The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, its base, are somewhat in flux; the period was established by Adam Sedgwick, who named it after Cambria, the Latin name of Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells; as a result, our understanding of the Cambrian biology surpasses that of some periods. The Cambrian marked a profound change in life on Earth. Complex, multicellular organisms became more common in the millions of years preceding the Cambrian, but it was not until this period that mineralized—hence fossilized—organisms became common; the rapid diversification of life forms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla.
Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates. Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren—with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm. Most of the continents were dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia; the seas were warm, polar ice was absent for much of the period. Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified; the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is difficult since the occurrence of similar trace fossils belonging to the Treptichnids group are found well below the T. pedum in Namibia and Newfoundland, in the western USA.
The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, in Spain. The Cambrian Period was followed by the Ordovician Period; the Cambrian is divided into ten ages. Only three series and six stages are named and have a GSSP; because the international stratigraphic subdivision is not yet complete, many local subdivisions are still used. In some of these subdivisions the Cambrian is divided into three series with locally differing names – the Early Cambrian, Middle Cambrian and Furongian. Rocks of these epochs are referred to as belonging to Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian; each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance: *Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.
The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago and ending at 485.4 million years ago. The lower boundary of the Cambrian was held to represent the first appearance of complex life, represented by trilobites; the recognition of small shelly fossils before the first trilobites, Ediacara biota earlier, led to calls for a more defined base to the Cambrian period. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian period, to be correlated worldwide by the earliest appearance of Treptichnus pedum. Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, it is the T. pedum ichnofossil assemblage, now formally used to correlate the base of the Cambrian. This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate.
A more precise date using modern radiometric dating yield a date of 541 ± 0.3 million years ago. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, to the disappearance of distinctive Ediacaran fossils. There are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata — which w
The Alpine ibex known as the steinbock, bouquetin, or ibex, is a species of wild goat that lives in the mountains of the European Alps. It is a sexually dimorphic species with larger males; the coat colour is brownish grey. Alpine ibex tend to live in rough terrain near the snow line, they are social, although adult males and females segregate for most of the year, coming together only to mate. Four distinct groups exist. During the breeding season, males fight for access to females and use their long horns in agonistic behaviours. After being extirpated from most areas by the 19th century, the Alpine ibex was reintroduced to parts of its historical range. All individuals living today descend from the stock in Gran Paradiso National Park in Aosta Valley; this national park was created to help the ibex to thrive. The ibex is the emblem of both the Vanoise National Park; the species is listed as of least concern by the IUCN, but went through a population bottleneck of less than 100 individuals. This has led to low genetic diversity across populations.
The Alpine ibex was first described by Carl Linnaeus in 1758. It is classified in the genus Capra with at least seven other species of wild goat. Both Capra and Ovis descended from a goral-like animal from the Miocene and early Pliocene, whose fossils are found in Kenya and Slovenia; the genus Tossunnoria appears in China during the late Miocene and appears to have been intermediate between gorals and goats. Fossils of Alpine ibex date back to the late Pleistocene, when it and the Spanish ibex evolved from the extinct Pleistocene species Capra camburgensis; the Nubian and Siberian ibex were considered to be subspecies of the Alpine ibex, giving populations in the Alps the trinomial of C. i. ibex. Compared with other members of its genus, the Alpine ibex has a duller coat, it has brownish grey hair over most of the body, a pale abdomen and darker markings on the chin and throat and in a stripe along the back. They moult twice a year, firstly in April or May, again in September, when they replace the short summer coat with thicker hair and a woolly undercoat.
Males grow to a height of 90 to 101 centimetres at the withers, with a body length of 149 to 171 centimetres and weigh from 67 to 117 kilograms. Females are noticeably smaller, with a shoulder height of 73 to 84 centimetres, a body length of 121 to 141 centimetres, a weight of 17 to 32 kilograms. Both male and female Alpine ibexes have large, backwards-curving, horns with numerous ridges along their length. At 69 to 98 centimetres, those of the males are larger than those of females, which reach only 18 to 35 centimetres in length; the Alpine ibex was, at one point, restricted only to the Gran Paradiso National Park in northern Italy, in the Maurienne Valley in the French Alps but i it was both reintroduced to most of the European Alps. Reintroductions started in 1906 into Switzerland. Alpine ibex are now found in most or all the Italian and French alpine ranges, southern Germany and Austria, it was introduced to Bulgaria and Slovenia. An excellent climber, its preferred habitat is the rocky region along the snow line above alpine forests, where it occupies steep, rough terrain at elevations of 1,800 to 3,300 metres.
