One of the biggest canyons in the world has been discovered buried beneath more than two miles of ice in Greenland.
The hidden canyon is up to half a mile deep, six miles wide and stretches for 466 miles beneath the country's giant ice sheet.
It is thought to have been carved out by a meandering river more than four million years ago – at a time before ice covered the area and humans were just beginning to evolve from primates.
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