The strange shapes seen in a rock from Mars that some researchers say are fossilised bacteria really are tiny micro organisms, say American researchers. But while they are confident the Mars rock contains fossilised life they cannot quite bring themselves to say it comes from the Red Planet, it might be Earthly contamination. Despite the uncertainty about their origin establishing that the small structures really were living things, and not just mineral globules, would be an advance in a field that has sharply divided opinions.