The
Great Oxygenation Event (
GOE), also called the
Oxygen Catastrophe,
Oxygen Crisis,
Oxygen Holocaust,
Oxygen Revolution, or
Great Oxidation, was the
biologically induced appearance of dioxygen (O
2) in Earth's atmosphere. Geological, isotopic, and chemical evidence suggest that this major environmental change happened around 2.3 billion years ago (2.3
Ga). [Image:Oxygenation-atm-2.svg|thumb|right|420px|O
2 build-up in the
Earth's atmosphere. Red and green lines represent the range of the estimates while time is measured in billions of years ago (Ga).
Stage 1 (3.85–2.45 Ga): Practically no O
2 in the atmosphere.
Stage 2 (2.45–1.85 Ga): O
2 produced, but absorbed in oceans and seabed rock.
Stage 3 (1.85–0.85 Ga): O
2 starts to gas out of the oceans, but is absorbed by land surfaces.
Stages 4 and 5 (0.85–present): O
2 sinks filled and the gas accumulates.]]