Constraints on Paleoproterozoic atmospheric oxygen levels

Significance Earth’s protracted oxygenation significantly transformed global biological and geochemical cycles. In particular, the rise of atmospheric oxygen above trace levels was an essential prerequisite for the development of animals. However, quantifying atmospheric oxygen levels in Earth’s middle age remains a daunting challenge. Here we use a combination of sedimentology, geochemical constraints, and oceanographic modeling to provide a quantitative estimate of Precambrian atmospheric oxygen. We provide evidence that atmospheric oxygen levels decreased significantly after the “Great Oxygenation Event” in Earth’s early history, to levels that would have negatively impacted the ecology of the earliest complex organisms.