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EvC Forum Science Forums Dates and Dating

# Potassium Argon Sensitivity Analysis

Author Topic:   Potassium Argon Sensitivity Analysis
Engineer
Member (Idle past 4583 days)
Posts: 65
From: KY, USA
Joined: 02-13-2009

 Message 1 of 64 (498763) 02-13-2009 5:46 PM

Hello to all. I am a registered mechanical engineer with a solid background in metrology, material science, nuclear physics, and material phase transformations. I am currently employed in a manufacturing industry.

I don't have a big dog in this fight over the age of the earth but I would like to perform a sensitivity analysis on the potassium-argon methodology. I liken it to a glass-manufacturing problem where you have to deal with gasses trapped inside molten silica and atmospheric contamination driven by partial pressure.

As I see it I would like to evaluate the following variables for a sensitivity analysis, plugging into the radioactive decay formula:

1) How much atmospheric argon can be absorbed into molten silica over a long period of time at atmospheric pressure, and the temperature slightly above the melting point? I need this in ppm.

2) What is the range of K40 in current year magma samples in ppm and the corresponding A40 for the same samples with no atmospheric contamination?

I will use the decay formulas and any other assumptions or correction factors deemed appropriate, and excess argon. I'll use the following methodology from Bureau Laboratories:

http://geoinfo.nmt.edu/labs/argon/Methods/home.html

PS: I think the assumption of zero captive argon in a lava sample is not a good assumption. I do not know how much this affects the result but I will evaluate that as a sensitivity.

thanks to all

 Replies to this message: Message 3 by Chiroptera, posted 02-13-2009 6:30 PM Engineer has responded

Posts: 4754
Joined: 11-11-2003

 Message 2 of 64 (498767) 02-13-2009 6:20 PM

Thread moved here from the Proposed New Topics forum.

Chiroptera
Inactive Member

 Message 3 of 64 (498769) 02-13-2009 6:30 PM Reply to: Message 1 by Engineer02-13-2009 5:46 PM

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.

 PS: I think the assumption of zero captive argon in a lava sample is not a good assumption. I do not know how much this affects the result but I will evaluate that as a sensitivity.

I'm not sure, but I think that the isochron method is commonly used in K-Ar dating. In that case, the amount of initial ratio of argon to potassium is irrelevant. The people at the labs you contact might also be able to fill you in on the basics of radiometric dating methods.

Edited by Chiroptera, : No reason given.

Edited by Chiroptera, : minor typo

Speaking personally, I find few things more awesome than contemplating this vast and majestic process of evolution, the ebb and flow of successive biotas through geological time. Creationists and others who cannot for ideological or religious reasons accept the fact of evolution miss out a great deal, and are left with a claustrophobic little universe in which nothing happens and nothing changes.
-- M. Alan Kazlev

 This message is a reply to: Message 1 by Engineer, posted 02-13-2009 5:46 PM Engineer has responded

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Engineer
Member (Idle past 4583 days)
Posts: 65
From: KY, USA
Joined: 02-13-2009

 Message 4 of 64 (498772) 02-13-2009 7:52 PM Reply to: Message 3 by Chiroptera02-13-2009 6:30 PM

quote:
I'm not sure, but I think that the isochron method is commonly used in K-Ar dating. In that case, the amount of initial ratio of argon to potassium is irrelevant. The people at the labs you contact might also be able to fill you in on the basics of radiometric dating methods.

The isochron method is based on variations in concentrations of the parent, the radioactive daughter, and the non-radioactive daughter in various minerals within the same sample.

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 homogeniety of the different mineral mixtures relative to atmospheric argon.

Apparantly another sample of "known age" must be used for comparison.

"In order for an age to be calculated by the 40Ar/39Ar technique, the J parameter must be known. For the J to be determined, a standard of known age must be irradiated with the samples of unknown age. Because this (primary) standard ultimately cannot be determined by 40Ar/39Ar, it must be first determined by another isotopic dating method. The method most commonly used to date the primary standard is the conventional K/Ar technique. The primary standard must be a mineral that is homogeneous, abundant and easily dated by the K/Ar and 40Ar/39Ar methods. Traditionally, this primary standard has been a hornblende from the McClure Mountains, Colorado (a.k.a. MMhb-1)."

According to this laboratory, this is a foundational assumption that is necessary for using the original potassium argon method to be usable:

"No non-atmospheric 40Ar was incorporated into the rock/mineral during or after its formation."

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 Colorodo.

So if atmospheric A40 enterred 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.

This is why I'd like to get a better handle on the solubility of atmospheric air into liquid glass. It must work something like oxygen diffusing into liquid water, which is sensitive to temperature, pressure, and time of exposure.

