Question

Early Earth was largely anoxic with very little oxygen present in the atmosphere. However, approximately 2 billion years ago, a rise in atmospheric oxygen concentration was recorded in the geological record. This event, known as the great oxygenation event (GOE), was caused by small microorganisms (cyanobacteria) that likely carried out the process of ____________________ .

Answer 1

Photosynthesis

Step-by-step explanation:

Cyanobacteria were the first prokaryotic organisms capable of oxygen-evolving complex. Photosynthesis needs an electron source, in this case water (H2O). By photo-oxidation of the water, oxygen (O2) is released (and hydrogen taken).

This led to the accumulation of oxygen in the atmosphere where it got to similar concentrations as in these days.