involved in regulating circadian rhythm
Period (periodic table), a horizontal row of the periodic table
"Period-" or "per-iod-", in some chemical compounds, "per" refers to oxidation state, and "iod" refers to the compound containing iodine
Unit of time or timeframe
Period (geology), a subdivision of geologic time
Period (physics), the duration of time of one cycle in a repeating event
Orbital period, the time needed for one object to complete an orbit around another
Rotation period, the time needed for one object to complete a revolution
Wavelength, the spatial period of a periodic wave
Sentence (linguistics), especially when discussing complex sentences in Latin syntax
Other uses
Period (school), a class meeting time in schools
Period (ice hockey), a division of play in an ice hockey game
Accounting period, often shortened to "period" in business, an accounting timeframe analogous to a month
See also
Duration (disambiguation)
Full stop (disambiguation)
Periodicity (disambiguation)
Periodization
List of time periods
History by period |
global warming (disambiguation) | Global warming is the ongoing increase in global average temperature that is causing climate change.
Global warming may also refer to:
a long-term rise in:
global surface temperature
ocean heat content
ocean temperature
sea surface temperature
Sea surface skin temperature, temperature of a sublayer near the surface
temperature anomaly, departure of a temperature from the temperature during a base period
Earth's Energy Imbalance, a measurable change in the planet's radiative equilibrium which quantifies its heating (or cooling) rate
Global Warming (Pitbull album), 2012
Global Warming (Sonny Rollins album), 1998
Global Warming: The Signs and The Science, a 2005 documentary film made by ETV
Global Warming: What You Need to Know, a 2006 documentary directed by Nicolas Brown
"Global Warming", a 2005 song by Gojira from the album From Mars to Sirius
See also
All pages with titles beginning with Global warming
All pages with titles containing Global warming
Global Warning (disambiguation) |
unstoppable global warming | Unstoppable global warming may refer to:
Runaway climate change
Unstoppable Global Warming, book by Fred Singer and Dennis T. Avery |
global warming hiatus | A global warming hiatus, also sometimes referred to as a global warming pause or a global warming slowdown, is a period of relatively little change in globally averaged surface temperatures. In the current episode of global warming many such 15-year periods appear in the surface temperature record, along with robust evidence of the long-term warming trend. Such a "hiatus" is shorter than the 30-year periods that climate is classically averaged over.Publicity has surrounded claims of a global warming hiatus during the period 1998–2013. The exceptionally warm El Niño year of 1998 was an outlier from the continuing temperature trend, and so subsequent annual temperatures gave the appearance of a hiatus: by January 2006, it appeared to some that global warming had stopped or paused. A 2009 study showed that decades without warming were not exceptional, and in 2011 a study showed that if allowances were made for known variability, the rising temperature trend continued unabated. There was increased public interest in 2013 in the run-up to publication of the IPCC Fifth Assessment Report, and despite concerns that a 15-year period was too short to determine a meaningful trend, the IPCC included a section on a hiatus, which it defined as a much smaller increasing linear trend over the 15 years from 1998 to 2012, than over the 60 years from 1951 to 2012. Various studies examined possible causes of the short-term slowdown. Even though the overall climate system has continued to accumulate energy due to Earth's positive energy budget, the available temperature readings at the Earth's surface indicate slower rates of increase in surface warming than in the prior decade. Since measurements at the top of the atmosphere show that Earth is receiving more energy than it is radiating back into space, the retained energy should be producing warming in the Earth's climate system.Research reported in July 2015 on an updated NOAA dataset casts doubt on the existence of a hiatus, and it finds no indication of a slowdown even in earlier years. Scientists working on other datasets welcomed this study, though they have expressed the view that the recent warming trend was less than in previous periods of the same length. Subsequently, a detailed study supports the conclusion that warming is continuing, but it also find there was less warming between 2001 and 2010 than climate models had predicted, and that this slowdown might be attributed to short-term variations in the Pacific decadal oscillation (PDO), which was negative during that period. Another review finds "no substantive evidence" of a pause in global warming. A statistical study of global temperature data since 1970 concludes that the term "hiatus" or "pause" is not justified. Some climate scientists, however, have questioned the claim that the hiatus is not supported by evidence, arguing that the recent corrections in data do not negate the existence of a hiatus.Independent of these discussions about data and measurements for earlier years, 2015 turned out to be much warmer than any of the earlier years, already before El Niño conditions started. The warmth of 2015 largely ended any remaining scientific credibility of claims that the supposed "hiatus" since 1998 had any significance for the long-term warming trend, and 2016 was even slightly warmer. In January 2017, a study published in the journal Science Advances cast further doubt on the existence of a recent pause, with more evidence that ocean temperatures have been underestimated. An April 2017 study found the data consistent with a steady warming trend globally since the 1970s, with fluctuations within the expected range of short term variability. A November 2017 joint study by scientists at the University of Fairbanks and Beijing University found that when missing data from the rapidly warming Arctic were interpolated and included in global temperature averages, the so-called hiatus disappeared entirely.
