A thoughtful and respectful post, mjacobsca =) Can you link me to the theory you read prior to Plait's regarding the Earth's orbital oscillation through the galactic plane?
Edit: I have found the source of the claim but mass extinction events also don't occur every 26Myrs.
http://en.wikipedia.org/wiki/Shiva_Hypothesis
I thought the same thing until I realized how likely it is that an impact event approx 35 Myrs ago triggered the ice age. I agree that one...
If high impact asteriods or comets aren't to blame, then do scientists know what exactly caused the Earth's wobble? (not referring to the Chandler wobble, btw). And, isn't it theorized that approx every 26 million years the fossil record indicates a mass extinction, coinciding with our solar...