The production of methane (CH4), especially through the action of methanogens in oxygen-free environments. Methanogens are microorganisms produce methane gas as a byproduct of anaerobic respiration.
Adapted from "methanogenesis." Merriam-Webster.com. Merriam-Webster, n.d. Web. 23 Nov. 2015. methanogen. (n.d.) Dorland's Medical Dictionary for Health Consumers. (2007). Retrieved September 11 2015 from http://medical-dictionary.thefreedictionary.com/methanogen