Evidence
Surface temperature changes: hiatus periods
Climate is the statistics (usually, mean or variability) of weather: the classical period for averaging weather variables is 30 years in accordance with the definition set by the World Meteorological Organization.Instrumental temperature records have shown a robust multi-decadal long-term trend of global warming since the end of the 19th century, reversing longer term cooling in previous centuries as seen in paleoclimate records. There has been considerable variability at shorter interannual to decadal periods, with hiatus periods showing less certain short-term trends. The 1998–2012 hiatus shows a rise of 0.05 [–0.05 to +0.15] °C per decade, compared with a longer term rise of 0.12 [0.08 to 0.14] °C per decade over the period from 1951 to 2012. The appearance of hiatus is sensitive to the start and end years chosen: a 15-year period starting in 1996 shows a rate of increase of 0.14 [0.03 to 0.24] °C per decade, but taking 15 years from 1997 the rate reduces to 0.07 [–0.02 to 0.18] °C per decade.
Other aspects of the climate system
While hiatus periods have appeared in surface-air temperature records, other components of the climate system associated with warming have continued. Sea level rise has not stopped in recent years, and Arctic sea ice decline has continued. There have been repeated records set for extreme surface temperatures.
Development of perception of post-1998 hiatus
The warm El Niño year of 1998 was exceptional: the IPCC Third Assessment Report of 2001 highlighted that the "high global temperature associated with the 1997 to 1998 El Niño event stands out as an extreme event, even taking into account the recent rate of warming."
Opponents of action on global warming used this peak to misleadingly suggest that warming had stopped; an April 2006 opinion piece by Bob Carter in the Daily Telegraph announced an 8-year halt, but was soon rebutted. The IPCC Fourth Assessment Report in 2007 reported that "2005 and 1998 were the warmest two years in the instrumental global surface-air temperature record since 1850. Surface temperatures in 1998 were enhanced by the major 1997–1998 El Niño but no such strong anomaly was present in 2005. Eleven of the last 12 years (1995 to 2006) – the exception being 1996 – rank among the 12 warmest years on record since 1850." The IPCC report was disputed by an open letter in the National Post with 94 signatories, which said "there has been no net global warming since 1998. That the current temperature plateau follows a late 20th-century period of warming is consistent with the continuation today of natural multi-decadal or millennial climate cycling."There were further claims in blogs and media of lack of warming since 1998, and an Investor's Business Daily article in 2008 even claimed the planet was cooling. In April 2009, a NOAA study showed that similar short-
term periods with no trend or even cooling had occurred previously in the years since 1901, and could even be found during the warming trend since 1975: it was easy to "cherry pick" the period 1998–2008 to support one view, but 1999–2008 showed a strong warming trend. They used computer simulations of future climate to show that it was "possible, and indeed likely, to have a period as long as a decade or two of 'cooling' or no warming superimposed on a longer-term warming trend." In July 2009 Jeb Bush said that global warming might not be occurring as mean temperatures had been cooler over six years. The decade to the end of 2010 was again the warmest on record, but David Rose in the Mail on Sunday argued that, excluding the 1998 "blip", global temperatures had been flat for 15 years.
