Distinguishing Pb from Pb???

In this message, John Paul wrote: Well, yes, that's true ... but irrelevant to radioisotope dating.In isochron methods (which are explained in Isochron Dating) the amount of initial radiogenic Pb isotope is determined by relationships between different isotopes, not by trying to sort out the difference between Pb generated since solidification and any other Pb.In concordia-discordia methods (which are, unfortunately, not clearly explained anywhere on the Web AFAIK) we use only special but common minerals such as zircons which incredibly strongly reject Pb at solidification; therefore essentially all the Pb in such minerals is generated after solidification. We can (and do) correct for the tiny amount of Pb present at solidification by using isotopic ratios, but this is only to get from a percent or so error to less than a percent, and wouldn't change the answer much if we didn't do it. uUt none of this involves trying to discern "Pb from U decay ... from Pb that has always been Pb."John Paul, what does your statement have to do with radioisotope dating?

Perhaps my explanation needs some clarification. Cook found that Pb can pick up free neutrons. IOW when someone looked at a sample they could NOT tell if that Pb was the result of decay or neutron capture. What that does is if someone where doing a U/Pb analysis there would be no way to be sure if it was correct.

Ah, that's totally different; you didn't mention the (nonexistant, BTW) free neutrons. It's also an old chestnut and long debunked. From a previous post of mine on this board:Melvin Cook was wrong. I'll cut to the chase and then discuss: "Cook's proposition and calculations, enthusiastically endorsed by Morris and Slusher, are based on data that do not exist and are, in addition, fatally flawed by demonstrably false assumptions" (Dalrymple, 1984).First, Melvin Cook was a Mormon and creationist and an expert in explosives. He published his critique in a creationist house organ, not a peer-reviewed journal (and, you can see below, it wouldn't have made it through peer review). He is not necessarily qualified to comment on radioisotope dating. Note that whenever you see "Nobel Prize nominee" you should be immediately suspicious; the Nobel comittee does not release the names of nominees.Second, when you see a reference to something so old {1966 - JRF}, alarm bells should go off in your head. Not because you suspect the scientists are covering up, but because you should know your pals are hiding part of the story; something's happened since then. Creationists are famous for telling only the portion of the story that they like, and for continuing to promulgate errors and lies long after the errors and lies are demonstrated. From "Science and Earth History", Arthur N. Strahler, Prometheus Books, 1999 (first published 1987), pp 137-138:

quote:

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Yet another line of attack used by creationists to undermine radiometric age determinations centers on the third assumption, that at the outset (time-zero) none of the final decay product (daughter isotope) was present and that none of that product was lost from the system. Slusher points out that not all lead isotopes in rocks are formed by radioactive decay (1981, p. 27). There may be present a supply of lead isotopes of nonradiogenic origin, and there is no way to distinguish them chemically from those produced in the decay system. Here, the creationists claim, is a possible source of major error in uranium/lead ages. A particular fly in the ointment seems to be the idea that nonradiogenic lead isotopes can be produced by "neutron reactions." Slusher states: "Neutron reaction corrections in the U-Th-Pb series reduce 'ages' of billions of years to a few thousand years because most of the Pb can be attributed to neutron reactions rather than to radioactive decay" (1981, p. 54).

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Dalrymple analyzes this argument, showing where the idea came from and showing that it has no substance (1984, pp. 92-94). The discussion is highly technical, with mathematical equations awesome to the average person; I attempt only to state the gist of the matter. It seems that creationist Melvin A. Cook published several articles criticizing conventional radiometric dates (references cited by Dalrymple). The thrust of his argument appears to be that lead-208 (Pb-208) got into particular ore masses through neutron reactions upon lead-207 (Pb-207), and that the latter came into existence through neutron reactions with lead-206 (Pb-206). This neutron activity was supposed to have taken place in bodies of uranium ore at various localities on several continents. It would, therefore, have seriously altered results of the usual uranium-lead age determinations on samples of those ores. Cook's suggestion is that, with a large amount of lead of nonradioactive origin being mistaken for the daughter product of the decay series, great age was arrived at, whereas the actual amount of true radiogenic lead is very small, and if correctly evaluated would yield a very young age.

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Dalrymple finds several serious fundamental flaws in Cook's argument and calculations. In a specific instance, Cook seems to have misread a dash in a data table to mean "zero," when, in fact, it meant "not measured." Even if the data were not flawed, there remains the problem that there were far too few free neutrons available at the ore body sites of the supposed neutron activity to have been responsible for the alleged magnitude of the effect. This problem of free neutron deficiency was acknowledged by Cook himself (1966, p. 54). {emphasis added - JRF} Dalrymple's conclusion is: "Cook's proposition and calculations, enthusiastically endorsed by Morris and Slusher, are based on data that do not exist and are, in addition, fatally flawed by demonstrably false assumptions" (1984, p. 94).

