See [0] for atmospheric oxygen levels over time. That dip from ~35% to ~15% atmospheric oxygen corresponds approximately to the permian extinction (~250 mya). M

See [0] for atmospheric oxygen levels over time. That dip from ~35% to ~15% atmospheric oxygen corresponds approximately to the permian extinction (~250 mya). My understanding is that there have been a number of oceanic hypoxic/anoxic events[1] in the history of the planet but that atmospheric oxygen levels have been relatively high since the oxygen holocaust[2]. [0]https://www.pnas.org/content/pnas/96/20/10955/F2.large.jpg https://www.pnas.org/content/pnas/96/20/10955/F2.large.jpg [1]https://en.wikipedia.org/wiki/Anoxic_event#Anoxic_events_in_Earth's_history https://en.wikipedia.org/wiki/Anoxic_event#Anoxic_events_in_... [2]https://en.wikipedia.org/wiki/Great_Oxidation_Event https://en.wikipedia.org/wiki/Great_Oxidation_Event