Noah's Flood
Surely almost every prehistoric civilization has experienced floods. They are big scary acts of god, many people die, and when a big one happens you can bet the talk about it for generations. Almost every culture has a flood myth.
Given this background, in a world imagined to be animated by god, the question is: why? This is where creative license kicks in. Ancient Hebrew "explained" the flood as retribution for being evil. the story grows in size just like any fish story: not only big, this flood was global proportions. Not on a few people sinning, but everyone on earth (save one family). As the story is retold is it embellished with other moral narratives. This is normal for an epic myth.
Noah's flood was based on an earlier story, but very much exaggerated. That is all there is to it.
Resources
- The Impossible Voyage of Noah's Ark - National Center for Science Education