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In some zones of Antarctica’s cold and dry desert, the extinction of cryptoendolithic microorganisms leaves behind inorganic traces of microbial life. The extinction of these microorganisms is considered to be the best terrestrial analogue of the disappearance of possible life on early Mars. In the present study, sandstone rock samples from several sites of the Dry Valleys known to harbour endolithic microorganisms, as well as samples with microbial fossils, were analysed by proton induced X-ray emission (PIXE). Our findings suggest significant differences in major element concentrations among the different zones within the same sample. In some sample fractions, these differences could be considered as traces of the microbial origin. However, other samples reveal contamination produced by allochthonous minerals of abiogenetic origin. (c) 2006 Elsevier B.V. All rights reserved.