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Author Topic:   Potassium Argon Sensitivity Analysis
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 5 of 64 (498775)
02-13-2009 8:45 PM


You would do well to learn something about the various methods before presuming to test and criticise them. A good place to start is Radiometric Dating: A Christian Perspective. If you want some heavy technical literature see Isotope Geochemistry (click "Lectures" on the left) and Radiogenic Isotope Geology
Of course geochronologists have considered the issue of contamination by atmospheric argon. The ratio of 40Ar/36Ar in the atmosphere is 295.5. Since 36Ar is not generated by radioactive decay, measuring it tells us how much of the 40Ar came from the atmosphere. See Atmospheric argon correction in the K-Ar dating of young volcanic rocks and Geochronology and Thermochronology by the 40Ar/39Ar Method, page 19.
The assumption that the radiogenic 40Ar was zero at solidification is well established and checked for rationally selected samples.
For example, the 40Ar/39Ar method (AKA Ar-Ar) covered in one of the above links above is not affected by "excess argon" present at solidification. (Ar-Ar can be applied to any sample suitable for K-Ar, so Ar-Ar has largely replaced K-Ar, although K-Ar still has a place). Isochron dating methods also are not affected by "initial daughter". Over half of the dates produced in the last 20 or so years are U-Pb concordia-discordia dates which are not affected by initial daughter 'cause it's just impossible for minerals like zircon to contain any significant amount of lead at solidification. All those methods indicate when the system has been opened (i.e. relevant material has been gained or lost), and the Ar-Ar and U-Pb methods can often produce a valid date even after the system has been opened.
The fact that all these disparate methods, based on different isotopes and different mechanisms of radioactive decay) almost always agree demonstrates incontrovertibly that the dates are real and the no-initial-Ar assumption is valid for rationally selected samples. For a minuscule sample of the concordant results see Radiometeric Dating Does Work! and Radiometric Ages of Some Early Archean and Related Rocks of the North Atlantic Craton.
I'm glad you think that you have no horse in the race, 'cause the race was over about 200 years ago … decades before Darwin published Origin. The outcome of the race was known before Darwin was born.

Replies to this message:
 Message 6 by Engineer, posted 02-13-2009 10:19 PM JonF has replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 9 of 64 (498850)
02-14-2009 9:32 AM
Reply to: Message 6 by Engineer
02-13-2009 10:19 PM


Some background: Ar-Ar is really two methods. The first is conversion of potassium to argon by irradiation. This makes the subsequent measurements easier and more precise because you're measuring only one element and looking for ratios of isotopes within that element. The second is making multiple age measurements by "step heating"; heating the sample to successively higher temperatures and making an age determination from the argon driven off at each step. If the age determinations are all the same that's powerful evidence that the system has remained closed. If most but not all of the age determinations are the same, that is powerful evidence of either open-system behavior and/or "excess argon" at solidification and that the agreeing age determinations are correct. It is essentially impossible that initial argon or added argon would be distributed through the sample in the same distribution as radiogenic argon; that's why the step heating procedure can differentiate. For tour-de-force example of this see 40Ar/39Ar Dating into the Historical Realm: Calibration Against Pliny the Younger (free registration required for full article), in which excess argon was present.
The step heating results can be presented on an isochron diagram, but usually are not; an age-spectrum plot is more common, like:
This is a little more involved, and I'm willing to take it on. The problem with the isochron method appears to be the assumption about proportional homogeneity of the different mineral mixtures relative to atmospheric argon.
Isochron methods in general have nothing to do with atmospheric argon. See Isochron Dating.
Apparently another sample of "known age" must be used for comparison.
Not in isochron methods. A sample of known age must be used for comparison in Ar-Ar, which is isochron-like but not really an isochron method. That known-age sample is usually but not always dated by K-Ar; as well it's dated by methods not involving argon.
In general, isochron methods do not involve a reference sample. See above.
Hence we are back to revisiting the assumptions of the "known standard," which must be validated by the originally proposed A40/K40 method applied to hornblende from Colorado.
Many different materials are used as standards in different labs and for samples of different ages. See How Serious are Errors in Ar40-Ar39 Dates and How Good are Their Monitoring Standards? and Intercalibration of international and domestic 40Ar/39Ar
dating standards
and the references in the latter.
So if atmospheric A40 entered the system of the "known standard", I'm not so sure the original method or the isochron method can handle this very well, and would like to evaluate it.
Note that the known-age standards are calibrated by methods that do not involve argon (as well as ordinary K-Ar dating). See above references.
What am I missing here?
You're missing the big picture, and you're missing a lot of knowledge about what's been done already.
You're looking for a systemic error in one family of methods. The other families (U-Pb concordia-discordia, Pb-Pb isochron, Sm-Nd isochron, Rb-Sr isochron. Re-Os isochron, stratigraphy, fission tracks, thermoluminescence, electron spin resonance, infra-red stimulated luminescence, ...) essentially always agree with that family when applied to the same rocks. There are three possibilities:
  1. The dates are correct.
  2. There is a systemic error that affects all methods equally.
  3. There are multiple independent systemic errors that coincidentally always affect all methods equally.
Nobody's seriously argued for #3. Since the majority of methods and tests do not involve argon at all, atmospheric argon is not a candidate for #2. Therefore atmospheric argon is not a systemic error in K-Ar and Ar-Ar, because if it were then K-Ar and Ar-Ar dates would not agree so well with the dates obtained by other independent methods.
The RATE group, comprised of those few YECs who understand dating methods, is arguing for accelerated nuclear decay (AND) as a candidate for #2. That's about the only thing that crosses almost all boundaries between methods. But we have lots of evidence for the constancy of radioactive decay, and AND would have a few noticeable side effects such as melting the Earth.
If you are really interested in the effect of atmospheric argon, ask your friends in that university geology department to let you into the library for a day or two to research what has been done in regards to atmospheric argon.

