Great Oxidation Event

The Great Oxidation Event was a major rise in atmospheric oxygen about 2.4 billion years ago, driven chiefly by oxygen-producing photosynthesis and transforming Earth’s environment.

Oxygenic photosynthesis: Photosynthesis that uses water as an electron donor and releases molecular oxygen. Cyanobacteria and other early organisms supplied the oxygen whose accumulation marks this event.
Archean: A geological eon spanning roughly 4.0 to 2.5 billion years ago. The event followed this eon, when atmospheric oxygen remained extremely scarce.
Great Oxidation Event extinction: The proposed crisis in which rising oxygen harmed organisms adapted to oxygen-free environments. Oxygen was toxic to many anaerobic microbes, although the scale of resulting biological loss is uncertain.
Neoarchean oxygenation: Evidence for localized or temporary oxygen increases before the Great Oxidation Event. It raises the question of whether oxygen production began long before it accumulated globally.
Cyanobacteria: A diverse group of bacteria that perform oxygenic photosynthesis. Their ancient oxygen production is a leading biological explanation for the atmospheric rise.
Paleoproterozoic: The first geological era of the Proterozoic Eon, lasting from 2.5 to 1.6 billion years ago. The Great Oxidation Event unfolded during this era.
Ozone layer: A region of the stratosphere enriched in ozone, which absorbs much of the Sun’s ultraviolet radiation. Atmospheric oxygen enabled ozone formation, changing surface exposure to ultraviolet light.
Atmospheric oxygenation models: Models that explain changes in atmospheric oxygen through biological production and geological consumption. Competing models differ on which changes in oxygen sources and sinks drove the event.
Methanogenesis: The microbial production of methane by anaerobic organisms. Declining atmospheric methane may have followed oxygenation and contributed to climatic cooling.
Stromatolite: A layered sedimentary structure produced through microbial activity, often involving mats of photosynthetic microbes. Ancient stromatolites provide evidence of microbial communities capable of oxygenic photosynthesis.

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