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_Comments on David Plaisted's "The Radiometric Dating Game" - Part 1_

_By Kevin R. Henke, Ph.D._
_________________________________________________________________

This article was originally posted by Dr. Henke to the talk.origins
newsgroup in early December 1998. I have placed it on the web with his
permission. All contents are © 1998,1999 by Dr. Kevin R. Henke. I have
edited the original text only as required to take advantage of the
HTML format, such as replacing text URLs with live links. But I have
not altered content in any substantial degree, and the text has been
approved by Dr. Henke prior to being made public.
[1]Tim Thompson

Dr. Henke is currently a post doctoral fellow in the [2]Department of
Chemistry at the [3]University of Kentucky. [4]Dr. David Plaisted
earned his PhD in computer science from [5]Stanford University in
1976, and is currently Professor of [6]Computer Science at the
[7]University of North Carolina, Chapel Hill.
_________________________________________________________________

_ABSTRACT_

Dr. David Plaisted has written a [8]"critique" of radiometric dating,
which appears on the [9]The True.Origin Archive. He claims on p. 2
(_the page numbers for Dr. Plaisted's report are based on placing a
copy into Microsoft Word® with a Times New Roman Font 12 single
spacing format_) that his report discusses a number of issues that
question the validity of radiometric dating. He further claims that
the issues in his report have not been adequately discussed in other
creationist documents. A review of his report, however, shows that
little, if any, of his material is original. He has simply recycled
erroneous claims from Slusher (1981) and other creationist sources. In
some cases, statements from Dr. Plaisted and his sources are word for
word identical to statements in Slusher (1981), but Slusher (1981) is
not properly quoted or referenced. Overall, the worn-out claims in
Plaisted's report were refuted long ago by Dalrymple (1984), Brush
(1983), Young (1982), and others. My report briefly discusses and
addresses some of the worn-out claims in Plaisted's report, but for
details consult my references.

_INTRODUCTION_

Like many creationists, Dr. Plaisted looks at the 4.5 billion year old
Earth as being in conflict with a literal interpretation of Genesis.
Many, if not, most Christians see no conflict between an ancient Earth
and Genesis. For example, Dr. Roger C. Wiens, a Christian, defends
radiometric dating in his essay [10]Radiometric Dating: A Christian
Perspective. However, as a young-Earth creationist, Dr. Plaisted
clearly feels that radiometric dating is a threat to his Biblical
views. This perceived threat is a clear motive for his attacks on
radiometric dating.

_PLAISTED'S MISUNDERSTANDING AND MISUSE OF BASIC GEOLOGICAL TERMS_

Often Dr. Plaisted is unfamiliar with the geological terms that he
uses. For example, on p. 4, he improperly refers to magma (subsurface
molten rock) as "lava." Specifically, he states:

"Lava that cools underground cools much more slowly, and can form
large crystals. This type of lava typically forms granite or
quartz."

Again on p. 22, he refers to extrusive igneous rocks as being
"basalts" and intrusive ones as often being "granites." Of course,
this is a gross oversimplification of the origin of igneous rocks that
may have come from another misguided creationist source, Gentry (1988,
p.130). Magma, not "underground lava," can solidify into granites,
gabbros, syenites or numerous other intrusive igneous rocks. Extrusive
igneous rocks not only include basalts, but also dacites, rhyolites,
and many others. Igneous rocks may contain quartz, muscovite, or a
number of other minerals. Dr. Plaisted (p. 3) also misuses the term
"mica." Micas are a group of platy silicate igneous and metamorphic
minerals. Dr. Plaisted (p. 4) states that "mica" excludes strontium.
Certainly, biotite, muscovite and other alkali (K, Na, and Li) micas
would tend to exclude strontium, but calcium-rich micas, such as
margarite, could contain a considerable amount of strontium.

_VARIABLE DECAY RATES?_

In a number of occasions, Dr. Plaisted speculates that decay rates for
radioactive isotopes could have been faster in the past than they
currently are (p. 2). Like many creationists, Dr. Plaisted (p. 5)
cites [11]Chapter 12 - How Old is the Earth, from the [12]Handy Dandy
Evolution Refuter, and claims that radioactive decay rates might have
been affected by increases in the amount of neutrinos, neutrons, or
cosmic rays hitting the Earth in the past. This is an old creationist
claim that was refuted long ago. First of all, _any_ radiation that
would penetrate the crust and change the decay rates of isotopes, most
certainly would have killed every life form on Earth. Now,
creationists might invoke miracles to magically explain how decay
rates could change without sterilizing the Earth. However, until they
have scientific proof, they might as well claim that the Earth was
created last week by fairies and that all of our memories are
illusions.

Dalrymple (1984, p. 88-89) refutes in some detail the various
creationist claims that radioactive decay rates may be influenced by
neutrinos, neutrons, and cosmic radiation, including Dudley's
"neutrino sea." Dalrymple points out that there is no evidence of an
abundant supply of neutrons to affect radiometric decay. If there had
been, the neutrons would have also noticeably affected the chemistry
of the more common elements. Because neutrinos have no charge and
little or no rest mass, they pass through the entire Earth without
leaving significant effects. If they can pass through the entire Earth
without significant effects, they are not likely to interact with
atomic nuclei and affect radioactive decay. As Brush (1983, p. 332)
and Dalrymple (1984, p. 89) state, Dudley's neutrino sea violates both
relativity and quantum mechanics. Not even Dudley himself agrees with
how creationists have applied his hypothesis (Dalrymple, 1984, p. 89).

