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.