Quick radiometric dating question- misused techniques

In the particular cases of Austin and his Mt. St. Helens dacite, and Snelling and his lava from Mt. Ngauruhoe, they were absolutely sure of one thing; the samples they chose were a mixture of old and recent material, and therefore the K-Ar method would return a date that is older than the recent material is, and most likely would return a date much older than the minimum that the K-Ar method could measure. See Young-Earth Creationist 'Dating' of a Mt. St. Helens Dacite: The Failure of Austin and Swenson to Recognize Obviously Ancient Minerals. And, from Snelling himself in ANDESITE FLOWS AT MT NGAURUHOE, NEW ZEALAND, AND THE IMPLICATIONS FOR POTASSIUM-ARGON "DATING":

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A second representative set (50-100 g from each sample) was sent progressively to Geochron Laboratories in Cambridge (Boston), Massachusetts, for whole-rock potassium-argon (K-Ar) dating - first a split from one sample from each flow, then a split from the second sample from each flow after the first set of results was received, and finally, the split from the third sample from the June 30, 1954 flow. ...

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Because the sample pieces were submitted as whole rocks, the K-Ar laboratory undertook the crushing and pulverising preparatory work. ...

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Steiner [90] stressed that xenoliths are a common constituent of the 1954 Ngauruhoe lava, but also noted that Battey [7] reported the 1949 Ngauruhoe lava was rich in xenoliths. All samples in this study contained xenoliths, including those from the 1975 avalanche material. ...

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{Emphasis addded}Whole-rock = crush the entire thing and test the result without separating anything.Xenolith (literally "foreign rock") = a piece of rock that is older than the lava flow that contains it. They may be easy or difficult to separate, but in this case they weren't separated.Smoking gun. Well, if you have an agenda like Snelling or Austin does, you pick a method that can be fooled, even though it's been almost completely supplanted by Ar-Ar that's much more difficult to fool, and even though other methods are significantly more widely used. Then you pick samples that are guaranteed to fool the method.If you are really interested in finding the age of a sample with no prior information, you do it with several methods and you do them on individual minerals separated from the rocks. Then if the methods agree you almost certainly have a good date.In the real world, as you know, you essentially always do have prior information.The K-Ar method (and almost all radiometric methods) boils down to measuring a quantity of stuff. (The best methods actually measure the ratio between the quantities of two different stuffs, and then use other information about the quantity of one to calculate the quantity of the other.) When a rock is old, there's a lot of stuff to measure. When the rock is young, there's not much stuff to measure. A K-Ar lab will start by cleaning as much previous sample material and argon from the equipment as is feasible. (If you tell them you think your sample is relatively young, they will take extra care in the cleaning process. And charge more.) Then they will measure your sample and the readouts will tell them there's Y amount of argon.Every few runs they will run the equipment with nothing in the sample holder. The readouts will say there's a non-zero amount of argon, call it X, which they can calculate as being equivalent to an age of Z years.If the amount they measure in your sample, X, is pretty much equal to Y, then they will report the age as Z years or less. If X is greater than Y they will report an age older than Z with appropriate error bars. If X is less than Y they will try to figure out whats going on.

Expanding a little on Dr. Bertsche's explanation ...I think of the Ar-Ar method as two methods. One, irradiating the sample, allows measuring the ratio of ³⁹Ar to ⁴⁰Ar instead of measuring the ratio of ⁴⁰Ar to ⁴⁰K. Measuring the ratio of two isotopes of the same element is easier and more accurate than measuring the ratio of two different elements. You could just vaporize the sample and calculate an age; but the other method, step-heating, allows compensating for various interfering phenomena as Dr. Bertsche explained.It's common to present the results of Ar-Ar analysis as step-heating diagrams. The horizontal axis is the heating step, from 0 to 100%, and the vertical axis is the age measured at that step. From Radiogenic Isotope Geology, the on-line version of a standard reference work (unfortunately the equations are unreadable), here's an great step-heating diagram for two Texas tektites in which there's no interfering phenomena and K-Ar would give the same result as Ar-Ar: If there's excess argon, you get more argon out early on, initally showing an erroneously old age but flatttening out into a "plateau" after the excess argon is exhausted (the sstep-heating diagram is on the bottom): If the material has been heated, leading to a loss of argon from places where it's loosely bound, you get an erroneously low age initially: if the sample has been heated a lot, you may not get a plateau, but you can tgry to get an estimate by modeling the argon loss:

Well, you might ask him how old the Earth and life are if we are wrong about all decay rates decay rates by a factor of 100 …Decay rates are known to within a few percent or better. One of the several reasons that U-Pb concordia-discordia dating is so often used is that the decay rte of uranium is known to much better than a percent. Bombs and reactors tend to attract lots of research money.The classic study on uranium is Jaffey A. H., Flynn K. F., Glendenin L. E., Bentley W. C., and Essling A. M. (1971). Precision measurement of half-lives and specific activities of ²³⁵U and ²³⁸U. Phys. Rev. C4, 1889—1906. Alas, this is not available online, but from Begemann, F., Ludwig, K. R., Lugmair, G. W., Min, K., Nyquist, L. E., Patchett, P. J., Renne, P. R. Shih, C.- Y., Villa, I. M. and Walker, R. J. (2001). Call for an improved set of decay constants for geochronological use. Geochim. Cosmochim. Acta 65, 111--21:

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The decay of 238U and 235U to 206Pb and 207Pb, respectively, forms the basis for one of the oldest methods of geochronology. While the earliest studies focused on uraninite (an uncommon mineral in igneous rocks), there has been intensive and continuous effort over the past three decades in U-Pb dating of more-commonly occurring trace minerals. Zircon in particular has been the focus of thousands of geochronological studies, because of its ubiquity in felsic igneous rocks and its extreme resistance to isotopic resetting.

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No decay constant of any radionuclide used for geochronology has been (or, arguably, can be) more-precisely measured than those of 238U and 235Ua consequence of the mode of decay (alpha), favorably short half-lives, and the availability of large quantities of isotopically pure parent nuclides. The most recent measurements by Jaffey et al. (1971) (Figs. 1, 2) quote precisions (recalculated to 95%-confidence limits) of 0.11% for 238U and 0.14% for 235U, with the somewhat cryptic statement that systematic errors, if present, will no more than double the quoted errors.

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There's been no studies since then that upset these findings.The bottom line is that, while we are improving our knowledge of decay rates all the time and some of our values may be off by as much as a few percent, there's no way that we are far enough off to make a YEC scenario conceivable, by thousands of orders of magnitude.And, indeed, the consilience of dates obtained with multiple methods using different isotopes with different decay modes is powerful evidence that our dates are correct to about the specified precision.Some useful links on consilience are Radiometeric Dating Does Work! (note that Table 2 includes the Hell Creek formation, from which the dinosaur bones with "blood cells" and "soft tissue" were extracted), Consistent Radiometric dates, Are Radioactive Dating Methods Consistent With Each Other? (one of my favorites), Are Radioactive Dates Consistent With The Deeper-Is-Older Rule?, Radiometric Dating, Radiometric Ages of Some Early Archean and Related Rocks of the North Atlantic Craton, and Radiometric Ages of Some Mare Basalts Dated by Two or More Methods.

Radioactive decay rates depend on some deep-down fundamental attributes of the universe, and if they changed traces would be left in a surprising number of places. The Constancy of Constants and The Constancy of Constants, Part 2 are good resources to start with the author is a well-knonw (in some circles) physicist.Yep, what we see in stars is a good measure. The Oklo reactor is also a great one; Oklo natural nuclear reactor and Natural nuclear fission reactorFinally, one strong indicator that radioactive decay rates havfen't changed to anything near the extent required dby creationists is teh fact that all life was not wiped out by the radiation, nor was all life killed by the melting of the Earth due to the heat released. The RATE group, composed of those few YECs who appear to know how bad the problem is, alludes to this. In Helium Diffusion Rates Support Accelerated Nuclear Decay they write:

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Samples 1 through 3 had helium retentions of 58, 27, and 17 percent. The fact that these percentages are high confirms that a large amount of nuclear decay did indeed occur in the zircons. Other evidence strongly supports much nuclear decay having occurred in the past [14, pp. 335-337]. We emphasize this point because many creationists have assumed that "old" radioisotopic ages are merely an artifact of analysis, not really indicating the occurrence of large amounts of nuclear decay. But according to the measured amount of lead physically present in the zircons, approximately 1.5 billion years worth at today’s rates of nuclear decay occurred. Supporting that, sample 1 still retains 58% of all the alpha particles (the helium) that would have been emitted during this decay of uranium and thorium to lead.

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{emphasis in original}And, in Helium Diffusion Age of 6,000 Years Supports Accelerated Nuclear Decay:

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Thus our new diffusion data support the main hypothesis of the RATE research initiative: that God drastically accelerated the decay rates of long half-life nuclei during the earth's recent past. For a feasibility study of this hypothesisincluding God's possible purposes for such acceleration, Biblical passages hinting at it, disposal of excess heat, preserving life on earth, and effects on stars, see Humphreys (2000, pp. 333-379). The last three problems are not yet fully solved, but we expect to see progress on them in future papers.

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Not yet fully solved, indeed. Needless to say no progress has been forthcoming in the five years since this paper appeared.Note that they implicitly acknowledge that there is no way that a natural process would accelerater defcay in the manner that they need; it rwequires a miracle. So it ain't science.

Well, I can't get at the second paper either. But measuring half-lives over a period of time much smaller than the half-life is fraught with peril. Stated uncertainties are best estimates, and are statistically based. They are not absolute boundaries. An uncertainly of ±x (2 σ ) means that their best estimate is that there is a 95% probability that the actual value lies between the quoted value + x and the quoted value - x. But there's a 5% chance it lies outside those bounds. And it's still an estimate and subject to its own errors. Again from Begemann, F., Ludwig, K. R., Lugmair, G. W., Min, K., Nyquist, L. E., Patchett, P. J., Renne, P. R. Shih, C.- Y., Villa, I. M. and Walker, R. J. (2001). Call for an improved set of decay constants for geochronological use. Geochim. Cosmochim. Acta 65, 111--21:

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Accurate radioisotopic age determinations require accurate decay constants of the respective parent nuclides. Ideally, the uncertainty on the decay constants should be negligible compared to, or at least be commensurate with, the analytical uncertainties of the mass spectrometric measurements entering the calculations. Clearly, this is not the case at present. The stunning improvements in the performance of mass spectrometers during the past three decades, starting with the seminal paper by Wasserburg et al. (1969), have not been accompanied by any comparable improvement in the accuracy of the decay constants.The uncertainties associated with direct half-life determinations are, in most cases, still at the percent level at best. The recognition of an urgent need to improve the situation is not new (cf., e.g., Renne et al., 1998; Min et al., 2000a); it has presumably been mentioned, at one time or another, by every group active in geo- or cosmochronology. The present contribution is intended to be a critical guide to the existing experimental approaches. Except in a few cases, we do not evaluate the individual reports on decay constants, and we also do not make any recommendations as to which values should be considered correct and be used by the dating community at large. This must, in our opinion, be left for existing commissions to decide, following the precedent of Steiger and Jager (1977).

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Three approaches have so far been followed to determine the decay constants of long-lived radioactive nuclides.

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1. Direct counting. In this technique, alpha, beta or gamma activity is counted, and divided by the total number of radioactive atoms. Among the difficulties of this approach are the self-shielding of finite-thickness solid samples, the low specific activities, imprecise knowledge of the isotopic composition of the parent element, the detection of very low-energy decays, and problems with detector efficiencies and geometry factors. Judged from the fact that many of the counting experiments have yielded results that are not compatible with one another within the stated uncertainties, it would appear that not all the difficulties are always fully realized so that many of the given uncertainties are unrealistically small, and that many experiments are plagued by unrecognized systematic errors. As the nature of these errors is obscure, it is not straightforward to decide which of the, often mutually exclusive, results of such counting experiments is closest to the true value. Furthermore, the presence of systematic biases makes any averaging dangerous. Weighted averaging using weight factors based on listed uncertainties is doubly dubious. It is well possible that reliable results of careful workers, listing realistic uncertainties, will not be given the weights they deserve—this aside from the question whether it makes sense to average numbers that by far do not agree within the stated uncertainties.

