Well, we shouldn't forget that life it self, the science behind abiogenesis contains still many open questions. The origin of life, might require so many conditions to come together, that most planets might be habitable, but actually end up as sterile rocks floating in space, because there was never a chance to form organic compounds comlex enough to support live, could very well be that if humans once get to those stars and planets, that they will find thousands of oceans full of just the first stages of the process, but it never moved past that. Who knows? Maybe we are after all the unicorns of this universe ... or all the other races out there have killed them self, kinda like we do now to our self :/. Well however that be, I think a scientist once described abiogenesis, like the act of balancing razors on top of each other, just a slightly bit to much of one element, or not enough of the other, and it simply doesn't work.