that God did it is not an explanation. it's a statement of faith. it's okay to say He did it but that doesn't make it a scientific answer to the question. I think there is a scientific answer to the question, but I am not sure what it is. I do have some ideas that I consider possible however.
one is the big bang theory. it has some problems but they may have answers. the problems are, it begs the question (what happened before the big bang?) and it requires some strange variables like dark matter and a "cosmological constant" that seem ad hoc (stuff made up for no good reason) to me. not my favorite explanation, but the questions are not completely unanswerable.
the other argument is that evolution/nature didn't need to "start" because the universe has always existed. a steady state theory (there are many possible variations of this) could be correct. the big-bang-little-crunch cycle idea is steady-state in a manner of speaking, but I'm not a fan of it either and it seems to lack evidence. a better steady state theory I guess would involve particulate matter getting created in the interstellar void, absorbing energy from the background radiation of the stars and turning it back into matter. At any given point in space there are billions of little light packets from nearby stars, so perhaps in certain conditions these are converted into interstellar dust clouds (possibly "virtual" particles that turn into matter over time) and eventually re-collapse into planetary nebulae and new stars.
in any case, I do know that it exists today and existed yesterday, and on back for quite a while. there's not apparently any curve towards non-existence either, so it seems reasonable to think it has lasted forever, changing the whole while. in other words evolution/change over time always has happened. this view makes it possible to think of God and Nature as philosophically the same entity since God has always been and always will be, and takes away the atheist's argument that believing in God is somehow over-complicating things.
as to abiogenesis, (the beginning of organic evolution) I think I posted something about the possibility of some kind of complex mineral salts or clays in geothermal vents as the cause/ancestors of the first organic microbes. I don't know the complete bottom-line mechanism, and neither do today's scientists apparently. however the answer is the same as for the universe: a scientific explanation exists, regardless of whether I or anyone living today knows what it is or not.