This article needs additional citations for verification.(May 2022) The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth. Dates in this article are consensus estimates based on scientific evidence, mainly fossils.
In biology, evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organization, from kingdoms to species, and individual organisms and molecules, such as DNA and proteins. The similarities between all present day organisms imply a common ancestor from which all known species, living and extinct, have diverged. More than 99 percent of all species that ever lived (over five billion)[1] are estimated to be extinct.[2][3] Estimates on the number of Earth's current species range from 10 million to 14 million,[4] with about 1.2 million or 14% documented, the rest not yet described.[5] However, a 2016 report estimates an additional 1 trillion microbial species, with only 0.001% described.[6] There has been controversy between more traditional views of steadily increasing biodiversity, and a newer view of cycles of annihilation and diversification, so that certain past times, such as the Cambrian explosion, experienced maximums of diversity followed by sharp winnowing.[7][8] Species go extinct constantly as environments change, as organisms compete for environmental niches, and as genetic mutation leads to the rise of new species from older ones. At long irregular intervals, Earth's biosphere suffers a catastrophic die-off, a mass extinction,[9] often comprising an accumulation of smaller extinction events over a relatively brief period.[10] The first known mass extinction was the Great Oxidation Event 2.4 billion years ago, which killed most of the planet's obligate anaerobes. Researchers have identified five other major extinction events in Earth's history, with estimated losses below:[11]
Smaller extinction events have occurred in the periods between, with some dividing geologic time periods and epochs. The Holocene extinction event is currently under way.[12] Factors in mass extinctions include continental drift, changes in atmospheric and marine chemistry, volcanism and other aspects of mountain formation, changes in glaciation, changes in sea level, and impact events.[10] In this timeline, Ma (for megaannum) means "million years ago," ka (for kiloannum) means "thousand years ago," and ya means "years ago." Hadean EonMoon 4600 Ma – 4000 Ma
Archean EonFragment of the Acasta Gneiss exhibited at the Museum of Natural History in Vienna The cyanobacterial-algal mat, salty lake on the White Sea seaside Halobacterium sp. strain NRC-1 4000 Ma – 2500 Ma
Proterozoic EonDetail of the eukaryote endomembrane system and its components Dinoflagellate Ceratium furca Blepharisma japonicum, a free-living ciliated protozoan Dickinsonia costata, an iconic Ediacaran organism, displays the characteristic quilted appearance of Ediacaran enigmata. 2500 Ma – 539 Ma. Contains the Palaeoproterozoic, Mesoproterozoic and Neoproterozoic eras.
Phanerozoic EonEmergence of animals and plants 539 Ma – present The Phanerozoic Eon (Greek: period of well-displayed life) marks the appearance in the fossil record of abundant, shell-forming and/or trace-making organisms. It is subdivided into three eras, the Paleozoic, Mesozoic and Cenozoic, with major mass extinctions at division points. Palaeozoic Era538.8 Ma – 251.9 Ma and contains the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian periods. With only a handful of species surviving today, the Nautiloids flourished during the early Paleozoic era, from the Late Cambrian, where they constituted the main predatory animals.[60] Haikouichthys, a jawless fish, is popularized as one of the earliest fishes and probably a basal chordate or a basal craniate.[61] Ferns first appear in the fossil record about 360 million years ago in the late Devonian period.[62]
Mesozoic Era
Plateosaurus engelhardti Cycas circinalis From 251.9 Ma to 66 Ma and containing the Triassic, Jurassic and Cretaceous periods.
Cenozoic Era66 Ma – present Mount of oxyaenid Patriofelis from the American Museum of Natural History The bat Icaronycteris appeared 52.2 million years ago Grass flowers
Historical extinctionsCaribbean monk seal Illustration of a Baiji, declared functionally extinct by the Baiji.org Foundation in 2006.[80][81] Western black rhinoceros, holotype specimen of a female shot in 1911 Thylacine shot in 1936
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