The simians are the monkeys, cladistically including the apes, the New World monkeys or platyrrhines, and the catarrhine clade consisting of the Old World monkeys and apes. The simian line and the line diverged about 60 million years ago. Forty million years ago, simians from Africa colonized South America, the remaining simians split 25 million years ago into apes and Old World monkeys. Under modern classification, the tarsiers and simians are grouped under the suborder Haplorhini while the strepsirrhines are placed in suborder Strepsirrhini, in anthropoidea, evidences indicate that the Old and the New World primates went through parallel evolution. Primatology, paleoanthropology, and other related fields are split on their usage of the synonymous infraorder names and Anthropoidea. According to Robert Hoffstetter, the term Simiiformes has priority over Anthropoidea because of the taxonomic term Simii by van der Hoeven, from which it is constructed, dates to 1833. In contrast, Anthropoidea by Mivart dates to 1864, while Simiiformes by Haeckel dates to 1866, Hoffstetter argued that Simiiformes is constructed like a proper infraorder name, whereas Anthropoidea ends in -oidea, which is reserved for superfamilies.
He noted that Anthropoidea is too easily confused with anthropoïdes, the simians are split into three distinct groups. The New World monkeys in parvorder Platyrrhini split from the rest of the line about 40 mya. This group split about 25 mya between the Old World monkeys and the apes
Australopithecus is an extinct genus of hominins. During that time, a number of australopithecine species emerged, including Australopithecus afarensis, A. africanus, A. anamensis, A. bahrelghazali, A. deyiremeda, A. garhi, and A. sediba. For some hominid species of time, such as A. robustus and A. boisei. If so, they would be considered robust australopiths, while the others would be gracile australopiths, however, if these species do constitute their own genus, they may be given their own name, Paranthropus. Australopithecus species played a significant part in human evolution, the genus Homo being derived from Australopithecus at some time after three years ago. Among other things, they were the first hominids to show the presence of a gene that causes increased length and ability of neurons in the brain, the duplicated SRGAP2 gene. One of the species eventually became the Homo genus in Africa around two million years ago, and eventually modern humans, H. sapiens sapiens. Gracile australopiths shared several traits with modern apes and humans, and were widespread throughout Eastern and Northern Africa around 3.5 million years ago, the earliest evidence of fundamentally bipedal hominids can be observed at the site of Laetoli in Tanzania.
This site contains hominid footprints that are similar to those of modern humans and have been dated to as old as 3.6 million years. The footprints have generally classified as australopith because that is the only form of prehuman known to have existed in that region at that time. Australopithecus anamensis, A. afarensis, and A. africanus are among the most famous of the extinct hominins, a. africanus was once considered to be ancestral to the genus Homo. However, fossils assigned to the genus Homo have been found that are older than A. africanus, the genus Homo either split off from the genus Australopithecus at an earlier date, or both developed from a yet possibly unknown common ancestor independently. According to the Chimpanzee Genome Project, the human and chimpanzee lineages diverged from a common ancestor about five to six years ago. Sahelanthropus tchadensis, commonly called Toumai, is seven million years old. One theory suggests that the human and chimpanzee lineages diverged somewhat at first, the brains of most species of Australopithecus were roughly 35% of the size of a modern human brain.
Most species of Australopithecus were diminutive and gracile, usually standing 1.2 to 1.4 m tall, in several variations is a considerable degree of sexual dimorphism, males being larger than females. According to one scholar, A. Furthermore, thermoregulatory models suggest that Australopithecus species were fully covered, more like chimpanzees and bonobos. Modern humans do not appear to display the same degree of sexual dimorphism as Australopithecus did, in modern populations, males are on average a mere 15% larger than females, while in Australopithecus, males could be up to 50% larger than females
John Edward Gray
John Edward Gray, FRS was a British zoologist. He was the brother of zoologist George Robert Gray and son of the pharmacologist and botanist Samuel Frederick Gray. Gray was Keeper of Zoology at the British Museum in London from 1840 until Christmas 1874 and he published several catalogues of the museum collections that included comprehensive discussions of animal groups as well as descriptions of new species. He improved the zoological collections to make them amongst the best in the world, Gray was born in Walsall, but his family soon moved to London, where Gray studied medicine. He assisted his father in writing The Natural Arrangement of British Plants, after being blackballed by the Linnean Society he turned his interest from botany to zoology. He began his career by volunteering to collect insects for the British Museum at age 15. He officially joined the Zoological Department in 1824 to help John George Children catalog the reptile collection, in 1840 he took over from Children as Keeper of Zoology, which he continued for 35 years, publishing well over 1000 papers.
