Oxidation of water to hydrogen peroxide at the rock–water interface due to stress-activated electric currents in rocks

Common igneous and high-grade metamorphic rocks contain dormant defects, which release electronic charge carriers when stressed. Rocks thereby behave like a battery. The charge carriers of interest are defect electrons h•, e.g. electronic states associated with O− in a matrix of O2−. Known as “positive holes” or pholes for short, the h• travel along stress gradients over distances on the order of meters in the laboratory and kilometers in the field. At rock–water interfaces the h• turn into •O radicals, e.g. highly reactive oxygen species, which oxidize H2O to H2O2. For every two h• charge carriers one H2O2 molecule is formed. In the laboratory the battery circuit is closed by running a Cu wire from the stressed to the unstressed rock. In the field closure of the circuit may be provided through the electrolytical conductivity of water. The discovery of h• charge carriers, their stress-activation, and their effect on Earthʹs surface environment may help better understand the oxidation of the early Earth and the evolution of early life.