Methane
Biological routes

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. Methanogens occur in landfills and soils, ruminants (for example, cattle), the guts of termites, and the anoxic sediments below the seafloor and the bottom of lakes.

This multistep process is used by these microorganisms for energy. The net reaction of methanogenesis is:

The final step in the process is catalyzed by the enzyme methyl coenzyme M reductase (MCR).
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