10 The World's Longest Mountain Chain Is 40,389 Miles Long—And Is Located Underwater

The world's longest mountain range runs 40,389 miles around the world, and 90% of it is covered by ocean water. Called the Mid-Ocean Ridge, this underwater range was formed by magma rising to fill gaps that formed as Earth's plates shifted. Its mountains average a depth of 8,200 feet below the water's surface. In comparison, the longest chain of mountains on land is South America's Andes, which is a paltry 4,350 miles long.