Alpine ibex are absent from woodland areas although adult males in densely populated areas may stay in larch and mixed larch-spruce woodland if there is no snow. Males spend the winter in coniferous forests. For most of the year and females occupy different habitat. Females rely on steep terrain more so than males. Males use lowland meadows during the spring, when snow melts and green grass appears, they climb to alpine meadows during the summer. When winter arrives, both sexes move to steep rocky slopes, they prefer slopes of 30 -- use small caves and overhangs for shelter. Home ranges are variable, depending on the availability of resources, vary in size throughout the year. Figures of anything from 180 to 2,800 hectares have been recorded. Home ranges tend to be largest during summer and autumn, smallest in winter and intermediate in spring. Female home ranges are smaller than those of males. Alpine ibexes appear to have a low rate of predation and in Gran Paradiso die of age, starvation or disease.
Alpine ibexes are herbivorous, with over half of their diet consisting of grasses, the remainder being a mixture of moss, flowers and twigs. If leaves and shoots are out of reach, they stand on their rear legs to reach this food. Grass genera that are the most eaten are Agrostis, Calamagrostis, Phleum, Poa and Trisetum; the climbing ability of the Alpine ibex is such that it has been observed standing on the sheer face of a dam, where it licks the stonework to obtain mineral salts. Although the Alpine ibex is a social species, they segregate sexually and spatially depending on the season. Four types of groups exist. Adult male groups, female-offspring groups, groups of young individuals 2–3 years old, mixed sex groups. Young groups are numerous at the beginning of summer but are expelled by females at the end of their gestation period. Female and offspring groups occur year-round, at least in an area of the French Alps. Mixed sex gro
The Nubian ibex is a desert-dwelling goat species found in mountainous areas of Algeria, Ethiopia, Israel, Lebanon, Saudi Arabia and Yemen. It is considered to be a subspecies of the Alpine ibex, but is considered a distinct species; the wild population is estimated at 1,200 individuals. Nubian ibexes stand around 65 -- weigh around 50 kilograms. Nubian ibexes are a light tan color, with a white underbelly. Nubian ibexes have long thin horns which extend up and backwards and down. In males these reach around a metre in length. Nubian ibexes live in rough dry mountainous terrain where they eat grasses and leaves and are preyed upon by leopards, common foxes and bearded vultures. Nubian ibexes are social and herds tend to consist of females and males up to the age of about three years; the males form more transitory bands of up to eight individuals. During the breeding season males join the female-based herds for the six to eight week rut. Large males do battle with much clashing of horns. Nubian ibexes are diurnal, meaning they are active during the rest during the night.
On 16 March 1959, the British established the Yob Wildlife Reserve in northern Eritrea to protect significant populations of Nubian ibex in the area. The International Union for Conservation of Nature has classified the Nubian ibex as "vulnerable"; this is on the basis that there are fewer than 10,000 mature individuals and the population is declining. Threats faced by the animal include competition with livestock for water and fodder, hunting pressure and habitat destruction; the Biblical heroine Yael's name means "Ibex" in Hebrew. The Nubian ibex in particular was in the BBC documentary Life, featured prominently in the popular television documentary series Planet Earth
The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago, to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, where rocks from this period were first studied; the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established. Fish reached substantial diversity during this time, leading the Devonian to be dubbed the "Age of Fishes." The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating every known aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral and pelvic fins evolved into legs.
In the oceans, primitive sharks became more numerous than in the Late Ordovician. The first ammonites, species of molluscs, appeared. Trilobites, the mollusc-like brachiopods and the great coral reefs, were still common; the Late Devonian extinction which started about 375 million years ago affected marine life, killing off all placodermi, all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, the early formation of the small continent of Euramerica in between; the period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough.
Murchison and Sedgwick named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya. In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian and Farlovian stages, the latter three of which are placed in the Devonian; the Devonian has erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed during its epochs and between geographic regions.
For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, North America, China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common; the Devonian Period is formally broken into Early and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower and Upper parts of the Devonian System. Early DevonianThe Early Devonian lasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, was followed by the Emsian, which lasted until the Middle Devonian began, 393.3± 2.7 million years ago. During this time, the first ammonoids appeared. Ammonoids during this time period differed little from their nautiloid counterparts; these ammonoids belong to the order Agoniatitida, which in epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida.
This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic era. Middle DevonianThe Middle Devonian comprised two subdivisions: first the Eifelian, which gave way to the Givetian 387.7± 2.7 million years ago. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments due to drastic environmental changes and due to the increasing competition and diversity of jawed fishes; the shallow, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, the ability to crawl out of the water and onto the land for short periods of time. Late DevonianFinally, the Late Devonian started with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivisi
The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 million years ago, to the beginning of the Permian Period, 298.9 Mya. The name Carboniferous means "coal-bearing" and derives from the Latin words carbō and ferō, was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the modern'system' names to be employed, reflects the fact that many coal beds were formed globally during that time; the Carboniferous is treated in North America as two geological periods, the earlier Mississippian and the Pennsylvanian. Terrestrial animal life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would evolve into amniotes, the first terrestrial vertebrates. Arthropods were very common, many were much larger than those of today. Vast swaths of forest covered the land, which would be laid down and become the coal beds characteristic of the Carboniferous stratigraphy evident today.
The atmospheric content of oxygen reached its highest levels in geological history during the period, 35% compared with 21% today, allowing terrestrial invertebrates to evolve to great size. The half of the period experienced glaciations, low sea level, mountain building as the continents collided to form Pangaea. A minor marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred at the end of the period, caused by climate change. In the United States the Carboniferous is broken into Mississippian and Pennsylvanian subperiods; the Mississippian is about twice as long as the Pennsylvanian, but due to the large thickness of coal-bearing deposits with Pennsylvanian ages in Europe and North America, the two subperiods were long thought to have been more or less equal in duration. In Europe the Lower Carboniferous sub-system is known as the Dinantian, comprising the Tournaisian and Visean Series, dated at 362.5-332.9 Ma, the Upper Carboniferous sub-system is known as the Silesian, comprising the Namurian and Stephanian Series, dated at 332.9-298.9 Ma.
The Silesian is contemporaneous with the late Mississippian Serpukhovian plus the Pennsylvanian. In Britain the Dinantian is traditionally known as the Carboniferous Limestone, the Namurian as the Millstone Grit, the Westphalian as the Coal Measures and Pennant Sandstone; the International Commission on Stratigraphy faunal stages from youngest to oldest, together with some of their regional subdivisions, are: A global drop in sea level at the end of the Devonian reversed early in the Carboniferous. There was a drop in south polar temperatures; these conditions had little effect in the deep tropics, where lush swamps to become coal, flourished to within 30 degrees of the northernmost glaciers. Mid-Carboniferous, a drop in sea level precipitated a major marine extinction, one that hit crinoids and ammonites hard; this sea level drop and the associated unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod. This happened about 323 million years ago, at the onset of the Permo-Carboniferous Glaciation.
The Carboniferous was a time of active mountain-building as the supercontinent Pangaea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America–Europe along the present line of eastern North America; this continental collision resulted in the Hercynian orogeny in Europe, the Alleghenian orogeny in North America. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural Mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China, South China continents were still separated from Laurasia; the Late Carboniferous Pangaea was shaped like an "O." There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and closed - Rheic Ocean, the small, shallow Ural Ocean and Proto-Tethys Ocean. Average global temperatures in the Early Carboniferous Period were high: 20 °C.
