> 2) The citing of rocks which date to 3.9 billion years as evidence that the
>    earth is actually at least that old.  The problem here is that no
>                                                                   ^^
>    verification of the accuracy of the dating method was given, while I had
>    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>    shown cases in which the same types of measurment methods (determination of
>    isotope ratios) had given wrong results.


      With regard to dating, bob, you never answered this post.
      I have not been wise enough to keep track of the dates when
      you have been asked to address these points, but after each
      previous posting you left Talk.origins for some months.

      [original post begins]

      Bob, while you're at it, you can try to explain the
      similar dataset from the Antarctic ice sheet (they've drilled
      a little deeper there, 160,000 + years).  Curiously, isotope
      ratios in these cores vary with periodicities which exactly match
      (within fairly narrow error bars) the periodicities of certain
      astronomical parameters (such as the obliquity of the earth's
      orbit, with  a periodicity of 41,000 years, and the precessional
      periods of about 19,000 and 23,000 years.

      Now, there are good theoretical reasons to expect such a match,
      (these orbital wobbles affect received sunlight)
      and indeed it is observed both in ice and sea-bottom cores.

      [insert july 91]

      These sea bottom cores now go back
      several million years and the astronomical periodicities
      are still there, and K-Ar dates are still in reasonable
      agreement (better than 10%) with astronomical dates.

      [original post resumed]

      The question for you, Bob, is this: Since the astronomical
      periods do *not* depend in any way on radiometric dating, and
      since these same periods show up in cores dated *by* radiometric
      dating (the dreaded K-Ar and uranium series dating) is this not
      an *independent* test of radiometric dating?  If not, why?

      The predictions as to time made by calculation of planetary
      orbits and by K-Ar dating agree very well - for a long time you've
      complained that K-Ar is not calibrated - well here it is.


      [july 91 insert]

      In recent months a 25 million year long record from the
      triassic (about 200 million years ago, for those of us
      who believe such things) has been obtained.  The rock
      is banded, and the bands form quite regular groupings.
      The smallest bands contain about 20,000 varves (annual
      layers) - and the precession cycle at that time was
      about 20,000 years long.  Coincidence?  Well, the
      precession cycle is modulated by the 100,000 year
      eccentricity cycle so the bands should occur in groups
      of five, with slightly different characteristics within
      the group.  They do.  Not enough?  There is also a
      400,000 year eccentricity cycle, so the large bands
      should be bunched in groups of four.  And they are.

      So K-Ar dating and varve count give the same spectral
      dependence, and both agree with astronomical calculations.

      Well before this result was obtained (it hasn't even
      been published yet) a simple climate model was used
      to estimate the power spectrum of maximum annual
      temperature at a similar site [see ref].  The low
      frequency end of this model's output agrees
      entirely with the observations.  The cores
      have not yet been measured accurately enough to
      compare the high frequencies.

      This is quite clear evidence that these bands are
      astronomical in origin, and thus *astronomy*, not
      radiometric dating, tells us that this sample of
      rock was laid down over 25,000,000 years.
      So the earth is at least that old.  Furthermore, since
      K-Ar dating gives the same length to this record we
      have no reason for not trusting within a few percent the
      K-Ar absolute age for this stratum, which is about
      200 million years.

      Well, Bob?


                                              Bill Hyde


References

The geological evidence was presented by Paul Olsen of
Lamont-Doherty at a recent workshop at Johns Hopkins.
Preprints should exist in a few months.  The theoretical
paper is Short, D. A., J. G. Mengel, T. J. Crowley, W. T.
Hyde and G. R. North 1991: Filtering of Milankovitch Cycles
by Earth's Geography. Quaternary Research. 35, 157--173.