A November 2011 study by statistician Grant Foster and Stefan Rahmstorf showed that after allowing for known short-term variability, there had been unabated warming since 1998 with no reduction from the rate over the preceding decade.
In January 2012 Rose claimed that the latest global temperatures showed 15 years without warming: the Met Office described this as "entirely misleading".In January 2013 James Hansen and colleagues published their updated analysis that temperatures had continued at a high level despite strong La Niña conditions, and said the "5-year mean global temperature has been flat for a decade, which we interpret as a combination of natural variability and a slowdown in the growth rate of the net climate forcing", noting "that the 10 warmest years in the record all occurred since 1998." Under the heading "Global Warming Standstill" they "noted that the 'standstill' temperature is at a much higher level than existed at any year in the prior decade except for the single year 1998, which had the strongest El Nino of the century. However, the standstill has led to a widespread assertion that 'global warming has stopped'."The Economist led an article 30 March 2013 with the sentence "Over the past 15 years air temperatures at the Earth’s surface have been flat while greenhouse-gas emissions have continued to soar, quoting Hansen as saying that ""the five-year mean global temperature has been flat for a decade." It discussed possible explanations of "the recent hiatus in rising temperatures", and suggested that it implied lower climate sensitivity.
There was a surge in media interest setting a misleading narrative, as in the Reuters headline "Climate scientists struggle to explain warming slowdown".
At the Science Media Centre in London in July 2013, journalists met Met Office scientists and were given a briefing document with three papers on "the recent pause in global warming" in surface temperatures. These said other indicators continued to show warming, at least part of the pause related to heat being exchanged into deep oceans, and it did not alter the risks of future warming or invalidate the physics behind the models: it meant only a 10% reduction in the most probable projection, so "the warming that we might have expected by 2050 would be delayed by only a few years".In preparing the IPCC Fifth Assessment Report (AR5), representatives of the U.S. government and the European Union wanted details of the slowdown or "hiatus", Germany and Hungary were concerned that a 15-year period was too short to determine a meaningful trend, but the IPCC included discussion of the topic.
One of the lead authors, Dennis L. Hartmann, subsequently said; "Going into the IPCC this time, I would have said that, well, the trend over a 15-year record is not really very meaningful, because of the natural interannual variability of the climate system. But as the IPCC evolved, it became more and more of a public issue, so we felt we had to say something about it, even though from an observational perspective, it's not a very reliable measure of long-term warming." He said "the apparent reduction in the observed warming rate" was "interesting on purely scientific grounds, but it does not have a huge impact on the scientific assessment and does not alter the basic facts." Research cited in the report had to be published by 15 March, which excluded more recent work such as a paper by NCAR scientists including Kevin E. Trenberth indicating that increased heat was going into ocean depths.A month before formal AR5 publication, a leaked draft of the report noted that "Models do not generally reproduce the observed reduction in surface warming trend over the last 10–15 years", but lacked clear explanations, and attracted wide media coverage.
On 16 August Reuters said the "panel will try to explain why global temperatures, while still increasing, have risen more slowly since about 1998 even though greenhouse gas concentrations have hit repeated record highs in that time".
The BBC on 19 August reported IPCC warnings that the final text would vary, and said "The panel will also outline why global temperatures have been rising more slowly since 1998, a controversial slowdown that scientists have been struggling to explain." It said the possibility that climate sensitivity was lower than previous estimates had been argued by "many sceptics" as a key factor, and "a good reason not to believe the more extreme predictions of those they dismiss as warmist conspirators."
