But you hit the key point - "before humans existed there was no oral history". That's exactly the reason Genesis has to be allegory, or at least fable. It's not as bad as telling children that storks bring babies or babies are found in a cabbage patch, but it's the same sort of thing. "Daddy, where did the moon come from?" Kids seek answers.
Our approach has always been to be honest with the kids. My eldest asked me about something when she was about three and I gave her the full scientific explanation (something like "how does a lightbulb work?"
. She sat there for a few moments digesting what I had just said and responded, "yeah", as if to confirm that I had gotten the correct answer. It took everything I had to avoid exploding in laughter.
We can no more prove that a god does not exist than we can prove that one does, although the lightening strike on the vatican an hour after the pope announced his resignation is pretty good evidence, just not conclusive. What makes you good or bad is how you are perceived by other creatures, mammal, insect, acquatic, or otherwise. A butterfly knows who is safe to land on and who is not. Critters have an instinct we can't hope to comprehend because we've abandoned such things. But even if you restrict it to humans, sometimes you can just tell something isn't right with someone.
Sartre's take on it was "hell is other people". I'm inclined to agree. Perhaps the worst outcome of death would to be stuck for all eternity watching home movies, reruns, of your own life. For those who are at peace with themselves, you could call that a heaven. For most of us, it would be a hell. But nobody can know until that time arrives, and by then there's nothing you can do about it. Arlo Guthrie's "Last Train to Glory" comes to mind.