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The timeline of life represents the current scientific theory outlining the major events during the development of life on Earth. Dates in this article are consensus estimates based on scientific evidence, mainly .
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 and , such as DNA and . The similarities between all present day organisms imply a common descent from which all known species, living and Extinction, have diverged. More than 99 percent of all species that ever lived (over five billion) are estimated to be Extinction event. Estimates on the number of Earth's current species range from 10 million to 14 million, with about 1.2 million or 14% documented, the rest not yet described. However, a 2016 report estimates an additional 1 trillion microbial species, with only 0.001% described.
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. Four diagrams of evolutionary models
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:
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.
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 .
| 4540 Ma | Planet Earth forms from the accretion disc revolving around the young Sun, perhaps preceded by formation of necessary for life in the surrounding protoplanetary disk of cosmic dust. |
| 4510 Ma | According to the giant-impact hypothesis, the Moon originated when Earth and the hypothesized planet Theia collided, sending into orbit myriad moonlets which eventually coalesced into our single Moon. The Moon's gravitational pull Tidal locking Earth's fluctuating axis of rotation, setting up regular climatic conditions favoring abiogenesis. |
| 4404 Ma | Evidence of the first liquid water on Earth which were found in the oldest known zircon crystals. |
| 4280–3770 Ma | Earliest possible appearance of life on Earth.
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| 4100 Ma | Earliest possible preservation of biogenic carbon. |
| 4100–3800 Ma | Late Heavy Bombardment (LHB): extended barrage by meteoroids impact event the inner planets. Thermal flux from widespread hydrothermal activity during the LHB may have aided abiogenesis and life's early diversification. Possible remains of Biotic material were found in 4.1 billion-year-old rocks in Western Australia. |
| 4000 Ma | Formation of a greenstone belt of the Acasta Gneiss of the Slave craton in northwest Canada - the oldest known rock belt. |
| 3900–2500 Ma | Cells resembling appear. These first organisms are believed to have been chemotroph, using carbon dioxide as a carbon source and redox inorganic materials to extract energy. |
| 3800 Ma | Formation of a greenstone belt of the Isua complex in western Greenland, whose isotope frequencies suggest the presence of life. The earliest evidence for life on Earth includes: 3.8 billion-year-old biogenic hematite in a banded iron formation of the Nuvvuagittuq Greenstone Belt in Canada; graphite in 3.7 billion-year-old Metasediment in western Greenland; and microbial mat in 3.48 billion-year-old sandstone in Western Australia. |
| 3800–3500 Ma | Last universal common ancestor (LUCA): split between bacteria and archaea.
Bacteria develop primitive photosynthesis, which at first did not produce oxygen. These organisms exploit a proton gradient to generate adenosine triphosphate (ATP), a mechanism used by virtually all subsequent organisms. |
| 3000 Ma | Photosynthesizing cyanobacteria using water as a reducing agent and producing oxygen as a waste product. Free oxygen initially oxidizes dissolved iron in the oceans, creating iron ore. Oxygen concentration in the atmosphere slowly rises, many bacteria and eventually triggering the Great Oxygenation Event. |
| 2800 Ma | Oldest evidence for microbial life on land in the form of organic matter-rich , Vernal pool and Alluvium sequences, some bearing microfossils. |
| 2500 Ma | Great Oxidation Event led by cyanobacteria's oxygenic photosynthesis. Commencement of plate tectonics with old marine crust dense enough to subduction. |
| 2400 Ma | Possible land Fungus evidence from molecules. |
| 2023 Ma | Formation of the Vredefort impact structure, one of the largest and oldest verified impact structures on Earth. The crater is estimated to have been between across when it first formed. |
| By 1850 Ma | Eukaryote cells, containing membrane-bound with diverse functions, probably derived from prokaryotes engulfing each other via phagocytosis. (See Symbiogenesis and Endosymbiont). Bacterial viruses () emerge before or soon after the divergence of the prokaryotic and eukaryotic lineages. Red beds show an oxidising atmosphere, favouring the spread of eukaryotic life. |
| 1500 Ma | Volyn biota, a collection of exceptionally well-preserved with varying morphologies. |
| 1300 Ma | Earliest land Fungus. |
| By 1200 Ma | Meiosis and Sex in single-celled eukaryotes, possibly even in the common ancestor of all eukaryotes or in the RNA world. Sexual reproduction may have increased the rate of evolution. |
| By 1000 Ma | First non-marine eukaryotes move onto land. They were photosynthetic and multicellular, indicating that plants evolved much earlier than originally thought. |
| Beginning of animal evolution. | |
| 720–630 Ma | Possible Snowball Earth which increased the atmospheric oxygen and decreased carbon dioxide, and was either caused by land plant evolution or resulted in it. Opinion is divided on whether it increased or decreased biodiversity or the rate of evolution. |
| 600 Ma | Accumulation of atmospheric oxygen allows the formation of an ozone layer. Previous land-based life would probably have required other chemicals to attenuate ultraviolet radiation. |
| 580–542 Ma | Ediacaran biota, the first large, complex aquatic multicellular organisms. |
| 580–500 Ma | Cambrian explosion: most modern animal phylum appear. |
| 550–540 Ma | Ctenophora (comb jellies), Sponge (sponges), Anthozoa ( and ), Ikaria wariootia (an early ). |
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 at division points.
