I left this as a comment on a post by another member but thought that it would be a good post as well..

Life is much more tenacious than we give it credit for. Yes this planet has shrugged off many life forms in its history but to think that ours is the only planet/place that life can or does exist in the universe is idiocracy. I think that life exists in one form or another in any place it possibly can. Just because it isn't 'human' or 'sentient' (in our definition of it) doesn't mean it isn't alive. I live in the desert of Arizona and all around me I see 'life' coming out of the cracks in the concrete and asphalt around me. No water, no care, no one making it happen. Everywhere I go I see 'life' coming out of the woodwork. "Life" as we know it, will in one form or another exist if it can. If it can't, it won't. Period.