There have been countless theories throughout time about how the world will end and how -- or if -- life will cease to exist. At the turn of the 21st century, conspiracy theorists claimed that the Y2K bug was only a small part of the impending devastation: The new century would bring about total destruction, and no one would survive. Others believe that Earth is slated for another ice age, which will kill off all living things. And according to astronomers, billions of years from now, the sun will become a red giant, expanding to a size larger than the Earth's orbit and consuming the Earth in the process. Even if the planet somehow survives, the sun will eventually shrink, becoming a white dwarf and gradually cooling off until it can no longer warm anything in the solar system.

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An apocalyptic view of Seattle sinking into the Puget Sound -- will something like this happen in 2012?

In 2006, Mel Gibson released a movie about the Mayan civilization. "Apocalypto" follows one man's journey from slavery back to his family. During the course of the movie, a young woman prophesizes that a man will bring an end to the Mayans and wipe out their civilization. In the real world, some theorists don't believe a man will be the end of the Mayans -- instead, a celestial event will be the cause. The Mayan calendar even gives us a date for this theoretical event: Dec. 21, 2012.

How did the Mayans develop a calendar that could predict the end of the world? How does the Mayan calendar work? Do the Mayans really believe we have only four years left on Earth, and if so, why is Dec. 21, 2012, doomsday? Read on to find out if the end is near.

Devastation Predictions ­Nostrad­amus Michel de Nostredame, also known as Nostradamus, was a 16th-century physician who also had a penchant for writing. He penned a series of prophecies, focusing prima­rily on wars, disasters and destruction. Using metaphors and mystery, Nostradamus wrote these prophecies as quatrains, or four-line verses. His followers say he predicted the rise of Hitler, the Apollo moon landing and the attacks on Sept. 11, 2001. His critics say his writings are nothing more than ancient horoscopes, written to tell of events that undoubtedly will occur again and again. To find out more about Nostradamus and his prophecies, read our article on How Nostradamus Works.