Oxygen was Earth's first great pollution disaster

Around 2.4 billion years ago, cyanobacteria began pumping out oxygen — a gas that was toxic to almost all life at the time. The 'Great Oxidation Event' caused a mass extinction of anaerobic organisms. The air you're breathing is the aftermath of a catastrophe.

— Donald E. Canfield, Oxygen: A Four Billion Year History — 2014
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