Ancient Waters of the Precambrian Shields: Implications for Subsurface Life and Astrobiology

Presenter: Barbara Sherwood Lollar, University of Toronto
When: November 25, 2013 11AM PST

Ancient H2-rich fracture waters in the Precambrian continental subsurface, with groundwater residence times ranging from millions of years [1] to billions of years [2], provide evidence of a previously unrecognized domain of the terrestrial hydrosphere. Here we report on results from > 30 sites and > 250 samples and boreholes in continental Precambrian sites worldwide. These ancient fracture waters, accessed via mines and underground research laboratories, contain mM concentrations of reduced gases (H2, CH4, ethane, propane, butane) as well as high concentrations of noble gases. This exploration of saline fracture waters more than a km below the Earth’s surface in Precambrian continental crust has identified environments equally as H2-rich as the hydrothermal vents and spreading centers, and sustaining microbial communities of H2-utilizing methanogens and sulfate reducers [3].

First identified in Ne isotope results from the Witwatersrand basin in South Africa [2], novel radiogenic isotope signatures have now been shown to be a consistent feature of these deep waters [3]. Integration of the noble gas signatures with compositional and isotopic information for the reduced gases provide constraints on the residence time of the fracture waters, the degree of interconnectivity of different groundwater systems, and an estimate of the amount of time these waters have been isolated from the surface. This presentation will address the distribution of ancient fluids at selected key reference sites; and the controls of this deep hydrosphere on the biodiversity and distribution of the subsurface microbial biosphere and carbon cycle. Since Mars, like the terrestrial Precambrian crust, consists of billions of years old, tectonically quiescent rocks with areas of ultramafic terrains with H2 producing potential – these results also have profound implications for the search for life on Mars and astrobiology.

References: [1] Lippmann-Pipke et al. (2011) Chem. Geol. 283, 287-296. [2] Holland et al., (2013) Nature 497, 367-360. [3] Lin et al. (2006) Science 314, 479-482.

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