Quick radiometric dating question- misused techniques

So let's say I'm a YEC and I'm mightily impressed by Steve Austin's erroneous dates for the Mount St. Helens lava. While evolutionists are metaphorically talking about how you can't measure sand grains with rulers, I'm thinking that Austin has done something clever. Here's what would be going through my head:You have a rock sample whose age you know nothing about. (I know that scientists understand rock-forming processes and they also will have recorded where in the geologic column the rock came from, but we're talking about a YEC here who thinks scientists are lying imbeciles.) How do you pick which dating method to use? If you use K-Ar like Austin did, you will get a date that says it's millions of years old. If it's very young rock, then you are very very wrong. That is what Austin showed.So my own question is, let's say with a blind sample,a.) How would you guess which radiometric method to try first?
b.) How do you know if the dates you've got are erroneous? (Besides the obvious fact that you'd date more than one sample by different methods to see if the dates correlate.)Thanks.Edited by LindaLou, : No reason given.

Thanks Nosy, that's clear now. But I'm still wondering what this data looks like that says that your sample is no older than the minimum age the method measures. Is it plotted on a graph? Does the machine spit out a piece of paper saying "fail"? Or is it simply a matter of observing that you have received the minimum date for your chosen method and therefore you need to try a method more suitable for a younger sample? Just curious; I will probably need to explain this in my own words at some point.Edited by LindaLou, : No reason given.

This is all interesting, and the creationists missing out a greater-than sign is pretty funny. But I wonder if someone could answer my question:

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is it simply a matter of observing that you have received the minimum date for your chosen method and therefore you need to try a method more suitable for a younger sample?

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Getting into a creationist's brain again (scary place), I'd be thinking (knowing next to nothing about real science) that a scientist dating a sample of unknown provenance (which is uncommon, I realise) and using K-Ar would "go with" the date they were given (presumably 100,000 years). Though if the result came back saying <100,000 years, that's clear enough -- is that what happens?Or, thinking of what Austin did, would you simply get wildly inaccurate results from this method because there's too much argon in young rock? In which case, if you got a sample from a lava field and didn't know it was very young (again, unlikely I realise), how would you know that a figure of millions of years was actually wrong? Is there a way of first being able to measure excess argon?Edited by LindaLou, : No reason given.

kbertsche and Jon, I think you've answered all of my questions and then some. I've learned a lot more about science from debating creationists than I did in school. Thanks very much

This is what I was dreading: a creationist who has been delving into scientific papers on radiometric decay rates, who doesn't understand them himself but can cherry-pick quotes from them that in his opinion suggest that scientists are unable to accurately determine the half-lives of radioactive isotopes. I would be able to say things about the correlation of dates using different methods, and that it looks to me like scientists are simply using more accurate techniques to refine the decay rates, but I'd like to be able to directly address some of the claims. Could anyone here who understands this stuff help me out?The first of the two papers is this PDF:
Strontium-92 half-life measurement through accurate -ray spectrometryHere's what the creationist quoted:

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... For these reasons, the half-life of 92Sr has been measured to solve a recently observed inconsistency with the quoted value in the nuclear data libraries: T1/2 = 2.71 0.01 h. In this work, a new value is proposed: T1/2 = 2.594 0.005 h. A better accuracy is achieved compared to previous evaluations. It also shows a good agreement with the most recent studies: T1/2 = 2.627 0.009 h.

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A weighted average from the three values was determined
for each fuel pin. Nevertheless, as the discrepancies were
sometimes beyond their reported uncertainties, the associated
uncertainty is calculated from the standard deviation between
the three values, with a multiplication factor tp() = 1.32 [15]
that arose from the low degree of freedom of the sample.

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...For these reasons, the half-life of 92Sr has been measured to solve a recently observed inconsistency with the quoted value in the nuclear data libraries: T1/2 = 2.71 0.01 h. In this work, a new value is proposed: T1/2 = 2.594 0.005 h. A better accuracy is achieved compared to previous evaluations. It also shows a good agreement with the most recent studies: T1/2 = 2.627 0.009 h.

