Oxygen was responsible for the very first mass extinction event in Earth's history, a catastrophic climate crisis known as the Great Oxidation Event that wiped out almost all existing life.

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Oxygen was responsible for the very first mass extinction event in Earth's history, a catastrophic climate crisis known as the Great Oxidation Event that wiped out almost all existing life. Around 2.4 billion years ago, cyanobacteria started producing massive amounts of oxygen via photosynthesis. The main problem was that oxygen was highly toxic to the anaerobic organisms that dominated the planet at the time. It also destroyed the protective methane greenhouse effect, plunging Earth into a massive global ice age. Now we literally depend on this highly reactive, corrosive gas just to breathe, meaning our entire modern existence is built upon the ruins of an ancient bacterial apocalypse