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 Earth's surface environment may help better understand the oxidation of the early Earth and the evolution of early life.