How low did it go? Study seeks to settle debate about oxygen in Earth's early atmosphere

Scientists have long debated how much molecular oxygen was in Earth's early atmosphere. About 2.4 billion years ago, there was a rise in oxygen that transformed Earth's atmosphere and biosphere, eventually making life like ours possible. This transition is called the "Great Oxidation Event." But how much oxygen was in the atmosphere before this time? Artist’s rendition of what the Earth could have looked like in the Archean Eon, from 4 billion to 2.5 billion years ago [Credit:...