>I am debating a Christian creationist, and he claims that the tidal 
>braking of the earth "proves" that the earth was recently created
>(<10K years).  I have done a few "back of the envelope" calculations
>to show this isn't so.  Yet, I'd like a more detailed analysis to 
>quote for him.  [ ... ]

   This same argument was put forth in a "letter to the editor" of the
Quarterly Journal of the Creation Research Society, about a decade ago,
by Thomas Barnes [1] (the same Barnes who also argued that the magnetic
field decay proved the Earth was no more than 10,000 years old). Barnes'
argument was based on a paper by Louis Slichter from the Journal of
Geophysical Research [2]. Slichter's paper was already 20 years old
when Barnes cited it, and already well "out of date" by then as well.

   The response is that the early work, and the "back of the envelope"
calculations are wrong. The tidal interaction between the Earth and moon
is dominated by the fluid oceans, which was not fully appreciated in the
early papers. Also note that Slichter's paper pre-dates the general
acceptance of plate tectonics in geophysics. We now know that the tidal
response function of the oceans changes with time depending on the
distribution of continental masses, and has a very complex resonance
spectrum. It also appears that the tidal interaction is currently in
resonance, which means that using the current rate of recession of the
moon from the Earth will produce an incorrectly young age for the system.

   You may find useful information or pointers in general textbooks
in geophysics that deal with the Earth-moon interaction, such as Lambeck
or Munk & MacDonald [3,4], or you may need to look through the "usual"
journals (JGR, Geophysical Journal International, Earth Moon and Planets,
etc.). I do have a paper by Kirk Hansen in my files that may help explain
things too [5]; however, it dates from 1982, and while the basics haven't
changed much since then, there could have been advances in methodology since
then, especially for describing the very complex oceanic response function.
You need to check the current literature, since this is an area of some
activity, and I have not really kept up with the topic, since by the early
80's it was easy to show the flaw in the argument anyway. All of my sources
here are, therefore, subject to dated conclusions.

[1] "Earth's Young Magnetic Age: An Answer to Dalrymple"
     Thomas G. Barnes
     Creation Research Society Quarterly,
     vol. 21, December 1984; pages 109-113
     See page 109, "Problems with Their Dates"

[2] "Secular Effects of Tidal Friction on the Earth's Rotation"
     Louis B. Slichter
     Journal of Geophysical Research,
     vol. 68, no. 14, July 15, 1963; pages 4281-4288
     
[3] "The Earth's Variable Rotation"
     (Geophysical Causes and Consequences)
     Kurt Lambeck
     Cambridge University Press, 1980
     QB633.L25          ISBN 0-521-22769-0

[4] "The Rotation of the Earth"
     (A Geophysical Discussion)
     W.H. Munk & G.J.F. Mac Donald
     Cambridge University Press, 1960, 1975
     ISBN 0-521-20778-9

[5] "Secular Effect of Oceanic Tidal Dissipation on the Moon's Orbit
     and the Earth's Rotation"
     Kirk S. Hansen
     Reviews of Geophysics and Space Physics,
     vol. 20, no. 3, August 1982; pages 457-480
     [Appendices derive oceanic tidal torque and potential, and show how
     to calculate the energy balance. The complexity involved shows why
     "back of the envelope" calculations should be looked at suspiciously.]
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