From: bill@bessel.as.utexas.edu (William H. Jefferys)
Newsgroups: talk.origins
Subject: Bob Bales Goofs
Date: 22 Dec 92 23:22:30 GMT
Organization: McDonald Observatory, University of Texas @ Austin

Bob Bales has struggled mightily and brought forth...a mouse.
He located two new "Killer" articles [3,5] that, he believes, show
that isochron dating may be inaccurate. Unfortunately, he didn't
read the articles very carefully, for they are about pseudoisochrons,
not isochrons, which are very different beasts. In [3], p. 1087,
the authors caution,
  
  "Before discussing the data on which this article is based,
   it is essential to distinguish between the simple isochron
   plot and the pseudoisochron plot utilized throughout our
   data presentation.

   In the isochron diagram for a group of igneous rocks their
   individual [87]Sr/[86]Sr composition as measured today
   (termed present-day ratios) are plotted against their
   respective Rb/Sr ratios. In the pseudoisochron diagram,
   however, the _initial_ [my emphasis--wj] [87]Sr/[86]Sr
   ratios are plotted against their respective Rb/Sr ratios.
   In other words, on a pseudoisochron diagram the [87]Sr/[86]Sr
   ratios of the samples already have been individually 
   "corrected back" to their time of crystallization by 
   using _independent information_ [my emphasis--wj] for
   the age of crystallization. When a plot of initial [87]Sr/[86]Sr
   against Rb/Sr does not define a horizontal array on the
   pseudoisochron diagram, then there is a hint that some
   precrystallization history in [87]Sr/[86]Sr has been
   preserved in the rocks..."

Pseudoisochrons, therefore, are not a way of dating a
rock, they are a way of understanding something about what
may have happened before the rock crystallized. For example,
one can learn about where the material from which the rock
crystallized came from (e.g., crust or mantle), etc. These
two articles, therefore, are irrelevant to the question
of the accuracy of isochron dating. 

In another article, Bales attempted to rebut my comments on
the Chayes letter [7]. It is evident that Bales simply doesn't 
understand the statistical mechanism that Chayes invokes. 
Chayes remarks, correctly, that uncorrelated quantities
X, Y, and Z, may result in a correlation in X/Z and Y/Z. But 
what Bales doesn't understand is that the resulting correlation is
very far from being a good, tight, straight-line relationship
such as one needs to derive a good isochron. As Brooks _et. al._
point out in their rebuttal, correlations of 0.999+ are
typical in isochron dating. Chayes' mechanism would not be able 
to produce ancient ages and large correlations in data for rocks
that were actually young. If Bales wishes to dispute this fact, let
him show us a numerical example of data for a zero-age rock for 
which X, Y, Z are uncorrelated, that nevertheless gives an age of,
let's say, 3 B.Y. when X/Z and Y/Z are plotted in an isochron
diagram, and for which which the quantities X/Z and Y/Z have
a correlation of 0.999.

The fact is (and this is why the editors published the letter,
to answer Bob's rhetorical question), the discussion between
Chayes and Brooks _et. al._ concerns the question of whether
there might be small errors in Rb/Sr dates induced by this
effect. Yes, probably there are, but in no way could they
give dates of billions of years from 10,000 year-old rocks.

I note that Bob has again listed [4] in his list of "evidence"
that isochrons may be inaccurate. I'll just remind everyone
that Peter Lamb rebutted this claim a year ago. The "isochrons"
in this article are in fact a good example of how the isochron
method is self-checking, since they are discrepant.

Bob continues to misuse Durrance, who was only talking about
gas-retention ages. Leakage of gases from a sample, such as
mentioned in the quote he gave, is not relevant to Rb/Sr dating
for which the materials are not gaseous. Drop this one, Bob,
you are making yourself look deceitful.

Bob has not supplied a model that can explain why isochron ages 
are closely correlated with ages determined by other,
completely independent techinques (such as stratigraphy). He
has not explained why the ages of the Hawaiian Island chain
are strongly correlated with their ages as determined by the
motion of the Pacific Plate as determined by lunar laser
ranging. Instead, he threw in the old red herring about the
rocks which K/Ar date wrong, and which is irrelevant since
this phenomenon is well understood and these rocks were not
used. Therefore, Bob has failed to meet my CHALLENGE.

The rest of Bob's mighty effort merely rehashes invalid points
that he has made before and which have been rebutted many times.
I haven't the time, nor the patience, and I'm going to ignore
it.

Bill


References:

[1] Eric Durrance (University of Exeter), _Radioactivity in Geology:
    Principles and Applications_

[2] G. Brent Dalrymple, Ph. D., "Radiometric Dating, Geologic Time, and the
    age of the Earth: A Reply to 'Scientific' Creationism," February, 1982,
    published by U.S Geological Survey.

[3] C. Brooks, D.E. James, and S.R. Hart, "Ancient Lithosphere: Its Role in
    Young Continental Volcanism," _Science_ Volume 193, September 17, 1976,
    pages 1086-1094

[4] Carter, Evensen, Hamilton, and O'Nions, "Neodymium and Strontium Isotope
    Evidence for Crustal Contamination of Continental Volcanos," _Science_,
    vol 202, November 17, 1978, pages 743-747

[5] Zartmen, Norton, and Stern, "Ancient Granite Gneiss in the Black Hills,
    South Dakota," _Science_, July 31, 1964, pg 479-481

[6] _Scientists Confront Creationism_, page 70, paperback edition

[7] Felix Chayes, "Use of Correlation Statistics with Rubidium-Strontium
    Systemics, _Science_, vol 196, June 10, 1977, pages 1234-1235