Coverage varied: on 22 August the National Geographic said the "draft IPCC report also dismisses a recent slowdown in global warming, attributing it to short-term factors." On 26 September, the day before formal publication, CBC News quoted The Heritage Foundation under the headline "Climate change reports temperature hiatus fuels skeptics".In late night negotiations over wording, the IPCC added clarifications including "due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends", but at the press conference releasing the IPCC Summary for Policymakers on 27 September, journalists focussed questions on the "pause" rather than the overall conclusions. This focus resulted in headlines such as "Global Warming Slowdown Seen as Emissions Rise to Record" from Reuters. The National Post used the subheading "IPCC report skeptics seize on lull in global warming". Even Nature headlined their news report "IPCC: Despite hiatus, climate change here to stay", though it said that "the 'hiatus' since the record hot year of 1998 — probably due to increased heat uptake by the oceans — is no sign that global warming has stopped, as some would like to hope", and quoted climatologist Thomas Stocker saying that "Comparing short-term observations with long-term model projections is inappropriate", and adding "We know that there is a lot of natural fluctuation in the climate system. A 15-year hiatus is not so unusual even though the jury is out as to what exactly may have caused the pause." He said that claims dismissing climate models would only be justified if "temperature were to remain constant for the next 20 years", and Brian Hoskins said other factors showed climate change.In a statement to the press in March 2016, Professor David Vaughan of the British Antarctic Survey said that recent increases in global temperature were not due to an unusually severe El Niño, but that the opposite is true. "This is a catch-up of a recent hiatus that has occurred in rising global temperatures. We are returning to normality: rising temperatures. This is an absolute warning of the dangers that lie ahead."
Factors
Temperature dataset coverage and homogenization
The instrumental temperature record does not cover the entire globe: there are areas of incomplete or missing data, particularly in polar regions and parts of Africa. The main temperature datasets take different approaches to allowing for this: HadCRUT does not extrapolate, and assumes that the global mean applies. When these regions have a different trend to the global average as at present, this causes a bias in the result which understates overall warming. The other datasets interpolate, producing differing trends. A 2014 study introduced a more sophisticated method of Kriging from the UAH satellite dataset, and found that this considerably reduced the hiatus.
Homogenization is necessary for all climate data to correct for non-climatic changes, such as introduction of different measurement instruments, changes in location of the instruments, or differences in the time of day that measurements are taken. The NOAA temperature dataset is regularly updated with refinements improving the allowance for known biases, including the effects of past changes in methods of collecting temperatures. In 2015 it changed from the Global Historical Climatology Network to the new International Surface Temperature Initiative databank which includes many more stations giving wider coverage of land surface temperatures, and the latest Extended Reconstructed Sea Surface Temperature dataset (version 4) which made improved allowances for biases, including the phased changeover from measuring ship water intake to using automatic buoys: the previous version made a simpler allowance for this. An article published in the American Association for the Advancement of Science (AAAS) Science journal in June 2015 by a team led by Thomas R. Karl, director of the NOAA data center, reported that these adjustments made very little difference to the temperature record, but the small change in recent years was sufficient to indicate that there had been no hiatus in the period from 1998 to 2014. They used the IPCC definition of the supposed hiatus as a slowdown in rate of temperature increase from 1998 to 2012, compared to the rate from 1951 to 2012, and again found no support for the idea of a "hiatus" or slowdown.
Natural variability
Natural climate variability can appear to slow down surface warming over short periods, but does not refute long-term climate change trends. Short-term hiatus periods of global warming are compatible with long-term climate change patterns. The North Atlantic Oscillation (NAO) leads to multidecadal variability in Northern Hemispheric mean surface temperature by 15–20 years through a delayed effect on the North Atlantic Ocean, and can be a useful predictor of multidecadal periods of warming and cooling in both AMO and Northern Hemispheric mean surface temperature. A study published in January 2015 proposed that the hiatus resulted from a 60-year oscillatory pattern of natural variability associated with the AMO and PDO, interacting with a secular warming trend due mainly to human caused increases in greenhouse gas levels.
