tgamble

<a href="http://www.rae.org/radiodat.html" target="_blank">http://www.rae.org/radiodat.html</a>

"The Potassium-Argon dating method suffers from both leaching and contamination problems. Rubidium-Strontium and Uranium-Lead also has problems of the same kind. Potassium, Rubidium and Uranium salts are highly soluble. In one case the age of a K-Ar sample was soaked under pouring water for four hours. This reduced the concentration of the potassium ions to the point that it increased the date of the rock dramatically."

No references are given (of course) but no doubt some people here can set things straight.

Dr.GH

Sample selection is very, very important. Also important is knowing what you are dating.

An example is a project I am getting started in the Lake Cahuilla basin here in So. Cal. As the ancient lake was drying, and receeding, algal tufa was exposed (kind of looks like coral). There are problems with carbon dates from the tufa, so I am going to use U/Th decay series dates. I am not dating the age that the tufa formed, but rather the last time it was leached. I am relying on the fact that uranium and thorium compounds have differnt solubilities.

There are computational methods (isochron dating) which can correct for a varity of depletion, and enhancement problems.

I would recommend

Dalrymple, G. Brent,
1991 The Age of the Earth
Stanford: Stanford University Press


Dickin, Alan P.
1997 Radiogenic Isotope Geology Cambridge:Cambridge University Press

Now, it is also the case that when creationists claim there are technical problems with radiometric dates, they imply that they are the only people who know about them, and that there are no proceedures to recognize (and correct) errors when they ocurr. I know of no creation 'scientists' that have ever done substantive research on radiometrics. They are very good at selecting inappropriate samples, applying inappropriate methods, and then misinterpreting their results.

A few links

An Animated Isochron Diagram
<a href="http://www.fleming-group.com/Isochron/Isochron2.html" target="_blank">http://www.fleming-group.com/Isochron/Isochron2.html</a>

The Radiometric Dating Game
<a href="http://www.cs.unc.edu/~plaisted/ce/dating.html" target="_blank">http://www.cs.unc.edu/~plaisted/ce/dating.html</a>

Radiometric Dating A Christian Perspective by Roger C. Wiens
<a href="http://asa.calvin.edu/ASA/resources/Wiens.html" target="_blank">http://asa.calvin.edu/ASA/resources/Wiens.html</a>

[ December 06, 2002: Message edited by: Dr.GH ]</p>

scigirl

that link didn't work for me.

scigirl

Dark Jedi

I doubt it's contents will either....

JonF

As I understand it (and I think I do) isochron dating can detect but not correct a variety of such problems.

Concordia-discordia dating can detect and under many circumstances correct for the effect of such problems, and has other advantages.

Damn good book, but not much on sample selection and preparation.

Now that's got some discussion of sample selection and preparation.

Aw, shucks, thanks ... but I'm not going to guarantee that page staying there forever, especially since it's been enshrined at <a href="http://www.talkorigins.org/faqs/isochron-dating/AnimatedIsochron.html" target="_blank">Watching a Rock Age on an Isochron Diagram</a> and it makes more sense there, as a sidebar to <a href="http://www.talkorigins.org/faqs/isochron-dating.html" target="_blank">Isochron Dating</a>; it doesn't really stand on its own.

And the commentary on that page: <a href="http://www.tim-thompson.com/plaisted-review.html" target="_blank">Comments on David Plaisted's "The Radiometric Dating Game" - Part 1</a>, <a href="http://www.tim-thompson.com/plaisted-review2.html" target="_blank">Comments on David Plaisted's "The Radiometric Dating Game" - Part 2</a>, and <a href="http://www.tim-thompson.com/plaisted-review3.html" target="_blank">Comments on David Plaisted's "The Radiometric Dating Game" - Part 3</a>.

Yup, that's a good one.

Also <a href="http://www.geol.umd.edu/pages/faculty/WALKER/GEOL650/650Topic4.htm" target="_blank">RADIOGENIC ISOTOPE SYSTEMS</a>, a fairly technical and extremely condensed outline with a little discussion of sample selection and preparation; <a href="http://geology.csupomona.edu/drjessey/class/gsc300/isotope1.pdf" target="_blank">Isotope Geochemistry</a> (PDF document), fairly technical; <a href="http://www.tim-thompson.com/radiometric.html" target="_blank">A Radiometric Dating Resource List</a>; <a href="http://gondwanaresearch.com/rate.htm" target="_blank">More Faulty Creation Science from The Institute for Creation Research</a> (temporarily no content while he reorganizes and addresses Humphrey's latest claims about helium loss); and just about anything by Kevin R. Henke, much of which you will find by searching the site at <a href="http://home.austarnet.com.au/stear/default.htm" target="_blank">No Answers in Genesis</a>

