Evolution of Atmospheric O2 Through the Phanerozoic, Revisited

An oxygen-rich atmosphere is essential for complex animals.The early Earth had an anoxic atmosphere, and understanding the rise and maintenance of high O-2 levels is critical for investigating what drove our own evolution and for assessing the likely habitability of exoplanets. A growing number of techniques aim to reproduce changes in O-2 levels over the Phanerozoic Eon (the past 539 million years).We assess these methods and attempt to draw the reliable techniques together to form a consensus Phanerozoic O-2 curve. We conclude that O-2 probably made up around 5-10% of the atmosphere during the Cambrian and rose in pulses to similar to 15-20% in the Devonian, reaching a further peak of greater than 25% in the Permo-Carboniferous before declining toward the present day. Evolutionary radiations in the Cambrian and Ordovician appear consistent with an oxygen driver, and the Devonian Age of the Fishes coincides with oxygen rising above 15% atm.

Automated summary

An oxygen-rich atmosphere is crucial for complex animals. The study aims to understand the changes in oxygen levels over the Phanerozoic Eon and concludes that oxygen levels were around 5-10% during the Cambrian, increased to 15-20% in the Devonian, and peaked over 25% in the Permo-Carboniferous before declining. The rise in oxygen levels aligns with significant evolutionary events.