Abiotic molecular hydrogen and hydrocarbons have been observed in a variety of geologic settings both on Earth and other planetary bodies. Owing in large part to the utilization of hydrogen and methane by chemosynthetic biological communities, the geologic production of these compounds has become the subject of intense scientific study. Geologically produced hydrogen and methane are also of interest as possible energy resources. This issue highlights recent developments in the understanding of geologic sources of hydrogen and methane, the biological utilization of these compounds, and the potential for human exploitation of these resources.
