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Geological history of oxygen
From Wikipedia, the free encyclopedia
Before photosynthesis evolved, Earth's atmosphere had no free diatomic oxygen (O2).[2] Small quantities of oxygen were released by geological[3] and biological processes, but did not build up in the atmosphere due to reactions with reducing minerals.
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Stage 1 (3.85–2.45 Ga): Practically no O2 in the atmosphere.
Stage 2 (2.45–1.85 Ga): O2 produced, but absorbed in oceans and seabed rock.
Stage 3 (1.85–0.85 Ga): O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer.
Stages 4 and 5 (0.85 Ga–present): O2 sinks filled, the gas accumulates.[1]
Oxygen began building up in the atmosphere at approximately 1.85 Ga. At current rates of primary production, today's concentration of oxygen could be produced by photosynthetic organisms in 2,000 years.[4] In the absence of plants, the rate of oxygen production by photosynthesis was slower in the Precambrian, and the concentrations of O2 attained were less than 10% of today's and probably fluctuated greatly.
The increase in oxygen concentrations had wide ranging and significant impacts on life. Most significantly, the rise of oxygen caused a mass extinction of anaerobic microbes and paved the way for multicellular life.