This discovery has provided historians with a unique perspective on the ancient human populations of the Americas.

Deep in the waters of the Yucatan Peninsula, Sam Meacham and Fred Devos are maneuvering their way through a network of caves. The pair have been under the surface for some time now, having traveled a half-mile or so submerged. But the ordeal turns out to be worth it, as finally they’re faced with a tiny opening in the rock before them. And what lies behind completely astonishes the intrepid divers.