He named many species, genera and families. During this period he collaborated with Benjamin Waterhouse Hawkins, the natural history artist. Knowsley Park, near Liverpool, had been founded by Edward Stanley, Gray married Maria Emma Smith in 1826. She helped him with his work, especially with her drawings. In 1833, he was a founder of what became the Royal Entomological Society of London, during his fifty years employed at the British Museum Gray wrote nearly 500 papers, including many descriptions of species new to science. He was active in malacology, the study of molluscs, on his death he was buried at St Marys Church, Lewisham. 1821, On the natural arrangement of Vertebrose Animals,1824, A revision of the family Equidae. 1824, On the natural arrangement of the pulmonobranchous Mollusca, annals of Philosophy, new series 8, 107–109. 1825, A list and description of species of shells not taken notice of by Lamarck. 1825, An outline of an attempt at the disposition of the Mammalia into tribes and families with a list of the genera apparently appertaining to each tribe, narrative of a Survey of the Intertropical and Western Coasts of Australia.
Performed between the years 1818 and 1822, with an Appendix, containing various subjects relating to hydrography and natural history
The Neogene is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the Pliocene, some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary. During this period and birds continued to evolve into modern forms. Early hominids, the ancestors of humans, appeared in Africa near the end of the period, some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the ocean currents from the Pacific to the Atlantic ocean. The global climate cooled considerably over the course of the Neogene, the terms Neogene System and upper Tertiary System describe the rocks deposited during the Neogene Period. The continents in the Neogene were very close to their current positions, the Isthmus of Panama formed, connecting North and South America.
The Indian subcontinent continued to collide with Asia, forming the Himalayas, sea levels fell, creating land bridges between Africa and Eurasia and between Eurasia and North America. The global climate became seasonal and continued an overall drying and cooling trend which began at the start of the Paleogene. The ice caps on both poles began to grow and thicken, and by the end of the period the first of a series of glaciations of the current Ice Age began and continental flora and fauna have a modern appearance. The reptile group Choristodera became extinct in the part of the period. Mammals and birds continued to be the dominant terrestrial vertebrates, the first hominids, the ancestors of humans, appeared in Africa and spread into Eurasia. In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones, grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses and bison. The Neogene traditionally ended at the end of the Pliocene Epoch, just before the definition of the beginning of the Quaternary Period.
However, there was a movement amongst geologists to include ongoing geological time in the Neogene, by dividing the Cenozoic Era into three periods instead of seven epochs, the periods are more closely comparable to the duration of periods in the Mesozoic and Paleozoic eras. The International Commission on Stratigraphy once proposed that the Quaternary be considered a sub-era of the Neogene, with a date of 2.58 Ma. In the 2004 proposal of the ICS, the Neogene would have consisted of the Miocene and Pliocene epochs, thus the Neogene Period ends bounding the succeeding Quaternary Period at 2.58 Mya. Digital Atlas of Neogene Life for the Southeastern United States — by San Jose State University via Web Archive
The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 Mya. It is the last period of the Mesozoic Era, the Cretaceous Period is usually abbreviated K, for its German translation Kreide. The Cretaceous was a period with a warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles and rudists, during this time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous ended with a mass extinction, the Cretaceous–Paleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary, the name Cretaceous was derived from Latin creta, meaning chalk. The Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series, in older literature the Cretaceous is sometimes divided into three series, Neocomian and Senonian.
