Microorganisms are important factors in the processes that govern the distribution of numerous chemical elements in the earth's crust. Carbon in particular undergoes an enormous variety of transformations as a consequence of microbial synthetic and degradative reactions. These reactions have importance in the study of organic geochemistry. Geochemical prospecting, however, has been limited by a lack of understanding of specific types of microbially mediated reactions and the extent to which they occur within the geosphere. Geochemical data interpretation for the purpose of finding oil and natural gas deposits would be enhanced by future research directed at: (1) defining the extent to which geochemically active microbes penetrate the earth's crust; (2) reinterpreting carb n isotope data in light of microbial reactions of formation, oxidation, and competition; (3) identifying novel microbial biomarkers; and (4) determining whether microbes can produce significant quantities of C₂+ gaseous hydrocarbons.

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