Some are claiming the Mayans predicted that the world will end on December, 21st, 2012.
That isn't true.
The Mayans only came up with a complex and accurate calendar based on the planets and stars, which ends on December 21st, 2012. There were no prophecies involved. It was a conclusion of a time cycle. (Yet, even if the Mayans had predicted the future for 2012, I would still laugh. They were an evil people who practiced human sacrifice, so they certainly wouldn't have been hearing from God.)
I am apalled that some are trying to interpret the end of the Mayan calendar to mean that Jesus is coming back on December 21st, 2012. Jesus warned us against predicting his coming in Matthew 24:36. "No one knows about that day or hour, not even the angels in heaven, nor the Son, but only the Father."
Oh, and the tribulation hasn't happened yet. (Do I sound a little sarcastic? Maybe its because I'm flabbergasted that people are taking this 2012 doomsday thing seriously.) How do I know the tribulation hasn't happened yet? Well, Daniel 9:24-27 tells us that the tribulation takes place during the last "week year" of 70 week years. (A week year being 7 years.) The countdown of week years began approximately in 444 B.C, and the 69th week of years ended around the time of Jesus' ministry and death. There is a 2000 year gap between the 69th and 70th week year, which is the age of the Church, or the time of the Gentiles.
You're shaking your head at me, but it does make sense. The 70 week years were declared for Israel -- no one else. In Ephesians 3:4-10, Pauls references the time of the Gentiles as a mystery not revealed to Daniel. We know when the tribulation or 70th week year will start, because it's marked by the antichrist's peace treaty with Israel. (Zechariah 12:2-3, Daniel 9:27)
Here is a great breakdown of the tribulation and the scriptures that reference it: http://www.genrev.org/2010/02/05/overview-of-the-tribulation/
Revelation 21: 1-2 does tell us that the first earth and heaven will pass away, and be replaced by a new heaven and a new earth. Then God's city, the New Jerusalem, will descend to the new earth, and God will dwell with His people forever. But this happens after the millennial reign of Christ, and the judgement of all people. So for all of you who are worried about the end of the word, it can't happen for another 1,007 years -- at least.