At https://archaeologynewsnetwork.blogspot.com/2019/12/breathing-new-life-i… … we are told there were at least three oxygenisation events that gave rise to Earth's breathable atmosphere – and they happened spontaneously. Does anything happen spontaneously? Presumably the vector is an unknown quantity. Other studies have pointed a finger at tectonic events – or indeed the idea that oxygen has an origin in the innards of the Earth. In the new study by Leeds University (published in the journal Science) we are told the Earth had no oxygen in its atmosphere or its oceans until 2.4 billion years ago when the first of three oxygenisation events occurred. The second event was 800 million years ago and the third, at 450 million years ago – way back into deep time. Large animlas require large levels of oxygen and evolved only after the last event.