December 21, 2012 marks the ending of the 13th b'ak'tun cycle of the Mayan Long Count Calendar, and it's also the last cycle of the Long Count. The Mayan Calendar ends December 21st, 2012. The 2012 Doomsday belief suggests that the Mayans foretold the end of the world at this time and, since the world is ending, there's no need to continue counting days or making calendars past that point. While that date would have had significance to the Mayans, there's no proof they actually believed the world would cease to exist. The ending of one calendar would start a new calendar, similar to how the current year ends on December 31st, but a new year is made at the same time. Some recent news articles are now calling into question the validity of the Mayan Calender saying that the end date of the calendar is recalculated to bypass December 2012 or that it has already passed.
2012 is based on a spec script (speculative script) co-written by director Roland Emmerich & co-producer Harald Kloser, indicating in the the end credits that the film was "inspired in part" by the book Fingerprints of the Gods by Graham Hancock. The film borrows several themes and elements from Jules Verne's rarely known novelette "The Eternal Adam", which shows a distant future archaelogist called Sofr-Ai-Sr, who belongs to a completely different civilization from ours called Hars-Iten-Schu, and someday finds a manuscript inside an aluminum box, narrating how in May 24th, 2XXX, a limousine driver called Modesto Simonet, his scientific boss (who wrote the manuscript), other scientifics on a vacation, and several other notable men and their families in Rosario, Mexico, survived a sudden flooding from the Atlantic Ocean by the heroic act of Simonet, who drove a car as fast as he could towards the mountains. In a matter of hours, the whole American Continent sinks in the ocean, except for the small island that used to be a mountain. They are rescued by a cargo ship, and they wander in a futile search for land anywhere else, only to discover that the tiny island was growing every time they passed by. The manuscript author ponders on the fate of Atlantis, and points a parallel with his situation. This old document leads Sofr to think that his civilization is descendant from those survivors after a period of mass involution of the human race, and that they survived thanks to a whole new continent that raised from the bottom of what used to be the Pacific Ocean for the survivors, and for Sofr is the only existing continent. Also, Sofr theorizes that is imminent that another global flooding happens someday. While the movie is far from an adapted work, a small credit would have been used instead of that of Graham Hancock, given the obvious allusions, but the reason why it wasn't the case is not known by the public.