Life On Earth

Big Bang 13 billion yrs ago

Ancient ancestors of modern bacteria were the first forms of life to appear on Earth, about 4 billion years ago.

For about 3 billion years, all organisms were microscopic, and bacteria and archaea were the dominant forms of life.

The basic timeline is a 4.5 billion year old Earth:

  • 3.8 billion years of simple cells (prokaryotes),
  • 3 billion years of photosynthesis,
  • 2 billion years of complex cells (eukaryotes),
  • 1 billion years of multicellular life,
  • 600 million years of simple animals,
  • 570 million years of arthropods (ancestors of insects, arachnids and crustaceans),
  • 550 million years of complex animals,
  • 500 million years of fish and proto-amphibians,
  • 475 million years of land plants,
  • 400 million years of insects and seeds,
  • 360 million years of amphibians,
  • 300 million years of reptiles,
  • 200 million years of mammals,
  • 150 million years of birds,
  • 130 million years of flowers,
  • 65 million years since the non-avian dinosaurs died out,
  • 2.5 million years since the appearance of the genus Homo,
  • 200,000 years since humans started looking like they do today,
  • 25,000 years since Neanderthals died out.

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