That's a good question.
I guess one way to "prove" that people existed that long ago would be to look at the evolution of languages. We know from our own experience how language changes over time. It is dynamic, but not enough to form into a whole other language within our own lifetime, yeah? So how long would it take for a new language to grow from an old one? Hundreds of years perhaps? And how about to evolve into the many different languages we have? Certainly thousands.
That, and carbon dating.
I think he was talking about individual people. Like Ghengis Khan.
Ah, right.
Hmmmm.
DNA studies in mummies? Aren't scientists able to trace the evolution of mitochondria DNA and be pretty darn specific about it? They couple that with carbon dating, written record, grave stones, oral tradition. I don't know what else...
Do you know anything about science or do you just watch CSI on your lunch breaks at Wall Mart?