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The Earth was formed. It is thought to have formed by collisions in the giant disc-shaped cloud of material that also formed the Sun. Gravity slowly gathered this gas and dust together into clumps that became asteroids and small early planets called planetesimals.
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The first life forms appeared on Earth. The history of life on Earth began about 3.8 billion years ago, initially with single-celled prokaryotic cells, such as bacteria.
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Oxygen first entered the Earth's atmosphere. Most scientists believe that for half of Earth's 4.6-billion-year history, the atmosphere contained almost no oxygen. Cyanobacteria or blue-green algae became the first microbes to produce oxygen by photosynthesis.
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The first eukaryotes appeared on Earth. Eukaryotes are organisms with a nucleus. The oldest evidence of eukaryotes is from 2.7 billion years ago.
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More complex forms of life took longer to evolve, with the first multi cellular animals not appearing until about 600 million years ago.
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During the Ordovician, most life was in the sea, so it was sea creatures such as trilobites, brachiopods and graptolites that were drastically reduced in number.
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Three quarters of all species on Earth died out in the Late Devonian mass extinction, though it may have been a series of extinctions over several million years, rather than a single event.
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At this time most of the dry land on Earth was joined into one huge landmass that covered nearly a third of the planet's surface.
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Pangea begins to break up. The movement of Earth's tectonic plates formed Pangaea and ultimately broke it apart.
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Permian–Triassic extinction event: The Permian mass extinction has been nicknamed The Great Dying, since a staggering 96% of species died out
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Triassic–Jurassic extinction event: Many types of animal died out, including lots of marine reptiles, some large amphibians, many reef-building creatures and large numbers of cephalopod molluscs. Roughly half of all the species alive at the time became extinct.
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Cretaceous–Paleogene extinction event: is famed for the death of the dinosaurs. However, many other organisms perished at the end of the Cretaceous including the ammonites, many flowering plants and the last of the pterosaurs.
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Homo erectus were the first of the hominina to leave Africa, and these species spread through Africa, Asia, and Europe between 1.3 to 1.8 million years ago. One population of H. erectus, also sometimes classified as a separate species Homo ergaster, stayed in Africa and evolved into Homo sapiens.