Effects of oceans
One proposal is that the hiatus was a part of natural climate variability, specifically related to decadal cooling in the eastern equatorial Pacific in the La Niña phase of the El Niño–Southern Oscillation (ENSO). This has been explained as due to unprecedented strengthening of Pacific trade winds in the last 20 years, so that surface warming has been substantially slowed by increased subsurface ocean heat uptake caused by increased subduction in the Pacific shallow overturning cells, and increased equatorial upwelling in the central and eastern Pacific. A March 2014 study found that climate models assuming natural variability which matched subsequent observations of ENSO phasing had produced realistic estimates of 15-year trends.A study published on August 3, 2014 reported that the rapid warming of the Atlantic Ocean has increased trade winds, thereby cooling temperatures in the Pacific Ocean. This, the study concluded, contributed to the hiatus because such winds trap heat in the deep ocean. Another study published later that month found evidence that a cycle of ocean currents in the Atlantic influences global temperatures by sinking large amounts of heat beneath the oceans, and suggested the hiatus might continue for ten more years because each phase of this cycle lasts for thirty years. The 60- to 80-year cycle of the atmospheric and oceanic variability over the North Atlantic was also linked to the hiatus by two studies published in 2013 and was used to infer the length of the hiatus. A new "delayed oscillator theory" of the North Atlantic decadal-scale air-sea coupling was further proposed in 2015 to understand the underlying physical mechanisms of the 60-80-year-quasi-periodic natural climate multidecadal variability.
Two papers were published by scientists of the NASA Sea Level Change Team in October 2014 in the same issue of Nature Climate Change. According to an October 6, 2014 NASA press release related to the papers, "One of the most prominent ideas is that the bottom half of the ocean is
taking up the slack, but supporting evidence is slim." In this press release, entitled, "NASA Study Finds Earth’s Ocean Abyss Has Not Warmed,"
NASA discussed research it had conducted that was "the first to test the idea using satellite observations, as well as direct temperature measurements of the upper ocean." NASA stated in this release, "The cold waters of Earth’s deep ocean have not warmed measurably since 2005, according to a new NASA study, leaving unsolved the mystery of why global warming appears to have slowed in recent years." With respect to the upper ocean, the release noted, "The temperature of the top half of the world's oceans – above the 1.24-mile mark – is still climbing, but not fast enough to account for the stalled air temperatures." NASA also emphasized in the same release, "Study coauthor Josh Willis of JPL said these findings do not throw suspicion on climate change itself. 'The sea level is still rising,' Willis noted. 'We're just trying to understand the nitty-gritty details.'".More specifically, one of these NASA studies was based on the fact that water expands as it gets warmer, and a straightforward subtraction calculation: From the total amount of sea level rise, they subtracted that due to the calculated expansion of the upper ocean down to 2,000 metres' (1.2 mi) depth based on data from Argo buoys, and that due to added meltwater worldwide. The remainder, representing the amount of sea level rise caused by warming in the deep ocean below that depth, was "essentially zero." Some recent studies reporting deep-ocean warming were referring to the upper half of the ocean, but below its topmost layer which goes down to about 700 metres' (0.43 mi) depth. According to the other NASA study, the upper layers of the Southern Ocean warmed at a much greater rate between 1970 and 2005 than previously thought (24–58 percent more than earlier estimates), because before the deployment of Argo buoys, temperature measurements in the Southern Ocean were "spotty, at best."That the oceans warmed in the past significantly faster than we thought would imply that the effects of climate change could be worse than currently expected, placing the planet's sensitivity to CO2 toward the higher end of its possible range.A study published in December 2014 found that it is likely that a significant cause of the hiatus was increased heat uptake across the Atlantic Ocean, Southern Ocean, and Equatorial Pacific Ocean.A study published in February 2015 found that Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation substantially accounted for the hiatus, and predicted that these cycles would soon begin to exert the opposite effect on global temperatures.A study published in November 2015 found evidence of "a phase difference between top-of-the-atmosphere radiation and global mean surface temperature such that ocean heat uptake tends to slow down during the surface warming hiatus." The same study reported that this finding was consistent with observations.
