Some 2.3 billion years ago, the Earth would have been unrecognizable to us. At that time, ancient microorganisms were the dominant life form; there were no animals, no plant life, and certainly no humans.
But then, something changed. Oxygen-producing cyanobacteria triggered the Great Oxidation Event (GOE), which introduced atmospheric oxygen to our planet and allowed life as we know it to flourish. For ancient microorganisms, however, the event should have been a death knell. Oxygen was toxic to them — yet somehow, they adapted and survived.
