Timeline of life

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, often comprising an accumulation of smaller extinction events over a relatively brief period. 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: • End Ordovician: 440 million years ago, 86% of all species lost, including most graptolites • Late Devonian: 375 million years ago, 75% of species lost, including most trilobites • End Permian, The Great Dying: 251 million years ago, 96% of species lost, including tabulate corals, and most trees and synapsids • End Triassic: 200 million years ago, 80% of species lost, including all conodonts • End Cretaceous: 66 million years ago, 76% of species lost, including all ammonites, mosasaurs, plesiosaurs, pterosaurs, and non-avian dinosaurs 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 impact events. == Detailed timeline ==

In this timeline, Ma (for megaannum) means "million years ago," ka (for kiloannum) means "thousand years ago," and ya means "years ago." Hadean Eon 4540 Ma – 4031 Ma Archean Eon exhibited at the Museum of Natural History in Vienna l-algal mat, salty lake on the White Sea seaside '' sp. strain NRC-1 4031 Ma – 2500 Ma Proterozoic Eon endomembrane system and its components '', a free-living ciliated protozoan '', an iconic Ediacaran organism, displays the characteristic quilted appearance of Ediacaran enigmata. 2500 Ma – 539 Ma. Contains the Palaeoproterozoic, Mesoproterozoic and Neoproterozoic eras. Phanerozoic Eon 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 Era 538.8 Ma – 251.9 Ma and contains the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian periods. s flourished during the early Paleozoic era, from the Late Cambrian, where they constituted the main predatory animals. '', a jawless fish, is popularized as one of the earliest fishes and probably a basal chordate or a basal craniate. first appear in the fossil record about 360 million years ago in the late Devonian period. s such as Dimetrodon were the largest terrestrial vertebrates in the Permian period, 299 to 251 million years ago. Mesozoic Era '' is the earliest-known ichthyopterygian. '' '' s were the dominant land animals on Earth. From 251.9 Ma to 66 Ma and containing the Triassic, Jurassic and Cretaceous periods. Cenozoic Era '' from the American Museum of Natural History '' appeared 52.2 million years ago terror bird and ground sloth at the Museu Nacional, Rio de Janeiro '' went extinct about 40,000 years ago as part of the Quaternary extinction event, along with every other Australian creature over . coexisted on Earth including modern humans and Homo floresiensis (pictured). s exceeded extant lions in size and ranged over much of North America until 11,000 BP. == See also ==