A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide, in many parts of the world, alternative local subdivisions are still in use. As with other geologic periods, the rock beds of the Cretaceous are well identified. No great extinction or burst of diversity separates the Cretaceous from the Jurassic and this layer has been dated at 66.043 Ma. A140 Ma age for the Jurassic-Cretaceous boundary instead of the usually accepted 145 Ma was proposed in 2014 based on a study of Vaca Muerta Formation in Neuquén Basin. Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a first step toward formally changing the age in the International Union of Geological Sciences, due to the high sea level there was extensive space for such sedimentation. Because of the young age and great thickness of the system. Chalk is a type characteristic for the Cretaceous. It consists of coccoliths, microscopically small calcite skeletons of coccolithophores, the group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea.
Chalk is not easily consolidated and the Chalk Group still consists of sediments in many places. The group has other limestones and arenites, among the fossils it contains are sea urchins, belemnites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous is usually a marine system consisting of competent limestone beds or incompetent marls
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that moves in a bipedal manner is known as a biped /ˈbaɪpɛd/. Types of bipedal movement include walking, running, or hopping, few modern species are habitual bipeds whose normal method of locomotion is two-legged. A larger number of modern species intermittently or briefly use a bipedal gait, several non-archosaurian lizard species move bipedally when running, usually to escape from threats. Many primate and bear species will adopt a bipedal gait in order to reach food or explore their environment, several arboreal primate species, such as gibbons and indriids, exclusively walk on two legs during the brief periods they spend on the ground. Many animals rear up on their hind legs whilst fighting or copulating, some animals commonly stand on their hind legs, in order to reach food, to keep watch, to threaten a competitor or predator, or to pose in courtship, but do not move bipedally.
The word is derived from the Latin words bi two and ped- foot, as contrasted with quadruped four feet and exclusive bipedalism can offer a species several advantages. While upright, non-locomotory limbs become free for other uses, including manipulation, digging, even though bipedalism is slower at first, over long distances, it has allowed humans to outrun most other animals according to the endurance running hypothesis. Bipedality in kangaroo rats has been hypothesized to improve locomotor performance, zoologists often label behaviors, including bipedalism, as facultative or obligate. Even this distinction is not completely clear-cut — for example, humans other than infants normally walk and run in biped fashion, but almost all can crawl on hands and knees when necessary. Even if one ignores exceptions caused by some kind of injury or illness, there are many cases, including the fact that normal humans can crawl on hands. This article therefore avoids the terms facultative and obligate, and focuses on the range of styles of locomotion used by various groups of animals.
There are a number of states of movement commonly associated with bipedalism, in most bipeds this is an active process, requiring constant adjustment of balance. One foot in front of another, with at least one foot on the ground at any time, one foot in front of another, with periods where both feet are off the ground. Moving by a series of jumps with both feet moving together, the great majority of living terrestrial vertebrates are quadrupeds, with bipedalism exhibited by only a handful of living groups. Humans and large birds walk by raising one foot at a time, on the other hand, most macropods, smaller birds and bipedal rodents move by hopping on both legs simultaneously. Tree kangaroos are able to walk or hop, most commonly alternating feet when moving arboreally, there are no known living or fossil bipedal amphibians. Many species of lizards become bipedal during high-speed, sprint locomotion, including the worlds fastest lizard, the first known biped is the bolosaurid Eudibamus whose fossils date from 290 million years ago
Sahelanthropus tchadensis is an extinct homininae species that is dated to about 7 million years ago, during the Miocene epoch, possibly very close to the time of the chimpanzee–human divergence. Few specimens are known, other than the partial skull nicknamed Toumaï, existing fossils include a relatively small cranium named Toumaï, five pieces of jaw, and some teeth, making up a head that has a mixture of derived and primitive features. The braincase, being only 320 cm³ to 380 cm³ in volume, is similar to that of extant chimpanzees and is less than the approximate human volume of 1350 cm³. The teeth, brow ridges, and facial structure differ markedly from those found in Homo sapiens, cranial features show a flatter face, u-shaped dental arcade, small canines, an anterior foramen magnum, and heavy brow ridges. No postcranial remains have been recovered, the only known skull suffered a large amount of distortion during the time of fossilisation and discovery, as the cranium is dorsoventrally flattened, and the right side is depressed.
