A Further Reply to Dr. Henke

A Further Reply to Dr. Henke

November 15, 1999

I do set My bow in the cloud

In November, 1999 Dr. Kevin R. Henke responded to my articles at



in an article entitled MORE YOUNG-EARTH CREATIONIST MISCONCEPTIONS ON RADIOMETRIC DATING. This article was posted to the talk.origins newsgroup and e-mailed to me personally. I thank Dr. Henke for the considerable effort he put into his reply. This is my further reply.

The root question is whether radiometric (that is, isotopic) dating is reliable, especially on fossil-bearing rocks. Dates for fossil-bearing strata obtained by radiometric dating are commonly in the hundreds of millions of year range, while a literal reading of the Bible implies that life has only existed on earth for six to ten thousand years. Actually, the title of Dr. Henke's article is misleading, because my main concern is not the age of the earth but the age of life, as Dr. Henke should have known from reading my previous articles. In this response to Dr. Henke's article I discuss the questions of concordances between different dating methods, the properties of various minerals and how they are used in dating, excess argon, mixings and isochrons, possible changes in decay rates, and a few other items of less significance.

Concordances Between Different Dating Methods

Harland et al (1990) gives 700-odd dates on which the geological time scale is based. Dr. Henke has carefully examined this list and found 28 instances in which different dating methods from the same location agree. There are also a few others that he did not explicitly mention. I appreciate his thoroughness. However, about 30 concordances among a list of over 700 dates, selected from a larger sample of unknown size by a process having unknown statistical properties, is not very impressive. In fact, one can explain some concordances on the basis of randomness. We know that there are at least four common dating methods, K-Ar, Rb-Sr, U-Pb, and Ar-Ar. Each method can be used on individual minerals or on whole rocks, and can be used to measure a simple daughter-to-parent ratio or can be used as an isochron. This gives us probably sixteen different methods in all, not counting Pb-Pb dating and fission track dating. If we assume that there are at least 10 samples (or collections of samples) from each area on the average that are datable by each method, we can obtain at least 160 dates from each location. Let's say 100 for simplicity. Among these there are about 5,000 pairs of dates, most of them between different methods, and just on the basis of chance we would expect many of these pairs to agree fairly closely. In fact, it would not be surprising to find pairs that agree with any expected age of the geological formation. In addition to this, geologists often select minerals and methods of dating (such as magnetic separation) to increase the chance that the different methods will agree, as I indicated in my last response to Dr. Henke.

For the sake of a simple probability analysis, suppose that the K-Ar dates for formations are generally taken as their accepted ages, and that the other methods have random values uniformly distributed between 0 and 600 million years on phanerozoic formations. This does not imply that the K-Ar dates are correct. If we define a concordance as an agreement of two dates to within ten percent, then the expected number of concordances is about five percent of the total number of dates, and most of these concordances will be between different methods. The observed number of concordances in Harland et al (1990) is about 30 out of over 700 dates, or somewhat under five percent. Although these probability assumptions are overly simplified, this shows that the observed number of concordances between different methods on the phanerozoic is not inconsistent with a random distribution of the non-K-Ar dates.

One should also remember that concordant dates can all be inherited from an earlier event. If a concordance does not agree with expectations, this can be explained as a later heating event or as an inheritance from an older event, so it does not upset the dating scheme. Woodmorappe (The Mythology of Modern Dating Methods, Institute for Creation Research, 1999, p. 30) references a couple of studies indicating that discordances among different dating methods are much more common than concordances.

The situation on the phanerozoic (Cambrian strata and above) is qualitatively much different than on meteorites, and possibly on some old rocks on earth, where concordances are very common. Therefore, conclusions about the reliability of radiometric dating should not be extrapolated from meteorites or older rocks on earth to the phanerozoic.

It's also interesting that the geological time scale is based on less than 800 dates. This undermines the often-quoted argument that hundreds of thousands of dates have been measured and there are only a few percent of them that do not agree with the expected dates. We are here dealing with a sample of less than 800 dates, not hundreds of thousands.

