Exploring the Preservation of Biosignatures in Extreme Environments

Author: Betts, Makayla Nicole

Year: 2026

Degree: Dissertation (Ph.D.)

Advisor: Sessions, Alex L.

Committee Members: Grotzinger, John P.; Orphan, Victoria J.; Leadbetter, Jared R.; Sessions, Alex L.

Option: Geobiology

Abstract

This thesis investigates how biosignatures are generated, modified, and preserved in extreme environments, with the goal of improving their interpretation in both Earth history and astrobiological contexts. Biosignatures—including isotopic compositions, molecular distributions, and cellular structures—are not static records of life but are shaped by the environmental and diagenetic processes that govern their formation and preservation. Constraining these processes is therefore essential for distinguishing biological signals from environmental overprints and for identifying conditions most conducive to long-term preservation.

To address this, I examine biosignature formation and preservation across three complementary systems. First, I characterize the isotopic signatures of microbial communities in Antarctic meltwater ponds on the McMurdo Ice Shelf, demonstrating that environmental heterogeneity – particularly differences in ice cover, salinity, and pond history – drives substantial variability in carbon, nitrogen, sulfur, and hydrogen isotopes, even among broadly similar microbial communities. These results highlight that biosignature expression is strongly modulated by environmental constraints and may differ from canonical expectations in extreme settings.

The second chapter investigates the mechanisms underlying the exceptional preservation of organic matter and intact cells in Mono Lake, a hypersaline, hyperalkaline soda lake. Through sediment incubation experiments that manipulate pH, salinity, sulfide, and ionic composition, I evaluate the relative influence of microbial degradation and abiotic stabilization. The results suggest that preservation cannot be attributed to a single mechanism but may arise from a combination of physicochemical constraints on microbial activity.

In the third chapter, I reviewed existing literature on microbial fossilization and conducted preliminary hydrous pyrolysis experiments to explore how biosignatures persist through diagenesis. This work identifies a key gap in current understanding: the role of aqueous geochemistry – particularly pH and salinity – in mediating organic–mineral interactions during burial and heating. Initial experimental results using Mono Lake sediments suggest that these parameters may influence the stability of cellular morphology and organic matter across mineral matrices.

Together, these studies demonstrate that biosignatures are emergent products of coupled biological, chemical, and physical processes, and that their preservation is highly sensitive to environmental context. This work emphasizes the need to integrate aqueous chemistry, mineralogy, and microbial ecology when interpreting biosignatures, with direct implications for reconstructing early Earth environments and guiding the search for life on other planetary bodies.