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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