Apparently, it's quite uncertain how much (if any) current volcanic activity there is, which would make organisms a possible source: http://www.popsci.com/mili

Apparently, it's quite uncertain how much (if any) current volcanic activity there is, which would make organisms a possible source: http://www.popsci.com/military-aviation-amp-space/article/2009-01/methane-may-point-life-mars http://www.popsci.com/military-aviation-amp-space/article/20... http://www.popsci.com/science/article/2010-09/mars-methane-changes-seasons-and-scientists-wonder-why http://www.popsci.com/science/article/2010-09/mars-methane-c...