The UNDERWORLD thesis of Hancock’s is that during near the end of the Ice Age there arose an advanced stone age coastal civilization - not advanced like they had cars or lasers but advances like the Egyptians and when the great melt happened this far flung coastal civilization/empire was drowned giving rise to the Atlantis myth and other flood myths with the survivors of the coastal flood moving inland to be among the less advanced humans of the inner continents who viewed the more advances coastal dwellers as gods or near gods. What survived are racial memories and some passed down knowledge turned to myth and legends but for the most part real evidence for this civilization is buried under the seas.
http://www.freerepublic.com/focus/f-chat/2355928/posts
I agree with much of Hancock. In addition to flooding at the end of the Ice Age, there was a massive meteorite impact in the Indian ocean about 4,800 years ago. There were also meteorite impacts in North America at the end of the Pleistocene.