In over my head

He always asks the really hard questions in the car. While I'm driving and there is no way to easily redirect his attention to his myriad toys or "Oh look at Nikita!" I think he knows I'm trapped and have to answer. It really isn't fair.
On the way to a bowling date today, Big Dog asks, "Was the earth made?"
Oh boy. So many answers. Mine? "Yes."
"And the people. Were they made?"
Slightly less self assured I say, "Well, kind of. You know, this is kind of a complex topic."
Undaunted he continues, "So how did they start? I mean when they made the earth, what part did the people start with?"
"You mean the planet? How did they make the planet?"
"Yes."
How do I explain the concept of expanding mass and the Big Bang to a kindergartner? Seriously? So I went simple, "People didn't make the planet. There is a theory that the universe and all the planets came from a kind of explosion. I believe that. Other people believe other things." See how I neatly skirted the religious stuff, but left room for later discussion if he heard other stories?
"Oh. But then were did the people come from?"
"Well, that's another toughie, buddy. I believe that we evolved from very tiny ancient bits of life that over long periods of time changed and grew. Eventually, after years and years and years we became people. Remember when we went to see the Lucy exhibit at the Science Center? I believe that at some point in time that is what we evolved from. Interesting right?"
Silence.
After a long pause, he started again.
"Well, I believe the explosion."
"Ok, that's good. I'm sure we can find more books at the library if you want to know more."
"I belive the explosion," he repeated. "But it is kind of silly, right?"
"That the universe was born of an explosion? Sure, I guess so."
"Yeah, I believe it, but mama, that's kind of crazy." And he left me hanging about his belief in evolution. Couldn't he have asked Mr. Dog about this stuff? He is a scientist after all.