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Re: Impacts and ETs

On Sun, 13 Feb 2005, David Marjanovic wrote:
> >  One reason for the rare Earth notion is the supposed
> > need for a stabilizing moon. Dinosaurian history
> > suggests otherwise. During the Mesozoic, the whole
> > world was warm. Since solar declination had relatively
> > little effect on temperature, obliquity shifts
> > probably wouldn't have either.
> I think you've misunderstood this. The idea is that without a large moon the 
> Earth would lose balance and tip over at chaotic intervals. Like Mars has 
> done -- on Mars there's no evidence of plate tectonics, but plenty of 
> glacial features on the equator. Imagine an obliquity shift of 90 that 
> takes, I don't know, days, or perhaps centuries, as opposed to one of 20 
> that takes 40,000 years. Just imagine. 

Tip over? Uranus currently has an inclination of almost 90 degrees. Do you
mean like that? Or our inclination stays the same while "tipping"?