Dr. Mike Baillie at the Queen’s University in Belfast, Ireland has made a very interesting discovery. He noticed that peaks in ammonium and nitrate in the ice core record, signatures of comet impacts with Earth, occur on or near baktun endings in the Mayan calendar. (The 13th and final baktun of the current calendar cycle ends on December 21, 2012.) This discovery suggests that the ancient Maya were aware of a cycle associated with repeated impacts of comets with Earth and that they engineered their calendar to track these cycles.
In his book The Order of Days, Mayan scholar David Stuart noted that these baktun endings were very important to the Maya and that they often constructed new temples and pyramids on these dates. He noted that the Temple of the Cross group of pyramids at Palenque were constructed on one such baktun ending.
As I noted in my book Mayan Calendar …