On the forcing mechanism for the H-2-driven deep biosphere

Heat produced in the mantle and core of the Earth by the decay of radioactive elements and Mineral fusion results in large-scale mantle convection. The outer shelf of the Earth that floats oil the convective mantle is divided into rigid lithospheric plates. Subduction of dense cold plates into the mantle leads to plate tectonics. At divergent plate margins heat is dissipated through hydrothermal convection cells. As ocean water is entrained into hydrothermal cells it interacts with fresh magmatic rocks and liberates ferrous iron. This iron reduces the ocean water to such in extent that it decomposes and forms hydrogen. Molecular hydrogen. as the most reduced component in the system. forms a basal component to a deep dark biosphere powered by metastable redox gradients. In this paper we review the driving force behind a hydrogen-driven deep biosphere. We present abundant observations of hydrogen produced at natural hydrothermal settings as well as in laboratory experiments. The key mineral reactions responsible for the bulk of this hydrogen production are then presented. A division of the reaction progression into an oxidized state and a reduced State is suggested. The amount Of hydrogen produced is insignificant in the oxidized state whereas it becomes proportional to the amount of ferrous iron oxidized in file reduced state. The bulk of basalt-hosted aquifers are expected to reside ill the oxidized state because Of file IOW Content Of ferrous minerals. whereas abundant olivine in ultramafic-hosted systems is responsible For large-scale hydrogen production. Today the majority of file seafloor is basaltic. The Archean seafloor oil the other hand consisted of fewer ultramafic exposures, but was dominated by ultramafic magnesium-rich lavas With a higher potential for hydrogen production than the present seafloor.