From: allenroy (allenroy@peoplepc.com)
Date: Wed Oct 15 2003 - 01:55:50 EDT
Steven M Smith wrote:
> Allen Roy wrote:
> >1. The acceptance or rejection of isometrically acquired ages for rock
> > depends upon factors other than the science/technology of isometric
> dating.
>
> I agree with this point ... but so what? Radiometric dating based on
> isotopic compositions in rocks is a tool, not a panacea. Radiometric dates
> are only one piece of evidence concerning the age of a rock. In addition,
> there may be stratigraphic evidence (where in the geologic column the dated
> rock is located), correlation with other layers in nearby exposures or
> drillholes, superposition (order of layers in the geologic column),
> structural evidence (faulting, folding, or other displacement of rock),
> evidence from the chemical composition of the rock, inclusions from other
> rock units, and evidence from other events that have changed the rock such
> as weathering, metamorphism, metasomatism, hydrothermal (hot water)
> alteration, or mineralization. When the radiometric date doesn't agree
> with the other lines of evidence, then it may be rejected. But that is not
> the end of the story, it is just the beginning of trying to figure out why
> the test failed. Was the method used inappropriately? Was there
> contamination during the collection, processing, or analytical stages?
> Were there unrecognized factors in the rock unit that could affect the
> isotopic composition? Is the radiometric date telling us something other
> than simply the time the rock was emplaced or extruded? etc. etc. etc.
All of it [the "explanations" above] are nothing
but pure rationalization needed
to try to save the fatally flawed methodology. As Woodmorappe says, "CMBN" --
If it works, Credit Methodology, it if doesn't, Blame Nature to save
methodology. If it doesn't work here, why should it work somewhere else? Why
trust it anywhere?
You say, "Is the radiometric date telling us something other than simply the
time the rock was emplaced or extruded?" But it is the BACKBONE assumption of
isometric dating that the emplacement and extrusion resets the clock. If it
doesn't reset the clock here, then why should I
believed that it reset the clock
elsewhere. Rationalizing it away when it doesn't work is pseudo-science.
> So, in effect, it appears that you are presenting the perfection of
> radiometric dating as a strawman argument. Should a radiometric dating
> procedure ever give us a result that doesn't agree with the other evidence,
> then all radiometric dating is invalid. We can then ignore all radiometric
> dates regardless of corroborating or conflicting evidence.
If your assumptions are wrong, your conclusions are wrong. If your assumptions
are wrong part of the time, your conclusions are wrong ALL of the time, because
there is no way to know, using the method, when they are correct or when they
are wrong. (T AND T = T) AND ( T AND F = F) = False
> > 3. If any rock unit is believed or known to be young, then any old
> isometric
> > age is rejected, not as inaccurate, but as irrelevant.
> > EVERYONE recognizes that the computed age of the Unikaret basalts based
> on
> > Rb-Sr cannot be the age of the crystallizing of the lava flows in the
> > "Cenozoic" because the "law of superposition" overrides the isotopically
> > derived age.
>
> This is incorrect. The radiometric age may be inaccurate but it is not
> irrelevant. It is telling us that there are additional factors to be
> considered. Your example of the young Unikaret basalts and Austin's 1.3
> billion year age is an excellent example of what I am referring to (as well
> as evidence that you did not completely read or consider the criticisms of
> Austin's work at <www.talkorigins.org/faqs/icr-science.html>). The date
> that Austin obtained may be a valid radiometric test result but the method
> he used does not give the age of the lava flow sitting at the surface but
> more likely the age of the source material in the mantle below the Grand
> Canyon. (See the criticism labeled "The wrong meaning is assigned to the
> dates.") The tests and the result may be valid but Austin has
> misinterpreted the data to mean that the radiometric data is giving the age
> of the multiple flows and, since that age is stratigraphically
> unreasonable, then all radiometric dating is invalid.
So 1.3 billion years for rock that could only have crystallized a few "million
years ago" is only "inaccurate?" Any technicians who processed the Uinkaret
lavas so inaccurately would not be working much longer in that field. There is
nothing inaccurate in the methodology of measuring ratios of isotopes and
computing ages. No one is going around saying that the measurements are
inaccurate. Rather, they say that the computed
dates do not have anything to do
with the actual age of the crystallization of the extruded lava. This simply
means that the computed ages are irrelevant to the age of the lava.
You said, "The date that Austin obtained may be a valid radiometric test result
but the method he used does not give the age of the lava flow sitting at the
surface but more likely the age of the source material in the mantle below the
Grand Canyon."
That is nothing but pure rationalization.
> Let me give another non-geological analogy. The Uinkaret basalts are like
> a fruitcake (except that the fruitcake is probably older! <grin>). Just
> like the fruit in the fruitcake, these basalts include pieces of rock from
> other sources (known as xenoliths or literally "foreign rocks"). According
> to the TalkOrigins FAQ, Austin has deliberately chosen a sampling method
> that dates the fruit and then interpreted that as the age of the cake.
Sorry:
The T.O. FAQ says "phenocryst" not "xenolith" And, as is typical of T.O., they
misinform and mislead by saying that a phenocryst is a "large mineral which
likely formed in the magma chamber." That is not the definition of phenocryst
--i.e. ìa large mineral crystal surrounded by smaller ones.î It is pure
speculation by T.O. that the larger crystal was formed in the magma chamber.
Austin did not go looking for old ages. He did the very same thing that any
other geologist would do in selecting crystals to find a single mineral crystal
age of the rock. T.O. implies that if Austin had used some on the smaller
mineral crystals he would have not gotten the old age. However, 5 whole rock
samples (made up primarily of the smaller mineral crystals) were also dated.
They all are in close concordance with themselves and the single crystal.
Allen
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