Editing Methanogenesis (section)

===Importance in carbon cycle===
Methanogenesis is the final step in the anaerobic decay of organic matter.  During the decay process, [[Oxidizing agent#Electron acceptor|electron acceptors]] (such as [[oxygen]], [[ferric]] [[iron]], [[sulfate]], and [[nitrate]]) become depleted, while [[hydrogen]] (H<sub>2</sub>) and [[carbon dioxide]] accumulate.  Light organics produced by [[fermentation (biochemistry)|fermentation]] also accumulate.  During advanced stages of organic decay, all electron acceptors become depleted except carbon dioxide.  Carbon dioxide is a product of most catabolic processes, so it is not depleted like other potential electron acceptors.

Only methanogenesis and fermentation can occur in the absence of electron acceptors other than carbon.  Fermentation only allows the breakdown of larger organic compounds, and produces small organic compounds.  Methanogenesis effectively removes the semi-final products of decay: hydrogen, small organics, and carbon dioxide.  Without methanogenesis, a great deal of carbon (in the form of fermentation products) would accumulate in anaerobic environments.