Hydrogen and methane from precambrian shield rocks and microbiological sinks for gases produced by water-rock interactions: energy for the deep biosphere

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Scientific investigations of the energy basis for deep subsurface microbial environments on earth are at the forefront of interdisciplinary collaboration between geologists, planetary scientists, microbiologists and astrobiologists and a major focus of my research program in Isotope Geochemistry of the Earth and Environment. Our deep biosphere research on the stable Precambrian cratons of Canada, South Africa and Finland has demonstrated that microbial life based on chemosynthesis rather than photosynthesis is not limited to those parts of the earth where significant magmatic or hydrothermal activity occurs. In the highly fractured geologically quiescent Shield terrains, over timescales of tens of thousands to millions of years, the products of low temperature (< approx. 200oC) water-rock interaction (WRI) can accumulate and serve as substrate for deep microbial communities. In particular, the Precambrian Shield sites we are studying contain mM levels of dissolved H2 - levels that place these waters among the most H2-rich environments on the planet. Our research also addresses developing diagnostic environmental parameters to distinguish between abiogenic hydrocarbons produced by WRI, from hydrocarbon gases produced by microbial processes, or found in sedimentary basin natural gas deposits. These discoveries have expanded our conception of the habitability of the earth's subsurface environment and may significantly increase estimates of the relative importance of the subsurface biosphere. Two lines of inquiry have arisen that will form the basis for the two Overall Objectives for this Discovery application. Objective I: Reevaluating frameworks for interpreting microbial CH4 isotopic signatures in cold environments in the North and Objective II: Investigating the significance of H2 and CH4 from Precambrian Shield rocks on a global scale through a coupled study of active gases and noble gases dissolved in fracture groundwaters.