Graham Hancock has an interesting theory of a worldwide civilization that was wiped out (along with the mastodon) by a comet hitting the north american icecap during the younger dryas period around 11000 years ago.<p><a href="http:&#x2F;&#x2F;www.amazon.com&#x2F;Magicians-Gods-Forgotten-Wisdom-Civilization&#x2F;dp&#x2F;1250045924" rel="nofollow">http:&#x2F;&#x2F;www.amazon.com&#x2F;Magicians-Gods-Forgotten-Wisdom-Civili...</a>