On a global scale, cyanobacteria like Nostoc were the cause of the 'Great Oxygenation Event' starting about three billion years ago Oxygen produced by the photosynthetic process started to accumulate ...On a global scale, cyanobacteria like Nostoc were the cause of the 'Great Oxygenation Event' starting about three billion years ago Oxygen produced by the photosynthetic process started to accumulate in the atmosphere, causing a biological catastrophe by eliminating much of the life present at the time whose metabolism was poisoned by oxygen. (see https://www.scientificamerican.com/article/origin-of-oxygen-in-atmosphere/ )
