From: <David_Bowman@georgetowncollege.edu>
> I don't think your argument is justified. Of course one tries to make
> use of all the data at one's disposal in finding a rock date. Usually
> this includes using some nonradiometric clues as to a ball park order of
> magnitude estimate for the age of the rock so an appropriate dating
> technique can be applied. But this assumption is not logically
> necessary. The main reason it is usually made is for mundane and
> practical concerns relating to the amount of expense and effort gone to
> to get a date. Using nonradiometric clues for a prior order of magnitude
> age estimate of a rock allows one to avoid wasting much time, effort and
> expense in getting the actual age. Often dating a rock radiometrically
> is a tedious, time consuming, and expensive task. ...
How one interprets radiometric or nonradiometric clues found in the rocks depends upon ones presuppositions or axioms. If you hold to the Principle of Uniformitarianism (or the Principle of Actualism) then you will automatically expect and look for old ages. If you hold to the idea of Catastrophism you will automatically expect and look for young ages. And when one expects and assumes there will be old ages, then one cannot then prove old ages by using radiometric or nonradiometric means. It would be a logical falacy to do so. It is perfectly logical to accept the old ages acquired by radiometric and nonradiometric methods if you already assume Actualism. But old ages cannot be used as evidence against Catastrophism because of the basic differences in presuppositions.
The only level on which to argue between Actualism and Catastrophism is concerning presuppositions. Creationary Catastrophism is based on religious presuppositions drawn from the Bible which one would accept as valid according to faith in the God of the Bible. Actualism is based on religious presuppositions drawn from the minds of men who accept naturalism on blind faith.
Allen
Because of this
> usually one doesn't want to needlessly waste resources by subjecting the
> rock to a whole battery of different dating techniques each with its own
> different usable age range of possible datable ages in the hope that
> the actual age of the rock will happen to fall in the usuable datable age
> range of one of the techniques in the battery of tests.
>
> Usually (as I understand it) in practice, if a dating technique is
> inappropriate for the actual age of the rock the technique just doesn't
> give an age with a usable error bar.
>
> For instance, suppose some technique uses a radioactive decay whose
> half-life is 10 million years, and the technology of the detection
> methods of counting the atoms of the relevant isotopes allows a decent
> estimate of the age as long as the age falls between 2% of this half-life
> and 15 half-lives. This means that the range of reasonably datable ages
> for the technique is between 200,000 yrs and 150,000,000 yrs. Now suppose
> that a rock to be dated with this method is actually only 120 years old
> because it came from a recent lava flow. Then the dating technique will
> typically *not* yield a false age in the usable range, but will give the
> inconclusive result that the age is just too young to date by that
> method. Maybe a naive application of the technique would indicate that
> the date is 70,000 yrs +/- 70,000 yrs. Since the error estimate for
> the technique includes an age of zero we see that the technique is
> just the wrong one to use on the rock. The only thing we can conclude
> from our dating method is that the rock's age is probably not any older
> than about 140,000 yrs.
>
> OTOH, suppose that the rock is actually 540,000,000 yrs old. Then again,
> the technique would typically not be able to arrive at an actual age. In
> this case the rock is so old that there is essentially no measurable
> amount of the parent isotope left in the sample. All that the technique
> would be able to say is that the rock is significantly older than
> 150,000,000 yrs old which corresponds to the age at the usable detection
> limit of the technique. The technique would not be expected to
> give a false age (such as an age of 120,000,000 yrs). Rather, it would
> not give any usable age at all.
>
> Of course, sometimes the rock's age is in the correct range for the
> technique and the technique might still not give a single clean
> predicted date. Such would be the case if some *other* assumption that
> needs to hold for the technique's validity breaks down. Although it
> is possible that the technique could even be completely fooled into
> predicting an incorrect date due to some process subsequent to the rock's
> formation that messed up the results, geologists typically are
> aware of the kinds of things that could go wrong and look for evidence
> in the rock's original environmental context that those distracting
> processes might have take place. Some techniques, such as the
> isochron methods, are hard to fool in this regard. For these techniques
> disruptive events subsequent to the rock's formation typically leave a
> tell-tale signature in the data analysis that either prevents a clean
> low error bar value from being predicted for the age, or even sometimes
> allows two separate dates to be extracted--one date for the rock's
> original formation and another date for the subsequent disruptive event.
>
> David Bowman
> David_Bowman@georgetowncollege.edu
>
>
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