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He thinks this shows "unacceptable uncertainties." I would tell him myself that the recent work has simply refined the figures but that's all I would be able to do. I really hate it when they cite stuff like this when it's clear they haven't a clue what it means themselves (and I'm struggling too!).The second citation is simply an abstract:
Half-life evaluations for 3H, 90Sr, and 90YAnd naturally these quotes have been cherry-picked:

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A recent paper has reviewed methods for the evaluation of discrepant sets of data and demonstrated the results of applying these methods to the published half-life data of 90Sr and 137Cs [MacMahon, T.D., Pearce, A., Harris, P., 2004. Convergence of techniques for the evaluation of discrepant data. Appl. Radiat. Isot. 60, 275-281]. The half-life data for 3H has been subject to a comprehensive review and critical evaluation by Lucas and Unterweger [2000. Comprehensive review and critical evaluation of the half-life of tritium. J. Res. Natl. Inst. Stand. Technol. 105, 541-549].

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...resulting in a recommended half-life of 4497(4) days. MacMahon et al. [Convergence of techniques for the evaluation of discrepant data. Appl. Radiat. Isot. 60, 275-281] highlighted problems in the evaluation of the discrepant half-life data of 90Sr, in particular the worrying upward trend in the data, where the weighted mean of all the measurements increases, on average, by 35 days each time a new measurement result is added.

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This is CTD, who migrated from this forum to the other one where I'm talking, which is run by creationists and where he gets to be a moderator, as opposed to, say, talking to real scientists here and being shown what ignorant nonsense he's spouting. He seems to see "inconsistencies" and "discrepancies" and my hunch is that they are small but I don't understand this data well enough to say how insignificant they are.added in edit
The author of the second paper, McMahon, is citing a previous paper of his own when mentioning "discrepant half-life data." The abstract is here: Convergence of techniques for the evaluation of discrepant dataIt looks to me like this is saying that when more data is obtained, the more obvious the "true" value becomes on a graph:

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The various evaluation techniques should converge towards the ”true’ value as the number of data in a data set increases, and the ”robustness’ of each evaluation technique can then be tested by the rate at which that technique converges.

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I think I could do an OK job of convincing CTD that he should leave things alone that he doesn't understand but it would be nice to try to address some of the above more specifically.Edited by LindaLou, : No reason given.Edited by LindaLou, : No reason given.Edited by LindaLou, : No reason given.Edited by LindaLou, : No reason given.

You're right about CTD, Percy. I've seen some of your posts at the Evolution Fairytale forum when I've been browsing and admire your restraint (though it's doubtlessly necessary on a forum like that which is run and moderated by creationists). It's the continual ad hom that can be a wind-up. I've been debating with him for about 2 years now I reckon, and yes, there never will be any convincing him. Thanks for the advice, it's good.

Thanks JonF and Coragyps, your info here has been very useful to me in constructing a reply. Without a grasp of some of the info you've given here, it's hard to know where address an attack against radiometric dating and decay rates. I am of course not surprised to hear that the decay rates of isotopes used to date rocks are known within a small margin of error. One of CTD's favourite arguments (which he hasn't tried on me yet) is that we're "guessing" because we can't be around for billions of years to make sure that, e.g., uranium continues along its predicted decay curve to lead and doesn't . . . I don't know, jump sideways and dance at the 2.36 million year mark or something. I think a good response to this would be to show that we can see isotopes decaying in ancient starlight -- I'm assuming we can, though I haven't researched this yet.

Great, thanks. I'm better with astronomy -- nuclear physics was never my strong point!added in edit
This is from one of JonF's favourite sources I think:
Evidence About Constants Being the Same in the Distant PastThis is a good counter to the claim that decay rates changed in the past, though Joe Meert's Were Adam and Eve Toast? works well too.Trying to find evidence of isotopes with longer half-lives elsewhere in the universe is proving more challenging at the moment.Edited by LindaLou, : No reason given.Edited by LindaLou, : No reason given.Edited by LindaLou, : No reason given.

My library of links is growing rapidly thanks to you.I've found interesting articles about uranium being detected in old Milky Way stars -- not what I was after, but great stuff to learn (which is why I do this I guess).I'm going to spend some time reading your links here but I'm still wondering how I would answer a claim that we don't know if isotopes with long half-lives really follow the entire logarithmic curve because we "weren't there" to watch it happen. Presumably they'd be trying to argue that the decay rates could be faster at some undefined point -- they certainly wouldn't be arguing that they are slower. In which case, all of this evidence about decay rates being constant would apply.

