Where did the oxygen built up in the Earth's atmosphere come from?
1 Answer
Jun 17, 2017
The oxygen in the atmosphere comes from photosynthesis.
Explanation:
Oxygen first appeared in quantity in the atmosphere about 3.5 billion years ago. It was caused by the evolution of cyanobacteria which are capable of photosynthesis which produces oxygen as a by product.
The arrival of photosynthesis caused what is sometimes known as the oxygen catastrophe. Oxygen was toxic to other lifeforms around at the time.
More recently most oxygen is produced by photosynthesis. The main sources being plants and phytoplankton. It makes up about 21% of the atmosphere.