| 535 Ma | Major diversification of living things in the oceans: (e.g. trilobites, ), chordates, , Mollusca, , Foraminifera and , etc. |
| 530 Ma | The first known footprints on land date to 530 Ma. |
| 520 Ma | Earliest Graptolithina. |
| 511 Ma | Earliest . |
| 505 Ma | Fossilization of the Burgess Shale |
| 500 Ma | Jellyfish have existed since at least this time. |
| 485 Ma | First vertebrates with true bones (Agnatha). |
| 450 Ma | First complete and Sea urchin appear. |
| 440 Ma | First agnathan fishes: Heterostraci, Galeaspida, and Pituriaspida. |
| 420 Ma | Earliest Actinopterygii, Trigonotarbida, and land . |
| 410 Ma | First signs of teeth in fish. Earliest Nautilida, Lycopodiophyta, and trimerophytes. |
| 488–400 Ma | First () and . |
| 395 Ma | First , Charales. Earliest Opiliones, , Hexapoda () and Ammonoidea. The earliest known tracks on land named the Zachelmie trackways which are possibly related to Ichthyostegalia. |
| 375 Ma | Tiktaalik, a lobe-finned fish with some anatomical features similar to early tetrapods. It has been suggested to be a transitional species between fish and tetrapods. |
| 365 Ma | Acanthostega is one of the earliest vertebrates capable of walking. |
| 363 Ma | By the start of the Carboniferous Period, the Earth begins to resemble its present state. Insects roamed the land and would soon take to the skies; swam the oceans as top predators, and vegetation covered the land, with Spermatophyte and soon to flourish. Four-limbed tetrapods gradually gain adaptations which will help them occupy a terrestrial life-habit. |
| 360 Ma | First and Pteridophyte. Land flora dominated by seed ferns. The Xinhang forest grows around this time. |
| 350 Ma | First large sharks, Chimaeridae, and hagfish; first crown tetrapods (with five digits and no fins and scales). |
| 350 Ma | Diversification of . |
| 325-335 Ma | First Reptiliomorpha. |
| 330-320 Ma | First amniote vertebrates ( Paleothyris). |
| 320 Ma | (precursors to mammals) separate from Sauropsida (reptiles) in late Carboniferous. |
| 305 Ma | The Carboniferous rainforest collapse occurs, causing a minor extinction event, as well as paving the way for amniotes to become dominant over amphibians and seed plants over ferns and lycophytes. First diapsid reptiles (e.g. Petrolacosaurus). |
| 280 Ma | Earliest , seed plants and Pinophyta diversify while Lepidodendrales and Equisetopsida decrease. Landform temnospondyl amphibians and pelycosaurs (e.g. Dimetrodon) diversify in species. |
| 275 Ma | Therapsid synapsids separate from pelycosaur synapsids. |
| 265 Ma | appear in the fossil record. |
| 251.9–251.4 Ma | The Permian–Triassic extinction event eliminates over 90-95% of marine species. Terrestrial organisms were not as seriously affected as the marine biota. This "clearing of the slate" may have led to an ensuing diversification, but life on land took 30 million years to completely recover. |
| 250 Ma | Mesozoic marine revolution begins: increasingly well adapted and diverse predators stress sessile marine groups; the "balance of power" in the oceans shifts dramatically as some groups of prey adapt more rapidly and effectively than others. |
| 250 Ma | Triadobatrachus massinoti is the earliest known frog. |
| 248 Ma | Sturgeon and paddlefish (Acipenseridae) first appear. |
| 245 Ma | Earliest Ichthyopterygia |
| 240 Ma | Increase in diversity of Eucynodontia and |
| 225 Ma | Earliest dinosaurs (Plateosauridae), first cardiid Bivalvia, diversity in , Bennettitales, and conifers. First Teleostei fishes. First mammals ( Adelobasileus). |
| 220 Ma | Seed-producing Gymnosperm forests dominate the land; herbivores grow to huge sizes to accommodate the large guts necessary to digest the nutrient-poor plants. First Fly and ( Odontochelys). First Coelophysoidea dinosaurs. First mammals from small-sized , which transitioned towards a nocturnal, insectivorous, and endothermic lifestyle. |
| 205 Ma | Massive Triassic/Jurassic extinction. It wipes out all except crocodylomorphs, who transitioned to an aquatic habitat, while dinosaurs took over the land and pterosaurs filled the air. |
| 200 Ma | First accepted evidence for infecting eukaryotic cells (the group Geminiviridae). However, viruses are still poorly understood and may have arisen before "life" itself, or may be a more recent phenomenon. Major extinctions in terrestrial vertebrates and large amphibians. Earliest examples of Thyreophora. |
