To the question posed by Glenn Dixon:
> And what is the rate at which the distance between the
> earth and moon is growing?
you responded:
> About 5.6 centimeters per year at present. This corresponds to
> a lengthening of the day by about 1.6 milliseconds per century.
> Interestingly, correlation of the length of day with ancient
> sediment layers indicates a non-linear increase over hundreds
> of millions of years, so that a simple backward extrapolation
> of present rates yields incorrect results. Ancient corals
> about 400 million years old show that the year was about 400
> days long then.
Interesting stuff. While I believe SOME non-linear change in the earth-
day length can be attributed to a decreased tidal effect over time as the
average earth-moon distance increases, this nonlinear effect must surely
be minor. So I strongly suspect that any appreciable deviation from
linearity that has been observed, or rather inferred from observations,
probably reflects observational errors of some sort. These could come in
many ways, such as in estimating the ancient coral age.
How about turning the problem around, and using the "observed" nonlinear
increase in earth-day length to recalibrate the ancient coral age? How
old would the ancient coral age need to be to make everything linear?
Gordon Simons