Lithoautotrophy in the subsurface: Table 1

If microorganisms can carry out primary production within the Earth’s crust, then the biosphere might not be totally dependent on surface-based photosynthesis. Potential chemical energy from purely geochemical sources within the earth can support growth of a number of known microorganisms, chiefly strict anaerobes, such as methanogens, homoacetogens, and sulfate-reducers. (Chemo)lithoautotrophic microorganisms have been detected in sedimentary systems, but they have not been shown to carry out primary production in situ, at least not without some dependence on surface-based photosynthesis. Microbial communities within igneous rock formations might, of necessity, be based on in situ primary production. Evidence has emerged for the presence of microorganism in basalt below the sea floor, but data on in situ activity are not yet in hand. Microbial communities have been observed, within continental flood basalts and granitic plutons, which appear to be based on in situ primary production by anaerobic bacteria. Geochemical measurements have confirmed that in situ activity is lithoautotrophic. This evidence for subsurface lithoautotrophic microbial ecosystems, which are not dependent on surface organisms, may have profound implications for life on the early Earth, and on other planets, including Mars.