11,000 years ago, the last ice age was ending . Glacial ice up to two miles thick covered a large part of the land, extending down to where I am writing in Philadelphia now. Though the retreat of the ice was generally gradual, Graham Hancock says that there were times when huge sheets of ice collapsed, and torrents of water poured to the sea, causing sudden rises in sea level. Plato knew nothing of the Bible, but from Greek oral history, he wrote of a global flood at about the right date. Among cultures as diverse as Native Americans and the Indian subcontinent, many have myths of an all-consuming flood in the ancient past.