“Subsurface Life on Earth and on Other Planets in the Solar System” with Barbara Sherwood Lollar (Department of Earth Sciences, University of Toronto, Canada)

The search for extraterrestrial life is a main motivator for the exploration of other planets and moons in the solar system and for the search for extrasolar planets. In the solar system, Mars, Europa and Enceladus – the latter two satellites of Jupiter and Saturn, respectively – are often cited as possibly harboring extraterrestrial life. The surface environments of these, however, are not conducive to life either because of low temperatures or harmful radiations or both. Instead, life may have originated and evolved in the underground, in oceans covered by kilometer thick ice layers for Europa and Enceladus and in the Martian soil. We know from Earth that extremophiles (life forms that tolerate extreme environmental conditions) can be found at depths of at least up to three kilometers. The recent National Academies Report – the 2018 Astrobiology Science Strategy for the Search for Life in the Universe emphasized the need for an expanded focus on investigation of subsurface environments and subsurface processes for our understanding of planetary evolution, habitability 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 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. 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, as well as that of ocean worlds and icy bodies such as Europa and Enceladus.

Barbara Sherwood Lollar CC FRS NAE FRSC – University Professor in Earth Sciences, University of Toronto is a Fellow of the American Geophysical Union (2015), the Geochemical Society (2019) and European Association of Geochemistry (2019). She is Co-Director of the Canadian Institute for Advanced Studies (CIFAR) program Earth 4D – Subsurface Science and Exploration and co-leads an ISSI working group on “Extant subsurface Life on Mars? Science, Tools & Missions Together”. She is currently a member of the Eni Prize Commission (2013-2021), the American Geophysical Union Honors and Recognition Committee, the United States National Academy of Sciences Space Studies Board, the U.S. National Academy Decadal Survey Steering Committee for Planetary Sciences and Astrobiology, the Fellows Selection Committee for the Royal Society London UK, among others. Recent awards include the 2020 Killam Prize for Natural Sciences, 2019 NSERC Gerhard Herzberg Gold Medal, 2019 C.C. Patterson Medal for Environmental Geochemistry, 2016 NSERC John Polanyi Award, 2014 International Helmholtz Fellowship, and 2012 Eni Award for Protection of the Environment.

Webinar was recorded on December 16, 2021