Not eventually finding life on Mars would be more than surprising, it would call into question a lot of what we thought about life and its origins. The way I look at it, physics begets chemistry begets biology. Mars may not be the Garden of Eden, but conditions aren't so inhospitable as to make life impossible, and for life it's a binary issue--if life's not impossible, then it's probable.

RL is absolutely correct that we have as yet found no evidence of life on Mars.

Which is why Dr. Nick engaged his droll sense of humor to declare Mars a dead planet "to a first approximation". He's right too. Given how closely we've studied Mars, we've pretty much been able to rule out any macroscopic life, so from here on it's microbes all the way down.

I don't think any of us will be particularly surprised when life is eventually discovered on Mars. And I think at least some of us actually want it enough to be on guard against premature celebration. We all remember the meteorite false alarm. It will indeed be a hugely historic discovery, and we ought to be careful to get it right.