Hydrothermal systems have been suggested as suitable environments for the
appearance of life on the Early Earth and may provide habitats for microorganisms on
Mars. The deposits created by these systems are preserved in the geological record.
This research investigates the key mineralogical, textural and biological markers
found in terrestrial hydrothermal deposits that can be used as analogues in the search
for evidence of life on Mars.
Samples of silica sinter from Iceland and New Zealand, the Rhynie Chert 396 Ma old
deposit from Aberdeenshire and hydrothermally altered impactites from the
Chicxulub impact crater have been analysed to understand the mineralogical
properties unique to the different hydrothermal conditions and the evidence of extant
or extinct microorganisms within them. Re-colonisation of basaltic substrates by hot
spring-derived cultures was also carried out. This research was conducted using a
multidisciplinary approach with the analytical techniques and instruments involved
currently used for in-situ and orbital observations of planetary bodies. The principal
techniques, Fourier Transform Infrared (FTIR) spectroscopy and Gas
Chromatography Mass Spectrometry (GCMS), were used due to their combined
capabilities in the identification of a variety of rocks and minerals, and a wide range
of organic compounds.
This PhD research has shown that FTIR in particular is an exceptional analytical
technique for use in astrobiological investigations. This research has characterised
hydrothermal deposits of different ages and created by different processes on Earth to
ascertain their potential for preserving organic compounds in similar deposits on
Mars. Results indicate that siliceous hydrothermal deposits of recent and ancient
formation yield biomolecular evidence for past and present microbial colonisation as
do hydrothermally altered impact deposits and re-colonised basaltic substrates. The
identification of mineralogical and biological information using FTIR reflectance
spectroscopy has wide implications in the search for life on Mars and other planetary
bodies.