NASA is so confident the world won't end on December 21st that they're releasing a video ahead of time.  The video "Why The World Didn't End Yesterday" was originally scheduled to be released on December 22nd, the day after the Mayan calendar supposedly indicates the end of the world.

So why is the video being released early?  Some people have a theory that NASA isn't sure anyone would ever see it on December 22nd so they're putting it out now.

Another theory is that they're concerned about people who take the end of the world thing too seriously and might do themselves in and possibly take others with them.

NASA released a statement on its website:

"The world will not end in 2012. Our planet has been getting along just fine for more than 4 billion years, and credible scientists worldwide know of no threat associated with 2012."