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Slusher, Harold S., 1981, "Critique of Radiometric Dating", 2nd ed. ICR Technical Monograph #2, Institute for Creation Research

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Dazlrymple, G. Brent, 1984, "How Old is the Earth? A Reply to 'Scientific' Creationism", in Awbrey and Thwaites, "Evolution vs Creation", Aztec Lecture Notes, San Diego State University, pp 66-131

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Finally, the most widely used dating method, concordia-discordia, would detect if this isotopic shuffling had happened. It didn't.

JonF:
Ah, that's totally different; you didn't mention the (nonexistant, BTW) free neutrons.John Paul:
Any first year chemistry student can tell you that free neutrons do indeed exist. Neutrons and positrons are emitted by radioactive nuclei.BTW your idol Dalrymple has been debunked by Milton, an open-minded evolutionist, in Milton's book Shattering the Myths of Darwinism. See chapter 5 of that book. Milton is not only a genius but also a member of the Geolgists' Association.PB 208 is the product of Th232. Two of the largest uranium deposits we find very little Th232 yet large amounts of Pb208.I see you mention Cook's religious affiliation. Whay don't you mention Dalrymple's bias?Neutron reactions? Nedutron capture would be the better terminology.JonF:
'Finally, the most widely used dating method, concordia-discordia, would detect if this isotopic shuffling had happened.John Paul:
Is that an assertion or can you back that up?One thing to remember- the earth can be made up of materials that are old, or have been through a process that has made them appear to be old, and still have been formed relatively recently.

Milton's "work" has been discussed here. He's a closed-minded anti-science crank all too willing to copy creationist work because it attacks science. Given that Milton is both strongly biased and quite happy to write on matters he doesn't understand at all you're going to need to provide actual arguments. As an authority he's a joke - relying on Milton is tantamount to admitting defeat.

This is what took so long? No evidence, no facts, just "some guy says you are wrong"?Next time try a little harder. Evidence would help. You are corect. I mis-"spoke". I should have set "not present in sufficient quantities, as pointed out by Dalrymple and conceded by Cook". See the yellow highlighted area of message 3Not my idol, just a proven-reliable source.Milton has no geological training or, as is apparent from his writings, geological knowledge. Anybody who is interested and ponys up 27 pounds per year is a member of the Geologists' Association (see http://www.geologist.demon.co.uk/membership.html); such membership is no indication of qualification for anything.I don't have Milton's book, how about you presenting his arguments and evidence and references in your own words? I'm not aware of any such bias. Dalrymple is admittedly "biased" in favor of scientific results in scientific arenas, but I thought that went without saying. Sure. I'm not going to try to type the equations in; see equations 9 and 10 at Radiometric Dating (about half-way down the page) and the concordia curve just below. Equations 9 and 10 are parametric equations of the concordia curve in terms of the parameter time. We get lots of samples that plot on the concordia curve. If Cook's proposed isotopic shuffling were going on, the reaction rate would have to depend not only on the quantity of precursors present and the amount of neutrons present, it would also have to depend on the amount of products present in order for a particular sample to remain on the concordia curve as the lead isotopes are converted.In Cook's proposed process the amount of ²⁰⁸Pb increases,the amount of ²⁰⁶Pb decreases, and the amount of ²⁰⁷Pb remains roughly the same (unless some other magical and currently unknown process is added to the mix). A sample on which Cook's proposed process acts would not plot on the concordia curve; as the process acts the point representing the sample would move off the curve along a roughly vertical line (²⁰⁷Pb/²³⁵U would remain about the same while ²⁰⁶Pb/²³⁸U would decrease, assuming roughly constant amounts of U since Cook is proposing that this process acts over times that are tiny compared to the half-lives of U).Therefore, the large number of samples we see that plot on the concordia curve proves that Cook's proposed process has not acted on those samples, unless some other unknown process that magically "moves" the samples back to the concordia curve and moves them back to a point on the curve that is significantly older than the real age.Proving that discordant points which lie on a straight line cannot be produced by Cook's process is left as an exercise for the student. It is physically possible for it to be the latter, but it is not; that would be like me winning the grand prize in the lottery 1,000 times in a row. Possible, but it doesn't happen.There are many dating methods, some involving radioactivity and some not involving radioactivity. The radiometric schemes involve different isotopes that decay by wildly different processes. All thes methods agree. If Cook's proposed process is operating, why do Rb-Sr, Ar-Ar, K-Ar, Pb-Pb, and Th-Pb methods agree so closely on the age of the Fen complex, as shown at Consistent Radiometric dates? And this is just one of many, many, many agreements between methods; how do you propose those agreements came to be?Even if Cook's proposed process is operating, creationists still need to come up with a scenario in which many different and independent and well-understood physical processes acted wildly different in the past, and acted wildly different in just such a manner as to fake the contents of all the rocks so as to show great and varying ages.