Even creationist John Morris (1994, p. 52-53) admits that there's no
convincing evidence that radiometric decay rates have significantly
changed over time. There is simply no known scientific mechanism that
could produce such changes. Dalrymple (1984, p. 88) states that decay
rates are essentially unaffected by temperatures between -186°C to
2000°C, at pressures that range from a vacuum to several thousand
atmospheres, and under different gravity and magnetic fields. Because
radioactive decay occurs within the nucleus of atoms while terrestrial
chemical processes only affect the outer electrons, it is not
surprising that the Earth's chemical and biological processes cannot
significantly affect radioactive decay rates.

_PLAISTED'S CONCERNS OVER DECAY CONSTANTS, INCLUDING THE K/AR
BRANCHING RATIO_

Dr. Plaisted claims (p. 5-6, 10, and 12) that the K/Ar branching ratio
and decay constants associated with radiometric dating are poorly
known. These accusations are simply outdated and bogus. For example on
p. 5, he states: "_Furthermore, there is still disagreement of 15
percent between the two preferred values for the U-238 decay
constant._" This is obviously an outdated statement. Harland et al.
(1990, p. 78) state that the half-lives associated with U/Pb dating
are known to better than 0.1%.

In another outdated argument on p. 10, Dr. Plaisted cites a letter
from an anonymous friend who states that the branching ratio for 40K
into 40Ar and 40Ca is poorly known. Dr. Plaisted and his allies (p.
12) even go as far as to state that geologists pick whatever branching
ratio provides the results that they want. On p. 5-6, Dr. Plaisted
further states that decay constants for different radiometric methods
have to be "adjusted" to comply with each other. Again, both Dalrymple
(1984, p. 91) and Young (1982, p. 99-100) refute these insulting
claims of dishonesty. These accusations are just plain wrong and were
derived from outdated creationist nonsense in Slusher (1981, p.
38-40); Morris (1981, p. 145) and Cook (1966, p. 65f). Specifically,
Slusher (1981, p. 38) claims that laboratory measurements of the ratio
vary from 0.11-0.126; however, he indicates that scientists may
deliberately "fudge" the values to as low as 0.08 to correspond with
U/Pb dates, which Slusher also doubts. Dr. Plaisted is simply
repeating this nonsense on p. 10 without identifying the outdated
sources of this crap. Specifically, statements by Dr. Plaisted on
p.4-5 and his anonymous friend (Slusher?) on p. 10-11 are often word
for word identical to Slusher (1981, p. 38-40), yet creationist
Slusher is never given credit (or more properly blame) for these
statements.

Dalrymple (1984, p. 91) states that the branching ratio was poorly
known until the early 1950's, but direct laboratory counting
measurements significantly reduced the error to within a few percent
by the mid- to late-1950's. Today, the branching ratio is known to
better than 1%. Harland et al. (1990, p. 76) further state that the
errors in the decay constants associated with K/Ar dating are on the
order of 0.5%. It would be nice if creationists, like Dr. Plaisted,
would read the writings of their critics rather than simply repeating
the same old errors over and over again. I must give credit to
creationists John Morris, Steve Austin, and John Woodmorappe. At least
they often find and publish new material for us to evaluate.

_HOW WELL DO MINERALS RETAIN ARGON?_

Dr. Plaisted wants to give his readers the impression that argon can
readily move in and out of minerals and, therefore, the gas is too
volatile for radiometric dating. Specifically, he quotes one of his
anonymous friends that claims that argon easily diffuses from minerals
(p. 11, also the identical statement is made in Slusher, 1981, p. 39).
Of course, these statements are inaccurate generalizations. Young
(1982, p. 101) notes that argon would more likely adsorb onto the
surfaces of the minerals rather than move into their tight structures.
Geochronologists are aware that excess argon may accumulate on mineral
surfaces and the surface argon would be removed before analysis.

Once 40Ar is produced by the decay of 40K within a mineral, the
ability of the mineral to retain the argon would depend on the
identity of the mineral and its thermal environment (e.g., Hyndman,
1985, p. 675-676). Hornblendes, for example, retain argon very well,
while biotites are less effective and feldspars readily leak the gas.
Geologists are familiar with the argon-retention abilities of
different minerals and use these differences to their advantage.

