The earth almost lost all oxygen 2.3 billion years ago

The transition of the Earth to a permanent oxygen host in the atmosphere was a stopping process that lasted 100 million years longer than previously believed, according to a new study.

When the Earth first formed 4.5 billion years ago, the atmosphere contained almost nothing oxygen. But 2.43 billion years ago, something happened: oxygen levels began to rise and then fall, followed by massive climate change, including a few icicles that may have covered the entire world with ice.