deep-ocean cores and a seminal paper by Hays , Imbrie , and Shackleton , "Variations in the Earth's Orbit: Pacemaker of the Ice Ages", in Science (1976) [1] did the theory attain its present state. http://en.wikipedia.org/wiki/Milankovitch_cycles   Tonyblue, April 13th, 2011 & PalmSunday, April 17th, 2011 Post last edited Apr 18th