http://www.newsweek.com/nasa-curiosity-rover-finds-potential-signs-ancient-life-mars-965686

It was to a great fanfare of publicity that researchers announced they had found evidence for past life on Mars in 1996. What they claimed they had discovered was a fossilized micro-organism in a Martian meteorite, which they argued was evidence that there had once been life on the Red Planet. Sadly, most scientists dismissed this claim in the decade that followed—finding other explanations for the rock’s formation.

While we know that Mars was habitable in the past, the case demonstrates just how hard it will be to ever prove the existence of past life on its surface. But now new results from NASA’s Curiosity rover, including the discovery of ancient organic material, have revived the hope of doing just that. Understandably, the authors of the two papers, published in the journal Science, are very careful not to make the claim that they have discovered life on Mars.