The Archean

[ archean ]

The Earth formed about 4600 million years ago. By at least 3800 million years ago there was life on earth in the form of bacteria and cyanobacteria or blue-green algae. The mounds near the beach are stromatolites made of sediments trapped by mats of cyanobacteria.

Stromatolites produced oxygen as a by-product of photosynthesis. In approximately 2800 million years enough oxygen was produced to make it possible for other life forms to evolve. These new organisms grazed on and competed with stromatolites so that the once dominant forms now only survive where conditions prevent "higher" organisms from getting a foothold--for example, in highly saline sabhka environments.

Painting by Peter Sawyer, Smithsonian Institute.