Lipids constitute resistant biomarkers that have been proposed as pacemakers in the search for possible microbial life-forms in Mars’ past.
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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)