However, cooling during the Middle Carboniferous reduced average global temperatures to about 12 °C. Lack of growth rings of fossilized trees suggest a lack of seasons of a tropical climate. Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are referred to as Permo-Carboniferous in age; the cooling and drying of the climate led to the Carboniferous Rainforest Collapse during the late Carboniferous. Tropical rainforests fragmented and were devastated by climate change. Carboniferous rocks in Europe and eastern North America consist of a repeated sequence of limestone, sandstone and coal beds. In North America, the early Carboniferous is marine
Berlin Zoological Garden
The Berlin Zoological Garden is the oldest and best-known zoo in Germany. Opened in 1844 it is located in Berlin's Tiergarten. With about 1,380 different species and over 20,200 animals the zoo presents one of the most comprehensive collection of species in the world; the zoo and its aquarium had more than 3.5 million visitors in 2017. It is one of the most popular worldwide. Regular animal feedings are among its most famous attractions. Globally known animals like Knut, the polar bear, Bao Bao, the giant panda have contributed to the zoo's public image; the zoo collaborates with many universities, research institutes, other zoos around the world. It maintains and promotes European breeding programmes, helps safeguard several endangered species, participates in several species reintroduction programs. Opened on 1 August 1844, the Zoologischer Garten Berlin was the first zoo in Germany; the aquarium opened in 1913. The first animals were donated by Frederick William IV, King of Prussia, from the menagerie and pheasantry of the Tiergarten.
The nearby U-Bahn station was opened the same year. In 1938, the Berlin Zoo got rid of Jewish board members and forced Jewish shareholders to sell their stocks at a loss, before re-selling the stocks in an effort to "Aryanize" the institution; the zoo has now commissioned a historian to identify these past shareholders and track down their descendants, according to a report by AFP. Zoo director Lutz Heck was named chief of the Oberste Naturschütz Behörde im Reichsforstamt by his friend Hermann Göring in the summer of 1938 and in this capacity he was the senior responsible person for the entire nature management. During World War II, the zoo area was hit by Allied bombs for the first time on 8 September 1941. Most damage was done during the bombardments on 22 and 23 November 1943. In less than 15 minutes, 30% of the zoo population was killed on the first day. On the second day the aquarium building was destroyed by a direct hit. Of the eight elephants only one survived, the bull Siam. 2-year-old hippo bull Knautschke was saved from the fire in his animal house.
Most damage was done during the Battle of Berlin. From 22 April 1945 onwards, the zoo was under constant artillery fire of the Red Army. Heavy fighting took place on the zoo area till 30 April; because of safety measures, some predators and other dangerous animals were killed by the zoo keepers. By the end of the war, the zoo was fortified with the Zoo Tower, a huge flak tower, one of the last remaining areas of Nazi German resistance against the Red Army, with its bunkers and anti-aircraft weapons defending against Allied air forces. At the entrance of the zoo, there was a small underground shelter for zoo keepers. During the battle, wounded German soldiers were taken care for here by female personnel and the wives of zookeepers. On 30 April, the zoo flak bunker surrendered. A count on May 31, 1945, revealed only 91 of 3,715 animals had survived, including two lion cubs, two hyenas, Asian bull elephant Siam, hippo bull Knautschke, ten hamadryas baboons, a chimpanzee, a black stork. After the battle, some animals were eaten by Red Army soldiers.
Following the zoo's destruction, it and the associated aquarium was reconstructed on modern principles so as to display the animals in as close to their natural environment as feasible. The success in breeding animals, including some rare species, demonstrates the efficacy of these new methods; the zoo came to be located in West Berlin, hence a second zoo – Tierpark Berlin – was built in the East. The Berlin Zoo is the most visited zoo in Europe, with more than 3.3 million visitors per year from all over the world. It is open all year long and can be reached by public transportation; the Berlin Zoologischer Garten railway station is one of Berlin's most important stations. Several modes of transport such as U-Bahn, S-Bahn and buses are interlinked here. Visitors can either enter the zoo through the exotically designed Elephant Gate beside the aquarium on Budapester Straße or through the Lion Gate on Hardenbergplatz; the zoo gaurs. The populations of rare deer and pigs are part of several captive breeding projects.
