This element that is vital to life now, once nearly killed all life on Earth!
Geological, isotopic, and chemical evidence suggest this major environmental change happened around 2.4 billion years ago.
Cyanobacteria, which appeared about 200 million years before the GOE, began producing oxygen by photosynthesis. Before the GOE, any free oxygen they produced was chemically captured by dissolved iron or organic matter.
The GOE was the point when these oxygen sinks became saturated and could not capture all of the oxygen that was produced by cyanobacterial photosynthesis.
After the GOE the excess free oxygen started to accumulate in the atmosphere.
When this occurred, nearly 99 % of all life on Earth was wiped out.