Sahelanthropus tchadensis may have walked on two legs, upon examination of the foramen magnum in the primary study, the lead author speculated that a bipedal gait would not be unreasonable based on basicranial morphology similar to more recent hominins. Further, according to recent information, what might be a femur of a hominid was discovered near the cranium—but which has not been published nor accounted for. All known material of Sahelanthropus was found between July 2001 and March 2002 at three sites, TM247, TM266, which yielded most of the material, including a cranium and a femur, and TM292. The discoverers claimed that S. tchadensis is the oldest known human ancestor after the split of the line from that of chimpanzees. The bones were found far from most previous hominin fossil finds, however, an Australopithecus bahrelghazali mandible was found in Chad by Mamelbaye Tomalta and Alain Beauvilain, Michel Brunet and Aladji H. E. With the sexual dimorphism known to have existed in early hominins, Sahelanthropus may represent a common ancestor of humans and chimpanzees, though no consensus has been reached yet by the scientific community.
The original placement of species as a human ancestor but not a chimpanzee ancestor would complicate the picture of human phylogeny. Another possibility is that Toumaï is related to humans and chimpanzees, but is the ancestor of neither. Brigitte Senut and Martin Pickford, the discoverers of Orrorin tugenensis, even if this claim is upheld the find would lose none of its significance, because at present, very few chimpanzee or gorilla ancestors have been found anywhere in Africa. Thus if S. tchadensis is a relative of the chimpanzees or gorillas. And S. tchadensis does indicate that the last common ancestor of humans and chimpanzees is unlikely to closely resemble extant chimpanzees, some researchers consider suggestions that Sahelanthropus is too early to be a human ancestor to have evaporated. Sediment isotope analysis of atoms in the fossil yielded an age of about 7 million years. In fact, Toumaï may have been reburied in the recent past, taphonomic analysis reveals the likelihood of one, perhaps two, burial
Several revisions in classifying the great apes have caused the use of the term hominid to vary over time. Its original meaning referred only to humans and their closest non-extant relatives and that restrictive meaning has now been largely assumed by the term hominin, which comprises all members of the human clade after the split from the chimpanzees. The current, 21st-century meaning of hominid includes all the great apes including humans, the most recent common ancestor of all Hominidae lived roughly 14 million years ago, when the ancestors of the orangutans speciated from the ancestral line of the other three genera. Those ancestors of the family Hominidae had already speciated from the family Hylobatidae, in the early Miocene, about 22 million years ago, there were many species of arboreally adapted primitive catarrhines from East Africa, the variety suggests a long history of prior diversification. Fossils at 20 million years ago include fragments attributed to Victoriapithecus, the most recent of these far-flung Miocene apes is Oreopithecus, from the fossil-rich coal beds in northern Italy and dated to 9 million years ago.
Species close to the last common ancestor of gorillas and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Molecular evidence suggests that between 8 and 4 million years ago, first the gorillas, and the split off from the line leading to the humans. Human DNA is approximately 98. 4% identical to that of chimpanzees when comparing single nucleotide polymorphisms, the earliest fossils argued by some to belong to the human lineage are Sahelanthropus tchadensis and Orrorin tugenensis, followed by Ardipithecus, with species Ar. kadabba and Ar. ramidus. The classification of the apes has been revised several times in the last few decades. The original meaning of the referred to only humans and their closest relatives—what is now the modern meaning of the term hominin. And the meaning of the taxon Hominidae changed gradually, leading to a different usage of hominid that today all the great apes including humans. A hominid is a member of the family Hominidae, the apes, gorillas, chimpanzees.
