Image Gallery: Japan Tsunami and Earthquake
Image Gallery: Japan Tsunami and Earthquake

A local resident stands next to a devastated house in Japan after the March 2011 magnitude 9.0 earthquake hit the area. Some people believe catastrophic events like this one are signs the end of the world is near. See pictures of the Japanese tsunami and earthquake.

Athit Perawongmetha/Getty Images

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 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.

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. But in the real world, it's not a Mayan woman but the Mayan calendar that some speculators believe foretells an apocalyptic event. It even gives us a potential date for the theoretical downfall: Dec. 21, 2012.

Many doomsayers hang onto the idea that this ancient calendar is a ticking time bomb that signals our fast-approaching demise during the 2012 winter solstice. While scholars pay little heed to these fervent forecasts, they're still interested in the calendar. For example, there is some lingering disagreement over which day marks the exact beginning of the Mayan calendar. One commonly referenced date is Aug. 11, 3114 B.C., although other researchers pinpoint dates such as Aug. 13, 3114 B.C. (which would actually shift the big day to Dec. 23).

So how does the Mayan calendar system work? Do the Mayans really believe we have only a limited time left on Earth, and if so, why would Dec. 21, 2012, be the appointed doomsday? Read on to find out if the end is near.