There might be life since the landing of Curiosity: http://www.wired.co.uk/news/archive/2012-09/11/curiosity-bac...
Even though I was aware of this possibility, reading this: ... was really depressing. If life is discovered on Mars with the same basic DNA code as on Earth, we may never know its origin or relationship to Earth-life... or at least it will make answering that question more difficult.Worried scientists at Nasa now estimate that there may be as many as 250,000 bacterial spores that could have survived both the journey to Mars and the landing. If Curiosity drills into the ground and strikes water, the Nasa team will have to assess the risk of continuing knowing that they could have permanently seeded life onto Mars. That might mean never knowing for sure whether life was ever indigenous to the Red Planet.