Great Oxidation Event (Paleoproterozoic)

Paleoproterozoic transition (2.46–2.06 Ga) when cyanobacterial photosynthesis first oxygenated Earth's atmosphere.

Specifications & Metrics

type: Standard Stratigraphic Chronology
timespan: ~2,460 – 2,060 Ma (Siderian to Rhyacian periods, Paleoproterozoic Era)
defining boundary: Disappearance of mass-independent sulfur isotope fractionation (MIF-S) near 2.4–2.3 Ga
proponents or Body: Preston Cloud (1968–1973), Heinrich Holland (1980s–2006), James Farquhar (2000)
key evidence: Banded iron formations (BIFs), continental red beds, loss of detrital pyrite/uraninite, Huronian glaciation

Driven by oxygenic photosynthesis in cyanobacteria, the Great Oxidation Event (2.46–2.06 Ga) shifted Earth's atmosphere from a weakly reducing N₂–CO₂–CH₄ state to a permanently oxidizing atmosphere with an ozone layer.
Dissolved ferrous iron (Fe²⁺) in anoxic Archean oceans initially buffered the released oxygen by precipitating alternating layers of magnetite, hematite, and chert as Banded Iron Formations (BIFs) before free O₂ accumulated in the air.
Atmospheric oxygenation oxidized atmospheric methane — triggering the planetary Huronian 'Snowball Earth' glaciation — and enabled the endosymbiotic evolution of aerobic mitochondria-bearing eukaryotes.