_METAMORPHISM AND ALTERATION BY WATER AND THEIR EFFECTS ON RADIOMETRIC
DATING_

In several places in his report (for example, p. 6-7), Dr. Plaisted is
concerned that radiometric dates may be unknowingly affected by the
movement of water through the rock or by metamorphic heating.
Fortunately, his concerns are largely unfounded. Before dating a
sample, a geologist will thoroughly evaluate the sample to determine
if it has undergone metamorphism or weathering. If the isotopes were
significantly affected by heating or water, in most cases the
mineralogy would also have been noticeably altered. Hydrothermal ("hot
water") alteration may involve the conversion of biotite to chlorite,
the oxidation of iron minerals to hematite and geothite, the
transformation of feldspars to clays and white micas, and the
conversion of pyroxenes and olivines to serpentines. Most of the
alteration products are very noticeable under a microscope and, some
like the oxidation of iron minerals, may be even noticeable in hand
specimens in the field. That is, weathered and altered rocks often
have iron stains. Metamorphosed rocks may have distinctive banding and
other textures that separate them from igneous and sedimentary rocks.
Furthermore, they may contain minerals that are rare in igneous or
sedimentary rocks, such as garnet, cordierite, kyanite, and
andalusite. Faults, weathering zones, structural deformations, and
other features at a field site would also warn geologists about
possible weathering, metamorphism and other alteration effects in the
outcrops. Even an undergraduate geology student would know enough to
avoid altered samples as part of a radiometric dating study. Sample
collectors would also want to know if the purpose of the radiometric
dating was to determine the age of any metamorphic events or the
original crystallization events for the igneous rocks. Depending upon
the purpose of the study, the appropriate igneous and/or metamorphic
samples would be collected.

_XENOLITHS AND XENOCRYSTS_

As magmas move through the crust towards the surface or as lava flows
over the Earth's surface, they may pickup chunks of surrounding rocks.
Sometimes, the magmas and lavas are not hot enough to melt the
captured rocks. Once the molten rock solidifies, the plucked rocks
remain trapped in the igneous matrix. These trapped rocks are called
xenoliths. If the trapped materials are individual minerals, they are
called xenocrysts.

Dr. Plaisted is very concerned that xenocrysts and xenoliths may
contaminate samples and produce false radiometric ages. Well,
geochronologists are concerned about xenoliths and xenocrysts too.
Geologists are also concerned about zoned phenocrysts (crystals) of
feldspar or other minerals. As a melt cools, calcium-rich feldspars
crystallize before the sodium-rich varieties. As the temperature of
the magma drops over thousands or even a few million years, more
sodium-rich varieties may crystallize. The sodium-rich feldspars may
form their own crystals or form as layers or zones on the older
calcium-rich feldspars. Obviously, the cores of zoned feldspars may
provide much older K/Ar dates than the more sodium-rich and younger
rims.

Xenoliths, zoned phenocrysts, and xenocrysts (like metamorphic and
weathering features) are often easily identified under the microscope
and sometimes even in the field. In some cases, a geologist may be
interested in dating xenoliths, zoned phenocrysts, or the xenocrysts.
However, obviously, if the geologist is interested in dating the
younger matrix, he/she will look for and avoid any xenoliths, zoned
phenocrysts or xenocrysts. While mainstream geologists know how to
avoid xenoliths, zoned phenocrysts, and xenocrysts when dating igneous
rocks, creationist Steve Austin apparently was not careful to avoid
them when he conducted his "research" at Mt. St. Helens or the Grand
Canyon, see " [13]A Criticism of the ICR's Grand Canyon Dating Project
by Chris Stassen and compare with [14]Excess Argon within Mineral
Concentrates from the New Dacite Lava Dome at Mt. St. Helens Volcano,
by Steven Austin. In his Mt. St. Helen's study, Austin collected what
he thought was a freshly solidified dacite. He removed the gabbro
xenoliths, but there's no mention if he found and removed any lighter
colored, less obvious xenoliths, such as andesites or quartz diorites.
Austin states that xenoliths of gabbro, quartz diorite, basalt, and
andesite are common at the Mt. St. Helen site.

Figure 4 in [15]Austin's report shows a [16]photomicrograph from one
of his dacite samples. Notice that the feldspars in the figure are
zoned. The zoning indicates that the feldspars have a long cooling
history. The cores of the feldspars could be hundreds of thousands or
a few million years older than the rims. As others have pointed out at
anti-creationism web sites, the zoning is probably why Austin got a
K/Ar age of 340,000 years for his feldspar/glass concentrate. The
glass may have crystallized in the 1980's as Austin expected, but the
feldspars may be much older. Bowen's reaction series (Perkins, 1998,
p. 93-95) states that olivines, pyroxenes and Ca-feldspars are the
first minerals to crystallize out of a mafic to intermediate magma. As
the magma cools and the temperature drops, hornblendes and more
sodium-rich feldspars may crystallize. As the temperature continues to
drop, feldspars even richer in sodium crystallize. By this time, the
magma may reach the surface and the remaining melt may be rapidly
quenched to a glass. If Austin really wanted to date the 1986
eruption, he should have only sampled the glass. This is NOT an easy
task and it may not be possible with a messy rock like this dacite.
Austin's K/Ar dates are consistent with Bowen's reaction series. The
pyroxene fractions which should have crystallized first, provide the
oldest ages of 1.7 -2.8 million years. The amphiboles, which
crystallized later, are in a fraction that provided a younger age of
0.9 million years. His glass and feldspar fraction is probably a
mixture of young glass, old Ca-feldspars, and sodium-rich feldspars
that have an intermediate age. Not surprisingly, this mixture gave a
younger age of about 340,000 years, but still much older than 1986 AD.
His whole rock age was no doubt affected by a mixture of young glass,
older feldspar and pyroxene phenocrysts and some possibly ancient
xenocrysts or lightly colored (hard to see) xenoliths. In conclusion,
Austin's results do NOTHING to refute the validity of K/Ar dating.

