"@seraphim 1. Krauss isn't making a claim. He's refuting Metaxes' claim that life is necessarily unique and rare. Metaxes can't make such a claim so emphatically when their remains the possibility that life can arise by multiple means. 2. True, we don't yet know exactly how life begins. But it is also true that the plausible theories for the possibility that it arises spontaneously, inevitably, and possibly more than once given the right conditions are increasing. See for example: http://www.sciencedump.com/con... Again, keep in mind here that Metaxes has made a bold claim that life has been "proven" by science to be extremely unlikely. If credible scientists are saying the opposite, than his claim is invalid. 3. Your statement here makes no sense to me. Life on earth has been "exposed" to the environment of earth. Krauss' point is simply that we have the life we have (on earth) because it evolved to the conditions of earth. Therefore, life on earth has the appearance of having been..." - Mark Traphagen