| 195 Ma | First pterosaurs with specialized feeding ( Dorygnathus). First Sauropoda dinosaurs. Diversification in small, dinosaurs: heterodontosaurids, Fabrosauridae, and Scelidosaurus. |
| 190 Ma | Pliosauroidea appear in the fossil record. First Lepidoptera ( Archaeolepis), , modern starfish, irregular echinoids, Corbulidae bivalves, and Bryozoa. Extensive development of . |
| 176 Ma | First dinosaurs. |
| 170 Ma | Earliest , , Cryptoclididae, Elasmosauridae Plesiosauria, and mammals. Sauropod dinosaurs diversify. |
| 168 Ma | First . |
| 165 Ma | First Batoidea and Glycymerididae bivalves. First . |
| 163 Ma | Pterodactyloidea pterosaurs first appear. |
| 161 Ma | dinosaurs appear in the fossil record ( Yinlong) and the oldest known eutherian mammal: Juramaia. |
| 160 Ma | Multituberculata mammals (genus Rugosodon) appear in eastern China. |
| 155 Ma | First blood-sucking insects (Ceratopogonidae), Rudists bivalves, and Cheilostomata bryozoans. Archaeopteryx, a possible ancestor to the birds, appears in the fossil record, along with Triconodontidae and Symmetrodonta mammals. Diversity in and theropod dinosaurs. |
| 131 Ma | First Pine. |
| 140 Ma | Orb-weaver spiders appear. |
| 135 Ma | Rise of the Flowering plant. Some of these flowering plants bear structures that attract insects and other animals to spread pollen; other angiosperms are pollinated by wind or water. This innovation causes a major burst of animal coevolution. First freshwater Pelomedusidae turtles. Earliest krill. |
| 120 Ma | Oldest fossils of , including both marine and Dictyochales. |
| 115 Ma | First monotreme mammals. |
| 114 Ma | Earliest . |
| 112 Ma | Xiphactinus, a large predatory fish, appears in the fossil record. |
| 110 Ma | First hesperornithes, toothed diving birds. Earliest Limopsidae, Verticordiidae, and Thyasiridae bivalves. |
| 100 Ma | First . |
| 100–95 Ma | Spinosaurus appears in the fossil record. |
| 95 Ma | First evolve. |
| 90 Ma | Extinction of ichthyosaurs. Earliest and Nuculanidae bivalves. Large diversification in angiosperms: magnoliids, rosids, Hamamelidaceae, Monocotyledon, and ginger. Earliest examples of . Probable origins of Placentalia mammals (earliest undisputed fossil evidence is 66 Ma). |
| 86–76 Ma | Diversification of therian mammals. |
| 70 Ma | Multituberculate mammals increase in diversity. First Yoldiidae bivalves. First possible ungulates ( Protungulatum). |
| 68–66 Ma | Tyrannosaurus, the largest terrestrial predator of western Laramidia, appears in the fossil record. First species of Triceratops. |
| +Cenozoic era (66 Ma – present) ! Date ! Event | |
| 66 Ma | The Cretaceous–Paleogene extinction event eradicates about half of all animal species, including , pterosaurs, plesiosaurs, , Belemnitida, rudist and Inoceramidae bivalves, most planktic foraminifers, and all of the dinosaurs excluding the birds. |
| 66 Ma | Rapid dominance of conifers and ginkgos in high latitudes, along with mammals becoming the dominant species. First Psammobiidae bivalves. Earliest . Rapid diversification in ants. |
| 63 Ma | Evolution of the Creodonta, an important group of meat-eating (Carnivore) mammals. |
| 62 Ma | Evolution of the first . |
| 60 Ma | Diversification of large, . Earliest true , along with the first Semelidae bivalves, Xenarthra, and Insectivora mammals, and . The ancestors of the carnivorous mammals (miacids) were alive. |
| 59 Ma | Earliest sailfish appear. |
| 56 Ma | Gastornis, a large flightless bird, appears in the fossil record. |
| 55 Ma | Modern bird groups diversify (first Passerine, , , swifts, ), first Archaeoceti ( Himalayacetus), earliest , , appearance of , mammals in the fossil record. Flowering plants continue to diversify. The ancestor (according to theory) of the species in the genus Carcharodon, the early Isurus Isurus hastalis, is alive. Ungulates split into artiodactyla and perissodactyla, with Cetacea of the former returning to the sea. |
| 52 Ma | First appear ( Onychonycteris). |
| 50 Ma | Peak diversity of dinoflagellates and Coccolithophore, increase in diversity of Pholadomyoida and heteroconch bivalves, Brontotheriidae, , , and appear in the fossil record, diversification of primates. |
