The Mayan calendar deal is a myth. It doesn't say that the world will end on that date. It simply shows that a celestial cycle will end on that date and then start over again. Why do you think the tablet containing it is circular like the face of a clock?
The only mystery is how were they able to track and predict the progress of the cycle with such astonishing accuracy without any astronomical instruments.
The world will someday "end" (not completely but made over as described in the Bible)but the Bible also says that no man will know the date and time so anyone who says he does is simply a false prophet.