Biota - Lifeforms

A group of unicellular organisms with rudimentary internal organization that began to appear near the end of the Archean Eon, prokaryotes.



The Archean oceans are thought to have been formed by the condensation of water from abundant volcanic eruptions.

The transfer of biologically produced free oxygen from the atmosphere to the sedimentary rocks was beneficial to photosynthetic organisms because it was toxic to them at the time.

Thus, the removal of this oxygen allowed early anaerobic organisms (life forms that do not require oxygen to breathe) to develop in the early oceans of the Earth.

Current oxygen levels in the atmosphere are thought to have accumulated slowly over time, beginning with an anoxic atmosphere in the Archean period.

Volcanoes release a lot of water vapor (H2O) and carbon dioxide (CO2), but very little free oxygen (O2). Even if the water vapor and carbon dioxide emitted by volcanoes were decomposed in the atmosphere in an inorganic way (photodissociation), the amount of free oxygen would be negligible.

Most of the free oxygen in the Archean atmosphere is produced by organic photosynthesis of carbon dioxide (CO2) and water (H2O) by anaerobic cyanobacteria (blue-green algae), which release oxygen as a byproduct of the process.