![The multiple roles of methanogens in the modern-day carbon cycle. Processes shown in red contribute to greenhouse gas production. Part of the methane is removed through microbial methane oxidation (A)MO and photochemical reactions, where e is a generic electron donor (e.g., sulfate, nitrate, arsenate, iron, or manganese) that is reduced to eH. Processes depicted in green sequester CO2, storing it long term as carbonates. Dashed arrows show the potential contribution of methanogen metabolism in the precipitation of carbonate minerals, which contributes to the storage of carbon in the lithosphere. The metabolic activity of methanogens may locally alter pH (a part of energy generation) and produce copious amounts of EPS (seen as a veil surrounding the cells in the microphotograph (yellow arrow)). These EPS bind cations (e.g., Ca, Mg) and act as a nucleation site, while elevated pH enhances the carbonate precipitation in microbial mats [228]. This contribution by methanogens may ultimately impact the production of microbialites [154]. Solid arrows show known effects; dashed lines indicate hypothetical effects. -- Geosciences via x-mol.net](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/05/Methanogens-Through-Time.png?resize=1200%2C716&ssl=1)
Methanogens, or methanogenic archaea (MA), are among the most ancient and widely distributed microorganisms, characterized by a unique metabolism that generates methane (CH4) as the terminal product of anaerobic respiration.
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![The multiple roles of methanogens in the modern-day carbon cycle. Processes shown in red contribute to greenhouse gas production. Part of the methane is removed through microbial methane oxidation (A)MO and photochemical reactions, where e is a generic electron donor (e.g., arsenate or sulfate) that is reduced to eH. Processes depicted in green sequester CO2, storing it long-term as carbonates. The size of the arrows relates to the relative biogeochemical importance of the process. The metabolic activity of methanogens may locally alter pH and produce copious amounts of EPS (seen as a veil surrounding the cells in the microphotograph (yellow arrow)). These EPS bind cations (e.g., Ca, Mg) and act as nucleation site, while elevated pH enhances the carbonate precipitation in microbial mats [196]. This contribution by methanogens may ultimately produce microbialites [183] -- preprints.org](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/01/Methanogens-Through-Geological.png?resize=1200%2C720&ssl=1)