This fun and informative video explains how our modern calendar was created through the years. Much of the standards in the modern calendar came from Roman emperor Julius Caesar and then Pope Gregory XIII.

However, the number of days in a week was influenced by the Hebrew calendar so that religious holidays could be observed. As the video mentions, some people predict this year, 2012, will mark the end of the world because it is the end of a 5,125-year-cycle in the Mesoamerican Long Count calendar. Researchers have found evidence that supports the date had significance in Mayan culture but have not found physical proof of a doomsday phenomenon.