[I]n his book The Logic of Chance: The Nature and Origin of Biological Evolution, evolutionary biologist Eugene Koonin has shown that the probability of merely attaining RNA replication and translation (a necessary requirement for even the simplest life) is less than 10^-1018. He concludes that it is highly unlikely to occur anywhere in the universe. His preferred explanation is that we are one of the lucky universes among a near-infinite number of universes.In other words, the odds against just one molecular function necessary for life to arise purely by chance are so unimaginably small if our universe is the only one that exists as to be all but impossible.
Koonin's solution is to posit a near infinite number of different universes, a multiverse, in which every event, no matter how improbable, will happen somewhere. Just as the likelihood of rolling double sixes in dice increases the more times you try, so, too, the likelihood of life arising somewhere increases the more universes there are. If the number of different universes approaches infinity, even the most incredibly improbable events will happen in at least one of them.
One (of many) difficulties with the multiverse theory, however, is that it's out of place in a scientific setting. There's no empirical evidence for a multiverse, nor could there be any since any observations we could make would be of objects in this universe. It's not that we're limited by the power of our telescopes, it's that even in principle we can't observe anything outside our universe. Thus the multiverse hypothesis is an example of a metaphysical idea. It can't be verified and it can't be falsified.
Dunston goes on to say:
From a materialistic, evolutionary perspective, our technologically advanced civilization is almost certainly unique in the universe. Indeed, if the origin of life is so improbable that we should not even be here, then it seems we are faced with an interesting choice. The first option is to grant Koonin's theory that we won a lottery against mind-staggering odds, requiring a near infinite number of unseen, untestable universes. The second option arises out of our observation that the universe and this particular planet seem to be incredibly fine-tuned to support life.Those are the only live options. One either believes that the universe was created by an intelligent agent or one believes that there are a near infinite number of universes out there. There's evidence for the first option but none for the second. Moreover, the first option has the philosophical virtue of being a lot simpler than the second.
In any case, the belief that life is a naturalistic phenomenon, a product of purposeless natural forces and processes, is, at bottom, a metaphysical, not a scientific belief because to be at all plausible it must rely on belief in a multiverse.