From: bobb@tekig1.PEN.TEK.COM (Robert W Bales)
Newsgroups: talk.origins
Subject: Response to Bill Jefferys, part 4
Date: 17 Dec 92 20:39:36 GMT


This part begins what must be central to any discussion of dating accuracy and/
or the age of the earth: an examination of the observed data on isochon dating
and a comparison of that evidence with the explanations and claims of the
old-earth and the young-earth theories.

#># me
#>  Bill
#   me

>Here are our DATA:

Before we look at the data, we can make some observations about what we need
to look for.  I've discussed these above, but I'll lay them out in detail:

1. The claim is being made that dates determined by isochrons are accurate.

2. This is a claim that a measurement method gives accurate results.

3. There are generally accepted standards in science and technology for
   validating whether or not a measurement method gives accurate results.

4. The claim in 1. should be accepted if and only if the isochron method is
   validated according to the generally accepted standard.

5. The generally accepted standard is that the measurement method give
   accurate results when measuring known values.

6. If, in the data, we find samples of rock with a known age and if the
   isochron correctly dates the rock which is billions of years old, and if
   the method never gives billions-of-years dates for rock known to be other
   ages, we can regard claim 1. as verified.  Otherwise, we cannot.

>We have literally tens of thousands of rocks containing straight-line
>isochrons. We have young rocks with horizontal isochrons.

We have young rocks with non-horizontal isochrons indicating age from tens of
millions to billions of years. [3]

>In many instances we have isochrons belonging to different decay systems, and
>in such cases we invariably find that they give the same dates.

As an example in which isochrons do not agree closely with each other, and
with other measurements, yet are still used to draw conclusions, we have a
study [5] which shows a  3-point isochon passing almost exactly through 2 of
the points and farther farther away from the 3rd.  This gives an age of 1.8
billion years.  Also assumption is made of the initial isotopic ratio to
derive an isochron giving an age of 2.5 billion years.  Zircons from the rock
were dated with uranium/thorium/lead techniques at from 1.56 to 2.55 billion
years.

>Very significantly, we have NO examples of rocks with negatively sloped
>isochrons.

I woder what the evidence is for this claim.  It would be quite impossible for
Bill or anyone else to know of every dating attempt through isochrons.  And
given what Bill said earlier about "properly determined" dates and about
the internal checks in the isochron method, it is quite possible (if not
quite probable) that if a negatively-sloped isochron were found, it would
be decided that the sample did not pass its checks and the data would be
quietly discarded.  How can Bill say that there has been no such discarded
data?

>We have numerous instances where rocks from many different parts of the 
>world are found associated with a given stratum of the geologic column,
>and invariably we find that they give the same isochron dates,

We know that what occurs to a sample can affect the radioactive date obtained.
The same stratum is likely to have been affected by similar processess, so
the dates would be expected to be the same, irrespective of their accuracy.

>and that the dates are in the same order as inferred from the order of rocks
>in the geologic column.

As I have pointed out before, the relative dates inferred from the geologic
column support equally *all* theories with the same relative dates.  Since
the young earth theory agrees with the geologic colum, it is supported equally
with the old-earth theory.

>We also have a number of examples where we can associate rocks with ages
>determined by other means.

These examples sometimes show radiactive dates to be very poor.

Bill, along with others in this group, apparently thinks that only dates
which agree are significant, and dates which don't agree are meaningless.  I
have presented a number of examples of such disagrement, and some reason is
always given why they can be ignored.  This is a double standard.

*All* data on dating accuracy must be considered.  If agreement between
different radioactive dates and between radioactive and other dates is to be
a reason to trust radioactive dates, then disagrement must be a reason not to
trust radioactive dates.

>For example, the speed of tectonic plates can be determined directly by lunar
>laser ranging.

The speed of the plates at the present time.  Is it claimed that this speed
has remained constant for millions or hundreds of millions of years?  If the
dates did not agree, would this be taken as evidence against the accuracy of
radioactive dates, or would speed variation be invoked as an explanation?

>Radiometric ages of rocks from the Hawaiian Islands agree with the ages
>inferred for them from the motion of the tectonic plate on which they are 
>located.

If you consider the radiometric data which agrees with the theory.  If you
consider all of the radiometric data from Hawaii, you will find some in
which the radiometric age disagrees with the known age by 7 orders of
magnitude. [6]

What is significant about this list is what is missing from it.  The exact
data which would be needed to verify that the isochron method gives accurate
results is conspicuous by its absence.  The only conclusion is that the
accuracy of isochron dating has not been verified.  No amount of handwaving,
theory, and unverified measurements can change the conclusions.

   Bob Bales
   Tektronix, Inc.

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