The Hidden Hydrogeosphere: Implications for deep subsurface microbiology and the search for life

Our research program at Toronto focuses on Earth analog systems – in particular, deep fracture waters preserved on geologically long time scales in the Precambrian cratons of Canada, Fennoscandia, and South Africa. Science has long relied on fluid inclusions – microscopic time capsules of fluid and gas encased in host rocks and fracture minerals – to access preserved samples of ore-forming fluids, metamorphic fluids, and remnants of the ancient atmosphere and hydrosphere. Until recently, groundwaters were thought to reflect only much younger periods of water-rock interaction (WRI) and Earth history, due to dilution with large volumes of younger fluids recharging from surface hydrosphere. In the last 10-20 years, global investigations in the world’s oldest rocks have revealed groundwaters flowing at rates > L/min from fractures at km depth in Precambrian cratons. With mean residence times ranging from Ma to Ga at some sites, and in the latter case, geochemical signatures of Archean provenance, not only do these groundwaters provide unprecedented samples for investigation of the Earth’s ancient hydrosphere and atmosphere, they are opening up new lines of exploration of the history and biodiversity of extant life in the Earth’s subsurface.