Video: Exploring Mexico's Otherworldly Cave of Crystals
Just watch out for Morlocks Silver miners first discovered Mexico's surreal Cave of Crystals almost a decade ago. The BBC recently took a rare tour of the underground cavern that contains the world's largest naturally grown crystals, where some selenite structures reach almost 33 feet in length. See those little dots climbing the crystals that look like ants? Those are people. Casual spelunkers can't enter the cave without risking their lives, unless they have the right breathing mask and cooling suit. Stifling temperatures of 122 degrees F combined with almost 100 percent humidity pose a deadly challenge for early explorers. Such conditions mean that every breath can lead to fluid condensing inside the lungs, which represents a less-than-ideal scenario for continued breathing. But the cave's wonders prove alluring once you get past the dangers. The BBC's new series "How the Earth Made Us" accompanies Iain Stewart, a geologist at the University of Plymouth...