title: Ahmose I

text: Ahmose descended from the Theban Seventeenth Dynasty. His grandfather and grandmother, Senakhtenre Ahmose and Tetisheri, had at least twelve children, including Seqenenre Tao and Ahhotep I. The brother and sister, according to the tradition of Egyptian queens, married, and had sons Kamose and Ahmose I, as well as several daughters. Ahmose I followed in the tradition of his father and married several of his sisters, making Ahmose-Nefertari his chief wife. They had several children including daughters Meritamun B, Sitamun A and sons Siamun A, Ahmose-ankh, Amenhotep I and Ramose A (the "A" and "B" designations after the names are a convention used by Egyptologists to distinguish between royal children and wives that otherwise have the same name). They may also have been the parents of Mutnofret, who would become the wife of later successor Thutmose I. Ahmose-ankh was Ahmose's heir apparent, but he preceded his father in death sometime between Ahmose's 17th and 22nd regnal year. Ahmose was succeeded instead by his eldest surviving son, Amenhotep I, with whom he might have shared a short coregency.


title: Ahmose I

text: There was no distinct break in the line of the royal family between the 17th and 18th dynasties. The historian Manetho, writing much later during the Ptolemaic Kingdom, considered the final expulsion of the Hyksos after nearly a century and the restoration of native Egyptian rule over the whole country a significant enough event to warrant the start of a new dynasty.


title: Ahmose I

text: Ahmose's reign can be fairly accurately dated using the Heliacal rise of Sirius in his successor's reign, but because of disputes over from where the observation was made, he has been assigned a reign from 1570–1546 BC, 1560–1537 BC, 1551–1527 BC and 1539–1514 BC by various sources. Manetho supposedly gives Ahmose a reign of 25 years and 4 months (but, as Manetho called the first ruler of his dynasty "Tethmosis", he probably intended someone else). This figure is seemingly supported by a 'Year 22' inscription from his reign at the stone quarries of Tura. A medical examination of his mummy indicates that he died when he was about thirty-five, supporting a 25-year reign if he came to the throne at the age of 10. The radiocarbon date range for the start of his reign is 1570–1544 BC, the mean point of which is 1557 BC.


title: Ahmose I

text: Alternative dates for his reign (1194 to 1170 BC) were suggested by David Rohl, but these were rejected by the majority of Egyptologists. A radiocarbon study published in 2010 suggested minor revisions in the traditional chronology but did not support Rohl's theory.


title: Ahmose I

text: The conflict between the local kings of Thebes and the Hyksos king Apepi had started during the reign of Ahmose's father, Seqenenre Tao, and would be concluded, after almost 30 years of intermittent conflict and war, during his own reign. Seqenenre Tao was possibly killed in a battle against the Hyksos, as his much-wounded mummy gruesomely suggests, and his successor Kamose (likely Ahmose's elder brother) is known to have attacked and raided the lands around the Hyksos capital, Avaris (modern Tell el-Dab'a). Kamose evidently had a short reign, as his highest attested regnal year is year 3, and was succeeded by Ahmose I. Apepi died around a decade later.


title: Ahmose I

text: Ahmose ascended the throne when he was still a child, so his mother, Ahhotep, reigned as regent until he was of age. Judging by some of the descriptions of her regal roles while in power, including the general honorific "carer for Egypt", she effectively consolidated the Theban power base in the years before Ahmose assumed full control. If in fact Apepi II was a successor to Apepi I, then he is thought to have remained bottled up in the delta during Ahhotep's regency, because his name does not appear on any monuments or objects south of Bubastis.


title: Ahmose I

text: Ahmose began the conquest of Lower Egypt held by the Hyksos starting around the 11th year of Khamudi's reign, but the sequence of events is not universally agreed upon.


title: Ahmose I

text: Analyzing the events of the conquest prior to the siege of the Hyksos capital of Avaris is extremely difficult. Almost everything known comes from a brief but invaluable military commentary on the back of the Rhind Mathematical Papyrus, consisting of brief diary entries, one of which reads


title: Ahmose I

text: While in the past this regnal year date was assumed to refer to Ahmose, it is today believed instead to refer to Ahmose's Hyksos opponent Khamudi since the Rhind papyrus document refers to Ahmose by the inferior title of 'Prince of the South' rather than king or pharaoh, as a Theban supporter of Ahmose surely would have called him. Anthony Spalinger, in a JNES 60 (2001) book review of Kim Ryholt's 1997 book, "The Political Situation in Egypt during the Second Intermediate Period, c.1800–1550 BC", notes that Ryholt's translation of the middle portion of the Rhind text chronicling Ahmose's invasion of the Delta reads instead as the "1st month of Akhet, 23rd day. "He-of-the-South" (i.e. Ahmose) strikes against Sile." Spalinger stresses in his review that he does not question Ryholt's translation of the Rhind text but instead asks whether:


title: Ahmose I

text: The Rhind Papyrus illustrates some of Ahmose's military strategy when attacking the Delta. Entering Heliopolis in July, he moved down the eastern delta to take Tjaru, the major border fortification on the Horus Road, the road from Egypt to Canaan, in October, totally avoiding Avaris. In taking Tjaru he cut off all traffic between Canaan and Avaris. This indicates he was planning a blockade of Avaris, isolating the Hyksos capital from help or supplies coming from Canaan.


title: Ahmose I

text: Records of the latter part of the campaign were discovered on the tomb walls of a participating soldier, Ahmose, son of Ebana. These records indicate that Ahmose I led three attacks against Avaris, the Hyksos capital, but also had to quell a small rebellion further south in Egypt. After this, in the fourth attack, he conquered the city. He completed his victory over the Hyksos by conquering their stronghold Sharuhen near Gaza after a three-year siege. Ahmose would have conquered Avaris by the 18th or 19th year of his reign at the very latest. This is suggested by "a graffito in the quarry at Tura whereby 'oxen from Canaan' were used at the opening of the quarry in Ahmose's regnal year 22." Since the cattle would probably have been imported after Ahmose's siege of the town of Sharuhen which followed the fall of Avaris, this means that the reign of Khamudi must have terminated by Year 18 or 19 of Ahmose's 25-year reign at the very latest.


title: Ahmose I

text: After defeating the Hyksos, Ahmose began campaigning in Syria and Nubia. A campaign during his 22nd year reached Djahy in the Levant and perhaps as far as the Euphrates, although the later Pharaoh Thutmose I is usually credited with being the first to campaign that far. Ahmose did, however, reach at least as far as Kedem (thought to be near Byblos), according to an ostracon in the tomb of his wife, Ahmose-Nefertari. Details on this particular campaign are scarce, as the source of most of the information, Ahmose, son of Ebana, served in the Egyptian navy and did not take part in this land expedition. However, it can be inferred from archaeological surveys of southern Canaan that during the late 16th century BC Ahmose and his immediate successors intended only to break the power of the Hyksos by destroying their cities and not to conquer Canaan. Many sites there were completely laid waste and not rebuilt during this period—something a Pharaoh bent on conquest and tribute would not be likely to do.


title: Ahmose I

text: Ahmose I's campaigns in Nubia are better documented. Soon after the first Nubian campaign, a Nubian named Aata rebelled against Ahmose, but was crushed. After this attempt, an anti-Theban Egyptian named Tetian gathered many rebels in Nubia, but he too was defeated. Ahmose restored Egyptian rule over Nubia, which was controlled from a new administrative center established at Buhen. When re-establishing the national government, Ahmose appears to have rewarded various local princes who supported his cause and that of his dynastic predecessors.


title: Ahmose I

text: With the re-unification of Upper and Lower Egypt under Ahmose, a renewal of royal support for the arts and monumental construction occurred. Ahmose reportedly devoted a tenth of all the productive output towards the service of the traditional gods, reviving massive monumental constructions as well as the arts. However, as the defeat of the Hyksos occurred relatively late in Ahmose's reign, his subsequent building program likely lasted no more than seven years, and much of what was started was probably finished by his son and successor Amenhotep I.


title: Ahmose I

text: Work from Ahmose's reign is made of much finer material than anything from the Second Intermediate Period, though the craftsmanship from his reign does not always match the best work from either the Old or Middle Kingdoms. With the Delta and Nubia under Egyptian control once more, access was gained to resources not available in Upper Egypt. Gold and silver were received from Nubia, Lapis Lazuli from distant parts of central Asia, cedar from Byblos, and in the Sinai the Serabit el-Khadim turquoise mines were reopened. Although the exact nature of the relationship between Egypt and Crete is uncertain, at least some Minoan designs have been found on objects from this period, and Egypt considered the Aegean to be part of its empire. Ahmose reopened the Tura limestone quarries to provide stone for monuments and used Asiatic cattle from Phoenicia to haul the stone, according to his quarry inscription.


title: Ahmose I

text: The art during Ahmose I's reign was similar to the Middle Kingdom royal Theban style, and stelae from this period were once more of the same quality. This reflects a possibly natural conservative tendency to revive fashions from the pre-Hyksos era. Despite this, only three positively identified statuary images of Ahmose I survive: a single shabti kept at the British Museum, presumably from his tomb (which has never been positively located), and two life-size statues; one of which resides in the New York Metropolitan Museum, the other in the Khartoum Museum. All display slightly bulging eyes, a feature also present on selected stelae depicting the pharaoh. Based on style, a small limestone sphinx that resides at the National Museum of Scotland, Edinburgh, has also been tentatively identified as representing Ahmose I.


title: Ahmose I

text: The art of glass making is thought to have developed during Ahmose's reign. The oldest samples of glass appear to have been defective pieces of faience, but intentional crafting of glass did not occur until the beginning of the 18th dynasty. One of the earliest glass beads found contains the names of both Ahmose and Amenhotep I, written in a style dated to about the time of their reigns. If glassmaking was developed no earlier than Ahmose's reign and the first objects are dated to no later than his successor's reign, it is quite likely that it was one of his subjects who developed the craft.


