Evidence for elevated and variable atmospheric oxygen in the Precambrian

•Two methods for estimating atmosphere O2 are combined to give a robust history of Precambrian first order oxygen trends.•Atmosphere O2 rises through the Neoarchean and reaches a maximum in the Paleoproterozoic at ~1800 Ma.•Atmosphere O2 decreases through Mesoproterozoic, but rises again toward the end of the Neoproterozoic.•Individual black shale formations indicate a general second order rise in atmosphere O2 over the period of deposition of the formation. Oxygen concentration in the Precambrian atmosphere-ocean system is currently estimated from a series of geochemical proxies that depend on the concentration of redox-sensitive trace elements or their isotopic ratios measured in organic-bearing marine shales. This research has indicated that atmospheric oxygen content throughout the Precambrian was very low,