Author ORCID Identifier
https://orcid.org/0000-0002-8254-556X
Date of Award
5-2025
Document Type
Thesis (Ph.D.)
Department or Program
Earth Sciences
First Advisor
William Leavitt
Abstract
Understanding how biological signals are recorded and preserved in organic molecules is central to reconstructing Earth’s history and guiding the search for life beyond our planet. Lipid biomarkers – organic molecules produced in cellular membranes – offer unique insights due to their structural diversity, taxonomic specificity, and long-term preservation potential. The hydrogen isotope values (δ²H) of lipid biomarkers track water in the growth environment with an often large offset due to biosynthetic effects. Certain lipids may retain their original H-isotopic composition for up to 108 years, enabling studies of past hydroclimate, metabolism, and ecology. The underlying controls on the δ²H composition of lipids produced by the domain Archaea remain poorly constrained. This dissertation investigates the δ²H values of archaeal isoprenoid glycerol dibiphytanyl glycerol tetraether lipids (iGDGTs), combining laboratory experiments, field observations, and planetary analog studies to evaluate their potential as hydroclimate proxies and biosignatures suitable for life detection beyond Earth. In lab experiments with the thermoacidophilic archaeon Sulfolobus acidocaldarius, I show that lipid-water H-isotope fractionation (2εL/W) is consistently large and negative across a wide range of environmental conditions, indicating that environmental water is the dominant H-source for lipids (Chapter 1). Isotope labeling experiments and mass-balance models further illuminate the role of metabolic pathways in determining lipid δ²H values (Chapter 2). A field survey of hydrothermal springs in Yellowstone National Park (USA) and El Tatio Geyser Field (Chile) reveals that archaeal lipid δ²H values are consistently depleted relative to environmental waters and provides the first environmental calibration of archaeal lipid δ²H (Chapter 3). Patterns in fractionation correlate with spring geochemistry, likely reflecting variation in community metabolism. Lipid hydrogen stable isotope probing (LH-SIP) experiments constrain lipid turnover to decadal timescales, confirming the persistence of these biosignatures in the sediments of hydrothermal springs (Chapter 4). Finally, I assess how these findings can inform life detection efforts on Mars, where hydrothermal deposits are considered high-priority targets for astrobiology exploration (Chapter 5). I highlight strategies that couple orbital-, drone-, and rover-scale methods to identify promising landing and sampling sites. Together, these results advance archaeal lipid δ²H as a geochemical and astrobiological tool and provide a framework for interpreting molecular biosignatures in terrestrial and planetary contexts.
Recommended Citation
Harris, Carolynn, "CHARACTERIZING THE PRODUCTION OF LIPID AND ISOTOPE BIOSIGNATURES BY EXTREMOPHILIC ARCHAEA IN LAB EXPERIMENTS AND TERRESTRIAL HOT SPRINGS" (2025). Dartmouth College Ph.D Dissertations. 348.
https://digitalcommons.dartmouth.edu/dissertations/348
