Great Oxidation Event

The Great Oxidation Event (GOE) was the period, roughly 2.4 to 2.0 billion years ago, when free oxygen first accumulated in Earth's atmosphere and shallow oceans. It is one of the most profound changes in the history of the planet and was caused by life.

The source of the oxygen was oxygenic photosynthesis by cyanobacteria, which split water at photosystem II. For hundreds of millions of years, oxygen was removed as quickly as it was made, by reacting with dissolved iron, volcanic gases and rocks. Only when these sinks were overwhelmed, perhaps with changes in volcanism and the burial of organic carbon, did oxygen begin to build up in the air.

Rocks older than about 2.4 billion years contain detrital pyrite and uraninite, minerals that oxidize away in an oxygen-rich atmosphere, and sulfur isotopes show a pattern of mass-independent fractionation that disappears after the event. Red beds and soils rich in oxidized iron appear afterward, and the great banded iron formations record iron oxidation in the ocean.

Oxygen destroyed atmospheric methane, a potent greenhouse gas, and the loss may have triggered the Huronian glaciation. Anaerobic organisms were confined to oxygen-free places, and oxygen paved the way for efficient aerobic respiration and, much later, an ozone layer and complex life. The event also expanded mineral diversity, as oxidation created thousands of new minerals. See oxygen in the atmosphere and the atmosphere of Earth.

• Cyanobacteria — the organisms that produced the oxygen
• Banded Iron Formation — the rocks that record iron oxidation
• Atmospheric Oxygen — the gas whose rise defined the event