This message is a reply to:
 Message 6 by Engineer, posted 02-13-2009 10:19 PM Engineer has replied

Replies to this message:
 Message 10 by Engineer, posted 02-14-2009 10:20 AM JonF has replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 12 of 64 (498863)
02-14-2009 2:10 PM
Reply to: Message 10 by Engineer
02-14-2009 10:20 AM


Perhaps I should be looking at another dating method.
U-Pb concordia-discordia is where it's at today. Sub-1% accuracy, widely applicable, straightforward, lots of labs have the equipment. Over 50% of the dates in the last 20-30 years are done by this method.
Having an independent method to verify a result is always good.
The various methods I've mentioned are independent.
What I really need to see is the data.
How much of the chemicals for each testing method are present in pristine magma inside the earth today, and inside magma that erupts?
Tell you what, send me a 100 petabyte USb hard drive and I'll see what I can dig up for you.
Seriously, you're kidding, right? That's boatloads of shitloads of data. None of which you know enough about to interpret. Take a few college courses in isotope geochemistry, then you'll be ready to ask meaningful and answerable questions.
Edited by JonF, : No reason given.

This message is a reply to:
 Message 10 by Engineer, posted 02-14-2009 10:20 AM Engineer has replied

Replies to this message:
 Message 13 by Engineer, posted 02-14-2009 3:34 PM JonF has replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 15 of 64 (498874)
02-14-2009 5:09 PM
Reply to: Message 13 by Engineer
02-14-2009 3:34 PM


Isn't A40 like 1 x 10 exp-14 moles/mole in a typical volcanic rock sample or something like that? I'm sure it can vary, but how about an average sample such as something to be tested. This is the kind of data I'm talking about.
There's raw data in at least one of the links I posted, Intercalibration of international and domestic 40Ar/39Ar
dating standards
.
Why are you so insistent on retracing 60+ year old footsteps? This has been establsihed and tested and reviewed and re-establsihed and re-tested and re-reviewed and ...
In the end there is typically a "gold standard" somewhere for verifying results, and that's what I'm looking for as well as the equivalent of a certification which typically documents all of the methodology, its uses and known limitations, and a set of procedures that might read something like this:
Sorry, no such thing. This is science, not engineering (and I'm a mechanical engineer by training, so I'm not disparaging engineering; it's just not the same as science). There's no gold standard, just the oversight by the scientific community. There's no recipe-like set of instructions, there's just learning established practices and why and how they are established like that. If there were recipes; there'd never be scientific progress creating new and better practices.
That's the difference between science and engineering. You're qualified to run a mass spec ... what would you do in this guy's shoes? A zircon that predates the universe.
Here's the answer: A zircon that predates the universe 2.
Sorry, no put-it-in-the-box-and-turn-the-crank-and-the-right-answer-pops-out. That's why I'm saying you don't have the knowledge to analyze the data. You need to know the background, not just what's written in the manual. You could run and maintain the equipment just fine, but you don't understand what you'd be doing.

