Re: Has the earths rotational speed been slowing down at a constant rate?

Hi Jeff,

   I believe that the Earth has been slowing down at a fairly constant rate 
for the past few hundred million years.  The effect comes from tidal 
friction.  As the moon goes around the Earth it raises tides as we all 
know.  It also raises tides in the solid Earth and this dissipates energy. 
(Converts Earth's rotational energy into heat).  However, angular momentum 
must be conserved since there is no real coupling with any other 
astronomical body to transfer angular momentum to, so the angular momentum 
of the Earth-moon system must remain constant.  The consequence is that the 
moon is getting further away from the Earth.  The rate of slowing down can 
be measured quite accurately by knowing where solar eclipses were observed 
in the past.  Since the Earth is slowing down, eclipses are not seen in 
exactly the places that we would predict.
   This also means that in the distant past the moon would have been much 
closer to the Earth than at present and the rate of slowing down would have 
been much higher as the energy dissipation would have been higher.  That's 
why I said earlier that the rate of slowing down had been fairly steady 
over the past few hundred million years but it probably was not if we look 
back over several billion years.  I am not sufficiently knowledgeable about 
the details to tell you exactly what length the day etc there was 
throughout the whole of the Earth's geological history but you can find 
much more at http://www.nap.edu/books/
ARC000033/html/81.html