by [ Great Oxygenation Event, GOE ]
A biological event that precipitated the appearance of free oxygen (O2) in Earth’s atmosphere, about 2.3 billion years ago.
Cyanobacteria, the first organisms capable of photosynthesis, appeared 200 million years before the GOE but the oxygen they produced was captured by dissolved iron and other oxygen sinks. The GOE was the point at which these oxygen sinks became saturated and free oxygen began accumulating in the atmosphere.
The GOE may have wiped out most of the Earth’s anaerobic inhabitants at the time due to oxygen toxicity. Additionally, the GOE may have triggered the longest ice age in the earth’s history, as free oxygen reacted with atmospheric methane, reducing the greenhouse effects of methane. Eventually, aerobic organism evolved and consumed oxygen, bring us to the current equilibrium between oxygen availability and utilisation.