_DO VARIOUS RADIOMETRIC DATING METHODS RARELY AGREE FOR CAMBRIAN AND
YOUNGER ROCKS?_

Dr. Plaisted (p. 14) states that he is not very interested in the
radiometric dating of meteorites and Precambrian terrestrial rocks. He
(p. 2, 14-15) wants to see evidence that different radiometric methods
give consistent results in Phanerozoic (Cambrian and younger) rocks
and also with any associated fossiliferous rocks. Dr. Plaisted (p. 2,
14-17) further claims that such comparisons rarely show agreement.
Once more, his claims are totally without merit. The geology
literature contains numerous studies where different methods (e.g.,
K/Ar and Rb/Sr) have been compared with each other and in some cases
with paleomagnetic data or fossils in associated sedimentary rocks.
Faul (1966) lists numerous examples. Young (1977, p. 190f) provides an
excellent example of fossil data confirming the results of Rb/Sr and
K/Ar dates for the Beemerville Nepheline Syenite in New Jersey. The
syenite intruded into the Ordovician Martinsburg Formation, but it
does not intrude into the overlying Lower Silurian Tuscarora
Formation. Cross-cutting relationships, fossil data, and the geologic
time scale indicate that the syenite should be 425 to 450 million
years old. Rb/Sr and K/Ar dating of the syenite yielded dates of 424
±20 million years, 436 ±41 million years, and 437 ±22 million years,
which are reasonably consistent. Harland et al. (1990) is yet another
excellent reference that discusses the calibration of the geologic
time scale. This book contains countless examples of comparisons
between different radiometric methods and additional comparisons with
fossil and paleomagnetic data.

Dr. Plaisted (p. 15) recognizes that a majority of radiometric dates
are K/Ar. He then expresses concern that an overreliance on the K/Ar
method may lead to inaccurate dating of samples. As a hypothetical
example, he assumes that 80% of the radiometric dates for a volcanic
deposit are K/Ar. In his example, the K/Ar dates are very consistent,
but still wrong. The other 20% of the dates on the volcanic consist of
highly variable results obtained with other radiometric methods. He
argues that geochronologists could still claim that overall the dates
for the volcanic are in "reasonable agreement," even though there is
no consistency between the results of the different methods and the
K/Ar dates, although consistent, are really erroneous. Of course,
Plaisted's scenario is nothing but another straw person argument.
Competent geologists would never mix their data in such a biased
manner. Such an approach is statistically invalid. The K/Ar results
may be averaged, but the literature overwhelmingly indicates that
results from Rb/Sr, U/Pb and other methods would be listed separately,
no matter how they compare with the K/Ar results (for example, see the
table in Dalrymple, 1991, p. 140-141).

_ATMOSPHERIC ARGON CONTAMINATION: A WIDESPREAD AND SERIOUS PROBLEM?_

Geochronologists are aware that argon in the Earth's atmosphere may be
a possible source of contamination for K/Ar dating. Dr. Plaisted (p.
6-7 and elsewhere) raises concerns about atmospheric contamination. A
review of Dalrymple (1984, p. 71) clearly indicates that Dr.
Plaisted's concerns are exaggerated. Specifically, Dalrymple states
that the correction for atmospheric argon contamination can be easily
done and is very accurate. Atmospheric argon has no significant affect
on the K/Ar dates as long as the atmospheric argon does not represent
a large percentage of the total argon. Obviously, the percentage would
not be great, except in very young samples. Furthermore, Dalrymple
(1984, p. 71) states that the atmospheric argon contribution is taken
into account when assigning errors to the K/Ar ages. In support of
Dalrymple's claims, Harland et al. (1990) demonstrate that K/Ar dating
can be consistent with U/Pb, Rb/Sr and other methods. Young (1982, p.
102) also points out that atmospheric Ar contamination cannot be used
by creationists to explain away lunar K/Ar dates of 3 to 4 billion
years old.

As discussed in Dalrymple (1991, p. 111-115), 40Ar/39Ar has been
developed as an alternative or supplement to K/Ar dating. 40Ar/39Ar
has a number of advantages over K/Ar and circumvents any atmospheric
argon contamination problems. The results of 40Ar/39Ar are impressive
and the method has recently been used to successfully date the 79 AD
eruption of Mt. Vesuvius to within seven years of the actual date!
(Renne, P.R. et al., 1997)

_IS THE EARTH'S UPPER CRUST CONTAMINATED WITH ARGON?_

Dr. Plaisted (p. 11 and elsewhere) claims that 40Ar would
preferentially rise from the Earth's interior and concentrate near the
Earth's surface. He claims that the concentration of argon near the
Earth's surface would contaminant the crustal rocks with excess argon
and produce false ages that are too old. Dr. Plaisted's views are not
new and were taken, sometimes word for word without proper
referencing, from Slusher (1981, p. 39).

