Scientists have discovered a hidden canyon in Greenland that is 750 kilometers long and as deep as the Grand Canyon in the United States.
Scientists pieced together radar data collected by airplanes over decades to build a picture of the canyon hidden from view by ice and snow.
They believe the canyon was a major pathway for water before it was covered by the ice sheet some 4 million years ago.
Even today, the mega-canyon still transports water that melted from glaciers to the edge of the ice sheet and into the ocean.
The canyon originates in the center of Greenland and runs to its northern coast.