First Cyanobacteria

3500 million years
or 854 meters to today

Geolo­gical era: Archean

Precurs­ors of cyanobac­teria (formerly called blue-green algae) are the first cells whose traces can be detec­ted in old rocks. Thanks to their cell membrane they were able to regu­late the exchange of substances and energy with their environment.
Lime­stone precip­it­a­tions (stro­matolites) of other microor­gan­isms are also detect­able from this period.

The carbon diox­ide origin­ally present in the atmo­sphere dissolves in the oceans and is used there to build up biomass. As a result, the atmo­sphere now consists almost entirely of nitro­gen. Oxygen is not yet present, and accord­ingly there is no ozone layer that protects against UV rays. During this period the super­con­tin­ent Ur might have formed.

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