I copy/pasted info from this site. I thought it interesting:
http://www.care2.com/greenliving/gregg-braden-a-new-world-age.html
It’s a 5,125 year long cycle that indigenous people have known as a great world age. And our great world age, the present world age, began in the biblical era in 3114 BC and it ends with a rare astronomical event on the winter solstice, December 21 the year 2012 AD.
It is a fact that we have lived at least four of the these world age cycles in the past. We are now completing the fifth and moving into the sixth world age cycle. And it is a fact that the close of each cycle in the past there have been great changes on the earth, physical changes that have been catastrophic to the people living during that time. We've actually entered into the 2012 window of change right around the year 1980. And the zone closes right around the year 2016.