![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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![Location of sediment sampling and pictures of resurrected species S. marinoi. (A) Map of the Baltic Sea (northern Europe) with the location of sediment core sampling (EMB262/6; 240 m water depth) in the eastern Gotland Basin (triangle). Additional sampling points of stratigraphy reference cores (points): M86-1a/36 [35], MSM62–60 [36], and P435-2-1 [34]. (B) Pictures of different Lugol-stained strains of S. marinoi. Strain SM_EGB_382_11 from 6871 ± 140 years of dormancy, SM_EGB_1_5 from 3 ± 2 years of dormancy, SM_EGB_107_1 from 1131 ± 110 years of dormancy, SM_EGB_20_4 from 58 ± 5 years of dormancy, and SM_EGB_232_2 from 3411 ± 120 years of dormancy. Scale bars = 20 μm. -- The ISME Journal](https://i0.wp.com/astrobiology.com/wp-content/uploads/2025/04/Resurrection-Of-A-Diatom-After.png?resize=1200%2C717&ssl=1)