PHOSPHORUS REDOX CHEMISTRY THROUGH TIME

In most geological systems, the element phosphorus is synonymous with phosphates. In general, this preference for the 5+ redox state is due to the thermodynamic stability of this oxyanion. However, we have shown that phosphorus can participate in redox reactions, especially if the phosphorus begins as a constituent of phosphide minerals such as schreibersite, (Fe,Ni)₃P. Schreibersite can react with water to form phosphorus anions of multiple oxidation states: hypophosphite with 1+, phosphite with 3+, and hypophosphate with 4+. Archean carbonate rocks (3.52 Ga) have been shown to bear phosphite as a major P anion, suggesting active redox chemistry of phosphorus on the early earth (Pasek et al. 2013).

This study has been expanded to include a number of other Archean rocks, finding prevalent phosphite in many older rock samples. Additionally, the production of phosphite from impact has been shown by chemical stratigraphy of a late Archean impact layer. Finally, phosphite has been detected in recent water samples, and is likely linked to microbiological processing of P compounds. These results suggest a long history for P redox chemistry occurring throughout the history of the earth, with potential impact on the development of life through time.

Reference

Pasek, M.A., Harnmeijer, J., Buick, R., Maheen, G. and Atlas, Z., 2013, Evidence for reactive reduced phosphorus species in the early Archean ocean. Proceedings of the National Academy of Science USA 110, 10089-10094.