title: Ahmose I

text: Ahmose resumed large construction projects like those before the Second Intermediate Period. In the south of the country he began constructing temples mostly built of brick, one of them in the Nubian town of Buhen. In Upper Egypt he made additions to the existing temple of Amun at Karnak and to the temple of Montu at Armant. According to an inscription at Tura, he used white limestone to build a temple to Ptah and the southern harem of Amun, but did not finish either project. He built a cenotaph for his grandmother, Queen Tetisheri, at Abydos.


title: Ahmose I

text: Excavations at the site of Avaris by Manfred Bietak have shown that Ahmose had a palace constructed on the site of the former Hyksos capital city's fortifications. Bietak found fragmentary Minoan-style remains of the frescoes that once covered the walls of the palace; there has subsequently been much speculation as to what role this Aegean civilization may have played in terms of trade and in the arts.


title: Ahmose I

text: Under Ahmose's reign, the city of Thebes became the capital for the whole of Egypt, as it had been under the 11th Dynasty in the early Middle Kingdom. It also became the center for a newly established professional civil service, where there was a greater demand for scribes and the literate as the royal archives began to fill with accounts and reports. Having Thebes as the capital was probably a strategic choice as it was located at the center of the country, the logical conclusion from having had to fight the Hyksos in the north as well as the Nubians to the south. Any future opposition at either border could be met easily.


title: Ahmose I

text: Perhaps the most important shift was a religious one: Thebes effectively became the religious as well as the political center of the country, its local god Amun credited with inspiring Ahmose in his victories over the Hyksos. The importance of the temple complex at Karnak (on the east bank of the Nile north of Thebes) grew and the importance of the previous cult of Ra based in Heliopolis diminished.


title: Ahmose I

text: Several stelae detailing the work done by Ahmose were found at Karnak, two of which depict him as a benefactor to the temple. In one of these stelae, known as the "Tempest Stele", he claims to have rebuilt the pyramids of his predecessors at Thebes that had been destroyed by a major storm. The Thera eruption in the Aegean has been implicated by some scholars as the source of the damages described in the Tempest Stele.


title: Ahmose I

text: The remains of Ahmose's pyramid in Abydos were discovered in 1899 and identified as his in 1902. Most of its outer casing stones had been robbed for use in other building projects over the years, and the mound of rubble upon which it was built has collapsed. However, two rows of intact casing stones were found by Arthur Mace, who estimated its steep slope as about 60 degrees, based on the evidence of the limestone casing (compare to the less acute 51 degrees of the Great Pyramid of Giza). Adjacent to the main pyramid temple and to its east, Harvey has identified two temples constructed by Ahmose's queen, Ahmose-Nefertary. One of these structures also bears bricks stamped with the name of Chief Treasurer Neferperet, the official responsible for re-opening the stone quarries at el-Ma'asara (Tura) in Ahmose's year 22. A third, larger temple (Temple C) is similar to the pyramid temple in form and scale, but its stamped bricks and details of decoration reinforce that it was a cult place for Ahmose-Nefertary.


title: Ahmose I

text: The axis of the pyramid complex may be associated with a series of monuments strung out along a kilometer of desert. Along this axis are several key structures: 1) a large pyramid dedicated to his grandmother Tetisheri which contained a stele depicting Ahmose providing offerings to her; 2) a rockcut underground complex which may either have served as a token representation of an Osirian underworld or as an actual royal tomb; and 3) a terraced temple built against the high cliffs, featuring massive stone and brick terraces. These elements reflect in general a similar plan undertaken for the cenotaph of Senwosret III and in general its construction contains elements which reflect the style of both Old and Middle Kingdom pyramid complexes.


title: Ahmose I

text: There is some dispute as to if this pyramid was Ahmose's burial place, or if it was a cenotaph. Although earlier explorers Mace and Currelly were unable to locate any internal chambers, it is unlikely that a burial chamber would have been located in the midst of the pyramid's rubble core. In the absence of any mention of a tomb of King Ahmose in the tomb robbery accounts of the Abbott Papyrus, and in the absence of any likely candidate for the king's tomb at Thebes, it is possible that the king was interred at Abydos, as suggested by Harvey. Certainly the great number of cult structures located at the base of the pyramid located in recent years, as well as the presence at the base of the pyramid of a cemetery used by priests of Ahmose's cult, argue for the importance of the king's Abydos cult. However, other Egyptologists believe that the pyramid was constructed (like Tetisheri's pyramid at Abydos) as a cenotaph and that Ahmose may have originally been buried in the southern part of Dra' Abu el-Naga' with the rest of the late 17th and early 18th Dynasties.


title: Ahmose I

text: This pyramid was the last pyramid ever built as part of a mortuary complex in Egypt. The pyramid would be abandoned by subsequent pharaohs of the New Kingdom, for both practical and religious reasons. The Giza plateau offered plenty of room for building pyramids; but this was not the case with the confined, cliff-bound geography of Thebes and any burials in the surrounding desert were vulnerable to flooding. The pyramid form was associated with the sun god Re, who had been overshadowed by Amun in importance. One of the meanings of Amun's name was "the hidden one", which meant that it was now theologically permissible to hide the Pharaoh's tomb by fully separating the mortuary template from the actual burial place. This provided the added advantage that the resting place of the pharaoh could be kept hidden from necropolis robbers. All subsequent pharaohs of the New Kingdom would be buried in rock-cut shaft tombs in the Valley of the Kings.


title: Ahmose I

text: Ahmose I's mummy was discovered in 1881 within the Deir el-Bahri Cache, located in the hills directly above the Mortuary Temple of Hatshepsut. He was interred along with the mummies of other 18th and 19th dynasty leaders Amenhotep I, Thutmose I, Thutmose II, Thutmose III, Ramesses I, Seti I, Ramesses II and Ramesses IX, as well as the 21st dynasty pharaohs Pinedjem I, Pinedjem II and Siamun.


title: Ahmose I

text: Ahmose I's mummy was unwrapped by Gaston Maspero on June 9, 1886. It was found within a coffin that bore his name in hieroglyphs, and on his bandages his name was again written in hieratic script. While the cedarwood coffin's style dates it squarely to the time of the 18th dynasty, it was neither of royal style nor craftsmanship, and any gilding or inlays may have been stripped in antiquity. He had evidently been moved from his original burial place, re-wrapped and placed within the cache at Deir el-Bahri during the reign of the 21st dynasty priest-king Pinedjem II, whose name also appeared on the mummy's wrappings. Around his neck a garland of "Delphinium" flowers had been placed. The body bore signs of having been plundered by ancient grave-robbers, his head having been broken off from his body and his nose smashed.


title: Ahmose I

text: The body was 1.63 m (64.17 in) in height. The mummy had a small face with no defining features, though he had slightly prominent front teeth; this may have been an inherited family trait, as this feature can be seen in some female mummies of the same family, as well as the mummy of his descendant, Thutmose II.


title: Ahmose I

text: Initial studies of the mummy were first thought to reveal a man in his 50s, but subsequent examinations have shown that he was instead likely to have been in his mid-30s when he died. The identity of this mummy (Cairo Museum catalog n° 61057) was called into question in 1980 by the published results of Dr. James Harris, a professor of orthodontics, and Egyptologist Edward Wente. Harris had been allowed to take x-rays of all of the supposed royal mummies at the Cairo Museum. While history records Ahmose I as being the son or possibly the grandson of Seqenenre Tao, the craniofacial morphology of the two mummies are quite different. It is also different from that of the female mummy identified as Ahmes-Nefertari, thought to be his sister. These inconsistencies, and the fact that this mummy was not posed with arms crossed over chest, as was the fashion of the period for male royal mummies, led them to conclude that this was likely not a royal mummy, leaving the identity of Ahmose I unknown.


title: Ahmose I

text: The mummy is now in the Luxor Museum alongside the purported one of Ramesses I, as part of a permanent exhibition called "The Golden Age of the Egyptian Military".


title: Ahmose I

text: Ahmose I was succeeded by his son, Amenhotep I. A minority of scholars have argued that Ahmose had a short co-regency with Amenhotep, potentially lasting up to six years. If there was a co-regency, Amenhotep could not have been made king before Ahmose's 18th regnal year, the earliest year in which Ahmose-ankh, the heir apparent, could have died. There is circumstantial evidence indicating a co-regency may have occurred, although definitive evidence is lacking.


title: Ahmose I

text: The first piece of evidence consists of three small objects which contain both of their praenomen next to one another: the aforementioned small glass bead, a small feldspar amulet and a broken stele, all of which are written in the proper style for the early 18th dynasty. The last stele said that Amenhotep was "given life eternally", which is an Egyptian idiom meaning that a king is alive, but the name of Ahmose does not have the usual epithet "true of voice" which is given to dead kings. Since praenomen are only assumed upon taking the throne, and assuming that both were in fact alive at the same time, it is indicated that both were reigning at the same time. There is, however, the possibility that Amenhotep I merely wished to associate himself with his beloved father, who reunited Egypt.


title: Ahmose I

text: Second, Amenhotep I appears to have nearly finished preparations for a sed festival, or even begun celebrating it; but Amenhotep I's reign is usually given only 21 years and a sed festival traditionally cannot be celebrated any earlier than a ruler's 30th year. If Amenhotep I had a significant co-regency with his father, some have argued that he planned to celebrate his Sed Festival on the date he was first crowned instead of the date that he began ruling alone. This would better explain the degree of completion of his Sed Festival preparations at Karnak. There are two contemporary New Kingdom examples of the breaking of this tradition; Hatshepsut celebrated her Heb Sed Festival in her 16th year and Akhenaten celebrated a Sed Festival near the beginning of his 17-year reign.


title: Ahmose I

text: Third, Ahmose's wife, Ahmose Nefertari, was called both "King's Great Wife" and "King's Mother" in two stelae which were set up at the limestone quarries of Ma`sara in Ahmose's 22nd year. For her to literally be a "King's Mother," Amenhotep would already have to be a king. It is possible that the title was only honorific, as Ahhotep II assumed the title without being the mother of any known king; though there is a possibility that her son Amenemhat was made Amenhotep I's co-regent, but preceded him in death.


