Generation of Reactive Oxygen Apecies on Pyrite Surfaces: Implications for the Oxidation of Algoma-type BIFs and the Origin of Life on an Aarly Earth

Abstract:

The generation of reactive oxygen species (ROS) H₂O₂ and ^•OH on pyrite surfaces in anaerobic environments plays an important role in the evolution of early Earth. Given the current precipitation mechanisms cannot well elucidate the genesis of Algoma-type BIFs in Archean, we proposed a likely pyrite-induced oxidation mechanism to explain the oxidation of Fe²⁺ ions in Archean oceans. In this study, a series of important environmental conditions including light intensity, wavelength and pH were considered and monitored to check their effects on the production of ROS in anaerobic pyrite suspensions. Based on the sulfur content of volatiles in modern submarine basalts and black smokers, we assumed that the concentration of H₂S in Archean hydrothermal fluids ranged from 0.5 to 55 mmol/kg. Combined with the experimental results of H₂O₂ producing rates under 150 mW/cm² irradiation at pH 3.0 and under dark at pH 6.0, the H₂O₂ flux of 6.9 × 10⁵–1.1 × 10⁹ mol/yr could be estimated in a thermal flow. This value covered the amount of H₂O₂ required for Fe²⁺ oxidation in Archean oceans to form the Algoma-type BIFs (1.7 × 10⁶–1.3×10⁷ mol/yr). In addition, ROS posses strong oxidization and are toxic to cells, so excessive ROS on the early earth would affect the origin of life.