Actually, it is not. The origin of life being an unsolved problem, there are a number of theories (or proto-theories) out there. Some of them hypothesize a "pre-biotic soup" of some sort (and I presume these differ from theory to theory); others don't. I would imagine, as layman in these matters, that life probably formed in some kind of solvent medium, most likey water, but I wouldn't close off other possibilities. We know, for instance, that some of the simpler amino acids are created naturally in interstellar dust clouds.
And this is different from faith in what way?
The only faith here is that common to all scientific fields: That any well reasonably well defined problem concerning the behavior or history of the natural world is potentionally soluble, and might explained by some theory consistent with what we otherwise know about the laws of nature.
In respect to those that assume the condition, it is. It is of those species that I write. I do not consider those theories involving space aliens.
How do we know such a thing? We have never been there. I do know that the famous "find" 3-4 years ago of what was supposed to be evidence of proteins on a martian meteorite was found to be false.