Contact between water vapor and silicate surface causes abiotic formation of reactive oxygen species in an anoxic atmosphere

Spontaneous generation of reactive oxygen species (ROS) in aqueous microdroplets or at a water vapor–silicate interface is a new source of redox chemistry. However, such generation occurs with difficulty in liquid water having a large ionic strength. We report that ROS is spontaneously produced when water vapor contacts hydrogen-bonded hydroxyl groups on a silicate surface. The evolution of hydrogen-bonded species such as hydroxyl groups was investigated by using two-dimensional, time-resolved FT-IR spectroscopy. The participation of water vapor in ROS generation is confirmed by investigating the reaction of D2O vapor and hydroxyl groups on a silicate surface. We propose a reaction pathway for ROS generation based on the change of the hydrogen-bonding network and corresponding electron transfer onto the silicate surface in the water vapor–solid contact process. Our observations suggest that ROS production from water vapor–silicate contact electrification could have contributed to oxidation during the Archean Eon before the Great Oxidation Event.