This message is a reply to:
 Message 13 by Engineer, posted 02-14-2009 3:34 PM Engineer has replied

Replies to this message:
 Message 19 by Engineer, posted 02-14-2009 10:26 PM JonF has replied
 Message 20 by Engineer, posted 02-14-2009 10:44 PM JonF has not replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 22 of 64 (498918)
02-15-2009 9:21 AM
Reply to: Message 19 by Engineer
02-14-2009 10:26 PM


I'm thrown into a lot of problems where "I don't have a background" -- what's new for an engineer? You might be right about this one with dating where I've finally met my technical match,
I didn't say you've met your technical match; I don't know whether or not you have.
So often I've heard it said in my profession -- if someone can't explain something to a technically minded audience, then they really don't understand it themselves. If they understood it then they could explain it.
Oh, I can explain it. I have already explained how atmospheric argon is compensated for. I have already explained how the Ar-Ar method works. If you really insist, I will explain how the U-Pb concordia-discordia method works.
But you are looking for far more than an explanation. I'm not going to try to type out a college-level course or two in this medium, where graphics and equations are limited, where it would take months to explain it, when there are so many better resources available to which you've been directed.
If you want to discuss some point or ask for a quick explanation, this is a great medium and group of people to do it in. But you're not trying to discuss, you're asking for great chunks of technical information and detail to be spoon-fed, and that's not appropriate here.
If some technical person in another discipline asks me about failure mechanics, I'd have a way to explain it with technical information.
OK, that's a good example, 'cause my undergraduate and graduate work was in that field. How would you teach someone about failure mechanics on this message board, starting from scratch? Not just explaining what it's about, teaching them enough evaluate a catastrophic bridge collapse on their own. Would you type out everything that's needed, including the equations, the figures, all the references? Or would you point them to good ways to learn it on their own?
The "you're to dumb to understand" approach, usually means someone has an agenda in my experience.
Nobody's said you're too dumb to understand. You are too ignorant to understand. The latter is fixable. Go thou and fix it.
If you have a better way for me to get the information I'm all ears. I don't think the internet is going to cut it.
Obviously you're not all ears. From Message 3:
quote:
Why are you asking for this on an internet message board? I would think that a research lab connected to a university or large company would be a better source.
They would also have experienced scientists and lab technicians who would probably be willing to give advice and pointers on the project. If your project sounds productive and fruitful, maybe some would be willing to become involved in it with you.
From Message 9:
quote:
If you are really interested in the effect of atmospheric argon, ask your friends in that university geology department to let you into the library for a day or two to research what has been done in regards to atmospheric argon.
From Message 12:
quote:
Take a few college courses in isotope geochemistry, then you'll be ready to ask meaningful and answerable questions.
Edited by JonF, : No reason given.

This message is a reply to:
 Message 19 by Engineer, posted 02-14-2009 10:26 PM Engineer has replied

Replies to this message:
 Message 25 by Engineer, posted 02-15-2009 12:09 PM JonF has replied
 Message 26 by Engineer, posted 02-15-2009 12:40 PM JonF has not replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 31 of 64 (498934)
02-15-2009 1:18 PM
Reply to: Message 25 by Engineer
02-15-2009 12:09 PM


