Where did the Earth's oxygen come from? New study hints at an unexpected source

The amount of oxygen in the Earth’s atmosphere makes it a habitable planet.

Twenty-one per cent of the atmosphere consists of this life-giving element. But in the deep past — as far back as the Neoarchean era 2.8 to 2.5 billion years ago — this oxygen was almost absent.

So, how did Earth’s atmosphere become oxygenated?