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 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.
Tim Thompson

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


Dr. David Plaisted has written a "critique" of radiometric dating, which appears on the 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.


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 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.


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.


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 Chapter 12 - How Old is the Earth, from the 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.


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.


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.


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.


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 " A Criticism of the ICR's Grand Canyon Dating Project by Chris Stassen and compare with 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 Austin's report shows a 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.


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).


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)


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.


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).


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 Woodmorappe's Collection of Bad Dates by Dave Matson, and also 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.


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.


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 The Geology of Gentry's "Tiny Mysteries", and by Lorence Collins in Polonium Halos and Myrmekite in Pegmatite and Granite.


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.


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.


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.


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).


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
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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