So what is the assumption for environmental radiation exposure over the past 4 billion years? Are you assuming it is a constant, or is this just a noise factor with small relative contribution anyway?
Sorry, you are wrong. Nothing that occurs on or in the Earth speeds up radioactive decay significantly.
And neutron flux doesn't speed up radioactive decay. Period. It does transmute elements, often into radioactive ones. If you want to claim otherwise, let's see a reference. You are damaging your credibility seriously by making this claim,
The neutron flux on Earth today is far from enough to have any noticeable effect. If the neutron flux were high enough in the past to have a significant effect, it would affect different methods differently and the consilience between methods, the big picture that you are studiously ignoring, would be disrupted.
In fact a high neutron flux would actually increase the age reported by some methods, such as 206Pb/207Pb, because of the difference in cross-sections for the various Pb+n reactions. See NEUTRON REACTIONS AND Pb-ISOTOPIC RATIOS and Addendum: Derivation of the Neutron Reaction Correction Equation
This is a common problem I must endure everyday in my profession -- selling a highly technical project to a usually non-technical group of high level executives that hold the purse-strings for funding.
I would start out by telling the non-technical executives how failure mechanics is useful to humankind -- how many lives it could have saved in certain situations -- by how it can save them from catastrophe and loses that their company has experienced. I would provide technical case studies where it has done so.
Next, I would propose my plan to reduce such failures, their cost, and provide their proposed benefits. Then I would stand behind my promises with accountabilities that they can measure with financial results.
Usually the executives are some of the most technically ignorant people around. They, however, must make the ultimate decisions and hold accountability. That's how it works in my world: good communication, good research, a good business case, and measurable results.
I had to do something similar to this for my most recently funded project where we have concrete floor-coating failures that must be fixed or risk environmental contamination. The mid-level executives demanded the technical research to back my claims. Nobody has a satisfactory explanation in my opinion and I have to swag technical judgment into the solution. My reputation is always on the line, I have not been defeated yet, and I thank the creator for my successes. I am unrelenting, but I know when to quit.
OK. Remember that bridge collapse in Minnesota on Aug 2, 2007? I think the engineers may have analyzed that wrong. I want to do my own analysis. Tell me how to do so. Now. In this forum. Include the data, please.
Do you see the similarity between my request and yours?

This message is a reply to:
 Message 25 by Engineer, posted 02-15-2009 12:09 PM Engineer has replied

Replies to this message:
 Message 32 by Engineer, posted 02-15-2009 1:37 PM JonF has replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 33 of 64 (498938)
02-15-2009 2:39 PM
Reply to: Message 32 by Engineer
02-15-2009 1:37 PM


I thought I did that in the previous post where K40 converts to A40 through irradiation done in a nuclear reactor located on the earth. You might not call it "nuclear decay" per se but the end result is the same.
It isn't nuclear decay. Most technical people appreciate the need for precise terminology.
On this forum nobody is getting paid -- so I don't really have the expectation.
Then why are you asking?

This message is a reply to:
 Message 32 by Engineer, posted 02-15-2009 1:37 PM Engineer has replied

Replies to this message:
 Message 36 by Engineer, posted 02-15-2009 2:48 PM JonF has not replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 39 of 64 (498948)
02-15-2009 4:21 PM
Reply to: Message 37 by Engineer
02-15-2009 2:58 PM


Re: messing with definitions is not scientific: it's a falsehood
Nuclear decay involves internal activation energy, but there are two ways to get A40 from K40.
Name 'em. {ABE} With references.
Personally I find it a little confusing to assume lava boiling out of a volcano supposedly has no argon in it. Maybe it's not enough to matter in many applications, but it does.
It's been proven to be not enough to matter in pretty much all applications (given rational sample selection), by its agreement with independent methods that are not subject to that possible type of problem. You got any evidence to the contrary, trot it out. Personal incredulity doesn't cut the mustard.
Someone might call A40 the daughter of "nuclear decay" per se from K40, but it is not necessarily so, as irradiation produces the same result.
You are getting more and more confused. The irradiation produces 39Ar from 39K. We measure the ratio of 39Ar to 40Ar, we know the ratio of 39K to 40K, we therefore know the ratio of 40K to 40Ar.
40Ar is produced by radioactive decay of 40K. Maybe in supernovae, too, but not in reactors. End of story.
Edited by JonF, : No reason given.

This message is a reply to:
 Message 37 by Engineer, posted 02-15-2009 2:58 PM Engineer has replied

Replies to this message:
 Message 41 by Engineer, posted 02-15-2009 4:30 PM JonF has replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 44 of 64 (498972)
02-15-2009 7:06 PM
Reply to: Message 41 by Engineer
02-15-2009 4:30 PM


Re: messing with definitions is not scientific: it's a falsehood
Yes indeed I am getting very confused. I read this table from a geochronology test lab:
http://geoinfo.nmt.edu/labs/argon/Methods/home.html#irrad
By gum you're right! Well, ya learn something new every day.
That's an interesting page. Did you notice the clear and concise explanation of how these undesirable reactions are monitored? So they are no promblem.
Just as "excess argon" at solidification is not a problem.

This message is a reply to:
 Message 41 by Engineer, posted 02-15-2009 4:30 PM Engineer has replied

Replies to this message:
 Message 45 by Engineer, posted 02-15-2009 7:22 PM JonF has not replied

  
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