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.

I have friends in a university geology department that I plan to use as resources. I'd like to see a good sensitivity analysis as I do in engineering. If you happen to see one on the internet, I'd greatly appreciate you sharing it.

 This message is a reply to: Message 3 by Chiroptera, posted 02-13-2009 6:30 PM Chiroptera has not yet responded

JonF
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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 responded

Engineer
Member (Idle past 4583 days)
Posts: 65
From: KY, USA
Joined: 02-13-2009

 Message 6 of 64 (498786) 02-13-2009 10:19 PM Reply to: Message 5 by JonF02-13-2009 8:45 PM

quote:
The assumption that the radiogenic 40Ar was zero at solidification is well established and checked for rationally selected samples.

Most Argon is 40Ar, whether in the earth or in the air. If argon is boiling off from inside the earth and then expelling itself with lava, how can it be assumed to be zero in the lava sample at the time of solidification?

In glass manufacturing there is a considerable problem with gases in the molten silica, causing bubbles and loss of clarity. The gases want to disolve into the melted silica based on partial pressure, temperature, and solubility.

If the gas would just expel itself to zero it would reduce chemical additions and process controls. Some of the clarity enhancing chemicals are rather toxic like arsenic. The cost savings would be nice, and safety would be improved.

So how does the natural gas expulsion process benefits molten lava but not the glass manufacturing industry where gases want to enter the liquid silica. Maybe the quantities we are talking about here are orders of magnitude below a significant error. I can't know without making comparisons.

What am I missing here?

I think I need to be looking at concentrations of the trapped gases in ppm versus the amount of A40 produced by decay.

PS: Thanks for the articles. I will study them.

Edited by Engineer, : No reason given.

Edited by Engineer, : No reason given.

Edited by Engineer, : No reason given.

 This message is a reply to: Message 5 by JonF, posted 02-13-2009 8:45 PM JonF has responded

 Replies to this message: Message 7 by Engineer, posted 02-13-2009 11:12 PM Engineer has not yet responded Message 9 by JonF, posted 02-14-2009 9:32 AM Engineer has responded

Engineer
Member (Idle past 4583 days)
Posts: 65
From: KY, USA
Joined: 02-13-2009

 Message 7 of 64 (498791) 02-13-2009 11:12 PM Reply to: Message 6 by Engineer02-13-2009 10:19 PM

I notice that Helium is a good fining agent for removing bubbles from glass:

http://www.freshpatents.com/Method-of-reducing-gaseous-inclusions-in-a-glass-making-process-dt20070802ptan20070175241.php

Argon probably aids this as well. Interesting.

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Coragyps
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Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002

 Message 8 of 64 (498792) 02-13-2009 11:22 PM Reply to: Message 7 by Engineer02-13-2009 11:12 PM

Welcome aboard, Engineer!

I'll bet that helium works in glass like it does in water: if you put enough through there, it displaces the other gases from solution. But helium is so poorly soluble (at least in water or crude oil) that very little stays behind to form bubbles. (We use helium to "degas" solutions before pumping them through core samples in the petroleum biz.)

I'd imagine that the reason helium is poorly soluble is that it's a very small nonpolar atom. Argon is nonpolar, too, but far more polarizable, so I'm betting it's more soluble.

Edited by Coragyps, : clarity

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JonF
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Posts: 6174
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 Message 9 of 64 (498850) 02-14-2009 9:32 AM Reply to: Message 6 by Engineer02-13-2009 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 responded

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

Engineer
Member (Idle past 4583 days)
Posts: 65
From: KY, USA
Joined: 02-13-2009

 Message 10 of 64 (498851) 02-14-2009 10:20 AM Reply to: Message 9 by JonF02-14-2009 9:32 AM

quote:
You're missing the big picture, and you're missing a lot of knowledge about what's been done already.

I'm not an expert yet on dating methods, and it really doesn't bother me that the earth is over 4 billion years old.

quote:
You're looking for a systemic error in one family of methods.

Actually I'm looking at this like any other engineering problem where I verify assumptions with data. I am quite familiar with the concept of closed systems, and I'm looking at those assumptions in the dating methods. I'm also pretty intimate with the concepts of arrhenius diffusivity in the process industries.

http://en.wikipedia.org/wiki/Arrhenius_equation

attached is an example of how CO2 invades polyethylene through diffusion:

http://www.composite-agency.com/messages/3945.html

One might assume polyethylene is a closed system but it is not, and it absorbs and releases gases and humidity in a matter of days. It can also be penetrated by liquid solution which carries chemicals with it.

The only real difference I see between the outside surface of the earth and the inside of the earth is temperature, pressure, and solar radiation. Of course the outside also has an atmosphere and some chemical differences, but much if not all of it came from inside at some point in time.

Perhaps I should be looking at another dating method. I've looked at the isochron method, and some of the theory behind it. I totally agree with physics -- the thing I question is assumptions and their basis going into the physics models. I don't think the rates of decay changed or anything like that. I'm more interested in validating closed system assumptions, before, during, and after a sample magma sample is deposited.

quote:
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:

quote:
The dates are correct.

If the assumptions are consistent then the results should be consistent as well, regardless of the validity of the assumptions. The physical equations are correct, and should produce results that are equally valid to the assumptions going into them.

quote:
There is a systemic error that affects all methods equally.

quote:
There are multiple independent systemic errors that coincidentally always affect all methods equally.

Having an independent method to verify a result is always good.

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?

Edited by Engineer, : No reason given.

 This message is a reply to: Message 9 by JonF, posted 02-14-2009 9:32 AM JonF has responded

 Replies to this message: Message 11 by RAZD, posted 02-14-2009 1:53 PM Engineer has not yet responded Message 12 by JonF, posted 02-14-2009 2:10 PM Engineer has responded

RAZD
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Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004

 Message 11 of 64 (498860) 02-14-2009 1:53 PM Reply to: Message 10 by Engineer02-14-2009 10:20 AM

If you want some fun ...
Hello Engineer, and welcome to the fray.

 Perhaps I should be looking at another dating method. I've looked at the isochron method, and some of the theory behind it. I totally agree with physics -- the thing I question is assumptions and their basis going into the physics models. I don't think the rates of decay changed or anything like that. I'm more interested in validating closed system assumptions, before, during, and after a sample magma sample is deposited.

One thing you might want to look into is the question of closed versus open systems in radio-halo formation.

See Are Uranium Halos the best evidence of (a) and old earth AND (b) constant physics? and polonium halos, where Gentry claims that these are closed systems and thus evidence for a young earth (ignoring the problem of the uranium halos in the same rocks showing extreme age to develop).

Note that the uranium halo is also evidence of no significant change in physics during their formation due to the constancy of alpha decay energy to form the rings being related to the constancy of decay rates.

Enjoy.

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 This message is a reply to: Message 10 by Engineer, posted 02-14-2009 10:20 AM Engineer has not yet responded

JonF
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Posts: 6174
Joined: 06-23-2003

 Message 12 of 64 (498863) 02-14-2009 2:10 PM Reply to: Message 10 by Engineer02-14-2009 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 responded

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

Engineer
Member (Idle past 4583 days)
Posts: 65
From: KY, USA
Joined: 02-13-2009

 Message 13 of 64 (498865) 02-14-2009 3:34 PM Reply to: Message 12 by JonF02-14-2009 2:10 PM

quote:
Tell you what, send me a 100 petabyte USb hard drive and I'll see what I can dig up for you.

I don't need a ton of data. The data I originally asked for is in ppm for parent, daughter, etc.

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.

We have a mass spectrometer at my quality lab. Also, I have to use optic devices to measure dust in the air that's less than 50 ppm. I work with this kind of data rather frequently, so it's not a big deal to me.

By the way, I am a six sigma black belt and a certified quallity engineer, so I'm qualified to validate measurement and testing methods regardless of who is using them. Though I might not be well versed in geology, I am well versed in metrology and how it is used to make measurements. I consider geochemistry just another chemistry problem.

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:

step 1 -- take geologic sample under CFR 123.4
step 2 -- prepare example in lab under procedure CFR 456.7
step 3 -- set up mass spectrometer using procedure CFR 8910.11
etc etc etc

I think I will take your advice and look at U-Pb concordia-discordia method instead. It sounds like you are proposing it as the gold standard.

Edited by Engineer, : No reason given.

 This message is a reply to: Message 12 by JonF, posted 02-14-2009 2:10 PM JonF has responded

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Engineer
Member (Idle past 4583 days)
Posts: 65
From: KY, USA
Joined: 02-13-2009

 Message 14 of 64 (498868) 02-14-2009 4:08 PM Reply to: Message 13 by Engineer02-14-2009 3:34 PM

OK so I'm looking at the Uranium-Lead method which has assumptions about lead and uranium in zirconia crystals.

Interesting. I used to work in a vibration lab that used piezo materials in their vibration transducers. Lead zirconate titanate is a good piezo material:

I think the lead is right in there with the zirconium as a chemical compound. It appears to be. It appears to take an extremely high pressure to "push" lead into this structure.

Edited by Engineer, : No reason given.

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JonF
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 Message 15 of 64 (498874) 02-14-2009 5:09 PM Reply to: Message 13 by Engineer02-14-2009 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.

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