Watch Brad Meltzer's Decoded Season 1 Episode 7 Online

There has long been speculation that on December 21, 2012, the world as we know it will end. Some predict that we'll be wiped out by a natural disaster like a giant tidal wave, an Earth-wide earthquake or a tremendous volcanic eruption. Others believe that on that day in December, the Earth will collide with a mysterious "Planet X," causing magnetic pole shifts, gravitational reversals or a black hole so big that our solar system will simply disappear. What's more, believers say that this news is not really news at all; on the contrary, they argue, we have known about the coming apocalypse since the ancient Maya predicted and recorded it on their Long Count calendar more than 2,200 years ago.