title: Ahmose I

text: Because of this uncertainty, a co-regency is currently impossible to prove or disprove. Both Redford's and Murnane's works on the subject are undecided on the grounds that there is too little conclusive evidence either for or against a coregency. Even if there was one, it would have made no difference to the chronology of the period because in this kind of institution Amenhotep would have begun counting his regnal dates from his first year as sole ruler. However, co-regency supporters note that since at least one rebellion had been led against Ahmose during his reign, it would certainly have been logical to crown a successor before one's death to prevent a struggle for the crown.


title: Hwacha

text: The hwacha or hwach'a (; Hanja: ; literally "fire cart") was a multiple rocket launcher and an organ gun of similar design which were developed in fifteenth century Korea. The former variant fired one or two hundred rocket-powered arrows while the latter fired several dozen iron-headed arrows or bolts out of gun barrels. The term was used to refer to other war wagons or other cart-based artillery in later periods, such as that developed by Byeon Yijung in the 1590s.


title: Hwacha

text: These weapons were notably deployed in the defense of the Korean Peninsula against the invading Japanese when they invaded in the 1590s. Some East Asian historians believe this technological breakthrough, alongside the turtle ship in the mid-16th century, had a distinctive effect during the war.


title: Hwacha

text: Firearms were recognized by Goryeo military leaders as being of utmost importance in national defense. Constituting a particular threat were Japanese raiders who frequently plundered coastal towns in increasing numbers from 1350 onward. Gunpowder and firearms explicitly for combating them on the sea were imported from China in 1374 but the necessary expertise for production was still restricted by Chinese government policy.


title: Hwacha

text: Numerous ancient Chinese documents relating to gunpowder based weapons such as the Huolongjing were acquired by the Koreans in addition to small samples of Chinese gunpowder which the Koreans reverse engineered.


title: Hwacha

text: Local production did not begin until Choe Mu-seon, having acquired the methods for purifying potassium nitrate from visiting Chinese merchants, accomplished it between 1374 and 1376. A government office for the development of gunpowder and firearms was established in 1377 with Choe appointed its head. A number of weapons were developed here, including hand-cannon and a series of rockets, in particular the "juhwa".


title: Hwacha

text: The hwacha further developed from the juhwa and the singijeon. The first hwacha was created in Korea in 1409 during the Joseon Dynasty by several Korean scientists, including Yi Do (이도, not to be mistaken for Sejong the Great, even though their names sound similar) and Choi Hae-san (최해산, son of Choe Museon).


title: Hwacha

text: Stronger and more effective hwachas were made in 1451 under the decree of King Munjong, by the king himself and his younger brother Pe. Im-Yung (Yi Gu, 임영대군 이구). The "Munjong Hwacha" is a well-known type that nowadays could fire 100 rocket arrows or 200 small Chongtong bullets at one time with changeable modules. At the time, 50 units were deployed in Hanseong (present-day Seoul) and another 80 on the northern border. By the end of 1451, hundreds of hwachas were deployed throughout the peninsula. Another variant was the "Mangam Hwacha". A boxed cart with large faces of a "dokkaebi" painted on all three sides. Armed with forty "seungja-chongtongs" with fourteen in the front and thirteen on the left and right sides, only two soldiers can manage it, one firing the rows and the other reloads. They can fire 600 bullets, with each barrel holding 15 shots each.


title: Hwacha

text: Hwachas saw action most extensively against the Japanese during their invasions of Korea. The hwachas were mostly placed in fortresses or citadels, and used defensively. They proved to be powerful in many battles, and were most prominent in the Battle of Haengju, in which 3,400 Koreans repelled 30,000 Japanese with the help of 40 hwachas. The Japanese samurai infantry, especially in the Battle of Haengju, typically advanced in dense formations, presenting ideal targets for the hwacha.


title: Hwacha

text: Hwachas were also used on panokseons under the navy of Admiral Yi Sun-sin to attack Japanese ships from a distance.


title: Hwacha

text: The hwacha's structure was very similar to a handcart, with a mobile wooden launchpad on the top containing 100 to 200 cylindrical holes, into which igniters like those of the sajeonchongtong (사전총통) were placed.


title: Hwacha

text: The ammunition, similar to the ancient Chinese fire arrows, consisted of a 1.1 m long arrow with the addition of a gunpowder-filled paper tube attached to the shaft just below the head. Approximately 100 projectiles were loaded and launched in one volley, and had a range of up to 2000 m.


title: Hwacha

text: One variant had 5 rows of 10 gun barrels in the launchpad, each of which could fire a bundle of four arrow-like projectiles.


title: Hwacha

text: The back side of the hwacha featured two parallel arms that allowed the operator to push and pull the machine, and a vertical strip designed for in-line attacks or stand ground-sentry positions.


title: Hwacha

text: The wagon-like wheels were usually fastened by wood pivots and iron axles. In order to reduce friction between the wheels and the axles, tar oil was used.


title: Hwacha

text: Hwachas were usually made of pine wood, although there are some versions made of oak. The ropes used were usually made of hemp.


title: Hwacha

text: The Korean army included siege engineers and blacksmiths in order to make repairs to the hwacha in case of damage due to poor road conditions, bad weather, or battle.


title: Hwacha

text: Unlike the cannons or mortars used in Western warfare during Middle Ages and the 16th century, which required heavy iron balls, hwachas fired arrows which were thin and light, making it an easy-to-maneuver siege weapon.


title: Hwacha

text: The holes in the hwacha's launching array ranged in diameter from 2.5 to 4 cm, which allowed thin Gungdo bow-like arrows to be fired and also admitted "sajeonchongtong" class igniters placed in the back side of the shooting board.


title: Hwacha

text: Singijeon-class projectiles were small arrows designed by Korean siege engineers specifically to be used in hwachas. Called "so" (소), or "small", they possessed a pouch of black powder attached in the bottom near to the fletching section. Besides the singijeon-class projectiles, hwacha could also fire 100 steel-tipped rockets.


title: Hwacha

text: Because of the large numbers of arrows fired from hwachas and the widespread damage of its attack, a dense formation presented an ideal target for hwachas.


title: Hwacha

text: The trajectory of the "so" projectiles was fairly flat and – like other spinning projectiles – affected by the Magnus effect. Operators used to fire the weapon at an elevation of nearly 45° to maximise range. Adverse weather conditions (wind, humidity, rain) during a battle generally limited their striking distance to about 100 m.


title: Hwacha

text: Hwachas' range could be extended if the siege weapon was situated on a hill or other elevated place. Singijeon arrows from that position had a range of about 500 yards (≈450 meters).


title: Hwacha

text: A 15th-century account from the Annals of Joseon Dynasty tells of an experiment in which the singijeon fired from a hwacha completely pierced a scarecrow armed with a suit of armour and shield, at the range of 80 paces (about 100 m).


title: Hwacha

text: Hwachas were mostly used in a defensive manner; however, some Western and East Asian historians have concluded that in some cases they were used offensively in sea-to-land attacks and in naval warfare as well, particularly in the Battle of Noryang Point, during the Imjin wars in 1598.


title: Hwacha

text: Hwachas were usually carried to battle highly escorted. Once the army settled down in trenches or base camps, the operators would assemble the siege weapon by placing the launching array on the top. Hwachas were similar to European trebuchets to transport, and required assembling before usage. All the pieces featured similar characteristics and the mobile launching array could be unpacked and easily placed on the wood frame on the top of cart.


title: Hwacha

text: Once a hwacha was set up for combat, the operators would use the gunpowder stored in a boot-like bag tied on each igniter to be used for each hole on the machine. After that, the operators were able to load the hwacha with arrows or iron spikes and be ready to shoot. To do so, they stepped back, covered their ears, and pulled the rope for each igniter.


title: Hwacha

text: At sea, manoeuvres were slightly different and more complex because the operator would need to find a proper and stable place to fire. Some Hwacha operators preferred to be on the rowers' deck where they were able to shoot from the windows, while others preferred to be on the main deck so they could shoot at the sails of the enemy ships. These kind of manoeuvres were particularly seen on Korean Panokseon warships.


title: The Missing (2003 film)

text: The Missing is a 2003 American Western film directed by Ron Howard and starring Tommy Lee Jones and Cate Blanchett. It is based on Thomas Eidson's 1996 novel "The Last Ride". The film is set in 1885 New Mexico Territory and is notable for the authentic use of the Apache language by various actors, some of whom spent long hours studying it. The film was produced by Revolution Studios, Imagine Entertainment, and Daniel Ostroff Productions and distributed by Columbia Pictures (Sony Pictures Releasing).


title: The Missing (2003 film)

text: In late 19th-century New Mexico, Samuel Jones arrives at the house of his adult daughter Magdalena "Maggie" Gilkeson, hoping to reconcile with her after abandoning her and her mother decades before. She is unable to forgive him, feeling he caused her mother's early death, and turns him away the next morning. Renegade Apache Pesh-Chidin, alias El Brujo and followers raid the area, killing settlers and taking young women and girls to sell into sex slavery in Mexico. Among those abducted is Maggie's eldest daughter, Lilly. Maggie's rancher boyfriend Brake Baldwin was among the settlers killed. Maggie secures her father's release from jail, and the two decide to go after the abducted girls, taking the youngest daughter Dot with them. The sheriff is unwilling to spare men for the mission.


title: The Missing (2003 film)

text: The party encounter some U.S. Cavalry soldiers at another ranch that was attacked by El Brujo. These men suspect Jones as having led the raiders, but Maggie eases the situation. The lieutenant in charge evades helping them, as he must lead his unit to carry out the forced relocation of captive Native Americans. Maggie, her father, and her younger daughter Dot are the only ones tracking El Brujo and his warriors.


title: The Missing (2003 film)

text: After the three fail to ambush the raiders, they are rescued by Kayitah, a Chiricahua friend of Jones. Kayitah and his son Honesco are also tracking El Brujo because Honesco's fiancee is among the captives. Kayitah and Honesco agree to join Maggie and her family. Kayitah tells her that her father had traveled for some time with his Chiricahua band, who called him "Chaa-duu-ba-its-iidan".


