Subsurface Habitability in the Earth’s Deep Hydrosphere: Implications for Planetary Science and Astrobiology





Subsurface Habitability in the Earth’s Deep Hydrosphere: Implications for Planetary Science and Astrobiology

Prof. Barbara Sherwood Lollar, University of Toronto

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 [1-3] 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.

Rich in reduced dissolved gases such as CH4 and H2 [4-5], these fracture waters have been shown to host extant microbial communities of chemolithoautotrophs dominated by H2-utilizing sulfate reducers and, in some cases, methanogens [6]. Recent estimates of global H2 production via WRI including radiolysis and hydration of mafic/ultramafic rock (e.g. serpentinization) show that the Precambrian continents are a source of H2 for life on par with estimates of H2 production from WRI calculated for the Earth’s marine lithosphere [5]. To date this extensive deep terrestrial habitable zone has been significantly under-investigated compared to the marine subsurface biosphere. Beyond Earth, these findings have relevance to understanding the role of chemical water-rock reactions in defining the potential habitability of the subsurface of Mars [7], as well as that of ocean worlds and icy bodies such as Europa and Enceladus [8-9]. This talk will address some of the highlights of recent exploration of the energy-rich deep hydrogeosphere, and connections to deep subsurface life on Earth and to planetary exploration and astrobiology. An overview of the key recommendations of the recent National Academies Report – the 2018 Astrobiology Science Strategy for the Search for Life in the Universe will be provided as well.

[1] Lippmann-Pipke et al. (2011) Chemical Geology 283:287-296. [2] Holland et al. (2013) Nature 497:367-360. [3] Warr et al. (2018) Geochimica Cosmochimica acta 222:340-362. [4] Sherwood Lollar et al. (2002) Nature 416:522-524. [5] Sherwood Lollar et al. (2014) Nature 516:379-382. [6] Lin et al. (2006) Science 314:479-482. [7] Michalski et al. (2018) Nature Geoscience 11:21-26. [8] Hand, K.P., et al. and the Project Engineering Team (2017): Europa Lander Science Definition Team Report. NASA JPL D-97667. [9] Waite et al. (2017) Science 356:155-159.


Short Bio


Dr. Barbara Sherwood Lollar, Companion of the Order of Canada and Fellow of the Royal Society of Canada, is a University Professor in Earth Sciences at the University of Toronto. She is a Canada Research Chair in Isotopes of the Earth and Environment, Norman Keevil Chair, and cross-appointed in the Departments of Chemistry, and Chemical Engineering and Applied Chemistry. 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, Canada Council Killam Fellowship and NSERC Accelerator, and Steacie Awards), the 2012 Eni Award for Protection of the Environment, 2012 Geological Society of America Geomicrobiology and Geobiology Prize, 2014 International Helmholtz Fellowship, 2015 Fellow of the American Geophysical Union, 2016 NSERC John Polanyi Award, 2016 Bancroft Award for the Royal Society of Canada and 2018 Logan Medal of the Geological Association of Canada. Sherwood Lollar is currently Director of the Earth, Atmosphere and Ocean Sciences Division of the Royal Society of Canada; Member of the Advisory Council to the Governor-General for the Order of Canada, and Chair of the United States National Academy of Sciences 2018 Review for the Strategy for Astrobiology and the Search for Life in the Universe. She has served in numerous advisory roles for the Canadian Space Agency, NSERC and NASA including the National Academies (NAS) Committee on Astrobiology and Planetary Sciences, NAS Committee on the Origin and Evolution of Life, and is currently a member of the U.S. National Academy of Sciences Space Studies Board (2016-2020).

For their 2019 joint annual meeting in Quebec City, the Geological Association of Canada, the Mineral Association of Canada, and the Canadian Chapter of the International Association of Hydrogeologists are deeply honoured to have Barbara Sherwood Lollar as keynote speaker for one of the plenary sessions at the meeting.