| 40 Ma | Modern-type butterflies and moths appear. Extinction of Gastornis. Basilosaurus, one of the first of the giant whales, appeared in the fossil record. |
| 38 Ma | Earliest . |
| 37 Ma | First Nimravidae ("false saber-toothed cats") carnivores — these species are unrelated to modern-type Felidae. First and ruminants. |
| 35 Ma | Poaceae diversify from among the monocot ; begin to expand. Slight increase in diversity of cold-tolerant and foraminifers, along with major extinctions of Gastropoda, reptiles, amphibians, and multituberculate mammals. Many modern mammal groups begin to appear: first Glyptodontidae, , , Peccary, and the first and . Diversity in Toothed whale and Baleen whale whales. |
| 33 Ma | Evolution of the Thylacinidae ( Badjcinus). |
| 30 Ma | First barnacle and , extinction of Embrithopoda and brontothere mammals, earliest Suidae and Felidae. |
| 28 Ma | Paraceratherium appears in the fossil record, the largest terrestrial mammal that ever lived. First . |
| 25 Ma | Pelagornis sandersi appears in the fossil record, the largest flying bird that ever lived. |
| 25 Ma | First deer. |
| 24 Ma | First . |
| 23 Ma | Earliest Struthio, trees representative of most major groups of have appeared by now. |
| 20 Ma | First , , and , increase in bird diversity. |
| 17 Ma | First birds of the genus Corvus (crows). |
| 15 Ma | Genus Mammut appears in the fossil record, first Bovidae and , diversity in Australian megafauna. |
| 10 Ma | Grasslands and are established, diversity in insects, especially ants and , increase in body size and develop Hypsodont, major diversification in grassland mammals and snakes. |
| 9.5 Ma | Great American Interchange, where various land and freshwater faunas migrated between North and South America. Armadillos, , Phorusrhacidae, Ground sloth, , and Meridiungulata traveled to North America, while , , saber-toothed cats, , , , , , and deer entered South America. |
| 9 Ma | First . |
| 6.5 Ma | First hominins ( Sahelanthropus). |
| 6 Ma | Australopithecines diversify ( Orrorin, Ardipithecus). |
| 5 Ma | First sloth and Hippopotamus, diversification of grazing herbivores like and , large carnivorous mammals like and the genus Canis, burrowing rodents, kangaroos, birds, and small carnivores, increase in size, decrease in the number of perissodactyl mammals. Extinction of nimravid carnivores. First . |
| 4.8 Ma | appear in the fossil record. |
| 4.5 Ma | diverge from land iguanas. |
| 4 Ma | Australopithecus evolves. Stupendemys appears in the fossil record as the largest freshwater turtle, first modern elephants, giraffes, zebras, lions, rhinoceros and appear in the fossil record |
| 3.6 Ma | grow to modern size. |
| 3 Ma | Earliest swordfish. |
| 2.7 Ma | Paranthropus evolves. |
| 2.5 Ma | Earliest species of Arctodus and Smilodon evolve. |
| 2 Ma | First members of genus Homo, Homo habilis, appear in the fossil record. Diversification of conifers in high latitudes. The eventual ancestor of cattle, aurochs ( Bos primigenus), evolves in India. |
| 1.7 Ma | Australopithecines go extinct. |
| 1.2 Ma | Evolution of Homo antecessor. The last members of Paranthropus die out. |
| 1.0 Ma | First . |
| 810 ka | First wolves |
| 600 ka | Evolution of Homo heidelbergensis. |
| 400 ka | First . |
| 350 ka | Evolution of . |
| 300 ka | Gigantopithecus, a giant relative of the orangutan from Asia dies out. |
| 250 ka | Anatomically modern humans appear in Africa. Around 50 ka they start colonising the other continents, replacing Neanderthals in Europe and other hominins in Asia. |
| 70 ka | Genetic bottleneck in humans (Toba catastrophe theory). |
| 40 ka | Last giant monitor lizards (Megalania) die out. |
| 35–25 ka | Extinction of . Domestication of . |
| 15 ka | Last woolly rhinoceros ( Coelodonta antiquitatis) are believed to have gone extinct. |
| 11 ka | Short-faced bears vanish from North America, with the last Megatheriidae dying out. All Equidae become extinct in North America. Domestication of various ungulates. |
| 10 ka | Holocene epoch starts after the Last Glacial Maximum. Last mainland species of woolly mammoth ( Mammuthus primigenus) die out, as does the last Smilodon species. |
| 8 ka | The Subfossil lemur dies out. |
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