Answer:
Researchers can decide whether oxygen existed in Earth's Archean air by searching for oxidized iron in rock. In the first place, there was just an almost no oxygen in the air. The oxygen that are being created by cyanobacteria is sufficient for the enduring procedure.
There will sufficiently just oxygen that will stay in the climate when the stones at the surface are appropriately and enough oxidized. In any case, as time passes by, confirmations said that the measure of oxygen in the Archean air is really expanding in a moderate enduring pace.