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2. Ingrowth. This technique relies on measuring the decay products of a well-known amount of a radioactive nuclide accumulated over a well-defined period of time. Where feasible, this is the most straightforward technique. Ingrowth overcomes the problems encountered with measuring large fractions of low-energy b-particles, as in the case of 87Rb and 187Re. It also comprises the products of radiation-less decays (which otherwise cannot be measured at all) like the bound-beta decay branch of 187Re and the possible contribution to the decay of 40K by electron capture directly into the ground state of 40Ar. Among the drawbacks of this approach is that the method is not instantaneous.The experiment must be started long before the first results can be obtained because long periods of time (typically decades) are required for sufficiently large amounts of the decay products to accumulate. Ingrowth-experiments further require an accurate determination of the ratio of two chemical elements (parent/daughter) as well as an accurate determination of the isotopic composition of parent and daughter element at the start of the accumulation (see below). Moreover, because of the hold-up in the chain of intermediaries, for uranium and thorium measuring the ingrowth of the stable decay products in the laboratory does not work at all.

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3. Geological comparison. This approach entails multichronometric dating of a rock and cross-calibration of different radioisotopic age systems by adjusting the decay constant of one system so as to force agreement with the age obtained via another dating system. In essence, because the half-life of 238U is the most accurately known of all relevant radionuclides, this amounts to expressing ages in units of the half-life of 238U.

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Note especially the paragraph numbered 1. Judged from the fact that many of the counting experiments have yielded results that are not compatible with one another within the stated uncertainties, it would appear that not all the difficulties are always fully realized so that many of the given uncertainties are unrealistically small, and that many experiments are plagued by unrecognized systematic errors. But such incompatibilities are not necessarily evidence of change (and if they are, the changes increase half-life as often as they decrease half-life). If there were changes, even a percent or so, there would be other far-reaching effects that we would easily detect. (I'm not enough of a physicist to specify what they would be, but look back at Steve Carlip's posts on constants and reflect of how far-reaching go those effects are). No, they are evidence that we don't understand all the difficulties and complications involved in measuring half-lives well enough to measure them to better than a few percent or so (except for uranium). But we certainly know enough to measure them to a few percent.But the real key is not to get down in the mud and wrestle with the creo on infinitesimal details. Changes less than several orders of magnitude are insufficient to make the creationist position tenable, and changes would have to be correlated among many different and independent mechanisms (alpha decay, beta decay, and electron capture decay … and their many sub-types). Keep pounding away at consilience between wildly different radiometric methods and even with non-radiometric methods (I posted a couple of links showing the latter), and ask for a scientifically verifiable mechanism that accounts for those results. Pound on the heat and radiation and observations of stars problems acknowledged by the RATE group.

Yes, I know all that. It's a losing proposition. That's why the key is not to go down in the mud, where the can use their lack of knowledge of what statistics, what error estimates are, and how utterly infinitesimal these differences are when compared to the changes proposed by YECs. They complain about extrapolating, then extrapolate over many orders of magnitude! You can't beat them at that game.Fundamentally they want a Biblical version of science; knowledge is graven in stone and known exactly.But I don't know anyone who's good at getting them to address the important points like consilience. If the decay rate for K is wrong, then so are all decay rates, and all by the same factor. To anyone with any knowledge of physics, that's ludicrous. mMybe this point can be gotten across to someone ignorant of physics. I don't know how to even get them to listen. Much of the answer is in my previous quote from that paper:

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No decay constant of any radionuclide used for geochronology has been (or, arguably, can be) more-precisely measured than those of 238U and 235Ua consequence of the mode of decay (alpha), favorably short half-lives, and the availability of large quantities of isotopically pure parent nuclides.

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I'll see if I can dig up the Jaffey paper.The reason we can be sure that they are known to a few percent of less is that all of the numerous measurements without known systematic error lie within a few percent or less. Does that prove it? No. Nothing is ever proven in science. It's established far beyond reasonable doubt ... but not beyond unreasonable doubt. Well,that's a situation in which you are near-certain to lose. Facts don't help much there. And I don't know how to teach somebody something that they refuse to learn. The Constancy of Constants
The Constancy of Constants, Part 2
Steve Carlip