Dr. Plaisted (p. 14) even suggests that argon concentrations in the
atmosphere would concentrate near the ground. Of course, such a layer
would not form because of atmospheric mixing by winds and because the
atomic weight of argon is not that much greater than N2 or O2, the
dominant gases in air. Helium and hydrogen, on the other hand, do
escape into space. The escape of helium from the Earth's atmosphere
undermines one of the creationists' favorite claims for a "young"
Earth (see Dalrymple, 1984, p. 112-113).

Young (1982, p. 100-101) refutes Slusher's claims of crustal
contamination by argon gas. Because argon is inert, the gas would tend
to diffuse through large fractures in the crust rather than into
minerals or small fractures within the minerals. That is, the argon
would take the path of least resistance. Again, Young (1982, p. 101)
states that argon would more likely adsorb onto the surfaces of the
minerals rather than into their tight structures. Hornblende, however,
appears to be an occasional exception. Hyndman (1985, p. 670) notes
that hornblendes may accumulate excess argon and give ridiculously old
K/Ar dates in some situations. Geochronologists are aware of which
minerals have problems with excess argon and would deal with them or
avoid them as part of K/Ar studies.

Dr. Plaisted does not present any evidence that excess argon is a
widespread problem in K/Ar dating. Without citing any references, he
(p. 14) simply claims that recent lava flows "often" have K/Ar ages of
200,000 years. Dalrymple (1984, p. 81-82; 1991, p.91-92), on the other
hand, notes that historically erupted volcanics rarely contain excess
argon. Young (1982, p. 103) cites examples of historically erupted
volcanics from Japan, Sicily, Hawaii, and Iceland that have no excess
argon. Of course, creationists (including Dr. Plaisted on p. 18) are
fond of citing and exaggerating exceptions and supposed exceptions,
such as the 1801 AD eruptions in Hawaii, which are discussed in
Funkhouser and Naughton (1968) and Dalrymple (1984, p. 81-82).
Funkhouser and Naughton (1968) were using K/Ar dating to study the
much older xenoliths in the flows and not the 200 year old matrix,
which explains the old dates.

_WHERE DOES 40AR COME FROM?_

Dr. Plaisted (p. 14) admits that 40Ar is only produced by radioactive
decay. This creates a great problem for young-Earth creationists. If
40Ar is only produced by radioactive decay, how can there be so much
of it on an Earth that is only 6,000 to 10,000 years old? Natural
biological and terrestrial chemical processes are not known to
fractionate the heavy isotopes that are involved in radiometric dating
(Miller, 1984, p. 33). How could that much 40Ar be concentrated
without the presence of other argon isotopes? Dr. Plaisted (p. 2, 13)
might claim that the excess 40Ar could have formed from increases in
the 40K decay rate in the dense and hot interiors of stars. This
suggestion is not supported by isochrons (as Dr. Plaisted suggests on
p. 13), meteorite chemistry, or the chemistry of the stellar
atmosphere. 36Ar and not 40Ar is the most abundant isotope in the
stellar atmosphere (Krauskopf, 1979, p. 530). For 40Ar to have been
concentrated on the Earth during the moment of its creation, the
isotope should also have been abundant in the solar nebula and in the
current solar atmosphere, but we see no evidence of this.

Dr. Plaisted (p. 10-11) cites an anonymous friend (whose statement
turns out to come word for word from Slusher, 1981, p. 39) who claims
that there is too much 40Ar in the atmosphere for the Earth to be 4.5
billion years old. According to this source, most of the argon had to
be primordial, or as creationists would probably claim: an "ex nihilo"
miracle from God. Dalrymple (1984, p. 83) rejects Slusher's claim and
states that the 40Ar content of the Earth's atmosphere is consistent
with the potassium content of the Earth's crust and mantle, and 4.5
billion years of terrestrial history.

One of Dr. Plaisted's friends complains (p.11) that rocks in areas
with complex geologic histories tend to have large discordances in
K/Ar dates. This is not unexpected, because rocks with complex
metamorphic and igneous histories could have experienced a number of
heating events. Such events would have released at least some of the
argon from the rocks, which would have produced discordances (see
Dalrymple, 1991, p. 93-94).

_QUOTATIONS OF WOODMORAPPE'S ERRONEOUS CLAIMS_

Dr. Plaisted uses some of the erroneous material from Woodmorappe
(1979) as part of an ineffective attack on the reliability of
radiometric dating. Interestingly, he may not trust all of
Woodmorappe's claims. On p. 15, Dr. Plaisted states:

"Now, several factors need to be considered when evaluating how often
methods give expected ages on the geologic column. Some of these are
taken from John Woodmoreappe's (sic, Woodmorappe) article on the
subject, but only when I have reason to believe the statements are
also generally believed."

