Permian

The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous period 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. The continent of Angara lay to the northeast of Pangaea. 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.
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, in which nearly 81% of marine species and 70% of terrestrial species died out, associated with the eruption of the Siberian Traps in Angara. It would take well into the Triassic for life to recover from this catastrophe; on land, ecosystems took 30 million years to recover.
Etymology.
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 region between the Volga and the Ural Mountains. Murchison identified "vast series of beds of marl, schist, limestone, sandstone and conglomerate” that succeeded Carboniferous strata in the region. Murchison named the period after the medieval kingdom of Permia that occupied the same region, which now lies in the Perm Krai of Russia. 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.
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 rock 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-Captianian 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 whos hard teeth like oral elements are key index fossils for most of the Palaeozoic and the Triassic.
The Cisuralian Series is named after the strata exposed on the western slopes of the Ural Mountains in Russia and Khazakhstan. 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.
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 postserrata."
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 Captianian was ratified as an international stage by the ICS in 2001. The GSSP for the base of the Captianian 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."
The Lopingian was first intoduced 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.
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, would reach their maximum height during the early Permian around 295 million years ago, comparable to the present Himalayas.
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, culmanating 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.
At the start of the Permian, the Earth was still in the Late Paleozoic icehouse, which began in the latest Devonian. At the beginning of the Pennsylvanian around 323 million years ago, glaciers began to form around the South Pole, which would grow to cover a vast area. This area extended from the southern reaches of the Amazon basin and covered large areas of southern Africa, as well as most of Australia and Antarctica. Cyclothems indicate that the size of the glaciers were controlled by Milankovitch cycles akin to recent ice ages, with glacial periods and interglacials. The oldest cyclotherms are around 313 million years old while the youngest are around 293 million years old, corresponding to the coldest part of the Late Paleozoic icehouse. Deep ocean temperatures during this time were cold due to the influx of cold bottom waters generated by seasonal melting of the ice cap. By 285 million years ago, temperatures warmed and the South Pole ice cap retreated, though glaciers would remain present in the upland regions of eastern Australia, the Transantarctic Mountains, and the mountainous regions of far northern Siberia until the end of the Permian. The Permian was cool in comparison to most other geologic time periods, with modest Pole to Equator temperature gradients. 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. The end of the Permian is marked by the much larger temperature excursion at the Permian-Triassic boundary, corresponding to the eruption of the Siberian Traps, which released more than 5 teratonnes of CO , more than doubling atmospheric carbon dioxide concentrations.
Life.
Marine biota.
Permian marine deposits are rich in fossil mollusks, echinoderms, and brachiopods. Brachiopods would reach an apex of diversity during the Permian. Fossilized shells of two kinds of invertebrates are widely used to identify Permian strata and correlate them between sites: fusulinids, a kind of shelled amoeba-like protist that is one of the foraminiferans, and ammonoids, shelled cephalopods that are distant relatives of the modern nautilus. By the close of the Permian, trilobites and a host of other marine groups became extinct. Conodonts experienced their lowest diversity of their entire evolutionary history during the Permian.
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.
From the Pennsylvanian subperiod of the Carboniferous period until well into the Permian, the most successful insects were primitive relatives of cockroaches. Six fast legs, four well-developed folding wings, fairly good eyes, long, well-developed antennae (olfactory), an omnivorous digestive system, a receptacle for storing sperm, a chitin-based exoskeleton that could support and protect, as well as a form of gizzard and efficient mouth parts, gave it formidable advantages over other herbivorous animals. About 90% of insects at the start of the Permian were cockroach-like insects ("Blattopterans").
Primitive forms of dragonflies (Odonata) were the dominant aerial predators and probably dominated terrestrial insect predation as well. , and all are effectively semi-aquatic insects (aquatic immature stages, and terrestrial adults), as are all modern odonates. Their prototypes are the oldest winged fossils, dating back to the Devonian, and are different in several respects from the wings of other insects. Fossils suggest they may have possessed many modern attributes even by the late Carboniferous, and it is possible that they captured small vertebrates, for at least one species had a wing span of . Several other insect groups appeared or flourished during the Permian, including the Coleoptera (beetles), Hemiptera (true bugs) and Orthoptera.
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. 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. Due to the end of terrestrial deposition around the end of the Cisuralian in North America and the beginning of the deposition of terrestrial sediments 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 occuring during the Roadian, suggesting that there was an extinction event, dubbed "Olsons 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 gorgonopsians and herbivorous dicynodonts, alongside large herbivorous pareiasaur parareptiles. Towards the very end of the Permian the first archosauriforms appeared, a group that would give rise to the pseudosuchians, dinosaurs, and pterosaurs in the following period. Also appearing at the end of the Permian were the first cynodonts, which would go on to evolve into mammals during the Triassic. Another group of therapsids, the therocephalians (such as "Lycosuchus"), arose in the Middle Permian. There were no flying vertebrates (though a family of gliding reptiles known as weigeltisaurs was present in the Late Permian).
Synapsids (the group that would later include mammals) thrived and diversified greatly at this time. 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.
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.
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 southern Gondwanan floristic region was dominated by the extinct woody gymnosperm "Glossopteris" for most of the Permian, extending to high southern latitudes. The ecology of glossopterids 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 climactic conditions. 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. Ninety 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.
An even more speculative hypothesis is that intense radiation from a nearby supernova was responsible for the extinctions.
It has been hypothesised that huge meteorite impact crater (Wilkes Land crater) with a diameter of around 500 kilometers in Antarctica represents an impact event that may be related to the extinction. The crater is located at a depth of 1.6 kilometers beneath the ice of Wilkes Land in eastern Antarctica. Scientists speculate that this impact may have caused the Permian–Triassic extinction event, although its age is bracketed only between 100 million and 500 million years ago. They also speculate that it may have contributed in some way to the separation of Australia from the Antarctic landmass, which were both part of a supercontinent called Gondwana. Levels of iridium and quartz fracturing in the Permian–Triassic layer do not approach those of the Cretaceous–Paleogene boundary layer. Given that a far greater proportion of species and individual organisms became extinct during the former, doubt is cast on the significance of a meteorite impact in creating the latter. Further doubt has been cast on this theory based on fossils in Greenland that show the extinction to have been gradual, lasting about eighty thousand years, with three distinct phases.
Many scientists argue that the Permian–Triassic extinction event was caused by a combination of some or all of the hypotheses above and other factors; the formation of Pangaea decreased the number of coastal habitats and may have contributed to the extinction of many clades.