Jon, I'm afraid I need to ask for your, or anyone else's help, again. This is regarding the two links the creationist has been trying to discuss -- I'll post them again here: Strontium-92 Half-life Measurement Through Accurate Y-Ray SpectrometryHe's trying to claim that new measurements had to be made because the decay rates changed. I explained that this article and the one below are about decay rates being measured more accurately, and I started to post evidence that decay rates have not actually changed, starting with SN1987a. I was accused of "misrepresenting links" and I have been banned, though it's possible that the ban will be lifted by the forum owner. Even if it isn't, I'd like to know how best to respond to the other comments here, because I'm curious. The creationist appears to admit that the above article shows that as the decay measurement is more accurate, the margin of error decreased. He's hung up on the fact that in the second article -- which is only an abstract -- the new measurement is outside the margin of error: Half-life evaluations for 3H, 90Sr, and 90Y.Wading through the meaningless babble in the creationist's post, here is the crux of the matter:

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The authors of the 92Sr pdf report obtaining fresh new results of decay time measurements which do not match up. Table four lists the measurements, and right beneath table four, it says

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A weighted average from the three values was determined for each fuel pin. Nevertheless, as the discrepancies were sometimes beyond their reported uncertainties, the associated uncertainty is calculated from the standard deviation between
the three values, with a multiplication factor tp() = 1.32 [15] that arose from the low degree of freedom of the sample.

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"Discrepancies were sometimes beyond their reported uncertainties" means they took measurements of values, and the measurements did not match, even allowing for the inaccuracy of the method. Plain as can be. It doesn't get any simpler than that.

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Now as to the question of what to make of it, there are two approaches. One can look and see here's a measurement, and here's another measurement; since they disagree I conclude a change took place.

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I don't understand enough about how these measurements are done, or how margins of error are calculated, to be able to comment. It's a difficulty in that I am unable to look at the full article, which no doubt explains how the old measurements were improved upon.

Hi JonF,Thanks for the info. It clarifies things for me, but it would be tricky to think of how to phrase some of this to a YEC without them going away thinking, "They're admitting that there's a lot of uncertainty, so none of those radiometric dates are right! It's a method that can't be trusted!" I can imagine them assuming that the decay rate for potassium, for example, is in error, and so while K-Ar dates are in consilience, they're all wrong.So, given the pitfalls described in the paper you quoted from, how is it that we can be confident that the decay rates of elements used in radiometric dating are known to within a few percent or less? How can we be sure that the decay rate of uranium is so precisely understood -- is it because, as you said a few posts back, there have simply been many studies because bombs are big business? How would they have avoided the problems with all the measuring techniques that you outlined? After all, you said,

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But measuring half-lives over a period of time much smaller than the half-life is fraught with peril.

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You couldn't say this in a debate with a YEC, because if your quote applies to isotopes with short half-lives, then it should certainly apply to the longer-lived ones used in radiometric dating. In the case of uranium, perhaps you could cite the unchanged diameter of halos?The final paragraph in your post is sensible, and I did those things. Unfortunately this is a YEC who is very touchy about the subject (understandably, because it invalidates his belief system) and who is also a moderator. If I'm even allowed back onto the forum, I am going to have to take on the subject of the specific isotopes in those papers and why the new measurements are outside of the margins of error, while making sure I don't say so much about uncertainties that the creationist feels free to believe that no radiometric dating method is accurate. I can do the former thanks to you, but the latter could be challenging.Could you tell me where I can find those posts by Steve Carlip that you mentioned? Thanks.Edited by LindaLou, : No reason given.

Hi RAZD, thanks for that. I've read information that you've posted here and at Herb Allure about uranium halos. It's particularly amusing that where you find the supposedly parentless polonium halos, there's always a source of uranium nearby, as well as rocks that radon can leach into (for lack of a better scientific term). The information about uranium decay that you linked to in your previous post is well written so that a layperson like me can gain some understanding. I'll have a more thorough read of the thread today.It was a sad day when Russ decided to start giving moderator positions to the most irritating YECs on the forum. If you get them too wound up, they can kick you out -- as you're well aware. Russ is considering whether CTD's claims that Linear and I have misrepresented those papers are justified. I don't have a great deal of faith in Russ' ability to be objective but you never know. If I'm through there for good, I can spend more time here.Edited by LindaLou, : No reason given.