title: The Missing (2003 film)

text: Together the two families find and free the women captives. Lilly accidentally alerts the bandits, resulting in the death of Kayitah. The survivors steal El Brujo's horses and flee to the mountains. The Mexican gang arrives to buy the women, and the kidnappers murder them and steal their horses to chase the fleeing women. Jones leads the group to a bluff he knows, with a strong defensive position. The kidnappers can only attack up a steep, narrow path. During a standoff, Jones tries to explain to Maggie why he abandoned the family, saying that "Chaa-duu-ba-its-iidan" means "shit for luck". Maggie says she does not forgive him.


title: The Missing (2003 film)

text: The group fights off an attack by the remaining kidnappers. Jones and Maggie hold off the attackers, but El Brujo stealthily climbs up the side of the cliff and injures Honesco, while his followers use fire arrows to spread panic in the camp. Maggie heads into the camp to fight El Brujo, but he ambushes her. Jones lights bushes on fire to slow down the attackers, and confronts El Brujo, who had kidnapped his granddaughter. Despite being stabbed, El Brujo gains the upper hand and tries to kill Maggie. Jones intervenes, and he and El Brujo fall off a cliff to their deaths. Maggie shoots at the last remaining kidnappers to scare them off.


title: The Missing (2003 film)

text: "The Missing" earned mixed reviews from critics. On Rotten Tomatoes, a review aggregator, the film has an approval rating of 58% based on 174 reviews; the average rating is 6.10/10. The website's critical consensus reads, "An expertly acted and directed Western. But like other Ron Howard features, the movie is hardly subtle." On Metacritic, the film has a score of 55 out of 100 based on 40 critics, indicating "mixed or average reviews". Audiences polled by CinemaScore gave the film an average grade of "B" on an A+ to F scale. Philip French of "The Observer" referred to the film as Howard's "finest film to date," and Michael Wilmington of the "Chicago Tribune" called it the "best and toughest western since "Unforgiven"."


title: The Missing (2003 film)

text: "The Missing" was well received among Native American populations within the United States. Many praised its use of Apache dialect, saying that it was so well spoken it could be understood by most Chiricahua-speaking adults. Actors such as Tommy Lee Jones, Jay Tavare, Simon R. Baker, and others had learned to speak some dialogue in the Chiricahua dialect of Apache; this was used throughout the film. Tavare has noted that only about 300 people are considered fluent speakers of Chiricahua today. Following screenings of the film, Native American students said that it stimulated pride among them because of its authenticity.


title: The Missing (2003 film)

text: "The Missing" grossed $27 million domestically and $11.4 million internationally for a worldwide total of $38.4 million.


title: History of life

text: The history of life on Earth traces the processes by which living and fossil organisms evolved, from the earliest emergence of life to present day. Earth formed about 4.5 billion years ago (abbreviated as "Ga", for "gigaannum") and evidence suggests that life emerged prior to 3.7 Ga. Although there is some evidence of life as early as 4.1 to 4.28 Ga, it remains controversial due to the possible non-biological formation of the purported fossils.


title: History of life

text: The similarities among all known present-day species indicate that they have diverged through the process of evolution from a common ancestor. Only a very small percentage of species have been identified: one estimate claims that Earth may have 1 trillion species. However, only 1.75–1.8 million have been named and 1.8 million documented in a central database. These currently living species represent less than one percent of all species that have ever lived on Earth.


title: History of life

text: The earliest evidence of life comes from biogenic carbon signatures and stromatolite fossils discovered in 3.7 billion-year-old metasedimentary rocks from western Greenland. In 2015, possible "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia. In March 2017, putative evidence of possibly the oldest forms of life on Earth was reported in the form of fossilized microorganisms discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada, that may have lived as early as 4.28 billion years ago, not long after the oceans formed 4.4 billion years ago, and not long after the formation of the Earth 4.54 billion years ago.


title: History of life

text: Microbial mats of coexisting bacteria and archaea were the dominant form of life in the early Archean Epoch and many of the major steps in early evolution are thought to have taken place in this environment. The evolution of photosynthesis, around 3.5 Ga, eventually led to a buildup of its waste product, oxygen, in the atmosphere, leading to the great oxygenation event, beginning around 2.4 Ga. The earliest evidence of eukaryotes (complex cells with organelles) dates from 1.85 Ga, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. Later, around 1.7 Ga, multicellular organisms began to appear, with differentiated cells performing specialised functions. Sexual reproduction, which involves the fusion of male and female reproductive cells (gametes) to create a zygote in a process called fertilization is, in contrast to asexual reproduction, the primary method of reproduction for the vast majority of macroscopic organisms, including almost all eukaryotes (which includes animals and plants). However the origin and evolution of sexual reproduction remain a puzzle for biologists though it did evolve from a common ancestor that was a single celled eukaryotic species. Bilateria, animals having a left and a right side that are mirror images of each other, appeared by 555 Ma (million years ago).


title: History of life

text: Algae-like multicellular land plants are dated back even to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2.7 Ga. Microorganisms are thought to have paved the way for the inception of land plants in the Ordovician period. Land plants were so successful that they are thought to have contributed to the Late Devonian extinction event. (The long causal chain implied seems to involve (1) the success of early tree archaeopteris drew down CO levels, leading to global cooling and lowered sea levels, (2) roots of archeopteris fostered soil development which "increased" rock weathering, and the subsequent nutrient run-off may have triggered algal blooms resulting in anoxic events which caused marine-life die-offs. Marine species were the primary victims of the Late Devonian extinction.)


title: History of life

text: Ediacara biota appear during the Ediacaran period, while vertebrates, along with most other modern phyla originated about during the Cambrian explosion. During the Permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became extinct in the Permian–Triassic extinction event . During the recovery from this catastrophe, archosaurs became the most abundant land vertebrates; one archosaur group, the dinosaurs, dominated the Jurassic and Cretaceous periods. After the Cretaceous–Paleogene extinction event killed off the non-avian dinosaurs, mammals increased rapidly in size and diversity. Such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify.


title: History of life

text: The oldest meteorite fragments found on Earth are about 4.54 billion years old; this, coupled primarily with the dating of ancient lead deposits, has put the estimated age of Earth at around that time. The Moon has the same composition as Earth's crust but does not contain an iron-rich core like the Earth's. Many scientists think that about 40 million years after the formation of Earth, it collided with a body the size of Mars, throwing crust material into the orbit that formed the Moon. Another hypothesis is that the Earth and Moon started to coalesce at the same time but the Earth, having much stronger gravity than the early Moon, attracted almost all the iron particles in the area.


title: History of life

text: Until 2001, the oldest rocks found on Earth were about 3.8 billion years old, leading scientists to estimate that the Earth's surface had been molten until then. Accordingly, they named this part of Earth's history the Hadean. However, analysis of zircons formed 4.4 Ga indicates that Earth's crust solidified about 100 million years after the planet's formation and that the planet quickly acquired oceans and an atmosphere, which may have been capable of supporting life.


title: History of life

text: Evidence from the Moon indicates that from 4 to 3.8 Ga it suffered a Late Heavy Bombardment by debris that was left over from the formation of the Solar System, and the Earth should have experienced an even heavier bombardment due to its stronger gravity. While there is no direct evidence of conditions on Earth 4 to 3.8 Ga, there is no reason to think that the Earth was not also affected by this late heavy bombardment. This event may well have stripped away any previous atmosphere and oceans; in this case gases and water from comet impacts may have contributed to their replacement, although outgassing from volcanoes on Earth would have supplied at least half. However, if subsurface microbial life had evolved by this point, it would have survived the bombardment.


title: History of life

text: The earliest identified organisms were minute and relatively featureless, and their fossils look like small rods that are very difficult to tell apart from structures that arise through abiotic physical processes. The oldest undisputed evidence of life on Earth, interpreted as fossilized bacteria, dates to 3 Ga. Other finds in rocks dated to about 3.5 Ga have been interpreted as bacteria, with geochemical evidence also seeming to show the presence of life 3.8 Ga. However, these analyses were closely scrutinized, and non-biological processes were found which could produce all of the "signatures of life" that had been reported. While this does not prove that the structures found had a non-biological origin, they cannot be taken as clear evidence for the presence of life. Geochemical signatures from rocks deposited 3.4 Ga have been interpreted as evidence for life, although these statements have not been thoroughly examined by critics.


title: History of life

text: Evidence for fossilized microorganisms considered to be 3.77 billion to 4.28 billion years old was found in the Nuvvuagittuq Greenstone Belt in Quebec, Canada, although the evidence is disputed as inconclusive.


title: History of life

text: Biologists reason that all living organisms on Earth must share a single last universal ancestor, because it would be virtually impossible that two or more separate lineages could have independently developed the many complex biochemical mechanisms common to all living organisms.


title: History of life

text: Life on Earth is based on carbon and water. Carbon provides stable frameworks for complex chemicals and can be easily extracted from the environment, especially from carbon dioxide. There is no other chemical element whose properties are similar enough to carbon's to be called an analogue; silicon, the element directly below carbon on the periodic table, does not form very many complex stable molecules, and because most of its compounds are water-insoluble and because silicon dioxide is a hard and abrasive solid in contrast to carbon dioxide at temperatures associated with living things, it would be more difficult for organisms to extract. The elements boron and phosphorus have more complex chemistries, but suffer from other limitations relative to carbon. Water is an excellent solvent and has two other useful properties: the fact that ice floats enables aquatic organisms to survive beneath it in winter; and its molecules have electrically negative and positive ends, which enables it to form a wider range of compounds than other solvents can. Other good solvents, such as ammonia, are liquid only at such low temperatures that chemical reactions may be too slow to sustain life, and lack water's other advantages. Organisms based on alternative biochemistry may, however, be possible on other planets.


title: History of life

text: Research on how life might have emerged from non-living chemicals focuses on three possible starting points: self-replication, an organism's ability to produce offspring that are very similar to itself; metabolism, its ability to feed and repair itself; and external cell membranes, which allow food to enter and waste products to leave, but exclude unwanted substances. Research on abiogenesis still has a long way to go, since theoretical and empirical approaches are only beginning to make contact with each other.