Berlin Zoo supports conservationists in other countries and as a partner of the Stiftung Artenschutz, a species protection foundation. Most of the animals are housed in enclosures designed to recreate their natural habitat; the zoo houses four types of great ape: orangutans, gorillas and bonobos. The carnivore house displays all big cats and many rare small predators, such as ring-tailed mongooses and narrow-striped mongooses from Madagascar. In the basement, visitors are invited to a view into the world of nocturnal animals; the bird house presents a walk-through aviary and offers a broad variety of forms, including several breeding species of hornbills and many parrots. Numerous big aviaries show waders and many other species; the Berlin Zoo is one of the few zoos to exhibit Luzon tarictic hornbills. The aquarium was built in 1913 as part of the Zoologischer Garten complex. In addition to fish and other aquatic life, it is home to most of the zoo's reptiles and invertebrates. Polar bear Knut was born in captivity at the zoo on 5 December 2006.
He and his twin brother or sister were directly rejected by their mother at day of birth. He was subsequently raised by zookeeper Thomas Dörflein and became the center of a mass media phenomenon that spanned the globe spawning numerous toys, media specials, DVDs, a
The Precambrian is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic eon, named after Cambria, the Latinised name for Wales, where rocks from this age were first studied; the Precambrian accounts for 88% of the Earth's geologic time. The Precambrian is an informal unit of geologic time, subdivided into three eons of the geologic 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, when hard-shelled creatures first appeared in abundance. Little is known about the Precambrian, despite it making up seven-eighths of the Earth's history, what is known has been discovered from the 1960s onwards; the Precambrian fossil record is poorer than that of the succeeding Phanerozoic, fossils from the Precambrian are of limited biostratigraphic use. This is because many Precambrian rocks have been metamorphosed, obscuring their origins, while others have been destroyed by erosion, or remain buried beneath Phanerozoic strata.
It is thought that the Earth coalesced from material in orbit around the Sun at 4,543 Ma, may have been struck by a large planetesimal shortly after it formed, splitting off material that formed the Moon. A stable crust was in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma; the term "Precambrian" is recognized by the International Commission on Stratigraphy as the only "supereon" in geologic time. "Precambrian" is still used by geologists and paleontologists for general discussions not requiring the more specific eon names. As of 2010, the United States Geological Survey considers the term informal, lacking a stratigraphic rank. 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 been found in Western Australia. Probable fossils 100 million years older have been found in the same area.
However, there is evidence. There is a solid record of bacterial life throughout the remainder of the Precambrian. Excluding a few contested reports of much older forms from North America and India, the first complex multicellular life forms seem to have appeared at 1500 Ma, in the Mesoproterozoic era of the Proterozoic eon. Fossil evidence from the Ediacaran period of such complex life comes from the Lantian formation, at least 580 million years ago. A 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 Vendian biota. Hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic eon. By the middle of the following Cambrian period, a diverse fauna is recorded in the Burgess Shale, including some which may represent stem groups of modern taxa; the increase 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.
Tracks from an animal with leg like appendages have been found in what was mud 551 million years ago. Evidence of the details of plate motions and other tectonic activity in the Precambrian has been poorly preserved, it is believed that small proto-continents existed prior to 4280 Ma, that most of the Earth's landmasses collected into a single supercontinent around 1130 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 2400–2100 Ma. 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 of nitrogen, carbon dioxide, other inert gases, was lacking in free oxygen. There is, evidence that an oxygen-rich atmosphere existed since the early Archean. At present, it is still believed that molecular oxygen was not a significant fraction of Earth's atmosphere until after photosynthetic life forms evolved and began to produce it in large quantities as a byproduct of their metabolism.
This radical shift from a chemically inert to an oxidizing atmosphere caused an ecological crisis, sometimes called the oxygen catastrophe. At first, oxygen would have combined with other elements in Earth's crust iron, removing it from the atmosphere. After the supply of oxidizable surfaces ran out, oxygen would have begun to accumulate in the atmosphere, the modern high-oxygen atmosphere would have developed. Evidence for this lies in older rocks that contain massive banded iron formations that were laid down as iron oxides. A terminology has evolved covering the early years of the Earth's existence, as radiometric dating has allowed real dates to be assigned to specific formations and features; the Precambrian is divided into