
Antarctica, which is nearly four times the size of the United States, is almost entirely covered by a miles-thick layer of ice.
But the South Pole hasn't always been frozen. So when was the last time Antarctica was ice-free?

Antarctica, which is nearly four times the size of the United States, is almost entirely covered by a miles-thick layer of ice.
But the South Pole hasn't always been frozen. So when was the last time Antarctica was ice-free?