title: History of life

text: Even the simplest members of the three modern domains of life use DNA to record their "recipes" and a complex array of RNA and protein molecules to "read" these instructions and use them for growth, maintenance and self-replication. The discovery that some RNA molecules can catalyze both their own replication and the construction of proteins led to the hypothesis of earlier life-forms based entirely on RNA. These ribozymes could have formed an RNA world in which there were individuals but no species, as mutations and horizontal gene transfers would have meant that offspring were likely to have different genomes from their parents, and evolution occurred at the level of genes rather than organisms. RNA would later have been replaced by DNA, which can build longer, more stable genomes, strengthening heritability and expanding the capabilities of individual organisms. Ribozymes remain as the main components of ribosomes, the "protein factories" in modern cells. Evidence suggests the first RNA molecules formed on Earth prior to 4.17 Ga.


title: History of life

text: Although short self-replicating RNA molecules have been artificially produced in laboratories, doubts have been raised about whether natural non-biological synthesis of RNA is possible. The earliest "ribozymes" may have been formed of simpler nucleic acids such as PNA, TNA or GNA, which would have been replaced later by RNA.


title: History of life

text: In 2003, it was proposed that porous metal sulfide precipitates would assist RNA synthesis at about and ocean-bottom pressures near hydrothermal vents. Under this hypothesis, lipid membranes would be the last major cell components to appear and, until then, the protocells would be confined to the pores.


title: History of life

text: A series of experiments starting in 1997 showed that early stages in the formation of proteins from inorganic materials including carbon monoxide and hydrogen sulfide could be achieved by using iron sulfide and nickel sulfide as catalysts. Most of the steps required temperatures of about and moderate pressures, although one stage required and a pressure equivalent to that found under of rock. Hence it was suggested that self-sustaining synthesis of proteins could have occurred near hydrothermal vents.


title: History of life

text: It has been suggested that double-walled "bubbles" of lipids like those that form the external membranes of cells may have been an essential first step. Experiments that simulated the conditions of the early Earth have reported the formation of lipids, and these can spontaneously form liposomes, double-walled "bubbles," and then reproduce themselves. Although they are not intrinsically information-carriers as nucleic acids are, they would be subject to natural selection for longevity and reproduction. Nucleic acids such as RNA might then have formed more easily within the liposomes than outside.


title: History of life

text: RNA is complex and there are doubts about whether it can be produced non-biologically in the wild. Some clays, notably montmorillonite, have properties that make them plausible accelerators for the emergence of an RNA world: they grow by self-replication of their crystalline pattern; they are subject to an analogue of natural selection, as the clay "species" that grows fastest in a particular environment rapidly becomes dominant; and they can catalyze the formation of RNA molecules. Although this idea has not become the scientific consensus, it still has active supporters.


title: History of life

text: Research in 2003 reported that montmorillonite could also accelerate the conversion of fatty acids into "bubbles," and that the "bubbles" could encapsulate RNA attached to the clay. These "bubbles" can then grow by absorbing additional lipids and then divide. The formation of the earliest cells may have been aided by similar processes.


title: History of life

text: A similar hypothesis presents self-replicating iron-rich clays as the progenitors of nucleotides, lipids and amino acids.


title: History of life

text: Wet-dry cycles at geothermal springs are shown to solve the problem of hydrolysis and promote the polymerization and vesicle encapsulation of biopolymers. The temperatures of geothermal springs are suitable for biomolecules. Silica minerals and metal sulfides at these environments have photocatalytic properties to catalyze biomolecules. Solar UV exposure also promotes the synthesis of biomolecules like RNA nucleotides. An analysis of hydrothermal veins at a 3.5 Gya geothermal spring setting were found to have elements required for the origin of life, which are potassium, boron, hydrogen, sulfur, phosphorus, zinc, nitrogen, and oxygen. Mulkidjanian and colleagues find that such environments have identical ionic concentrations to the cytoplasm of modern cells. Fatty acids in acidic or slightly alkaline geothermal springs assemble into vesicles after wet-dry cycles as there is a lower concentration of ionic solutes at geothermal springs since they are freshwater environments, in contrast to seawater which has a higher concentration of ionic solutes. For organic compounds to be present at geothermal springs, they would have likely been transported by carbonaceous meteors. The molecules that fell from the meteors were then accumulated in geothermal springs. As for the evolutionary implications, freshwater heterotrophic cells that depended upon synthesized organic compounds later evolved photosynthesis because of the continuous exposure to sunlight as well as their cell walls with ion pumps to maintain their intracellular metabolism after they entered the oceans.


title: History of life

text: Catalytic mineral particles at these environments likely catalyzed organic compounds. Scientists simulated laboratory conditions that were identical to white smokers and successfully oligomerized RNA, measured to be 4 units long. Another experiment that replicated conditions also similar white smokers, with phospholipids present resulted in the assembly of vesicles. Exergonic reactions at hydrothermal vents are suggested to have been a source of free energy that promoted chemical reactions, synthesis of organic molecules, and are inducive to chemical gradients. In small rock pore systems, membranous structures between alkaline seawater and the acidic ocean would be conducive to proton gradients. Small mineral cavities or mineral gels could have been a compartment for abiogenic processes. A genomic analysis supports this hypothesis as they found 355 genes that likely traced to LUCA upon 6.1 million sequenced prokaryotic genes. They reconstruct LUCA as a thermophilic anaerobe with a Wood-Ljungdahl pathway, implying an origin of life at white smokers.


title: History of life

text: The Panspermia hypothesis does not explain how life arose originally, but simply examines the possibility of it coming from somewhere other than Earth. The idea that life on Earth was "seeded" from elsewhere in the Universe dates back at least to the Greek philosopher Anaximander in the sixth century BCE. In the twentieth century it was proposed by the physical chemist Svante Arrhenius, by the astronomers Fred Hoyle and Chandra Wickramasinghe, and by molecular biologist Francis Crick and chemist Leslie Orgel.


title: History of life

text: There are three main versions of the "seeded from elsewhere" hypothesis: from elsewhere in our Solar System via fragments knocked into space by a large meteor impact, in which case the most credible sources are Mars and Venus; by alien visitors, possibly as a result of accidental contamination by microorganisms that they brought with them; and from outside the Solar System but by natural means.


title: History of life

text: Experiments in low Earth orbit, such as EXOSTACK, have demonstrated that some microorganism spores can survive the shock of being catapulted into space and some can survive exposure to outer space radiation for at least 5.7 years. Scientists are divided over the likelihood of life arising independently on Mars, or on other planets in our galaxy.


title: History of life

text: Microbial mats are multi-layered, multi-species colonies of bacteria and other organisms that are generally only a few millimeters thick, but still contain a wide range of chemical environments, each of which favors a different set of microorganisms. To some extent each mat forms its own food chain, as the by-products of each group of microorganisms generally serve as "food" for adjacent groups.


title: History of life

text: Stromatolites are stubby pillars built as microorganisms in mats slowly migrate upwards to avoid being smothered by sediment deposited on them by water. There has been vigorous debate about the validity of alleged stromatolite fossils from before 3 Ga, with critics arguing that they could have been formed by non-biological processes. In 2006, another find of stromatolites was reported from the same part of Australia, in rocks dated to 3.5 Ga.


title: History of life

text: In modern underwater mats the top layer often consists of photosynthesizing cyanobacteria which create an oxygen-rich environment, while the bottom layer is oxygen-free and often dominated by hydrogen sulfide emitted by the organisms living there. Oxygen is toxic to organisms that are not adapted to it, but greatly increases the metabolic efficiency of oxygen-adapted organisms; oxygenic photosynthesis by bacteria in mats increased biological productivity by a factor of between 100 and 1,000. The source of hydrogen atoms used by oxygenic photosynthesis is water, which is much more plentiful than the geologically produced reducing agents required by the earlier non-oxygenic photosynthesis. From this point onwards life itself produced significantly more of the resources it needed than did geochemical processes.


title: History of life

text: Oxygen became a significant component of Earth's atmosphere about 2.4 Ga. Although eukaryotes may have been present much earlier, the oxygenation of the atmosphere was a prerequisite for the evolution of the most complex eukaryotic cells, from which all multicellular organisms are built. The boundary between oxygen-rich and oxygen-free layers in microbial mats would have moved upwards when photosynthesis shut down overnight, and then downwards as it resumed on the next day. This would have created selection pressure for organisms in this intermediate zone to acquire the ability to tolerate and then to use oxygen, possibly via endosymbiosis, where one organism lives inside another and both of them benefit from their association.


title: History of life

text: Cyanobacteria have the most complete biochemical "toolkits" of all the mat-forming organisms. Hence they are the most self-sufficient, well-adapted to strike out on their own both as floating mats and as the first of the phytoplankton, providing the basis of most marine food chains.


title: History of life

text: Eukaryotes may have been present long before the oxygenation of the atmosphere, but most modern eukaryotes require oxygen, which is used by their mitochondria to fuel the production of ATP, the internal energy supply of all known cells. In the 1970s, a vigorous debate concluded that eukaryotes emerged as a result of a sequence of endosymbiosis between prokaryotes. For example: a predatory microorganism invaded a large prokaryote, probably an archaean, but instead of killing its prey, the attacker took up residence and evolved into mitochondria; one of these chimeras later tried to swallow a photosynthesizing cyanobacterium, but the victim survived inside the attacker and the new combination became the ancestor of plants; and so on. After each endosymbiosis, the partners eventually eliminated unproductive duplication of genetic functions by re-arranging their genomes, a process which sometimes involved transfer of genes between them. Another hypothesis proposes that mitochondria were originally sulfur- or hydrogen-metabolising endosymbionts, and became oxygen-consumers later. On the other hand, mitochondria might have been part of eukaryotes' original equipment.


title: History of life

text: There is a debate about when eukaryotes first appeared: the presence of steranes in Australian shales may indicate eukaryotes at 2.7 Ga; however, an analysis in 2008 concluded that these chemicals infiltrated the rocks less than 2.2 Ga and prove nothing about the origins of eukaryotes. Fossils of the algae "Grypania" have been reported in 1.85 billion-year-old rocks (originally dated to 2.1 Ga but later revised), indicating that eukaryotes with organelles had already evolved. A diverse collection of fossil algae were found in rocks dated between 1.5 and 1.4 Ga. The earliest known fossils of fungi date from 1.43 Ga.


