Do you want to understand the "end of Earth" prediction based on the Mayan calendar? Does this help?
1 - The calendar that "predicts" the "world will end on 12/21/2012" does not predict that. It predicts entering a new age for civilization. People have interpreted that to mean the end of the world. But ...
2 - A new find revealed a newer Mayan calendar that goes out another 6000 years (at least) into the future. Obviously, that implies the Mayan's didn't believe the Earth would be destroyed on 12/21/2012.
3 - The Mayan calendar can't be compared to modern calendar (leap year) because it has little to do with the Earth's rotation around the sun. People who say the Mayan calendar doesn't take into account leap years are correct ... but misunderstand how the Mayan calendar works and that it doesn't *need* to account for leap years. It is based on wider astronomical cycles.