article_snippet.sent: This theory can also help explain a period in Earth’s history known as the Great Oxygen Transition, 2.2 billion years ago.
article_snippet.sent: Here, oxygen levels began to rapidly rise from 0.0001 per cent of present levels to the 21 per cent of the atmosphere we see today.
article_snippet.sent: Rapid melting across the entirety of Earth could have given rise to these increased levels of oxygen in the atmosphere.
article_snippet.sent: Evidence for This theory comes from oxygen isotopes studied in rocks in China and Russia.