The complicated history of how the Earth’s atmosphere became breathable
Enlarge (credit: Aurich Lawson | Getty Images)
The Great Oxygenation Event, which occurred around 2.4 billion years ago, was one of the biggest transformations of our planet. Before it, there was practically no oxygen in the atmosphere; after, there was.
Conventionally, the rise of oxygen is seen as life triumphantly terraforming a passive planet. But we're learning now that Earth was an active participant, and it took two more big lifts of oxygen over the succeeding 2 billion years before it reached breathable levels. So which was more responsible for oxygen's rise on Earth: the evolution of life or the evolution of the planet? Nature or nurture? And does the same answer apply to all of the rises of oxygen in Earth's past?
It's a question beyond curiosity about our past, as it also affects how we might interpret signs of life on exoplanets.