Hadean Eon → Origin of Life (3900 MA)

Earth is estimated to be about 4600 million years old, and for much of that history it has been home to life in one weird form or another.

Indeed, some scientists think life appeared the moment our planet's environment was stable enough to support it.

The earliest evidence for life on Earth comes from fossilized mats of cyanobacteria called stromatolites in Greenland that are about 3700 million years old. Ancient as their origins are, these bacteria (which are still around today) are already biologically complex—they have cell walls protecting their protein-producing DNA, so scientists think life must have begun much earlier. In fact, there are hints of life in even more primeval rocks: 4100 million year old zircons from Western Australia contain high amounts of a form of carbon typically used in biological processes.

Around the conclusion of the Hadean Eon, primitive prokaryotic cells developed glycosis, a process for oxidizing organic molecules which set the foundation for modern life.

Prokaryotic cell