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Re: Impacts and ETs
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.