Date of Award
Master of Science in Biological and Environmental Sciences (MSBES)
Serpentinizing systems host long-lived reactions in which an ultramafic (or mafic) rock package, rich in reduced species, is progressively metamorphosed via hydration and oxidation into a serpentine-dominated mineral assemblage. On Earth, this process drives redox gradients in related water-rock systems: hydrogen gas is produced, reduced minerals are transformed to oxidized counterparts, and hydrocarbon chains (with potential to fuel chemosynthetic microbes) are released. The life sustaining capacity and abundance of serpentinite on/in silicate planetary bodies make such systems astrobiologically intriguing.
The Mars 2020 rover, equipped with a DUV Raman, is likely to explore serpentinite deposits (exposed selectively at crater rim sites) during its time in Jezero crater. However, very few studies have explored the efficacy of spectroscopic methods in detecting biosignatures in the challenging context of serpentinites. In this study, Raman and FTIR spectroscopy are used to analyze serpentine minerals after time series incubations in organic solutions with and without an active microbial culture, to determine whether sterile and inoculated (live) organic-rich solutions leave different micro-scale organic signatures. We also tested the impact of dessication on organic films on the mineral surfaces. We find that fluorescence presents significant challenges to detailed analysis. However, changes in spectral character as a function of time and the presence of life are evident. The association of organic material with all samples is rapid, evidenced by quick changes to spectra in the form of fluorescence, aliphatic (simple C-H bonding) peaks from 2800 to 3000 cm-1, amine and amide peaks above 3000 cm-1 detected via Raman spectroscopy, and subtle changes in FTIR spectra. Data interpretation relied on ratioing of peak heights of CH3 and CH2 groups (R3/2) and principal component analysis (PCA)s were performed but the true strength of these analyses remains in the combination of Raman and FTIR spectroscopic techniques, which produce complimentary data streams and enable the differentiation of all 5 experimental groups (pre-incubation, live incubation, sterile incubation, live desiccated, and sterile desiccated).
Sousa, Alexander, "DISTINGUISHING LIVING AND NON-LIVING SURFACE DEPOSITION ON SERPTENTINE: IMPLICATIONS FOR BIOSIGNATURES AND ASTROBIOLOGY" (2019). Open Access Master's Theses. Paper 1745.