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Project Progress

Studies of deep subsurface, ecosystems hosted by ancient groundwater are directly relevant to the exploration for extant life in the subsurface of Mars. Laboratory investigations focus on determining the types of prebiotic compounds that form in the subsurface and assessing whether life itself could have been spawned beneath a planet’s surface. Field investigations focus on deep subsurface groundwater sampled at commercial mines in South African and Canadian Archaean rocks. Field sites have been selected for both colonized groundwater ecosystems and uncolonized groundwater.

There was significant progress during the past year on four types of laboratory experiments addressing molecular structures and stable isotopic compositions of hydrocarbons produced during water/mineral reactions. First, experiments generating abiogenic hydrocarbons under hydrothermal conditions (400°C, 500 bars) were conducted in collaboration with Q. Fu, J. Horita and William Seyfried Jr. of the Pennsylvania State University team using gaseous sources of H₂ and CO₂, rather than the traditional method of using formic acid. Second, experiments were conducted to produce abiogenic hydrocarbons via Fischer-Tropsch synthesis using iron powder catalysts instead of magnetite. These investigations included both CO₂ and CO carbon sources in a collaboration with T. McCollom of the University of Colorado, Boulder team. Third, spark discharge experiments were successfully completed, for the first time combining both carbon and hydrogen isotopic measurements on the hydrocarbon products of methane polymerization. Fourth, collaboration on experiments with G. Cody, P. Morrill and M. Fogel of the Carnegie team were sucessful in determining ²H isotopic characterization of C1-C4 hydrocarbons produced during abiogenic synthesis. There is widespread scientific interest in finding a definitive means to resolve abiogenic versus biogenic hydrocarbons in order to refine the debate concerning origins of methane in the Martian atmosphere.

Ground water and gases recovered from Canadian Shield sites are being compared with similar samples from the South Africa mines as a means to develop a model for distinguishing between microbial gases and abiogenic end-members in these Precambrian Shield field settings. Geochemical, isotopic and microbiological data suggest that the methanogenic microbes utilize abiogenic gases, specifically H₂, as an energy source in the deep subsurface. The association of high concentrations of H₂ with ¹³C-enriched CH₄ end-members combined with H₂ depletion in the ¹³C-depleted methanogenic end-members is consistent with abiogenic gases supporting H₂ autotrophy linked to methanogenesis in the deep subsurface. Continuing efforts to increase the sensitivity of analytical techniques have resulted in more detailed data on the isotopic composition of Shield gases than previously possible. These refined observations have been used to develop a mass balance model, adding substantially to evidence for an abiogenic origin via polymerization. Fieldwork has been carried out at three new Precambrian Shield settings; Soudan Mine (Minnesota); Kidd Creek Mine (Ontario) and Thompson Mine (Manitoba) (Figure 2). Shield gases sampled at deep ground water intersections in many mines in Canada and South Africa reflect a predominantly abiogenic origin due to water-rock interaction, but with carbon isotope depletion and hydrogen isotope enrichment due to mixing with a component of microbially produced methane.

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