New York Times: At one point several hundred thousand years ago, snow began falling over the center of the earths largest island. The snow did not melt, and in the years that followed, storms brought even more. All around Greenland, the arctic temperatures remained low enough for the snow to last past spring and summer. It piled up, year after year, century after century, millennium after millennium. Eventually, the snow became the Greenland ice sheet, a blanket of ice so huge that it covered 650,000 square miles...