Woodmorappe's (1979) nonsense has been extensively attacked by
Dalrymple (1984) (see [17]Woodmorappe's Collection of Bad Dates by
Dave Matson, and also [18]Geochronology According to John Woodmorappe
by Steven Schimmrich). After reviewing many of the references in
Woodmorappe (1979) for myself, I discovered numerous other
misquotations and other misuses of the literature in his article. Of
the 429 or so "anomalous" dates in Woodmorappe (1979), 94 (21.9%)
involve illite and glauconite, which (because of their crystalline
structures) are notoriously unreliable in giving K-Ar dates.
Geochronologists know that illite and glauconite K/Ar dates are often
untrustworthy. K/Ar ages from these minerals are often published to
better understand the types of conditions that cause them to produce
unreliable dates rather than to assign actual ages. Woodmorappe is
clearly misusing illite and glauconite dates to simply pad his list.

In another example, Woodmorappe (1979, p. 112) quotes Brookins and
Norton (1975, his reference #199) and states that the expected age of
a granite from Massachusetts was about 580 million years old, while
the Rb/Sr whole rock analysis provided an unlikely value of 894 ± 58
million years. A review of Brookins and Norton (1975) indicates that
the granite was cataclastic and foliated. In other words, the rock had
been deformed by faulting. Therefore, it's not surprising that the
Rb/Sr date is in error. Woodmorappe is simply constructing and
attacking an invalid straw person by using this date.

In other examples, Woodmorappe (1979) claims that papers contain
inconsistent dates, when discussions in those papers indicate that the
data are reasonable. For example, Woodmorappe (1979, p. 106) claims
that Naumov and Mukhina (1977, Woodmorappe reference #80) were
expecting the ages of the Korvunchana volcanics in the former Soviet
Union to be more than 225 million years old or older than the Late
Permian/Early Triassic boundary. A review of Naumov and Mukhina (1977)
shows that their ages were 172 to 270 million years with most of them
in the reasonable range of 246 to 270 million years old. The authors
state that the fossil data in the area are not very conclusive and
that ages as recent as Jurassic (which would include the low date of
172 million years) for the volcanics may be possible.

Among the citations of Woodmorappe (1979), Dr. Plaisted (p. 17) refers
to a ridiculously old Rb/Sr "date of 34 billion years." Dalrymple
(1984, p. 77f) discusses the origin of this "date" and denounces
Woodmorappe (1979) for creating this fictitious date by misreading an
isochron plot for the Pahrump Group Diabase in California (see the
original source: Faure and Powell, 1972). The diabase shows a terrible
scatter on the 87Sr/86Sr versus 87Rb/86Sr plot and does not provide a
Rb/Sr date. Radiometric dating on related rocks, however, indicates
that the diabase is about 1.2 billion years old. On the badly
scattered diagram, two age-meaningless "reference isochrons" are drawn
to bracket the badly scattered data. One reference isochron is "1.09
billion years." The other is a "34 billion years." These reference
isochrons have no time meaning. They are simply drawn in as a guide
for the reader in much the same way that a flying pilot may refer to
the position of another plane as being between "9 and 11 O'Clock" from
her position. In this case, the "9 to 11 O'Clock" has no time meaning,
but simply indicates that the other plane is from the left to the
front left of the pilot. Because Woodmorappe wants radiometric dating
to look as bad as possible, he cites the 34 billion year old reference
isochron as if it were real and ignores the 1.09 billion year
reference isochron and the actual age estimate of 1.2 billion years.
By assigning a false age of 34 billion years to the diabase,
Woodmorappe (1979, p. 122) gives the ridiculous impression that Rb/Sr
dating is claiming that the rock is seven times as old as the age of
the Earth and about twice the age of the Big Bang.

Woodmorappe (1985) is an inadequate attempt to deal with some of
Dalrymple's criticisms. Overall, Woodmorappe has failed to provide
scientific evidence to show that the vast majority of K/Ar, U/Pb, and
Rb/Sr dates are inconsistent, and not reasonably accurate and real.
For young-Earth creationists, _not a single_ radiometric date of
greater than 10,000 years can be tolerated or their interpretation of
Genesis is invalidated.

Dr. Plaisted (p. 20) cites other examples from the literature of
invalid K/Ar dates. From Woodmorappe (1979, p. 122), he quotes Gerling
et al. (1968) (Woodmorappe reference #297) who got K/Ar dates of 7 to
15 billion years on some chlorites. In another example from a web
site, Dr. Plaisted (p. 20-21) quotes Evernden et al. (1964), which
states that some devitrified (altered) glasses of known ages gave
results that were too young. Both chlorites and devitrified glasses
are alteration products. Therefore, unreasonable K/Ar dates are
expected with these materials because the alteration events would have
caused the argon to move in or out of the materials. Obviously,
geochronologists would avoid these materials if they wanted
quantitative dates.

