Interpretation of biosignatures in extreme environments, and their potential impact for the search for life on Mars

• Main Author: Nauny, Philippe É. M.
• Format: Thesis
• Language: unknown
• Published: University of Glasgow 2019
• Subjects: astrobiology, biosignatures, Mars, biomarkers, lipids, DNA, Chile, Atacama, Sairecabur, Iceland, Hverfall.; Hverfjall; Iceland
• Online Access: https://dx.doi.org/10.5525/gla.thesis.77875; http://theses.gla.ac.uk/id/eprint/77875

The search for life beyond Earth, and on Mars in particular, is one of the key points of astrobiology research. However, space missions are expensive and time-consuming. Simulating such missions at analogue sites on Earth can thus save time and money whilst working in natural settings. This thesis presents three studies of biosignatures from three different martian analogues. These biosignatures were linked — when possible — to environmental parameters observed at their sampling sites. The first study was set in a hot a dry environment in the Atacama Desert in Chile. It aimed to identify biolipids and genetic material in soil samples, along a high-resolution shallow depth profile in a dry alluvial fan. Signs of microbial life were observed at the surface, despite the extreme environmental conditions, and at deeper depths — together with degraded plant material — above a layer of very fine grained sands and silts. Overall, biolipids of plant origin showed the strongest concentrations, despite the quasi-absence of plants at the surface. The poor quality of the DNA sequencing results prevented their interpretation. The sedimentation history of the sampling site seemed to be more complex than what could be observed at the surface. The second study was on the flank of the Sairecabur, a high-altitude volcano in Chile. Soil samples, taken along four depth profiles following an altitude gradient, were analysed for their biolipids and genetic material content. Again, biolipids of plant origin showed the strongest concentrations — both at vegetated and barren sites — and the poor quality of the DNA sequencing results prevented their interpretation. Additionally, the variable environmental and physico-chemical conditions at the different sampling sites makes it more challenging to draw conclusions regarding the altitude gradient. The third study took place inside the crater of Hverfjall, a tuff ring volcano in Iceland. Colonisation of the crater by life was studied by measuring microbial activity and biolipids in soil samples along a transect across the crater, and by considering the relationship between the results and the wind patterns over and within the crater. The results indicate that wind may be a major factor for controlling the deposition and removal of biosignatures in Hverfjall’s crater. All three sites were isolated environments. Despite this, lipid biomarkers, genetic material or microbial activity were observed at each of these sites. Molecules produced by plants were also found everywhere despite the general absence of nearby plants, implying some external source for the molecules. Aeolian input is probably the dominant factor for spreading biosignatures to these isolated locations. The high altitude sites on the Sairecabur can serve as analogues to for a Noachian Mars, when the planet lost its global habitability, whereas the Atacama desert is an analogue for present-day Mars. Hverfall serves as an analogue for both past and present Mars, focusing on wind dispersal of biomarkers. The results obtained suggest that if any active biomarker source (i. e. life) were to be identified on Mars, downwind sampling represents an alternative means by which to sample biomarkers whilst avoiding any direct contamination of the source.