Oxygenation of the Proterozoic Earth's surface: An evolving story

Abstract

Proterozoic Earth surface oxygenation is an intensely debated topic central to understanding the evolution of complex life. Over the past decade, the emerging story is that Proterozoic background atmospheric O2 levels were stable but low over 10- to 100-million-year time frames, perhaps up to a few percent PAL. Surface oceans had low and variable O2 over the same spans, perhaps up to a few 10s of μM, but the deep oceans were typically anoxic. Only for short periods of time were these low background O2 levels seemingly disturbed during transient oxygenation events. This could even be the case during the Neoproterozoic, a time classically thought to mark a stepwise change in Earth's surface O2 levels concurrent with the rise of animals.