During the most recent Ice Age, enormous quantities of water were tied up as ice in vast continental glaciers that covered much of continental Europe, Asia, and North America. In places these glaciers became as much as four kilometers (two and a half miles) thick. As a direct consequence, sea levels fell dramatically. It has been estimated that at the peak of the last Ice Age, some 20,000 years ago, mean sea levels were more than one hundred meters (some 350 feet) lower than at present, exposing up to one hundred miles of additional shoreline that is today underwater. Recently, some geologists have produced dramatic hypotheses based on observations made while drilling into the floors of the Persian Gulf, into which the Tigris and Euphrates Rivers empty, and the Black Sea, which forms the northern coastline of Anatolia to the north and west of Mesopotamia.

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