A hominine is a member of the subfamily Homininae, chimpanzees, a hominin is a member of the tribe Hominini and humans. A homininan is a member of the subtribe Hominina of the tribe Hominini, a human is a member of the genus Homo, of which Homo sapiens is the only extant species, and within that Homo sapiens sapiens is the only surviving subspecies. For each clade it is indicated approximately when newer extant clades emerged, some texts will refer to Homonini as the Hominina branch. Many scientists, including paleoanthropologists, continue to use the term hominid to mean humans, as mentioned, Hominidae was originally the name given to the family of humans and their close relatives, with the other great apes all being placed in a separate family, the Pongidae. However, that eventually made Pongidae paraphyletic because at least one great ape species proved to be more closely related to humans than to other great apes. Most taxonomists today encourage monophyletic groups—this would require, in this case, many biologists now assign Pongo to the family Hominidae
Chimpanzees are one of the two species of the genus Pan, the other being the bonobo. Together with gorillas, they are the only exclusively African species of ape that are currently extant. Native to sub-Saharan Africa, both chimpanzees and bonobos are found in the Congo jungle. In addition, P. troglodytes is divided into four subspecies, based on genome sequencing, the two extant Pan species diverged around one million years ago. The most obvious differences are that chimpanzees are somewhat larger, more aggressive and male-dominated, while the bonobos are more gracile and their hair is typically black or brown. Males and females differ in size and appearance, both chimps and bonobos are some of the most social great apes, with social bonds occurring among individuals in large communities. Fruit is the most important component of a diet, they will eat vegetation, honey, insects. They can live over 30 years in both the wild and captivity and bonobos are equally humanitys closest living relatives.
As such, they are among the largest-brained, and most intelligent of primates, they use a variety of sophisticated tools and construct elaborate sleeping nests each night from branches and they have both been extensively studied for their learning abilities. There may even be distinctive cultures within populations, field studies of Pan troglodytes were pioneered by primatologist Jane Goodall. Both Pan species are considered to be endangered as human activities have caused declines in the populations. Threats to wild populations include poaching, habitat destruction. Several conservation and rehabilitation organisations are dedicated to the survival of Pan species in the wild, the first use of the name chimpanze is recorded in The London Magazine in 1738, glossed as meaning mockman in a language of the Angolans. The spelling chimpanzee is found in a 1758 supplement to Chambers Cyclopædia, the colloquialism chimp was most likely coined some time in the late 1870s. The common chimpanzee was named Simia troglodytes by Johann Friedrich Blumenbach in 1776, the species name troglodytes is a reference to the Troglodytae, an African people described by Greco-Roman geographers.
Blumenbach first used it in his De generis humani varietate nativa liber in 1776, the genus name Pan was first introduced by Lorenz Oken in 1816. An alternative Theranthropus was suggested by Brookes 1828 and Chimpansee by Voigt 1831, troglodytes was not available, as it had been given as the name of a genus of wren in 1809. The International Commission on Zoological Nomenclature adopted Pan as the official name of the genus in 1895
Haplorrhini is a clade containing the tarsiers and the simians. The name is spelt Haplorrhini, the simians include catarrhines, and the platyrrhines. The extinct omomyids, which are considered to be the most basal haplorhines, are believed to be closely related to the tarsiers than to other haplorhines. Haplorhines share a number of derived features that distinguish them from the strepsirrhine wet-nosed primates, the haplorhine upper lip, which has replaced the ancestral rhinarium found in strepsirrhines, is not directly connected to their nose or gum, allowing a large range of facial expressions. Their brain-to-body mass ratio is greater than the strepsirrhines. Haplorhines have a plate, unlike the postorbital bar found in strepsirrhines. All anthropoids have a uterus, tarsiers have a bicornate uterus like the strepsirrhines. Most species typically have single births, although twins and triplets are common for marmosets, despite similar gestation periods, haplorhine newborns are relatively much larger than strepsirrhine newborns, but have a longer dependence period on their mother.
