From: bobb@tekig1.PEN.TEK.COM (Robert W Bales)
Newsgroups: talk.origins
Subject: Response to Bill Jefferys, part 2
Date: 17 Dec 92 20:35:58 GMT


Continuing discussion of the accuracy of the isochron dating method:

#># me
#>  Bill
#   me

>In other words, when using the isochron method, you will KNOW if the system
>has not remained closed. Such rocks are not used in isochron dating. They
>CANNOT be used for proper isochron dating,

Then why is it that  non-creationist geologists recognize a "problem of
inherited age?" [3] The authors in question believe that the age has meaning
for events before the rock was last crystalized, but say that their results
could be caused by contamination.

More importantly, if you want to claim accuracy for isochron dates, you need
to know which rocks CAN be used.  This seems to be determined from isochron
theory.  You choice of rocks is only as good as the theory. *And until you
have verified the theory against data obtained from methods completely
independent of isochrons, you do not know how good the theory is.*

>because for rocks with such histories the data do not plot on an isochron.
>Therefore, Durrance's comments do not apply to properly determined isochron
>dates.

Once again. one of Durrance's points was contamination.  Observations show
that data from rocks believed to contaminated DO plot on isochrons and DO give
erroneous ages.  Direct experimental observation shows the above statement to
be false.

The focus of this discussion is the accuracy of isochon dating.  So in the
way Bill and others use "properly determined," they are begging the question.
They assume a date is properly determined if the theory says it is: in other
words, in trying to show that the theory is correct, they assume that it is
correct.

>Nor did Durrance intend his comment to apply to isochron dating, since he
>was only discussing gas-retention ages, specifically K-Ar ages.

In his own words, Durrance says he is discussing "geologic materials and
and enviornments." Durrance also says: 

     "In decay schemes in which gaseous daughters are produced, such as. . .
     [Potassium-Argon and Uranium-Lead]. . .for example, the loss of the
     daughter by diffusion, even through compact materials, can be
     considerable." (page 287) [1]

In common English usage, when 'A' is  given as an example of 'B,'  'B'
includes cases *in addition to* the specific case 'A.'

>You should give up this  line of argument, Bales. It is not truthful. It is
>a flagrant misuse of Durrance's words.

In the work by Durrance, in other college geology texts,  and in scietific
journals,  I have found and cited a number of reasons why isotope ratios in
general and isochrons in particular may not be representative of age as well
as experimental cases in which isotope ratios in general and isochrons in
particular were found to misrepresent the age of the sample.

There is no doubt (at least no more than for any other scientific data) that
the data is truthful.  My conclusionions, which are my own, differ from those
of others.  However, to claim that someone has said exactly what they have
said is not a misuse of anything.

   Bob Bales
   Tektronix, Inc.

I help Tektronix make their instruments. They don't help me make my opinions.