How the Properties of Minerals Affect Dating Methods

Dr. Henke states that the properties of various minerals are known and used by geologists in determining which radiometric dates are reliable. However, glauconies are considered one of the more unreliable minerals for dating by Faure (1986, p. 71) and others, and dates from glauconies make up a considerable portion of the dates listed in Harland et al (1990). Even "good" minerals for K-Ar dating such as biotite are only considered by Faure (1986, p. 71) to be "often reliable." Faure (1986, p. 72) lists some minerals as often containing excess argon, while others do so only rarely. Dickin (1995, p. 248) states that excess argon can collect in "crystal dislocations and defect structures." Since all crystals can have defects and dislocations, all minerals can have excess argon. Thus a date from an unreliable mineral can be accepted if it is in agreement with expectations, and a date from a reliable mineral cannot always be trusted. Besides the problem of excess argon, it can always be argued that the date was inherited from an earlier event, or reset by a later event. It can also be argued that the sample is a xenolith or a xenocryst. I also gave a number of quotations in my last reply to Dr. Henke indicating that minerals are chosen not for their a priori properties, but because they give dates that are in line with expectations. Thus the properties of a mineral play only a minor role in whether the date measured is accepted or not.

Dr. Henke cites the Eldora quartz monzonite stock (Faure, 1986, p. 69-70) which reveals the temperatures at which various minerals lose argon. This is interesting, but does not deal with the propensity of these minerals to incorporate excess argon when they form, or to adsorb it after they cool.

Excess Argon

Excess (or inherited) argon is argon that did not result from radioactive decay of potassium, and can lead to incorrect K-Ar dates. This argon can either have been present when the mineral formed, or have entered later. Excess argon can make K-Ar dates too old by an arbitrary amount. In order to reliably date rocks, this must be taken into account. The question is whether excess argon can always be detected. In reality, no method appears to be foolproof for detecting excess argon, and no one can say for sure whether argon present in a sample is excess or radiogenic. The tests used to detect excess argon (the spectrum test and isochrons) can all have problems.

Dr. Henke mentions a statement of Dalrymple (1984) that excess argon is rarely found in volcanoes that erupted in historic times. I gave a reference to the contrary. It would be appropriate to give the evidence on which Dalrymple bases his statement. Furthermore, the number of volcanoes having excess argon today is not necessarily the same as it was in the past.

Dr. Henke states that the flow of argon is primarily out of a rock rather than into it, precluding the possibility of excess argon. At high temperatures, argon will indeed flow from a rock containing much argon to a rock containing little argon. At low temperatures, the reverse is clearly true, because essentially no diffusion of argon occurs at low temperatures, but argon still accumulates on the surface of rocks. In fact, the longer the rock is exposeed, the more argon it can accumulate, and this argon can become so firmly embedded in the rock that it cannot be removed even by baking in a vacuum, according to references I gave in my last reply.

Dr. Henke cites a reference that shale often has more argon near the surface than lower down, attempting to discredit my proposal for excess argon as coming from the mantle. But wherever excess argon comes from, it can be removed by heat, so the properties of shale have no bearing on the question.

Dickin (1995, p. 250) states that argon is not preferentially incorporated into any mineral at the time of formation. This implies that it can appear in any mineral, and that any mineral can have excess argon.

Dr. Henke also mentions a so-called "3-dimensional test" for excess argon. I read Faure (1986) and Dickin (1995) and am not sure what test this is referring to. Furthermore, if there were a foolproof test for excess argon, then Faure and Dickin would have been sure to mention it.

A possible source of excess argon is argon that diffuses up from the mantle of the earth. Dr. Henke belittles this concern and implies that it is mainly a concern of creationists: "Like Slusher (1981) and other creationists, Dr. Plaisted has an overriding concern that 40Ar rises from the mantle, routinely migrates into a wide variety of minerals, and fools geologists by producing K-Ar dates that are too old." This is not just a concern of creationists, but is mentioned in Faure (1986, pp. 72, 79) as a possible source of excess argon.

Excess Argon and Cooling Lava

Dr. Henke asserts that as lava or magma cools, it cracks, permitting the flow of argon, so that argon from the center of the lava or magma will have time to escape, since the center takes longer to cool. He implies that this eliminates the problem of excess argon. He also states that sediment is highly permeable to argon, also removing the problem of excess argon.

However, we know that cool rocks permit much less diffusion of argon than hot ones. Even if the rock has cracks, most of the surface area of cooling lava will be covered by cool rock, which will obstruct the flow of argon. So it is only reasonable to assume that argon will tend to be trapped inside in many cases and give K-Ar ages that are too old. Besides, if Dr. Henke's scenario were valid, then we should never have a problem with excess argon, but in fact it is very common, even according to geologists. Dr. Henke asserts that "excess argon in plutonic rocks is rare," citing Harland et al (1990, p. 75) who state that "excess Ar in intrusive rocks is rare." However, Dickin (1995, p. 250) says that excess argon "may be a particular problem in plutonic rocks." Of course, whether argon in a rock is excess or not is largely a matter of interpretation, and no one can say for sure where the argon came from. If excess argon is never a problem, then why do geologists use isochrons and the 3-dimensional test and the spectrum test to attempt to detect it? Finally, if argon diffuses through sediment so easily, then this is not a problem, because it would explain how argon rising from the mantle could enter cooling lava and magma and give K-Ar ages that are much too old.

Dr. Henke questions the relevance of the fact that ancient lava flows were often flat. I discussed this before, and will not repeat myself here. He also questions how I know that ancient lava flows were often flat. For constructing a geological time scale, one needs lava flows that are narrowly bounded in time, which implies that they are bounded above by a flat layer of sediment. I also don't recall seeing volcano-shaped lava flows in the midst of sediment, though they may exist.

Mixings and Isochrons

I asserted that mixings often create isochrons having no age significance, but Dr. Henke, citing Dalrymple (1984), disputes this. Dalrymple states that mixing processes are unlikely in magma. However, Faure (1986, p. 141) mentions that mixings can occur as magma rises through the earth, Dickin (1995, pp. 43-35) discusses mixings in the mantle. Faure (1986, p. 147) also discusses how mixings can produce isochrons having no age significance. He states that mixings are an important geological phenomenon. Geologists themselves often suggest that spurious isochrons are caused by mixings. Dr. Henke repeats an argument of Dalrymple (1984) that isochrons produced by mixings should tend to have a negative slope as often as a positive slope. However, it is easy to imagine the probability distribution being biased so that isochrons with a positive slope are preferred to those with a negative slope. There are also a number of mixing processes that can create isochrons with a positive but not a negative slope, as I will indicate. Dalrymple (1984) attempts to explain away the fact that many published isochrons have correlations suggesting mixings, saying that such correlations do not prove a mixing. But it is difficult to imagine probability distributions that would cause so many isochrons to have such correlations, unless they were indeed caused by mixings. I also did not see Dalrymple's arguments about mixings repeated in Faure (1986) or Dickin (1995).

Here is a mixing process that can create K-Ar isochrons. Suppose that we have lava with uniform potassium and argon 40 concentrations, and considerable excess argon 40, but very little argon 36. Then suppose that some argon 36 and argon 40 from the atmosphere enters the lava, more in some places than others. This will produce a nice K-Ar isochron, but the age will be meaningless, and much too large. Such an isochron may have a correlation suggesting a mixing, but this does not matter, as isochrons having such correlations are routinely accepted as valid by geologists. This process can produce isochrons with a positive, but not a negative, slope. The assumptions of this process also seem natural in lava which does not cool slowly, as one would expect the concentration of potassium to be relatively uniform.

Here is another process that can only create isochrons with a positive slope. Suppose we have two sources, both having the same percentage of Sr88. One source also has substantial Rb87 and Sr87 and the other source has very little of either. Then a mixing will produce an isochron giving an age equal to the daughter-to-parent age of the first source. In this way, daughter to parent ages can be converted to isochrons. Therefore any process that can disturb daughter-to-parent ages can also lead to isochrons giving false ages.

Woodmorappe (1999, p. 70) gives references stating that even if an isochron does not have a mixing correlation, it can still be caused by a more complex mixing process.

It is also of note that isochrons cannot always be done; I imagine that it is difficult to do them on glauconies, for example. And the points may not line up as required in an isochron.

