Biogenic methane is produced in nature by two dominant processes, methanogenesis and thermogenesis. Because both of these processes usually involve the decomposition of products derived from biological organic materials, the resulting methane is termed biogenic. During methanogenesis, two metabolic pathways are followed in the generation of microbial methane — carbonate reduction (CO2 + 4H2 = CH4 + 2H2O) taking place mainly in marine depositional settings, and methyl-type fermentation (CH3 COOH = CH4 + CO2), occurring mainly in fresh-water settings (Whiticar et al., 1986). Methanogens, the microorganisms that perform methanogenesis, live only in anaerobic, reducing environments at temperatures between −1.2° and 110°C (Whiticar, 1994).
Thermogenesis is the process that forms thermal methane from the thermochemical decomposition of biological organic material, buried to depths exceeding about 1000 m, where temperatures are sufficient to break organic chemical bonds. Typically this...
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Kvenvolden, K.A. (1998). BiogenicMethane and gas hydrate. In: Geochemistry. Encyclopedia of Earth Science. Springer, Dordrecht. https://doi.org/10.1007/1-4020-4496-8_24
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