Welcome to Gaia! ::

AD only came about because the majority of the West, the dominant military and political powers were Christian, and adopted that for ease.

Also, to whoever said 'atheism' is a belief system, it is not. People do not understand this. Atheism is the utter lack of belief in a deity of any shape or form, and leave it at that. The people you argue with are anti-theists, who actively seek to deny a 'God'.

Sometimes I just like to look up at the stars when the sky is otherwise empty. No clouds. No vision obstructions, i.e. trees. If you ever find yourself in a scenario of such with this person ask him to just look at the stars with you for a little. Just look at the stars. After a minute or so of silence say, "Dust, rocks and gas, huh?" He'll probably say something along the lines of "What?"
You: "That's how you believe all of this was created right? Dust, rocks and gas?"
HIm: Something along the lines of "What are you trying to say"
You: "I don't know. It seems to me a tad odd that something as asinine as dust rocks and gas could make something like this. and the more important question is, how did that get here?"

The whole point is to get down to the point where he asks "Where did God come from then?"

"I don't know, I may never know, but that's okay with me. Because I do know one thing. Magically appearing rocks dirt and gas couldn't make something this beautiful.

You may need to improvise. The main point is to not argue it on an intellectual field. That is where he feels most at home at and you can't argue it that way. We smart people are stubborn like that, you should know. Statistics, facts, all of that stuff won;t make any difference, cause he has his own to back his case up. Get him with the beauty of nature.