One mile under Greenland's ice sheet lies a 460-mile long canyon that went unknown to scientists until now.

The discovery was several decades in the making as NASA and researchers from Germany and the United Kingdom used radar data collected by aircraft over thousands of miles to piece together the landscape.

The depth of the bedrock was determined by measuring the amount of time it took radio waves to travel through the ice and bounce back from the bedrock underneath, NASA explained in a statement. The longer it took, the deeper the bedrock.

The newly-discovered canyon is longer than the Grand Canyon, according to NASA. It is 2,600-feet deep in some places, which compares to segments of the Grand Canyon.

The canyon is thought to pre-date the ice sheet, which is at least 4 million years old.

The findings were reported in the journal Science on Thursday, Aug. 29.

Watch the video below to learn more about Greenland's mega-canyon, courtesy of NASA: