Re: Pull of the Moon

["Richard W. Travsky" <rtravsky@uwyo.edu>]

On Tue, 18 Apr 2006, Phil Bigelow wrote:
> On Tue, 18 Apr 2006 11:48:55 +0100 Steve White
> <steve_d_white@hotmail.com> writes:
> > I have a question. I read sometime back that the moon has been slowly
> > moving
> > further out of orbit and that during the Mesozoic
>
> Indeed it was. The Moon is constantly "stealing" rotational energy from
> the Earth (by causing tidal drag on the Earth's angular momentum).
> Earth's days are getting longer.  This "stolen" energy is then used to
> push the moon into a higher orbit.   Voila, conservation of energy.
>
> > it was actually
> > something
> > like a quarter closer to Earth (but don't quote me on that).
>
> I asked a similar question a while ago on the vrtpaleo list, the only
> difference was that I was seeking an algorithm to calculate a rate of
> separation vs. time curve.  I didn't get any answers then, but I have
> since learned that such an algorithm cannot be created, because the
> "true" curve probably doesn't follow a strict mathematical formula.  To
> be sure, in a "perfect" 2-body system, the curve of the changing rate of
> separation (in cm/year) would start out high near the Y-axis (the moon is
> hypothesized to have formed at a distance of only 14,000 miles from Earth
> when it was formed ~4.4 Gya) and then the rate of separation decreases
> with geologic time (today: at 238,000 miles, with a rate of separation of
> 1.5 inches per year).  But the E-M system isn't a perfect system, and
> that real curve is probably bumpy and jagged.

Ok, I got curious and went looking. Found

"Geological constraints on the Precambrian history of Earth's rotation and 
the Moon's orbit" by George E. Williams, Reviews of Geophysics, Volume 38, 
Issue 1, p. 37-60 (RvGeo Homepage)

from 2000. In the abstract (hope the special chars paste ok)

 Paleotidal and paleorotational values provided by late Neoproterozoic
 (~620 Ma) tidal rhythmites in South Australia are validated by these
 tests and indicate 13.1 +- 0.1 synodic (lunar) months/yr, 400 +- 7 solar
 days/yr, a length of day of 21.9 +- 0.4 h, and a relative Earth-Moon
 distance a/a0 of 0.965 +- 0.005. The mean rate of lunar recession since
 that time is 2.17 +- 0.31 cm/yr, which is little more than half the
 present rate of lunar recession of 3.82 +- 0.07 cm/yr obtained by lunar
 laser ranging. The late Neoproterozoic data militate against significant
 overall change in Earths moment of inertia and radius at least since 620
 Ma.

I vaguely recall asking once about length of day and what effect that
might have had on warm/cold bloodedness, since a shorter day could
mean day/night temperature differentials may not have been as important,
the reason being that a shorter night means less time for shedding heat.

22 hours doesn't seem that much of a difference...

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