Ultimately I believe that if an appropriate adjustment were made to the periods of the ice ages to account for this distortion, it would show that, in fact, the ice ages of Earth and Mars are synchronised and happen at regular intervals, about every 5 million years.

I believe the ice ages occur because this is when the orbits change. They are part of the planet's adjustment as the orbits move outwards and away from the sun. They come in groups of 4 smaller ice ages every 200 to 250 thousand years, as the planet settles in the new orbit. This also accounts for, and is a reaction to, the periodic change in obliquity ( tilting on its axis back and forth at different angles towards the sun ). However, I believe this subject of obliquity also confuses the issue of expansion and obscures the concept of contraction ( see: 'Mars Mission-13: Obliquity').

( my proposed cause of the orbit change is the original impact. this will be dealt with in future drafts. See: Full Sequence and Notes )