If someone argues that you don't have all the answers to this and that- thus God exists... it becomes fair to counter with another one word explanation: nature. Don't let them put their troubled ignorance on you.
I'm not sure how "nature" answers it, but I'm not what has become a typical conservative believer (the type who insists that the Bible is a literal science text, which it clearly isn't, or insists that its Genesis timeline is accurate, etc.).
I'm not sure how "nature" answers anything. I mean, sure, I'm there with the whole "there is no god" thing, but something to remember is that these people are not arguing in good faith. Nothing you ever say is going to convince them, and certainly not this.