Anoxic photochemical weathering of pyrite on Archean continents.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 35767603.
- Also identified by DOI 10.1126/sciadv.abn2226 and PMC identifier 9242442.
- 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
Sulfur is an essential element of life that is assimilated by Earth's biosphere through the chemical breakdown of pyrite. On the early Earth, pyrite weathering by atmospheric oxygen was severely limited, and low marine sulfate concentrations persisted for much of the Archean eon. Here, we show an anoxic photochemical mechanism of pyrite weathering that could have provided substantial amounts of sulfate to the oceans as continents formed in the late Archean. Pyrite grains suspended in anoxic ferrous iron solutions produced millimolar sulfate concentrations when irradiated with ultraviolet light. The Fe<sup>2+</sup><sub>(aq)</sub> was photooxidized, which, in turn, led to the chemical oxidation of pyritic sulfur. Additional experiments conducted with 2.68 Ga shale demonstrated that photochemically derived ferric iron oxidizes and dissolves sedimentary pyrite during chemical weathering. The results suggest that before the rise of atmospheric oxygen, oxidative pyrite weathering on Archean continents was controlled by the exposure of land to sunlight.