title: History of life

text: Plastids, the superclass of organelles of which chloroplasts are the best-known exemplar, are thought to have originated from endosymbiotic cyanobacteria. The symbiosis evolved around 1.5 Ga and enabled eukaryotes to carry out oxygenic photosynthesis. Three evolutionary lineages of photosynthetic plastids have since emerged: chloroplasts in green algae and plants, rhodoplasts in red algae and cyanelles in the glaucophytes. Not long after this primary endosymbiosis of plastids, rhodoplasts and chloroplasts were passed down to other bikonts, establishing an eukaryotic assemblage of phytoplankton by the end of the Neoproterozoic Eon.


title: History of life

text: The defining characteristics of sexual reproduction in eukaryotes are meiosis and fertilization, resulting in genetic recombination, giving offspring 50% of their genes from each parent. By contrast, in asexual reproduction there is no recombination, but occasional horizontal gene transfer. Bacteria also exchange DNA by bacterial conjugation, enabling the spread of resistance to antibiotics and other toxins, and the ability to utilize new metabolites. However, conjugation is not a means of reproduction, and is not limited to members of the same species – there are cases where bacteria transfer DNA to plants and animals.


title: History of life

text: On the other hand, bacterial transformation is clearly an adaptation for transfer of DNA between bacteria of the same species. This is a complex process involving the products of numerous bacterial genes and can be regarded as a bacterial form of sex. This process occurs naturally in at least 67 prokaryotic species (in seven different phyla). Sexual reproduction in eukaryotes may have evolved from bacterial transformation.


title: History of life

text: The disadvantages of sexual reproduction are well-known: the genetic reshuffle of recombination may break up favorable combinations of genes; and since males do not directly increase the number of offspring in the next generation, an asexual population can out-breed and displace in as little as 50 generations a sexual population that is equal in every other respect. Nevertheless, the great majority of animals, plants, fungi and protists reproduce sexually. There is strong evidence that sexual reproduction arose early in the history of eukaryotes and that the genes controlling it have changed very little since then. How sexual reproduction evolved and survived is an unsolved puzzle.


title: History of life

text: The Red Queen hypothesis suggests that sexual reproduction provides protection against parasites, because it is easier for parasites to evolve means of overcoming the defenses of genetically identical clones than those of sexual species that present moving targets, and there is some experimental evidence for this. However, there is still doubt about whether it would explain the survival of sexual species if multiple similar clone species were present, as one of the clones may survive the attacks of parasites for long enough to out-breed the sexual species. Furthermore, contrary to the expectations of the Red Queen hypothesis, Kathryn A. Hanley et al. found that the prevalence, abundance and mean intensity of mites was significantly higher in sexual geckos than in asexuals sharing the same habitat. In addition, biologist Matthew Parker, after reviewing numerous genetic studies on plant disease resistance, failed to find a single example consistent with the concept that pathogens are the primary selective agent responsible for sexual reproduction in the host.


title: History of life

text: Alexey Kondrashov's "deterministic mutation hypothesis" (DMH) assumes that each organism has more than one harmful mutation and the combined effects of these mutations are more harmful than the sum of the harm done by each individual mutation. If so, sexual recombination of genes will reduce the harm that bad mutations do to offspring and at the same time eliminate some bad mutations from the gene pool by isolating them in individuals that perish quickly because they have an above-average number of bad mutations. However, the evidence suggests that the DMH's assumptions are shaky because many species have on average less than one harmful mutation per individual and no species that has been investigated shows evidence of synergy between harmful mutations.


title: History of life

text: The random nature of recombination causes the relative abundance of alternative traits to vary from one generation to another. This genetic drift is insufficient on its own to make sexual reproduction advantageous, but a combination of genetic drift and natural selection may be sufficient. When chance produces combinations of good traits, natural selection gives a large advantage to lineages in which these traits become genetically linked. On the other hand, the benefits of good traits are neutralized if they appear along with bad traits. Sexual recombination gives good traits the opportunities to become linked with other good traits, and mathematical models suggest this may be more than enough to offset the disadvantages of sexual reproduction. Other combinations of hypotheses that are inadequate on their own are also being examined.


title: History of life

text: The adaptive function of sex remains a major unresolved issue in biology. The competing models to explain it were reviewed by John A. Birdsell and Christopher Wills. The hypotheses discussed above all depend on the possible beneficial effects of random genetic variation produced by genetic recombination. An alternative view is that sex arose and is maintained as a process for repairing DNA damage, and that the genetic variation produced is an occasionally beneficial byproduct.


title: History of life

text: The simplest definitions of "multicellular," for example "having multiple cells," could include colonial cyanobacteria like "Nostoc". Even a technical definition such as "having the same genome but different types of cell" would still include some genera of the green algae Volvox, which have cells that specialize in reproduction. Multicellularity evolved independently in organisms as diverse as sponges and other animals, fungi, plants, brown algae, cyanobacteria, slime molds and myxobacteria. For the sake of brevity, this article focuses on the organisms that show the greatest specialization of cells and variety of cell types, although this approach to the evolution of biological complexity could be regarded as "rather anthropocentric."


title: History of life

text: The initial advantages of multicellularity may have included: more efficient sharing of nutrients that are digested outside the cell, increased resistance to predators, many of which attacked by engulfing; the ability to resist currents by attaching to a firm surface; the ability to reach upwards to filter-feed or to obtain sunlight for photosynthesis; the ability to create an internal environment that gives protection against the external one; and even the opportunity for a group of cells to behave "intelligently" by sharing information. These features would also have provided opportunities for other organisms to diversify, by creating more varied environments than flat microbial mats could.


title: History of life

text: Multicellularity with differentiated cells is beneficial to the organism as a whole but disadvantageous from the point of view of individual cells, most of which lose the opportunity to reproduce themselves. In an asexual multicellular organism, rogue cells which retain the ability to reproduce may take over and reduce the organism to a mass of undifferentiated cells. Sexual reproduction eliminates such rogue cells from the next generation and therefore appears to be a prerequisite for complex multicellularity.


title: History of life

text: The available evidence indicates that eukaryotes evolved much earlier but remained inconspicuous until a rapid diversification around 1 Ga. The only respect in which eukaryotes clearly surpass bacteria and archaea is their capacity for variety of forms, and sexual reproduction enabled eukaryotes to exploit that advantage by producing organisms with multiple cells that differed in form and function.


title: History of life

text: By comparing the composition of transcription factor families and regulatory network motifs between unicellular organisms and multicellular organisms, scientists found there are many novel transcription factor families and three novel types of regulatory network motifs in multicellular organisms, and novel family transcription factors are preferentially wired into these novel network motifs which are essential for multicullular development. These results propose a plausible mechanism for the contribution of novel-family transcription factors and novel network motifs to the origin of multicellular organisms at transcriptional regulatory level.


title: History of life

text: The Francevillian biota fossils, dated to 2.1 Ga, are the earliest known fossil organisms that are clearly multicellular. They may have had differentiated cells. Another early multicellular fossil, "Qingshania", dated to 1.7 Ga, appears to consist of virtually identical cells. The red algae called "Bangiomorpha", dated at 1.2 Ga, is the earliest known organism that certainly has differentiated, specialized cells, and is also the oldest known sexually reproducing organism. The 1.43 billion-year-old fossils interpreted as fungi appear to have been multicellular with differentiated cells. The "string of beads" organism "Horodyskia", found in rocks dated from 1.5 Ga to 900 Ma, may have been an early metazoan; however, it has also been interpreted as a colonial foraminiferan.


title: History of life

text: Animals are multicellular eukaryotes, and are distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at certain life stages. All animals except sponges have bodies differentiated into separate tissues, including muscles, which move parts of the animal by contracting, and nerve tissue, which transmits and processes signals. In November 2019, researchers reported the discovery of "Caveasphaera", a multicellular organism found in 609-million-year-old rocks, that is not easily defined as an animal or non-animal, which may be related to one of the earliest instances of animal evolution. Fossil studies of "Caveasphaera" have suggested that animal-like embryonic development arose much earlier than the oldest clearly defined animal fossils. and may be consistent with studies suggesting that animal evolution may have begun about 750 million years ago.


title: History of life

text: Nonetheless, the earliest widely accepted animal fossils are the rather modern-looking cnidarians (the group that includes jellyfish, sea anemones and "Hydra"), possibly from around , although fossils from the Doushantuo Formation can only be dated approximately. Their presence implies that the cnidarian and bilaterian lineages had already diverged.


title: History of life

text: The Ediacara biota, which flourished for the last 40 million years before the start of the Cambrian, were the first animals more than a very few centimetres long. Many were flat and had a "quilted" appearance, and seemed so strange that there was a proposal to classify them as a separate kingdom, Vendozoa. Others, however, have been interpreted as early molluscs ("Kimberella"), echinoderms ("Arkarua"), and arthropods ("Spriggina", "Parvancorina"). There is still debate about the classification of these specimens, mainly because the diagnostic features which allow taxonomists to classify more recent organisms, such as similarities to living organisms, are generally absent in the Ediacarans. However, there seems little doubt that "Kimberella" was at least a triploblastic bilaterian animal, in other words, an animal significantly more complex than the cnidarians.


title: History of life

text: The small shelly fauna are a very mixed collection of fossils found between the Late Ediacaran and Middle Cambrian periods. The earliest, "Cloudina", shows signs of successful defense against predation and may indicate the start of an evolutionary arms race. Some tiny Early Cambrian shells almost certainly belonged to molluscs, while the owners of some "armor plates," "Halkieria" and "Microdictyon", were eventually identified when more complete specimens were found in Cambrian lagerstätten that preserved soft-bodied animals.


title: History of life

text: In the 1970s there was already a debate about whether the emergence of the modern phyla was "explosive" or gradual but hidden by the shortage of Precambrian animal fossils. A re-analysis of fossils from the Burgess Shale lagerstätte increased interest in the issue when it revealed animals, such as "Opabinia", which did not fit into any known phylum. At the time these were interpreted as evidence that the modern phyla had evolved very rapidly in the Cambrian explosion and that the Burgess Shale's "weird wonders" showed that the Early Cambrian was a uniquely experimental period of animal evolution. Later discoveries of similar animals and the development of new theoretical approaches led to the conclusion that many of the "weird wonders" were evolutionary "aunts" or "cousins" of modern groups—for example that "Opabinia" was a member of the lobopods, a group which includes the ancestors of the arthropods, and that it may have been closely related to the modern tardigrades. Nevertheless, there is still much debate about whether the Cambrian explosion was really explosive and, if so, how and why it happened and why it appears unique in the history of animals.


