Earth's Crust

Fourteen thousand years ago, a thick ice sheet a mile deep covered the continent of North America. Concealed beneath this vast expanse of ice, one of the worlds greatest geological mysteries, The Great Lakes, were forming. The Great Lakes are the worlds largest fresh water system but how these Great Lakes formed is still a mystery that scientists are trying to figure out. Many theories abound as to what gouged out the depths of these lakes. Were the deepest lake basins formed by the formidable grinding powers of a giant glacier? Or were they the result of an almighty comet crashing through the atmosphere and exploding about the site of the lakes? Naked Science explores all the possibilities of how these vast inland seas of blue gold were formed.