It would seem that some kind of event took place that caused flooding throughout the world. As far as I know, every civilaztion on earth has a flood story. The trick would be to tie these stories together in a timeframe to discover when the event happened. I'm sure someone has come to that conclusion already. Anyway, there is much evidence to suggest lost cities throughout the world that are now underwater or overgrown in jungles, etc.
Re: evidence of time frame for a universal flood.
Check out the 7/24/06 post "Terrestrial Evidence of a Nuclear Catastrophe in Paleoindian Times." Lots of interesting although technical detail. Also many comments already. If you know how to put this in red, that would be helpful. I am new to computers and don't know how.