How did cyanobacteria help add oxygen to Earth’s atmosphere?

Cyanobacteria, also known as blue-green algae, were the first organisms to evolve oxygenic photosynthesis, a process that fundamentally transformed Earth’s atmosphere.21

Unlike other photosynthetic bacteria that use compounds like hydrogen sulfide as electron donors, cyanobacteria utilize water as their electron source. During this process, they release oxygen as a metabolic waste product.213

The accumulation of atmospheric oxygen occurred in stages:
* Oceanic Sinks: Initially, the oxygen produced by cyanobacteria was consumed by reacting with abundant volcanic-derived ferrous iron in the oceans, forming iron-rich deposits known as banded iron formations (BIFs).3
* Oxygen Oases: As these chemical sinks were depleted, localized environments called "oxygen oases" formed where oxygen levels rose, allowing for the development of aerobic metabolism.4
* Atmospheric Transformation: As cyanobacteria proliferated, oxygen production eventually overwhelmed the global supply of oxidizable materials, leading to the transition from a reducing atmosphere to an oxidizing one.453

This shift enabled the rise of complex aerobic organisms and the formation of the ozone layer, which protects life from harmful ultraviolet radiation.253