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Timeline of evolution

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This timeline outlines the major events in the development of life on Earth. For context, see biology, evolution and the geologic timescale.

All given times are approximate estimates. We use the abbreviations "MYA" for "million years ago" and "TYA" for "thousand years ago".

Life on Earth
Date Event
4500 MYA The planet Earth forms from the accretion disk revolving around the young Sun.
4100 MYA The surface of the Earth cools down enough for the crust to solidify.
4000 MYA Life appears, probably first as self-reproducing RNA molecules. The atmosphere does not contain any free oxygen.
3900 MYA Cells resembling prokaryotes appear. These first organisms are chemoautotrophs[?]: they use carbon dioxide as a carbon source and oxidize inorganic materials to extract energy. Later prokaryotes invent glycolysis, a set of chemical reactions that free the energy of organic molecules such as glucose. Glycolysis employs ATP molecules as short term energy currency and is used in almost all organisms unchanged to this day. Prokaryotes remain the dominant life form on Earth today.
3900 MYA The split between the bacteria and the archaea occurs.
3500 MYA Bacteria develop primitive forms of photosynthesis which at first do not produce oxygen. These organisms generate ATP by exploiting a proton gradient, a mechanism still used in virtually all organisms.
3000 MYA Photosynthesizing cyanobacteria evolve; they use water as reductant, thereby producing oxygen as waste product. The oxygen initially oxydizes dissolved iron in the oceans, creating iron ore. Then the oxygen concentration in the atmosphere rises, acting as a poison for many bacteria.
2500 MYA Some bacteria evolve the ability to utilize oxygen to more efficiently use the energy from organic molecules such as glucose. Virtually all organisms using oxygen employ the same set of reactions, the citric acid cycle and oxidative phosphorylation.
2100 MYA More complicated cells appear: the eukaryotes, which contain various organelles. The closest relatives of these are probably the Archaea. Most have organelles which are probably derived from symbiotic bacteria: mitochondria, which use oxygen to extract energy from organic molecules and appear similar to today's Rickettsia, and often chloroplasts, which derive energy from light and synthesize organic molecules and originated from cyanobacteria and similar forms.
1200 MYA Sexual reproduction evolves and leads to an explosion in the rate of evolution. While most life occurs in oceans and lakes, some cyanobacteria may already have lived in moist soil by this time.
1000 MYA Multicellular organisms appear: algae and seaweeds living in the oceans.
600 MYA Sponges (Cnidaria), Jellyfish (Ctenophora), flat worms Platyhelminthes and other multicellular animals appear in the oceans.
565-525 MYA The Cambrian explosion, a rapid set of evolutionary changes, creates all the major body plans (phyla) of modern animals.
475 MYA The first primitive plants move onto land, having evolved from green algae living along the edges of lakes. They are accompanied by fungi, and very likely plants and fungi work symbiotically together.
450 MYA Arthropods, with an exoskeleton that provides support and prevents water loss, are the first animals to invade the land. Among the first are Myriapoda[?] (millipedes and centipedes), later followed by spiders and scorpions.
365 MYA Insects evolve on land and in fresh water from the myriapods. Some fresh water lobe-finned fish (Sarcopterygii) develop legs and give rise to the Tetrapoda. This happens in the water; tetrapods then use their legs to move out onto land, probably to hunt insects. Lungs evolve from swim bladders. Amphibians still retain many characteristics of the early tetrapods.
360 MYA Plants evolve seeds, structures that protect plant embryos and enable plants to spread quickly on land.
300 MYA Evolution of the amniotic egg[?] gives rise to the Amniota[?], reptiles who can reproduce on land. Insects evolve flight. Dragonflies (Odonata) still resemble these early insects. Vast forests of club moss[?] (lycopods), horsetails[?], and tree ferns cover the land; when these decay they will eventually form coal.
250 MYA The Permian-Triassic extinction event wipes out about 95% of all animal species, the most severe mass extinction known. The archosaurs[?] split from other reptiles. They will later diversify into crocodiles[?], dinosaurs, birds and pterosaurs. Teleosts[?] evolve from among the Actinopterygii (ray-finned fish), and eventually become the dominant fish group.
220 MYA The climate is very dry, and dry-adapted organism are favored: the archosaurs[?] and the gymnosperms[?]. The first mammals appear; they evolved from synapsid reptiles. Initially, they stay small. Gymnosperms (mostly conifers) are the dominant land plants. Plant eaters will grow to huge sizes during the dominance of the gymnosperms to have space for large guts to digest the poor food offered by gymnosperms
200 MYA Birds evolve from theropod[?] dinosaurs. Modern amphibians evolve: the Lissamphibia; including Anura (frogs), Urodela (salamanders), and Caecilia[?]
180 MYA The supercontinent Pangea begins to break up into several land masses. The largest is Gondwana, made up of the land masses which are now Antarctica, Australia, South America, Africa, and India
130 MYA Angiosperm plants evolve flowers, structures that attract insects and other animals to spread pollen. The evolution of the angiosperms cause a major burst of animal evolution. Half of all known dinosaur species are from the last 30 MY of the Mesozoic, after the rise of the angiosperms.
65 MYA The Cretaceous-Tertiary extinction event wipes out about half of all animal species including all non-avian dinosaurs, probably because of a cooling of the climate precipitated by the giant impact of a meteor. Mammals increase in diversity and size. Some will later return back to the sea (whales, sirenians and seals) and others will evolve flight (bats).
45 MYA Cetaceans (whales) evolve from mesonychids[?], carnivorous ungulates probably most closely related to the artiodactyls.
35 MYA Grasses evolve from among the angiosperms.
10 MYA The climate begins to dry, savannas and grasslands take over the earlier forests. The apes go into decline, and monkeys rise. This is the heyday of the horses spread throughout the Northern hemisphere. After 10 MYA they decline in the face of competition with the artiodactyls.
3 MYA The australopithecines (early hominines) evolve in the savannas of Africa. North and South America become joined, allowing migration of animals.
1800 TYA Homo erectus evolves in Africa and migrates to other continents, primarily south Asia.
130 TYA Neanderthals (Homo Neanderthalensis) evolve from Homo erectus and live in Europe and the Middle East.
100 TYA The first anatomically modern humans (Homo sapiens) appear in Africa some time before this. They also evolved from Homo erectus. Modern humans enter Asia via the Middle East.
50 TYA Modern humans expand from Asia to Australia and Europe. Expansion along the coasts happens faster than expansion inland.
30 TYA Modern humans enter North America from Siberia in numerous waves, some later waves across the Bering land bridge, but early waves probably by island-hopping across the Aleutians. At least two of the first waves had left few or no genetic descendants among Americans by the time Europeans arrived across the Atlantic Ocean.
27 TYA Neanderthals die out leaving Homo sapiens as the only living species of humans.
15 TYA Humans develop agriculture and, along with it, permanent settlements and cities. These appear first in what is now Iraq.
10 TYA Humans reach Tierra del Fuego at the tip of South America, the last continental region to be inhabited by humans, excluding Antarctica.
4 TYA Recorded history begins.

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