How the Geochemistry of Sediments can inform our Understanding of the Habitability of past Earth and planetary Environments (Virtual)

Friday, January 29, 2021 - 1:10pm
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Dr. Elizabeth Swanner, Dept. Geology and Atmospheric Sciences (GEAT), Iowa State University

Host - Vela

In a sentence, geochemistry applies equilibrium and kinetic constants derived from reductionist experiments to identify the processes controlling the distribution of elements and their isotopes in complex Earth environments and materials. As a low-temperature (also called “aqueous”) geochemist, I specifically investigate the distribution of metals in aquatic systems as an archive of information about past biological, chemical, and geological events. Much of my work centers around redox-sensitive elements that are relatively abundant in Earth’s crust, for instance the transition metals iron manganese, and the cosmopolitan and stinky element sulfur. These elements are redox-active under aqueous conditions at earth’s surface, and so can provide a source of energy to microorganisms that can catalyze and conserve energy from redox transformations through cellular electron transport chains (and, they are also bioessential nutrients). Depending on the redox state and environmental conditions (e.g., Eh, pH, presence of ligands, etc.), all of these elements can dissolve out of or precipitate into minerals. Thus, they form “chemical sediments” that archive information about their formation mechanism and prevailing environmental conditions (i.e. they are “proxies”).


In this seminar I will evangelize for the discipline of geochemistry, but also share case studies from my own research. We are currently studying lakes where chemical sediments are deposited under anoxic conditions. Anoxic lakes are truly “microbial worlds”, and so make great analogs for evaluating the hypotheses generated through observational and historical sciences regarding the origins and activity of early microbial life on Earth or putative microbial life on other planetary bodies. The iron-, manganese-, and sulfur-enriched chemical sediments we observe forming in anoxic lakes have some similarities to sediments detected in the former lakebed discovered in Gale crater, Mars. We are comparing our analyses of terrestrial lake sediments with elemental analyses of iron and manganese-enriched sediments by the ChemCam laser-induced breakdown spectroscopy (LIBS) instrument onboard the Curiosity Rover. Our findings have implications both for the presence of oxygen and microbes on Mars’s surface during its aqueous past.

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