title: History of life

text: Most of the animals at the heart of the Cambrian explosion debate are protostomes, one of the two main groups of complex animals. The other major group, the deuterostomes, contains invertebrates such as starfish and sea urchins (echinoderms), as well as chordates (see below). Many echinoderms have hard calcite "shells," which are fairly common from the Early Cambrian small shelly fauna onwards. Other deuterostome groups are soft-bodied, and most of the significant Cambrian deuterostome fossils come from the Chengjiang fauna, a lagerstätte in China. The chordates are another major deuterostome group: animals with a distinct dorsal nerve cord. Chordates include soft-bodied invertebrates such as tunicates as well as vertebrates—animals with a backbone. While tunicate fossils predate the Cambrian explosion, the Chengjiang fossils "Haikouichthys" and "Myllokunmingia" appear to be true vertebrates, and "Haikouichthys" had distinct vertebrae, which may have been slightly mineralized. Vertebrates with jaws, such as the acanthodians, first appeared in the Late Ordovician.


title: History of life

text: Adaptation to life on land is a major challenge: all land organisms need to avoid drying-out and all those above microscopic size must create special structures to withstand gravity; respiration and gas exchange systems have to change; reproductive systems cannot depend on water to carry eggs and sperm towards each other. Although the earliest good evidence of land plants and animals dates back to the Ordovician period (), and a number of microorganism lineages made it onto land much earlier, modern land ecosystems only appeared in the Late Devonian, about . In May 2017, evidence of the earliest known life on land may have been found in 3.48-billion-year-old geyserite and other related mineral deposits (often found around hot springs and geysers) uncovered in the Pilbara Craton of Western Australia. In July 2018, scientists reported that the earliest life on land may have been bacteria living on land 3.22 billion years ago. In May 2019, scientists reported the discovery of a fossilized fungus, named "Ourasphaira giraldae", in the Canadian Arctic, that may have grown on land a billion years ago, well before plants were living on land.


title: History of life

text: Oxygen began to accumulate in Earth's atmosphere over 3 Ga, as a by-product of photosynthesis in cyanobacteria (blue-green algae). However, oxygen produces destructive chemical oxydation which was toxic to most previous organisms. Protective endogenous antioxidant enzymes and exogenous dietary antioxidants helped to prevent oxidative damage. For example, brown algae accumulate inorganic mineral antioxidants such as rubidium, vanadium, zinc, iron, copper, molybdenum, selenium and iodine, concentrated more than 30,000 times more than in seawater. Most marine mineral antioxidants act in the cells as essential trace elements in redox and antioxidant metalloenzymes.


title: History of life

text: When plants and animals began to enter rivers and land about 500 Ma, environmental deficiency of these marine mineral antioxidants was a challenge to the evolution of terrestrial life. Terrestrial plants slowly optimized the production of new endogenous antioxidants such as ascorbic acid, polyphenols, flavonoids, tocopherols, etc.


title: History of life

text: A few of these appeared more recently, in last 200–50 Ma, in fruits and flowers of angiosperm plants. In fact, angiosperms (the dominant type of plant today) and most of their antioxidant pigments evolved during the Late Jurassic period. Plants employ antioxidants to defend their structures against reactive oxygen species produced during photosynthesis. Animals are exposed to the same oxidants, and they have evolved endogenous enzymatic antioxidant systems. Iodine in the form of the iodide ion I- is the most primitive and abundant electron-rich essential element in the diet of marine and terrestrial organisms; it acts as an electron donor and has this ancestral antioxidant function in all iodide-concentrating cells, from primitive marine algae to terrestrial vertebrates.


title: History of life

text: Before the colonization of land there was no soil, a combination of mineral particles and decomposed organic matter. Land surfaces were either bare rock or shifting sand produced by weathering. Water and dissolved nutrients would have drained away very quickly. In the Sub-Cambrian peneplain in Sweden, for example, maximum depth of kaolinitization by Neoproterozoic weathering is about 5 m, while nearby kaolin deposits developed in the Mesozoic are much thicker. It has been argued that in the late Neoproterozoic sheet wash was a dominant process of erosion of surface material due to the lack of plants on land.


title: History of life

text: Films of cyanobacteria, which are not plants but use the same photosynthesis mechanisms, have been found in modern deserts in areas unsuitable for vascular plants. This suggests that microbial mats may have been the first organisms to colonize dry land, possibly in the Precambrian. Mat-forming cyanobacteria could have gradually evolved resistance to desiccation as they spread from the seas to intertidal zones and then to land. Lichens, which are symbiotic combinations of a fungus (almost always an ascomycete) and one or more photosynthesizers (green algae or cyanobacteria), are also important colonizers of lifeless environments, and their ability to break down rocks contributes to soil formation where plants cannot survive. The earliest known ascomycete fossils date from in the Silurian.


title: History of life

text: Soil formation would have been very slow until the appearance of burrowing animals, which mix the mineral and organic components of soil and whose feces are a major source of organic components. Burrows have been found in Ordovician sediments, and are attributed to annelids (worms) or arthropods.


title: History of life

text: In aquatic algae, almost all cells are capable of photosynthesis and are nearly independent. Life on land required plants to become internally more complex and specialized: photosynthesis is most efficient at the top; roots extract water and nutrients from the ground; and the intermediate parts support and transport.


title: History of life

text: Spores of land plants resembling liverworts have been found in Middle Ordovician rocks from . Middle Silurian rocks from contain fossils of true plants, including clubmosses such as "Baragwanathia"; most were under high, and some appear closely related to vascular plants, the group that includes trees.


title: History of life

text: By the Late Devonian , abundant trees such as "Archaeopteris" bound the soil so firmly that they changed river systems from mostly braided to mostly meandering. This caused the "Late Devonian wood crisis" because:


title: History of life

text: Animals had to change their feeding and excretory systems, and most land animals developed internal fertilization of their eggs. The difference in refractive index between water and air required changes in their eyes. On the other hand, in some ways movement and breathing became easier, and the better transmission of high-frequency sounds in air encouraged the development of hearing.


title: History of life

text: The oldest known air-breathing animal is "Pneumodesmus", an archipolypodan millipede from the Middle Silurian, about . Its air-breathing, terrestrial nature is evidenced by the presence of spiracles, the openings to tracheal systems. However, some earlier trace fossils from the Cambrian-Ordovician boundary about are interpreted as the tracks of large amphibious arthropods on coastal sand dunes, and may have been made by euthycarcinoids, which are thought to be evolutionary "aunts" of myriapods. Other trace fossils from the Late Ordovician a little over probably represent land invertebrates, and there is clear evidence of numerous arthropods on coasts and alluvial plains shortly before the Silurian-Devonian boundary, about , including signs that some arthropods ate plants. Arthropods were well pre-adapted to colonise land, because their existing jointed exoskeletons provided protection against desiccation, support against gravity and a means of locomotion that was not dependent on water.


title: History of life

text: The fossil record of other major invertebrate groups on land is poor: none at all for non-parasitic flatworms, nematodes or nemerteans; some parasitic nematodes have been fossilized in amber; annelid worm fossils are known from the Carboniferous, but they may still have been aquatic animals; the earliest fossils of gastropods on land date from the Late Carboniferous, and this group may have had to wait until leaf litter became abundant enough to provide the moist conditions they need.


title: History of life

text: The earliest confirmed fossils of flying insects date from the Late Carboniferous, but it is thought that insects developed the ability to fly in the Early Carboniferous or even Late Devonian. This gave them a wider range of ecological niches for feeding and breeding, and a means of escape from predators and from unfavorable changes in the environment. About 99% of modern insect species fly or are descendants of flying species.


title: History of life

text: Tetrapods, vertebrates with four limbs, evolved from other rhipidistian fish over a relatively short timespan during the Late Devonian (). The early groups are grouped together as Labyrinthodontia. They retained aquatic, fry-like tadpoles, a system still seen in modern amphibians.


title: History of life

text: Iodine and T4/T3 stimulate the amphibian metamorphosis and the evolution of nervous systems transforming the aquatic, vegetarian tadpole into a "more evolved" terrestrial, carnivorous frog with better neurological, visuospatial, olfactory and cognitive abilities for hunting. The new hormonal action of T3 was made possible by the formation of T3-receptors in the cells of vertebrates. Firstly, about 600-500 million years ago, in primitive Chordata appeared the alpha T3-receptors with a metamorphosing action and then, about 250-150 million years ago, in the Birds and Mammalia appeared the beta T3-receptors with metabolic and thermogenetic actions.


title: History of life

text: From the 1950s to the early 1980s it was thought that tetrapods evolved from fish that had already acquired the ability to crawl on land, possibly in order to go from a pool that was drying out to one that was deeper. However, in 1987, nearly complete fossils of "Acanthostega" from about showed that this Late Devonian transitional animal had legs and both lungs and gills, but could never have survived on land: its limbs and its wrist and ankle joints were too weak to bear its weight; its ribs were too short to prevent its lungs from being squeezed flat by its weight; its fish-like tail fin would have been damaged by dragging on the ground. The current hypothesis is that "Acanthostega", which was about long, was a wholly aquatic predator that hunted in shallow water. Its skeleton differed from that of most fish, in ways that enabled it to raise its head to breathe air while its body remained submerged, including: its jaws show modifications that would have enabled it to gulp air; the bones at the back of its skull are locked together, providing strong attachment points for muscles that raised its head; the head is not joined to the shoulder girdle and it has a distinct neck.


title: History of life

text: The Devonian proliferation of land plants may help to explain why air breathing would have been an advantage: leaves falling into streams and rivers would have encouraged the growth of aquatic vegetation; this would have attracted grazing invertebrates and small fish that preyed on them; they would have been attractive prey but the environment was unsuitable for the big marine predatory fish; air-breathing would have been necessary because these waters would have been short of oxygen, since warm water holds less dissolved oxygen than cooler marine water and since the decomposition of vegetation would have used some of the oxygen.


