The early Earth was characterised by anaerobic environmental conditions and a geological context very different from those of the Earth today. Sediments of largely mafic to ultramafic composition were deposited in shallow water environments bathed by hydrothermal fluids. Early Mars, on the other hand, was more or less a “land-locked planet” with isolated water-filled basins/craters compared to the water world of the early Earth. But on a microbial scale, the geological and environmental parameters of both planets were very similar. It is for this reason that the traces of primitive life contained in early terrestrial sediments make excellent analogues for the study of possible life on Mars. Although Early Archaean (~3.5 Ga) terrestrial life was more diversified than martian life is expected to be, the excellent preservation of chemotrophic microbial signatures helps us to understand what to look for on Mars. Utilisation of these analogues for testing instrumentation to be flown to Mars in the European/Russian ExoMars mission aids understanding of the potential limitations of space instrumentation – and supports the rationale for sample return from Mars.

Westall, F., et al., 2015, Biosignatures on Mars: what, where and how? Implications for the search for Martian life. Astrobiology, vol 15, pp 998-1029.

Westall, Fet al., 2015. Archean (3.33 Ga) microbe-sediment systems were diverse and flourished in a hydrothermal context. GEOLOGY, July 2015; v. 43; no. 7; p. 615–618