Isotopic and geochemical tracers of fracture fluids in Precambrian cratons: Time capsules for the deep biosphere

最近，我们的国际团队在南非前寒武纪岩石勘探钻孔排出的含盐裂缝水中，在地表以下2.8公里处发现了地球上一些最孤立的微生物生态系统（Lin et al. 2006, Science）。像海底的热液喷口一样，这些深层裂缝水是地球上最富h2的环境，也是广泛的水-岩反应的其他产物的储藏库，包括非生物成因的碳氢化合物和放射性成因的惰性气体（Sherwood Lollar et al., 2002 Nature）。我们在南非的团队最近的结果，以及我们在加拿大前寒武纪地膜上的初步结果表明，这些自由流动的裂缝水中稀有气体的成分已经超过20亿年了——证明了这些地下水与地表光球的分离是在一个以前无法识别的时间尺度上进行的（Lippmann-Pipke， Sherwood Lollar等人，2011年化学地质学；Holland， Sherwood Lollar等人，2012年在Nature上修订）。虽然我们已经了解了很多，但这些令人兴奋的结果揭示了更多有趣的科学问题，这些问题对于理解地球上生命的分布和地下深处的可居住性具有根本性的重要性；地壳深部流体和还原气体（甲烷、氢）的起源和年龄；以及地球化学（地下的水岩蚀变反应）对地下生命的支持程度。“发现”号的研究项目集中在加拿大地盾上的前寒武纪岩石中尚未被调查的地点，重点解决上述问题——它们对我们理解这个星球的可居住性、地球上生命的进化具有深远的意义；以及其他行星或卫星地下存在生命的可能性。

Some of the most isolated microbial ecosystems on Earth have recently been discovered by our international team at 2.8 km below the Earth's surface in saline fracture waters discharging from exploration boreholes in the Precambrian rocks of South Africa (Lin et al. 2006, Science). Like the hydrothermal vents on the ocean floor, these deep fracture waters are the most H2-rich environments on the planet, and are repositories of other products of extensive water-rock reaction including abiogenic hydrocarbons and radiogenic noble gases (Sherwood Lollar et al., 2002 Nature). Recent results by our team in South Africa, and preliminary results at our sites on the Precambrian Shield in Canada, indicate components of the noble gases in these free flowing fracture waters are more than 2 Billion years old - attesting to the isolation of these groundwaters from the surface photosphere on a previously unrecognised timescale (Lippmann-Pipke, Sherwood Lollar et al., 2011 Chemical Geology; Holland, Sherwood Lollar et al., 2012 in revision at Nature). While much has been learned, these exciting results have opened up yet more intriguing scientific questions of fundamental importance for understanding the distribution of life on Earth and the habitability of the deep subsurface; the origin and age of deep crustal fluids and reduced gases (methane, hydrogen); and the degree to which geochemistry (water-rock alteration reactions in the subsurface) can support subsurface life. Focused on as yet under investigated sites in Precambrian rocks on the Canadian Shield, this Discovery research program is focused on addressing the above questions - with their profound implications for our understanding the habitability of this planet, the evolution of the life on Earth; and the potential for life in the subsurface on other planets or moons.