title: History of life

text: Later discoveries revealed earlier transitional forms between "Acanthostega" and completely fish-like animals. Unfortunately, there is then a gap (Romer's gap) of about 30 Ma between the fossils of ancestral tetrapods and Middle Carboniferous fossils of vertebrates that look well-adapted for life on land, during which only some fossils are found, which had five digits in the terminating point of the four limbs, showing true or crown tetrapods appeared in the gap around 350 Ma. Some of the fossils after this gap look as if the animals which they belonged to were early relatives of modern amphibians, all of which need to keep their skins moist and to lay their eggs in water, while others are accepted as early relatives of the amniotes, whose waterproof skin and egg membranes enable them to live and breed far from water. The Carboniferous Rainforest Collapse may have paved the way for amniotes to become dominant over amphibians.


title: History of life

text: Amniotes, whose eggs can survive in dry environments, probably evolved in the Late Carboniferous period (). The earliest fossils of the two surviving amniote groups, synapsids and sauropsids, date from around . The synapsid pelycosaurs and their descendants the therapsids are the most common land vertebrates in the best-known Permian () fossil beds. However, at the time these were all in temperate zones at middle latitudes, and there is evidence that hotter, drier environments nearer the Equator were dominated by sauropsids and amphibians.


title: History of life

text: The Permian–Triassic extinction event wiped out almost all land vertebrates, as well as the great majority of other life. During the slow recovery from this catastrophe, estimated to have taken 30 million years, a previously obscure sauropsid group became the most abundant and diverse terrestrial vertebrates: a few fossils of archosauriformes ("ruling lizard forms") have been found in Late Permian rocks, but, by the Middle Triassic, archosaurs were the dominant land vertebrates. Dinosaurs distinguished themselves from other archosaurs in the Late Triassic, and became the dominant land vertebrates of the Jurassic and Cretaceous periods ().


title: History of life

text: During the Late Jurassic, birds evolved from small, predatory theropod dinosaurs. The first birds inherited teeth and long, bony tails from their dinosaur ancestors, but some had developed horny, toothless beaks by the very Late Jurassic and short pygostyle tails by the Early Cretaceous.


title: History of life

text: While the archosaurs and dinosaurs were becoming more dominant in the Triassic, the mammaliaform successors of the therapsids evolved into small, mainly nocturnal insectivores. This ecological role may have promoted the evolution of mammals, for example nocturnal life may have accelerated the development of endothermy ("warm-bloodedness") and hair or fur. By in the Early Jurassic there were animals that were very like today's mammals in a number of respects. Unfortunately, there is a gap in the fossil record throughout the Middle Jurassic. However, fossil teeth discovered in Madagascar indicate that the split between the lineage leading to monotremes and the one leading to other living mammals had occurred by . After dominating land vertebrate niches for about 150 Ma, the non-avian dinosaurs perished in the Cretaceous–Paleogene extinction event () along with many other groups of organisms. Mammals throughout the time of the dinosaurs had been restricted to a narrow range of taxa, sizes and shapes, but increased rapidly in size and diversity after the extinction, with bats taking to the air within 13 million years, and cetaceans to the sea within 15 million years.


title: History of life

text: The first flowering plants appeared around 130 Ma. The 250,000 to 400,000 species of flowering plants outnumber all other ground plants combined, and are the dominant vegetation in most terrestrial ecosystems. There is fossil evidence that flowering plants diversified rapidly in the Early Cretaceous, from , and that their rise was associated with that of pollinating insects. Among modern flowering plants "Magnolia" are thought to be close to the common ancestor of the group. However, paleontologists have not succeeded in identifying the earliest stages in the evolution of flowering plants.


title: History of life

text: The social insects are remarkable because the great majority of individuals in each colony are sterile. This appears contrary to basic concepts of evolution such as natural selection and the selfish gene. In fact, there are very few eusocial insect species: only 15 out of approximately 2,600 living families of insects contain eusocial species, and it seems that eusociality has evolved independently only 12 times among arthropods, although some eusocial lineages have diversified into several families. Nevertheless, social insects have been spectacularly successful; for example although ants and termites account for only about 2% of known insect species, they form over 50% of the total mass of insects. Their ability to control a territory appears to be the foundation of their success.


title: History of life

text: The sacrifice of breeding opportunities by most individuals has long been explained as a consequence of these species' unusual haplodiploid method of sex determination, which has the paradoxical consequence that two sterile worker daughters of the same queen share more genes with each other than they would with their offspring if they could breed. However, E. O. Wilson and Bert Hölldobler argue that this explanation is faulty: for example, it is based on kin selection, but there is no evidence of nepotism in colonies that have multiple queens. Instead, they write, eusociality evolves only in species that are under strong pressure from predators and competitors, but in environments where it is possible to build "fortresses"; after colonies have established this security, they gain other advantages through co-operative foraging. In support of this explanation they cite the appearance of eusociality in bathyergid mole rats, which are not haplodiploid.


title: History of life

text: The earliest fossils of insects have been found in Early Devonian rocks from about , which preserve only a few varieties of flightless insect. The Mazon Creek lagerstätten from the Late Carboniferous, about , include about 200 species, some gigantic by modern standards, and indicate that insects had occupied their main modern ecological niches as herbivores, detritivores and insectivores. Social termites and ants first appear in the Early Cretaceous, and advanced social bees have been found in Late Cretaceous rocks but did not become abundant until the Middle Cenozoic.


title: History of life

text: The idea that, along with other life forms, modern-day humans evolved from an ancient, common ancestor was proposed by Robert Chambers in 1844 and taken up by Charles Darwin in 1871. Modern humans evolved from a lineage of upright-walking apes that has been traced back over to "Sahelanthropus". The first known stone tools were made about , apparently by "Australopithecus garhi", and were found near animal bones that bear scratches made by these tools. The earliest hominines had chimpanzee-sized brains, but there has been a fourfold increase in the last 3 Ma; a statistical analysis suggests that hominine brain sizes depend almost completely on the date of the fossils, while the species to which they are assigned has only slight influence. There is a long-running debate about whether modern humans evolved all over the world simultaneously from existing advanced hominines or are descendants of a single small population in Africa, which then migrated all over the world less than 200,000 years ago and replaced previous hominine species. There is also debate about whether anatomically modern humans had an intellectual, cultural and technological "Great Leap Forward" under 100,000 years ago and, if so, whether this was due to neurological changes that are not visible in fossils.


title: History of life

text: Life on Earth has suffered occasional mass extinctions at least since . Although they were disasters at the time, mass extinctions have sometimes accelerated the evolution of life on Earth. When dominance of particular ecological niches passes from one group of organisms to another, it is rarely because the new dominant group is "superior" to the old and usually because an extinction event eliminates the old dominant group and makes way for the new one.


title: History of life

text: The fossil record appears to show that the gaps between mass extinctions are becoming longer and the average and background rates of extinction are decreasing. Both of these phenomena could be explained in one or more ways:


title: History of life

text: Biodiversity in the fossil record, which is "...the number of distinct genera alive at any given time; that is, those whose first occurrence predates and whose last occurrence postdates that time" shows a different trend: a fairly swift rise from ; a slight decline from , in which the devastating Permian–Triassic extinction event is an important factor; and a swift rise from to the present.


title: Stalactite

text: "stalassein" ('to drip') is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble and that can be deposited as a colloid, or is in suspension, or is capable of being melted, may form a stalactite. Stalactites may be composed of lava, minerals, mud, peat, pitch, sand, sinter, and amberat (crystallized urine of pack rats). A stalactite is not necessarily a speleothem, though speleothems are the most common form of stalactite because of the abundance of limestone caves.


title: Stalactite

text: The corresponding formation on the floor of the cave is known as a stalagmite. Mnemonics have been developed for which word refers to which type of formation; one is that "stalactite" has a C for "ceiling", and "stalagmite" has a G for "ground". Another example is that "stalactites" "hang on "T"ight" and "stalagmites" ""M"ight grow up" – with emphasis on the ""T"" and ""M"" linked to similar sounding words.


title: Stalactite

text: The most common stalactites are speleothems, which occur in limestone caves. They form through deposition of calcium carbonate and other minerals, which is precipitated from mineralized water solutions. Limestone is the chief form of calcium carbonate rock which is dissolved by water that contains carbon dioxide, forming a calcium bicarbonate solution in caverns. The chemical formula for this reaction is:


title: Stalactite

text: This solution travels through the rock until it reaches an edge and if this is on the roof of a cave it will drip down. When the solution comes into contact with air the chemical reaction that created it is reversed and particles of calcium carbonate are deposited. The reversed reaction is:


title: Stalactite

text: An average growth rate is a year. The quickest growing stalactites are those formed by a constant supply of slow dripping water rich in calcium carbonate (CaCO) and carbon dioxide (CO), which can grow at per year. The drip rate must be slow enough to allow the CO to degas from the solution into the cave atmosphere, resulting in deposition of CaCO on the stalactite. Too fast a drip rate and the solution, still carrying most of the CaCO, falls to the cave floor where degassing occurs and CaCO is deposited as a stalagmite.


title: Stalactite

text: All limestone stalactites begin with a single mineral-laden drop of water. When the drop falls, it deposits the thinnest ring of calcite. Each subsequent drop that forms and falls deposits another calcite ring. Eventually, these rings form a very narrow (≈4 to 5 mm diameter), hollow tube commonly known as a "soda straw" stalactite. Soda straws can grow quite long, but are very fragile. If they become plugged by debris, water begins flowing over the outside, depositing more calcite and creating the more familiar cone-shaped stalactite.


title: Stalactite

text: Stalactite formation generally begins over a large area, with multiple paths for the mineral rich water to flow. As minerals are dissolved in one channel slightly more than other competing channels, the dominant channel begins to draw more and more of the available water, which speeds its growth, ultimately resulting in all other channels being choked off. This is one reason why formations tend to have minimum distances from one another. The larger the formation, the greater the interformation distance.