_INTERLABORATORY STUDIES OF RADIOMETRIC DATES_

Plaisted (p. 24) calls for double-blind radiometric tests on
Phanerozoic outcrops using different methods and different
laboratories. Of course, interlaboratory studies on radiometric dating
and multiple analyses on outcrops with different methods are nothing
new. Examples are cited in Harland et al. (1990) for Phanerozoic
samples and Dalrymple (1991) for meteorites and Precambrian outcrops.
One of the older and well-known interlaboratory studies is Lanphere
and Dalrymple (1965). The results of this study are also described in
some detail in Jaeger (1979, p. 23-25). In Lanphere and Dalrymple
(1965), 55 laboratories were sent a muscovite standard for dating. The
average K/Ar date for the muscovite was 83.0 million years and the
average Rb/Sr date was reasonably close at 85.7 million years.
Interlaboratory standard deviations were only 1.2% for the K/Ar dates
and 2.8% for the Rb/Sr dates. These excellent results refute
creationist claims that K/Ar and Rb/Sr methods are inconsistent or
imprecise.

_DO GENTRY'S HALOS REFUTE CONSTANT RADIOMETRIC DECAY RATES?_

Plaisted (p. 24-26) cites studies from the 1920's by Joly and more
recent studies by Gentry to claim that pleochroic haloes indicate that
decay rates have not been constant over time. Brush (1983, p. 333-334)
discusses this issue and shows that the halos do not support any
changes in radioactive decay constants. Joly even conceded that his
critics were right (Brush, 1983, p. 333). The use of radiohaloes by
Gentry and others to support creationism has been further undermined
by Odom and Rink (1989) and Wakefield (1987/1988). Additional
criticism of Gentry's claims are given by Wakefield in [19]The Geology
of Gentry's "Tiny Mysteries", and by Lorence Collins in [20]Polonium
Halos and Myrmekite in Pegmatite and Granite.

_FAULTY ISOCHRONS?_

Dr. Plaisted (p. 26) is very skeptical that isochron dating is
reliable. He (p. 26-28) raises a number of often-used creationist
objections to isochron dating, which have already been refuted by
Dalrymple (1984, p. 83-86) and Young (1982, p. 103-110). In
particular, Plaisted (p. 27-28) is concerned that the mixing of magmas
may generate false isochrons. Dalrymple (1984, p. 84-87) discusses
this topic, and with the help of 87Sr/86Sr vs 1/Sr plots, shows that
mixing may be detected and does not explain away the validity of most
isochrons.

_DATING OF THE ATLANTIC SEA FLOOR_

Dr. Plaisted (p. 28) does not trust K/Ar dates for basalts from the
Atlantic sea floor. He feels that they may have been contaminated with
excess 40Ar and, therefore, appear a lot older than they really are.
Strahler (1987, p. 204-210) discusses the problems with some K/Ar
dates of sea floor basalts and provides paleomagnetic and other data
to support the old age of the ocean crust.

_DATING OF METEORITES_

Dr. Plaisted's objections (p. 28-29) to dating meteorites consist of
more old and invalid accusations. He accuses geochronologists of using
"fudge factors" to estimate the amount of the original daughter
product in the sample. Dalrymple (1984, p. 82) states that knowledge
of the initial amount of the daughter product is not even needed to
obtain reliable ages with isochron methods. Furthermore, if the
original concentration of the daughter product is desired, it may be
read off at the y-intercept for the isochron (Dalrymple, 1984, p. 73,
82-87). Dalrymple (1991, chapter 6) contains extensive information on
meteorites and their radiometric ages. Most, if not all, of Plaisted's
objections and questions (p. 28-29) would be answered if only he would
read the references that I cite in this report.

_CONCLUSIONS_

Plaisted's report contains little or no original material, but simply
recycles old arguments from Slusher (1981) and other creationist
sources. These creationist accusations were refuted long ago by
Dalrymple (1984), Brush (1983) and Young (1982).

_REFERENCES_

_Brookins, D.G. and S.A. Norton_, 1975
_Rb/Sr Whole-Rock Ages Along the PreCambrian-Cambrian Contact, East
Side of the Berkshire Massif, Massachusetts_
Geological Society of America Abstracts with Programs, v. 7, p. 30-31.

_Brush, Stephen G._, 1983
_Finding the Age of the Earth: By Physics or By Faith_
p. 296f, in Zetterberg, J. P., (Ed.), "Evolution versus Creationism:
The Public Education Controversy"
Oryx Press.

_Cook, M. A._, 1966
_Prehistory and Earth Models_
Max Parrish, London.

_Dalrymple, G. B._, 1984
_How Old is the Earth?: A Reply to `Scientific' Creationism_
In "Proceedings of the 63rd Annual Meeting of the Pacific Division,
American Association for the Advancement of Science"
vol. 1, pt. 3, Frank Awbrey and William Thwaites (Eds).

_Dalrymple, G. B._, 1991
_The Age of the Earth_
Stanford University Press, 1991

_Evernden, J.F., D.E. Savage, G.H. Curtis, and G.T. James_, 1964
_Potassium-argon dates and the Cenozoic Mammalian Chronology of North
America_
American Journal of Science, v. 262, p. 145-198.

_Faul, H._, 1966
_Ages of Rocks, Planets, and Stars_
McGraw- Hill, New York.

_Faure, G. and J.L. Powell_, 1972,
_Strontium Isotope Geology_
Springer-Verlag, Berlin.

