As part of the Water Institute's WaterTalks lecture series, Barbara Sherwood Lollar, University Professor in Earth Sciences at the University of Toronto, presents, 'Exploration of the Earth's Deep Hydrogeosphere and Subsurface Microbial Life.' Light refreshments will be provided. More information Geochemists have 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 (terrestrial) or mixing from the over-lying oceans. The earliest periods of Earth's fluid history were largely thought to have been overprinted by mixing, and/or geochemically reset, at least on a macroscopic scale Global investigations in the world's oldest rocks have recently revealed groundwaters flowing at rates > L/min from fractures at km depth in Precambrian cratons. Rich in reduced dissolved gases such as CH4 and H2, these fracture waters have been shown to host extant microbial communities of chemolithoautotrophs dominated by H2-utilizing sulfate reducers and, in some cases, methanogens. With mean residence times ranging from Ma to Ga at some sites, and in the latter case, geochemical components of Archean provenance, not only do these groundwaters provide unprecedented samples for investigation of the Earth's deep hydrogeosphere and early atmosphere, they are opening up new lines of exploration of the history and biodiversity of extant microbial life in the Earth's subsurface. Speaker bio Dr.Barbara Sherwood Lollar, C.C. FRSC is a University Professor in Earth Sciences at the University of Toronto. She is Research Chair in Isotopes of the Earth and Environment, Director of the Stable Isotope Laboratory, and Past-President of the Geochemical Society. In 2015 she was named a Fellow of the American Geophysical Union. Sherwood Lollar has published extensively in research on stable isotope geochemistry and hydrogeology, the fate of carbon-bearing fluids and gases such as CO2, CH4 and H2 in ancient fracture waters in the Earth's crust, and the role of deep subsurface microbial populations in carbon cycling. She has been a recipient of academic awards including the NGWA Darcy Lecturer, Steacie, Killam and NSERC Accelerator Awards and most recently the 2012 Eni Award for Protection of the Environment 2012 Geological Society of America Geomicrobiology and Geobiology Prize, and 2016 NSERC John Polanyi Award. She is currently a member of the National Academies of Sciences Space Studies Board and Chair of the National Academies State of the Science of Astrobiology 2018 committee.