For more information about Professor Lollar, please see her website.

Abstract:

Insights into Habitability and Astrobiology from Exploration

of Earth Analogue Environments
Barbara Sherwood Lollar

Dept of Earth Sciences, University of Toronto, ON, M5S 3B1, CA and Institut de Physique du
Globe de Paris (IPGP), Université Paris Cité, 1 rue Jussieu, 75005, Paris, France
barbara.sherwoodlollar@utoronto.ca
Over the past few decades, first on the deep ocean floor, and then expanding to the
continental lithosphere, Earth analogue studies have revealed previously unexplored
localities and unexpected processes, together challenging us to think more broadly and
universally about the fundamentals of habitability. Scientists investigating microbial
communities identified water-rock chemical reactions such as serpentinization and
radiolysis that produce critical electron donors (e.g. hydrogen) and electron acceptors (e.g.
sulfate) capable of sustaining chemolithotrophic microbial communities in the oceanic and
terrestrial crust. Such processes of water-rock reaction have now been shown to be a major
driver hydrogen and sulfur cycles in the subsurface of the planet, and increasingly their role
in the deep carbon cycle is being investigated.
Subsurface “rock-eating” microbial communities have been shown to be sustained
on long time scales, isolated from the surface hydrologic cycle. Both field and laboratory
discoveries are expanding the spectrum of water-rock reactions that drive the H, S and C
deep cycles and provide mechanisms for sustaining deep subsurface life in the absence of
interaction with a surface photosphere. Discussions of habitability typically focus on the
necessity for fluid mixing and/or spatial geochemical gradients, but recent discoveries
suggests apparently thermally and spatially “stagnant” systems may still be habitable
through radiolysis. New insights from terrestrial analogue sites suggest potential models for
planetary habitability capable of sustaining chemolithotrophic life on bodies where
photosynthesis may never have arisen. These terrestrial discoveries have catalysed an
expanded search for habitable environments on planets, exoplanets and moons to include
not only surface based life but potentially subsurface biospheres.