axt113 on 06 October 2010
Simpler explanation, big floods happen from time to time near large rivers and lakes, which is where early humans lived , so early humans thought that such a flood meant the entire world was flooded, and some schmoe who survives the flood with his family on a boat with some animals they owned thinks god chose him as special, then like all good tall tales, it gets bigger as its told and retold
Underwater cities are easy to answer, living too close to a shore where floods can wash away mud huts and buildings, or where Tsunamis hit and bam the story of underwater cities comes along
