2500 million years
or 610 meters to today
Geological era: Proterozoic/Siderian
Cells are developing the ability to produce energy from sunlight ever more efficiently. Over millions of years, the oxygen produced leads to the formation of water insoluble metal salts in the oceans. This results in the significant banding layers which are being mined today. The iron concentration in the water decreases, so that free oxygen appears. This oxygen is toxic to life at this time and the first major extinction (“Great oxygen catastrophe”) affects most species. Organisms that live in an oxygen-free environment remain unaffected. New species that can tolerate oxygen or even gain a lot of energy from it spread.
After the first oxygen enters the atmosphere, its share increases steadily. At the same time, the carbon dioxide content is decreasing. The Earth is predominantly covered by oceans. Only occasionally do volcanic cones or elevated clods of earth (cratons) tower above the water surface.