Devitrified Glass

Dr. Henke disputes a quotation I gave concerning devitrified glass. If one reads the quote, the assumption of Evernden et al is that the K-Ar date of the devitrified glass gives the date of the devitrification, but not necessarily the date of the lava flow. When devitrification occurs, glass can lose argon. Evernden et al were puzzled because the K-Ar date of the devitrified glass was young even though it appeared that the devitrification occurred at the same time as the lava flow. Here is a case where a young, possibly correct date is rejected by geologists due to long-age presuppositions.

Radiation and Decay Rates

I considered the possibility that radiation, specifically neutrinos, could influence decay rates. Dr. Henke asks how radiation could reset radiometric clocks. It should be obvious from my articles that if decay rates were increased rapidly, then radiometric dates would rapidly become very old, resetting the clocks. Dr. Henke states that since so few neutrinos interact with matter, it is unlikely that they could influence decay rates. I admit that this seems strange. However, such a prodigious number of neutrinos are produced that they might influence decay rates even if only a small percentage of them interact. To determine whether this could happen requires a detailed calculation. Complicating the matter are 1) that the physics of neutrinos is still not completely understood and 2) the radiation from supernovae and black holes is not isotropic, but concentrated in narrow beams, based on recent observations. This makes it more difficult to estimate the amount and energy of the radiation produced, and also means that if the solar system were in one of these high-intensity beams of radiation, the intensity of radiation would be greatly increased. Such radiation would not necessarily sterilize the earth, as Dr. Henke suggests, but it might heat it up and lead to volcano eruptions and steam escaping from the earth, precipitating the Flood. But such radiation might indeed destroy life. It need not be neutrinos that produce such effects, but could be other kinds of radiation, such as gamma rays. It would only be necessary for radiation to increase decay rates near the surface of the earth, since fossils are mostly found in sedimentary rock, and all sedimentary rock was once near the surface. At this point, we don't have enough information to know whether radiation from a nearby supernova could have produced such a catastrophe, but the possibility is worth considering.

I suggested that such a supernova might have increased radiometric dates by about 600 million years and produced the observed one percent discrepancy in dates observed in meteorites. This would invalidate dates on the phanerozoic. Dr. Henke states that a one percent discrepancy on the phanerozoic is not significant, but this comment is irrelevant to my point.

The following comment by Keith Wanser, a creationist physicist, quoted in Creation Ex Nihilo 21(4) p. 40 is significant:

Actually, it turns out that when you get the nucleus "excited", decay is going to be much quicker, making things look vastly "older". People have been talking recently about magnetic stars giving off big bursts of gamma rays; there are all sorts of ways that radiometric "clocks" could have been reset catastrophically, during the Flood, for example.
Concerning the possibility that a change in the speed of light could have affected decay rates, Dr. Henke says that any such change would have been small. However, some (non-creationist) cosmologists are proposing very large changes in the speed of light. Dr. Henke also says that observations of distant supernovae show that rates of decay have not changed. This is not conclusive, however, because there is reason to believe that the speed of light and decay rates would change by the same amount. Since a slowdown in light would make distant objects appear in slow motion (think about it), the decay rate would not appear to have changed.

The Use of the Literature

Dr. Henke suggests I read Odin's two volume survey of radiometric dating. This would serve little purpose, since Harland et al (1990) used all the dates from Odin that they could. It is true that this might indicate which dates were obtained by isochrons. However, it would have taken only a little space for Harland et al to have included this information, and would have saved the reader considerable effort. This is after all part of the purpose of a book, to save the reader from chasing down many separate references.

Dr. Henke suggests that I read still more references. I have already read a number of the most central books about this topic without finding the pot at the end of the rainbow that would show that radiomatric dating is valid on the phanerozoic. How many more should I read, and to what purpose? It would aid this exchange if Dr. Henke would be more careful to read my responses and not misunderstand or misrepresent them in his subsequent replies.

Finally, I recommend Woodmorappe (1999) as a good source of quotations from the geological literature about problems with radiometric dating.

