Oxygen catastrophe

The first mass extinction on Earth occurred around 2.5 billion years ago, when a photosynthesizing bacterium appeared and released so much oxygen into the atmosphere that anaerobic life was largely wiped out. This is often called the Great Oxygenation Event, the Oxygen Catastrophe, or the Oxygen Holocaust.

The Great Oxygenation Event, the beginning of which is commonly known in scientific media as the Great Oxidation Event (GOE, also called the Oxygen Catastrophe, Oxygen Crisis, Oxygen Holocaust, Oxygen Revolution, or Great Oxidation) was the biologically induced appearance of dioxygen (O2) in Earth's atmosphere. Geological, isotopic, and chemical evidence suggests that this major environmental change happened around 2.45 billion years ago (2.45 Ga), during the Siderian period, at the beginning of the Proterozoic eon. The causes of the event remain unclear.(*)

Oceanic cyanobacteria, which evolved into coordinated[clarification needed] (but not multicellular or even colonial) macroscopic forms more than 2.3 billion years ago (approximately 200 million years before the GOE), were the first microbes to produce oxygen by photosynthesis. Before the GOE, any free oxygen they produced was chemically captured by dissolved iron or by organic matter. The GOE started when oxygen produced by the cyanobacteria started escaping into the atmosphere after other oxygen reservoirs were filled

(*) The cause of the event was extraterrestrial influenced.