Volcanic activity
Several studies have proposed that possible slower surface warming during this period was caused in part by increased sulfur emissions from volcanic activity. A study published in November 2014 found that more sulfur dioxide had been emitted from small volcanoes than previously thought over the period 2000-2013. The study's lead author, David Ridley, said this could help explain why climate models did not predict slower surface warming.
Other factors
Additional proposed causes of the decreased rate of surface warming in about 1999-2014 include the emission of pine-smelling vapors from pine forests, which have been shown to turn into aerosols, and the ban on chlorofluorocarbons as a result of the Montreal Protocol, since they were potent greenhouse gases in addition to their ozone-depleting properties. Spurious differences in observed warming rates may also arise from the mathematics of trend analysis itself, particularly when the study period is brief and regression assumptions are violated.
Length of hiatus in relation to climate models
Two independent studies published in August 2014 concluded that, once surface temperatures start rising again, it is most likely that "they will keep going up without a break for the rest of the century, unless we cut greenhouse gas emissions." Watanabe et al said, "this warming hiatus originated from eastern equatorial Pacific cooling associated with strengthening of trade winds," and that while decadal climate variability has a considerable effect on global mean surface temperatures, its influence is gradually decreasing compared to the ongoing man-made global warming. Maher et al found that under the existing and projected high rates of greenhouse gas emissions there is little chance of another hiatus decade occurring after 2030, even if there were a large volcanic eruption after that time. They went on to say that most non-volcanic warming hiatuses are associated with enhanced cooling at the surface in the equatorial Pacific, which is linked to the Interdecadal Pacific Oscillation.
Reports by scientific bodies
National Academy of Sciences-Royal Society Report
A joint report from the UK Royal Society and the US National Academy of Sciences in February 2014 said that there is no "pause" in climate change and that the temporary and short-term slowdown in the rate of increase in average global surface temperatures in the non-polar regions is likely to start accelerating again in the near future. "Globally averaged surface temperature has slowed down. I wouldn’t say it's paused. It depends on the datasets you look at. If you look at datasets that include the Arctic, it is clear that global temperatures are still increasing," said Tim Palmer, a co-author of the report and a professor at University of Oxford.
World Meteorological Organisation climate report
When announcing the annual World Meteorological Organisation climate report in March 2014, the WMO secretary-general Michel Jarraud said that there had been no pause, with 2013 continuing a long-term warming trend showing "no standstill in global warming". 2013 had been the sixth-warmest year on record, and 13 of the 14 warmest years on record had occurred since the start of 2000. He said that "The warming of our oceans has accelerated, and at lower depths. More than 90 percent of the excess energy trapped by greenhouse gases is stored in the oceans."The 2013 annual report stated that "While the rate at which surface air temperatures are rising has slowed in recent years, heat continues to be trapped in the Earth system, mostly as increased ocean heat content. About 93 percent of the excess heat trapped in the Earth system between 1971 and 2010 was taken up by the ocean." From 2000 to 2013 the oceans had gained around three times as much heat as in the preceding 20 years, and while before 2000 most of the heat had been trapped between the sea surface and 700 meters (0.43 mi) depth, from 2000 to 2013 most heat had been stored between 700 and 2,000 meters (2,300 and 6,600 ft) depth. It proposed this could be due to changes in atmospheric and ocean circulation around the tropical Pacific Ocean, interacting with the El Niño–Southern Oscillation and the Pacific Decadal Oscillation.
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