Oxygen revolution
Main article: Great Oxygenation Event See also: Ozone layer Lithified stromatolites on the shores of Lake Thetis , Western Australia . Archean stromatolites are the first direct fossil traces of life on Earth. A banded iron formation from the 3.15 Ga Moories Group, Barberton Greenstone Belt , South Africa . Red layers represent the times when oxygen was available; gray layers were formed in anoxic circumstances. The earliest cells absorbed energy and food from the surrounding environment. They used fermentation , the breakdown of more complex compounds into less complex compounds with less energy, and used the energy so liberated to grow and reproduce. Fermentation can only occur in an anaerobic (oxygen-free) environment. The evolution of photosynthesis made it possible for cells to derive energy from the Sun. Most of the life that covers the surface of the Earth depends directly or indi...