Minor Matters

Dr. Henke states, "Dr. Plaisted continues to cite erroneous and insulting claims from Slusher (1981, p. 38) that scientists tend to `fudge' the K-Ar branching ratio." This is completely false. I managed to determine the true situation about the branching factor from Harland et al (1990), since Dr. Henke's previous reply did not completely settle the issue in my mind. In my previous response, I acknowledged that the true value of the branching factor has been known and used since the mid-fifties. Even Dalrymple did not refer to Slusher's statement about this in as severe terms as Dr. Henke did. Slusher was using an outdated reference, which is an understandable mistake.

Dr. Henke asserts that Slusher's claim that there is far too much argon 40 to be produced by decay of potassium 40 in 4.5 billion years, is based on an erroneous branching factor. This cannot be true, because the branching factor error would only change the amount of argon 40 generated by a factor of about 1.5. I already discussed the situation concerning this claim in my previous response to Dr. Henke.

Dr. Henke misunderstands my use of the one percent discrepancy in meteorite dates. He states, "However, doing the math, we see that a 1% error for a 550 million year old Cambrian rock is 5.5 million years and not 45-50 million years." I encourage Dr. Henke and others to read my previous reply to see my comments on this matter.

Dr. Henke states, "it takes up to about 1 million years for glaucony to transformation to glauconite (Faure, 1986, p. 78)." This statement is probably based on assumptions from radiometric dating, which is itself at issue in this discussion.

Dr. Henke states, "Dr. Plaisted is concerned that minor heating or groundwater interactions may somehow add or remove argon and mess up K-Ar dates without leaving any other chemical or mineralogical changes." In fact, it is not only I that am concerned, as the following quotation from my previous response shows: "Faure (1986, p. 123) verifies that modest increases in temperature of one or two hundred degrees centigrade can have drastic effects on radiometric dates without any observable changes in the rocks. Faure (1986, p. 69) mentions specifically that heating can cause argon loss without any other physical or chemical changes in the rock."

Concerning errors in K-Ar dating due to atmospheric argon, Dr. Henke states, "Dr. Plaisted omits the next critical sentence in Dickin (1995, p. 247), which indicates that these errors are NOT a problem for old and/or K-rich samples." Unfortunately, I could not determine exactly how much atmospheric argon can be deposited on or in a rock in various lengths of time. Unless we know this, we cannot decide how old a rock has to be for this not to be a problem. But geologists are sufficiently concerned about it to try to account for atmospheric argon whenever K-Ar dates are measured.

Concerning a statement I quoted from Harland et al (1990), Dr. Henke responds

In response to this consistency between fossils and radiometric dating, all Dr. Plaisted can do is accuse Harland et al. (1990) of "circular reasoning" based on the old fallacious creationist mantra: "rocks date the fossils and the fossils date the rocks."
Actually, I have accepted the reality of the geological sequence, and so I found this statement from Harland et al to be rather curious. The statement from Harland et al follows:

Biologic evolutionary history, especially for Phanerozoic time, has given us not only the principal means of time-correlation but the basis of the unique progressive traditional stratigraphic scale.

This statement does make me wonder whether the creationist claim of circular reasoning has some validity. Probably what is meant is simply that there appears to be a regular progression of life forms which can be of use in dating, independently of whether evolution is true.

Dr. Henke states, "Therefore, the following quotation by Dr. Plaisted from somewhere in Harland et al. (1990) (see http://www.cs.unc.edu/~plaisted/ce/harland.html ), which Dr. Plaisted calls a `bombshell,' is really a dud: ... " Unfortunately, Dr. Henke omitted the part of the quotation that I considered a bombshell, thus completely misrepresenting me and attempting as often is the case to make me look ridiculous.

Another example of Dr. Henke's ridicule is the quotation "Of course, geochronologists don't scan the surface of mineral grains looking for argon "dust bunnies" in cracks to vacuum up. The samples are baked under a vacuum (Dickin, 1995, p. 246)." But I gave a quotation that baking under a vacuum is not always able to remove atmospheric argon.


Dr. Henke's replies have been useful for me as prompts to examine the literature more closely. However, on checking the literature, I found that many of his points are not valid. In addition, it appears that Dr. Henke does all he can to heap abuse on me and other creationists, attempting to make creationism appear in the worst possible light. There are also some cases in which my earlier replies are misunderstood or misrepresented. But I think that anyone who has the stamina to read through our exchange will learn a lot about the subject.

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