Reconciling evidence of oxidative weathering and atmospheric anoxia on Archean Earth.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 34586856.
- Also identified by DOI 10.1126/sciadv.abj0108 and PMC identifier 8480925.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Evidence continues to emerge for the production and low-level accumulation of molecular oxygen (O<sub>2</sub>) at Earth’s surface before the Great Oxidation Event. Quantifying this early O<sub>2</sub> has proven difficult. Here, we use the distribution and isotopic composition of molybdenum in the ancient sedimentary record to quantify Archean Mo cycling, which allows us to calculate lower limits for atmospheric O<sub>2</sub> partial pressures (<i>P</i>O<sub>2</sub>) and O<sub>2</sub> production fluxes during the Archean. We consider two end-member scenarios. First, if O<sub>2</sub> was evenly distributed throughout the atmosphere, then <i>P</i>O<sub>2</sub> > 10<sup>–6.9</sup> present atmospheric level was required for large periods of time during the Archean eon. Alternatively, if O<sub>2</sub> accumulation was instead spatially restricted (e.g., occurring only near the sites of O<sub>2</sub> production), then O<sub>2</sub> production fluxes >0.01 Tmol O<sub>2</sub>/year were required. Archean O<sub>2</sub> levels were vanishingly low according to our calculations but substantially above those predicted for an abiotic Earth system.