Understanding Evolution

Important events in the history of life (text-only version)

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A timeline can provide additional information about life's history not visible on an evolutionary tree. These include major geologic events, climate changes, radiation of organisms into new habitats, changes in ecosystems, changes in continental positions, and major extinctions. Explore the timeline below to view some of the major events in life's history.

130,000 Anatomically modern humans evolve. Seventy thousand years later, their descendents create cave paintings — early expressions of consciousness.
4 million In Africa, an early hominid, affectionately named "Lucy" by scientists, lives. The ice ages begin, and many large mammals go extinct.
65 million A massive asteroid hits the Yucatan Peninsula, and ammonites and non-avian dinosaurs go extinct. Birds and mammals are among the survivors.
130 million As the continents drift toward their present positions, the earliest flowers evolve, and dinosaurs dominate the landscape. In the sea, bony fish diversify.
225 million Dinosaurs and mammals evolve. Pangea has begun to break apart.
248 million Over 90% of marine life and 70% of terrestrial life go extinct during the Earth's largest mass extinction. Ammonites are among the survivors.
250 million The supercontinent called Pangea forms. Conifer-like forests, reptiles, and synapsids (the ancestors of mammals) are common.
360 million Four-limbed vertebrates move onto the land as seed plants and large forests appear. The Earth's oceans support vast reef systems.
420 million Land plants evolve, drastically changing Earth's landscape and creating new habitats.
450 million Arthropods move onto the land. Their descendants evolve into scorpions, spiders, mites, and millipedes.
500 million Fish-like vertebrates evolve. Invertebrates, such as trilobites, crinoids, brachiopids, and cephalopods, are common in the oceans.
555 million Multi-cellular marine organisms are common. The diverse assortment of life includes bizarre-looking animals like Wiwaxia.
3.5 billion Unicellular life evolves. Photosynthetic bacteria begin to release oxygen into the atmosphere.
3.8 billion Replicating molecules (the precursors of DNA) form.
4.6 billion The Earth forms and is bombarded by meteorites and comets.

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