A persistently low level of atmospheric oxygen in Earth's middle age

Resolving how Earth surface redox conditions evolved through the Proterozoic Eon is fundamental to understanding how biogeochemical cycles have changed through time. The redox sensitivity of cerium relative to other rare earth elements and its uptake in carbonate minerals make the Ce anomaly (Ce/Ce*) a particularly useful proxy for capturing redox conditions in the local marine environment. Here, we report Ce/Ce* data in marine carbonate rocks through 3.5 billion years of Earth's history, focusing in particular on the mid-Proterozoic Eon (i.e., 1.8 - 0.8 Ga). To better understand the role of atmospheric oxygenation, we use Ce/Ce* data to estimate the partial pressure of atmospheric oxygen (pO(2)) through this time. Our thermodynamics-based modeling supports a major rise in atmospheric oxygen level in the aftermath of the Great Oxidation Event (similar to 2.4 Ga), followed by invariant pO(2) of about 1% of present atmospheric level through most of the Proterozoic Eon (2.4 to 0.65 Ga).

Automated summary

This research reveals the evolution of atmospheric oxygen levels throughout Earth's geological history, with a particular focus on the mid-Proterozoic Eon. The results support a significant rise in atmospheric oxygen level following the Great Oxidation Event, followed by a relatively stable pO(2) of around 1% of present atmospheric level during most of the Proterozoic Eon.