This difference in size and dependence is credited to the complexity of their behavior. The taxonomic name Haplorhini derives from the Ancient Greek haploûs and rhinos and it refers to the lack of a rhinarium or wet nose, which is found in many mammals, including strepsirrhine primates. Haplorhini and its sister clade, diverged about 65 million years ago, the fossil Archicebus may be similar to the most recent common ancestor at this time. The other major clade within Haplorhini, the simians, is divided into two parvorders and Catarrhini, the New World monkeys split from catarrhines about 40 mya, while the apes diverged from Old World monkeys about 25 mya. The available fossil evidence indicates both the hominoid and cercopithecoid clades originated in Africa. The following is the listing of the living families, and their placement in the Order Primates, ORDER PRIMATES Suborder Strepsirrhini, lorises
A primate is a mammal of the order Primates. In taxonomy, primates include two distinct lineages and haplorhines, Primates arose from ancestors that lived in the trees of tropical forests, many primate characteristics represent adaptations to life in this challenging three-dimensional environment. Most primate species remain at least partly arboreal, with the exception of humans, who inhabit every continent except for Antarctica, most primates live in tropical or subtropical regions of the Americas and Asia. Based on fossil evidence, the earliest known true primates, represented by the genus Teilhardina, an early close primate relative known from abundant remains is the Late Paleocene Plesiadapis, c. Molecular clock studies suggest that the branch may be even older. The order Primates was traditionally divided into two groupings and anthropoids. Prosimians have characteristics more like those of the earliest primates, and include the lemurs of Madagascar, simians include monkeys and hominins.
Simians are divided into two groups, catarrhine monkeys and apes of Africa and Southeast Asia and platyrrhine or New World monkeys of South, catarrhines consist of Old World monkeys and great apes, New World monkeys include the capuchin and squirrel monkeys. Humans are the only extant catarrhines to have spread successfully outside of Africa, South Asia, New primate species are still being discovered. More than 25 species were described in the decade of the 2000s. Considered generalist mammals, primates exhibit a range of characteristics. Some primates are primarily terrestrial rather than arboreal, but all species possess adaptations for climbing trees, locomotion techniques used include leaping from tree to tree, walking on two or four limbs, knuckle-walking, and swinging between branches of trees. Primates are characterized by large brains relative to other mammals, as well as a reliance on stereoscopic vision at the expense of smell. These features are developed in monkeys and apes and noticeably less so in lorises.
Three-color vision has developed in some primates, most have opposable thumbs and some have prehensile tails. Many species are dimorphic, differences include body mass, canine tooth size. Primates have slower rates of development than other similarly sized mammals and reach maturity later, depending on the species, adults may live in solitude, in mated pairs, or in groups of up to hundreds of members. The relationships among the different groups of primates were not clearly understood until relatively recently, for example, ape has been used either as an alternative for monkey or for any tailless, relatively human-like primate
The Precambrian is the earliest period of Earths history, set before the current Phanerozoic Eon. The Precambrian is a supereon that is subdivided into three eons of the time scale. It spans from the formation of Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 541 million years ago, the Precambrian accounts for 89% of geologic time. Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earths history, the Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and fossils from that time are of limited biostratigraphic use. This is because many Precambrian rocks have been metamorphosed, obscuring their origins, while others have been destroyed by erosion. A stable crust was apparently in place by 4,412 Ma, the term Precambrian is recognized by the International Commission on Stratigraphy as a general term including the Archean and Proterozoic eons. It is still used by geologists and paleontologists for general discussions not requiring the more specific eon names and it was briefly called the Cryptozoic eon.
A specific date for the origin of life has not been determined, carbon found in 3.8 billion year old rocks from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have found in Western Australia. Probable fossils 100 million years older have been found in the same area, there is a fairly solid record of bacterial life throughout the remainder of the Precambrian. The oldest fossil evidence from that era of such complex life comes from the Lantian formation of the Ediacarian period, a very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran or Vendian biota, hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic era. By the middle of the following Cambrian period, a diverse fauna is recorded in the Burgess Shale. The explosion in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life, while land seems to have been devoid of plants and animals and other microbes formed prokaryotic mats that covered terrestrial areas.
Evidence of the details of plate motions and other activity in the Precambrian has been poorly preserved. It is generally believed that small proto-continents existed prior to 4280 Ma, the supercontinent, known as Rodinia, broke up around 750 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, one of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a Snowball Earth. The atmosphere of the early Earth is not well understood, most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, and was lacking in free oxygen