 The more important source of methane at depth (crystalline bedrock) is abiotic.Abiotic means that methane is created from inorganic compounds, without biological activity, either through magmatic processes or via water-rock reactions that occur at low temperatures and pressures, like serpentinization.Most of Earth's methane is biogenic and is produced by methanogenesis, a form of anaerobic respiration only known to be conducted by some members of the domain Archaea.