Heterogenous microbial habitability on Mars and its implications for the search for life
Mars appears to have had habitable conditions in terms of the presence of water at various times and at various locations on its surface since the Noachian and into the early Hesperian, as well as intermittently into the Amazonian. However, conditions necessary for the appearance of life are not the same as those for established or dormant life. This fact has huge implications for the presence of life on the planet, its preservation, and the search for traces of martian life. Given the punctuated nature of martian habitability through time and space, life on Mars is unlikely to have had the chance to evolve into more complex forms, for instance those using photosynthesis, and was (is?) most likely chemotrophic in nature.
Study of the traces of such life forms in the most ancient (early Archaean, 3.5-3.3 Ga), well-preserved terrestrial sediments dating back to the equivalent of Noachian/Early Hesperian times, can inform us about the nature of the preserved biosignatures, their distribution, and what methods to use to identify them. These studies show that, where present, chemotrophic life is abundant in volcanic sediments (much of the surface of Mars is volcanic) but, because of its small size <1µm), the morphological, chemical and isotopic signatures are different.
Westall et al., 2013. Habitability on Mars from a microbial point of view. Astrobiology, 13, 887-897.
Westall, F. et al 2011, Early life on Earth and Mars: a case study from ~3.5 Ga-old rocks from the Pilbara, Australia. Planet. Space Sci. 59:1093–1106
The astrobiology seminar series is run by the UK Centre for Astrobiology based in the School of Physics & Astronomy. Astrobiology is a multi-disciplinary subject and the seminar series actively encourages attendance by undergraduates, postgraduates and academic staff from other departments..