_Funkhouser, J.G. and J.J. Naughton_, 1968
_Radiogenic Helium and Argon in Ultramafic Inclusions from Hawaii_
Geophys. Res. J., v. 73, p. 4601-4607.

_Gentry, Robert V._, 1988
_Creation's Tiny Mystery_
2nd Edition, Earth Science Associates, Knoxville.

_Gerling, E.K., I.M. Morozova, and V.D. Sprintsson_, 1968
_On the Nature of Excess Argon in Some Minerals_
Geochemistry International, v. 9, n. 6, p. 1090.

_Harland, W.B.; R.L. Armstrong; A.V. Cox; L.E. Craig; A.G. Smith; and
D.G. Smith_, 1990
_A Geologic Time Scale 1989_
Cambridge University Press, Cambridge.

_Hyndman, Donald W._, 1985
_Petrology of Igneous and Metamorphic Rocks_
2nd ed., McGraw-Hill Book Company, New York.

_Jaeger, E._, 1979
_The Rb-Sr Method_
p. 13f in Jaeger, E. and J. C. Hunziker, _Lectures in Isotope Geology_
Springer- Verlag, Berlin.

_Krauskopf, Konrad B._, 1979 _Introduction to Geochemistry_
McGraw-Hill, New York.

_Lanphere, M.A. and G.B. Dalrymple_, 1965
_An Interlaboratory Standard Muscovite for Argon and Potassium
Analyses_
J. Geophys. Res., v. 70, p. 3497-3503.

_Miller, K. R._, 1984
_Scientific Creationism Versus Evolution: The Mislabeled Debate_
p. 18f, in Montagu, A. (Ed.) _Science and Creationism_
Oxford Univ. Press, Oxford.

_Morris, Henry M._ (Ed.), 1981
_Scientific Creationism_
ninth printing, Creation-Life Publishers, San Diego, CA, ("general"
edition).

_Morris, John_, 1994
_The Young Earth_
Creation-Life Publishers, Inc., Master Books Division, Colorado
Springs, Colorado.

_Naumov, V.A. and A.M. Mukhina_, 1977
_Absolute Age of Volcanic Formations of the Central Siberial Platform_
International Geology Review, v. 19, p. 951f.

_Odom, A. Leroy and William J. Rink_
_Giant Radiation-induced Color Halos in Quartz: Solution to a Riddle_
Science, vol. 246, October, 1989, p. 107-109.

_Perkins, D._, 1998
_Mineralogy_
Prentice-Hall, Upper Saddle River, New Jersey.

_Renne, P.R., W.D. Sharp, A.L. Deino, G. Orsi, L. Civetta_, 1997
_Ar-40/Ar-39 dating into the historical realm: Calibration against
Pliny the Younger_
Science 277(5330): 1279-1280 (29 August 1997)

_Slusher, H. S._, 1981
_Critique of Radiometric Dating_
Institute for Creation Research, Monograph #2, San Diego, CA.

_Strahler, A. N._, 1987
_Science and Earth History: The Evolution/Creation Controversy_
Prometheus, Buffalo, NY.

_Wakefield, J. Richard_
_Gentry's Tiny Mystery---Unsupported by Geology_
Creation/Evolution 22:13, Winter 1987/1988.

_Woodmorappe, J._
_Radiometric Geochronology Reappraised_
Creation Research Society Quarterly, vol. 16, September, 1979, p.
102f.

_Woodmorappe, J._
_A Reply to G. Brent Dalrymple_
Creation Research Society Quarterly, vol. 21, March 1985, p. 184f.

_Young, Davis A._, 1977
_Creation and the Flood: An Alternative to Flood Geology and Theistic
Evolution_
Baker Book House, Grand Rapids, MI.

_Young, Davis A._, 1982a
_Christianity and the Age of the Earth_
Zondervan, Grand Rapids, MI.
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References

1. file://localhost/www/sat/files/tim_thompson/index.html
2. http://www.chem.uky.edu/
3. http://www.uky.edu/
4. http://www.cs.unc.edu/~plaisted/
5. http://www.stanford.edu/
6. http://www.cs.unc.edu/
7. http://www.unc.edu/
8. http://www.firinn.org/trueorigin/dating.htm
9. http://www.firinn.org/trueorigin/to_home.htm
10. http://asa.calvin.edu/ASA/resources/Wiens.html
11. http://www.parentcompany.com/handy_dandy/hder12.htm
12. http://www.parentcompany.com/handy_dandy/hdertoc.htm
13. http://www.talkorigins.org/faqs/icr-science.html
14. http://www.icr.org/research/sa/sa-r01.htm
15. http://www.icr.org/research/sa/sa-r01.htm
16. http://www.icr.org/research/sa/sa-r01e.jpg
17. http://www.secular.org/library/modern/dave_matson/young-earth/additional_topics/bad_dates.html
18. http://www.talkorigins.org/faqs/woodmorappe-geochronology.html
19. http://www.csun.edu/~vcgeo005/gentry/tiny.htm
20. http://www.csun.edu/~vcgeo005/revised8.htm
21. file://localhost/www/sat/files/tim_thompson/radiometric.html