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.

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