[ClearCase_guy]

It's the oscillation of the orbit that really confuses me. Maybe -- maybe -- ice sheets could perturb our orbit. But once the ice sheets disappear, would the orbit "spring back" to it's original path? And could that be done repeatedly over many thousands of years?

I'm thinking that a law of Thermodynamics is being violated here with orbital paths oscillating despite no energy change being recorded.

[Lonesome in Massachussets]

The earth’s orbit and tilt are far form stationary.

http://en.wikipedia.org/wiki/Milankovitch_cycles

Says it better than I can.