PK:
Milton's "work" has been discussed here.John Paul:
I have seen the way people "discuss" things here. More like
misrepresent.PK:
He's a closed-minded anti-science crank all too willing to copy creationist work because it attacks science.John Paul:
Reality says he is more open minded than most evolutionm
ists. You included. What science do Milton & Creationists attack?And why should I listen to you PaulK? Have you bothered bringing any of your objections to Milton? Or like most evolutionists do you have to talk about someone behind their back without giving them a chance to respond?This message has been edited by John Paul, 05-21-2004 06:30 PM

Give us some Milton on this topic if you want it discussed.If you can get Milton to post we'd be only too glad to have him visit.Until you introduce something of his that you suggest is of value we will go on the little that has been introduced in other threads and was clearly wrong.

I notice that you do not give Milton's argument. I consider this as conceding that the arguments given by Milton are inadequate and Milton's "authority" is the only basis for your assertion.And you know damn well that creationists and Milton disagree with much of geology to name just one branch of science.Please produce some of this "reality" that says that Milton is "open-minded". Do you perhaps mean his attacks on science and scientists for not accepting the existence of the paranormal ?I find the evience that Milton is closed-minded is quite obvious. An open-minded person would make a reasonable attempt to understand the position he is criticising. Milton is intelligent enough that we can assume that if he made such an attempt we would not see blatant misunderstandings of simple and easily-grasped points. However we do see such misunderstandings in Miltons writings on evolution. I discuss such errors in this thread Milton & Selection See posts 1 & 8.Since Milton does make such errors I conclude that he wishes only to dismiss the opposing viewpoint without giving it even reasonable consideration - ergo he is closed-minded.

JonF, the bottom line, and Cook's reasoning, is based on the fact we find Pb208 where it shouldn't be. By rights all there should be is Pb206 as it, and not Pb208, are the final product of the decay chain of the minerals found in that location. IOW the ONLY way Pb208 could have arisen is via neutron capture. And if we can get Pb208 from Pb206 then it stands to reason that we can get Pb206 from Pb204.from earlier:
One thing to remember- the earth can be made up of materials that are old, or have been through a process that has made them appear to be old, and still have been formed relatively recently.JonF:
It is physically possible for it to be the latter, but it is not;John Paul:
It is not only physically possible but darn likely.JonF:
that would be like me winning the grand prize in the lottery 1,000 times in a row. Possible, but it doesn't happen.John Paul:
Yes it could happen- by (intelligent) design.

I notice that you did not introduce any evidence whatsoever, nor did you address the fact that concordia-discordia dating would detect it if Cook's proposed mechanism were active. How do you propose that we get so many samples that plot on the concordia curve if Pb isotopes are being shuffled? This is a major point to which you must respond, or just give up. Where's your evidence that "we find Pb208 where it shouldn't be"? AFAIK there are no measurements that are inconsistent with Pb208 being primordial as far as the Earth is concerned. An ad-hoc unsupported assertion, with no evidence, invented only to save your peculiar world view. Please show your calculations that it is "darn likely" (and if you want to use Dembski's explanatory filter, definitely show your calculations). Sorry, Occam's razor excludes that until you have some evidence that cannot be explained by existing mainstream models.

I did a little research.Pb208 is the final decay product of Th232. Cook noted that there were a very few deposits in which there was Pb208 and no Th232, and claimed that the Pb208 could only have come from neutron capture of other lead isotopes, and claimed that he could correct for this neutron capture and derive a young age for the deposits.First, neutron capture is far from the only mechanism of obtaining Pb208 without Th232 being present; preferential incorporation of {relatively volatile} lead at solidification comes to mind. Second, there is a strong correlation between quantities of Th232 and P208 in the vast majority of all deposits; neutron capture does not explain that. Third, there is no evidence for a source of anywhere near sufficient numbers of fast neutrons to convert the observed Pb208. Fourth, concordia-discordia dating contradicts the claims as I have detailed in previous posts.Your turn ... let's see some discussion of what I've presengted and some evidence instead of handwaving and unsupported claims.

I know this thread is long-dead and John Paul has moved on to even more obnoxious behavior elsewhere, but just for the record: Dalrymple's paper How Old is the Earth: A Response to “Scientific” Creationism is now on-line. It was this discussion that prompted me to get it on-line … since it so clearly shows the many mistakes Cook made. The portion that is relevant to this thread is at NEUTRON REACTIONS AND Pb-ISOTOPIC RATIOS. The argument is summarized at Claim CD016It turns out that, in addition to the errors discussed previously in this thread, Cook misread the tables in a secondary source. He assumed that "---" meant "zero" when it really meant "small and not measured", as he would have seen if he had checked the primary source. There is no ²⁰⁸Pb where it shouldn't be. There is no evidence for sufficient free neutrons (Cook's only evidence was the supposed conversion that he derived from his misreading of the table) and plenty of evidence for insufficient free neutrons. And, even if there were enough free neutrons and lead was converted by neutron capture, Cook's assumption, possibly reasonable at the time, that the cross-section for ²⁰⁶Pb → ²⁰⁷Pb is the same as for ²⁰⁷Pb → ²⁰⁸Pb was known to be wrong by 1984; when you include the effect of unequal cross-sections, neutron capture reactions make the meaasured age slightly younger than the true age, which is scant comfort for creationists.Q.E.D. and R.I.P.