Question

The appearance of free oxygen in the earths atmosphere led to the "great oxidation event" where did all of this oxygen come from

Answer 1

So there's a simple explanation for the Great Oxidation Event. It was the cyanobacteria, pumping out unwanted oxygen, that transformed Earth's atmosphere. ... That means the cyanobacteria were busy pumping out oxygen for at least half a billion years before oxygen started appearing in the air.

Step-by-step explanation: