Doctor of Philosophy
Dr. Gordon Osinski
Meteorite impacts are ubiquitous throughout our solar system and are a fundamental geological process on rocky and icy planetary bodies. Though initially detrimental to biology, an impact event can favourably change the availability and habitability of a substrate for endolithic organisms, which are then able to (re)colonize micro-fractures and pore spaces created during the impact. The colonization of rocks by endolithic communities is an advantageous trait, especially in environments such as hot or cold deserts, where temperature shifts, low water availability and high UV indices pose a significant problem. On Mars, similar conditions – albeit, more extreme – prevail. In these instances, impact structures could provide refuge to endolithic organisms. Previous work has shown the increase of microbial biomass with shock level in sedimentary rocks, related to increases in porosity. However, sedimentary rocks experience a collapse of pore spaces at pressures over ~35 GPa and, thus, do not support endolithic colonization at pressures higher than this. In contrast, the porosity of crystalline rocks such as gneisses increases proportionally until vapourization. This study considers shocked gneisses from the 39 Ma, 23 km diameter Haughton impact structure, Devon Island, Canada, and investigates the relationship between shock metamorphism and microbial colonization. Utilizing a variety of microscopy techniques, the subsurface community was visualized and the biomass levels calculated with increasing shock metamorphism. Average cell abundance was found to increase with shock level, with a maximum of 108 cells/g. It was found that microbial biomass did increase with increasing porosity, and was not affected by reductions in trace element concentrations of the rock, likely being more dependent on exogenous nutrients within meteoric waters or supplied aerially. It can be concluded that crystalline substrates can become habitats for endolithic organisms through the process of impact metamorphism, providing an excellent refuge in extreme environments. On Mars where the substrate is largely basaltic, it is suggested that impact craters would be an excellent target for life detection due to extensive deposits of shocked basalt. These more mafic rocks, coupled with the presence of hydrothermal activity, would have potentially provided significant colonization potential on early Mars and may continue to provide refuge today.
Pontefract, Alexandra Janine, "Impact Craters as Habitats for Life: Endolithic Colonization of Shocked Gneiss from the Haughton Impact Structure, Devon Island, Canada" (2013). Electronic Thesis and Dissertation Repository. Paper 1668.