The second great oxygenation
Oxygen rises again after a billion years flat — and complex life follows almost immediately.
- When
- Known to
- ± 100 million years
- Era
- Neoproterozoic, Proterozoic
From around 800 million years ago atmospheric oxygen climbs well above the low Proterozoic plateau, and the deep oceans begin to ventilate. The causes are argued over — continental rifting, phosphorus delivery, algal burial of carbon — but the correlation with biological innovation is hard to miss. Animals large enough to need substantial oxygen appear within this window, and could not plausibly have existed before it.