[ December 06, 2002: Message edited by: JonF ]

[ December 06, 2002: Message edited by: JonF ]</p>

JonF

It's faintly possible for that to happen, if the sample is very small and is cracked; otherwise there's no way for the soluble salts to move through the solid rock into the water. That's one reason why samples are always selected from the unweathered interior of uncracked minerals. Of course, in many minerals used in radiometric dating systems the parent and daughter isotopes are not present as soluble salts, but as substitutions for similar atoms in the crystal lattice or entrapped in the crystal lattice. I suspect a typical creationist ploy, selecting samples that no geologist would try to use for radiometric dating.

For example, the study of Mt. St. Helens rock referred to in the next paragraph of that page ("Recent studies of Mt. St. Helens rock known to have come from the 1980 eruption (Creation Ex Nihilo Technical Journal, see
<a href="http://www.christiananswers.net" target="_blank">www.christiananswers.net</a> yielded erroneous dates in the millions of years."), which is reported at <a href="http://www.icr.org/research/sa/sa-r01.htm" target="_blank">Excess Argon within Mineral Concentrates
from the New Dacite Lava Dome at Mount St. Helens Volcano</a>. The samples all contained phenocrysts (conspicuous, usually large, crystals embedded in porphyritic igneous rock) which might well be xenoliths (literally "foreign rocks") that are older than the lava flow and mess up the dating. He discusses this possibility briefly in the discussion, but pretty much just dismises the possibility without adequate justification.

Getting back to the soluble salts question, the problem may exist in some cases, but it is irrelevant. Plain-vanilla Potassium-Argon dating is subject to various fairly uncommon errors, and is essentially never used today except as a check on other methods (the self-checking Argon-Argon method, which also uses potassium and argon, is used instead). All the widely-used methods that use various combinations of Uranium-Thorium-Lead are self-checking in that they essentially always indicate when a problem such as leaching has occurred, and can sometimes still give a good age even in the presence of leaching. U-Th-Pb systems are extremely widely used (partly because the half-life of Uranium is known to a greater precision than any other half-life ... bombs, you know), and a lot of the recent and current research has focused on sample selection and preparation to obtain samples that have not been modified since solidification, because concordant (see below) dates are much preferred to the discordant dates from samples that have been modified. It's gotten to the point that a large majority of the currently published dates are concordant or extremely near-concordant, indicating that it is virtually certain that the samples have undergone no significant disruption since solidification.

(You may well not understand "concordant" and "discordant". I can't even try to explain it in this limited medium. There's a fairly good not-particularly-technical explanation in "The Age of the Earth", G. Brent Dalrymple. I don't know of a good explanation on the Web.)

{edited to fix link - scigirl}

[ December 06, 2002: Message edited by: scigirl ]</p>

JonF

Oh, I neglected to mention ... Rubidium-Strontium is one of those systems where the parent and daughter isotopes are typicallly not present as salts. Rubidium substitutes for potassium and strontium substitutes for calcium in crystal lattices.

And Rb-Sr dating is always performed using isochron methodology, which detects any leaching problems with 99.9999% or so certainty.

[ December 06, 2002: Message edited by: JonF ]</p>

Valentine Pontifex

It is a shame that there is no good explanation of concordia-discordia dating on the web that is not geared to upperclassmen/graduate students.

But then again if there was one, t.o. regulars would face the prospect of trying to explain it to Zoe...

JonF

Maybe one of these days ...

Don't even let the thought cross your mind! Gives me chills ...

beausoleil

Creationists believe that the assumptions of radiometric dating are invalid and cannot be proven. These assumptions are: (
[1) the radioactive element decays at a constant rate
(2) the rock crystal being analyzed is not contaminated by infusion of excess end product
(3) the rock crystal contained no end product when it was formed
(4) leaching of the parent element out of the rock sample did not occur.

None of these are assumptions

[1] is tested by compaing dates in different systems.
[2] and [3] are catered for by the use of the isochron method - one seeks concentrations of the daughter that correlate with the parent - inherited or acquired daughter would not so correlate.
the presence of an isochron is a test of [4]. An isochron requires different minerals to record the same ratio of daughter atoms to parent atoms. Different minerals do not all respond to leaching in the same way, hence they wouldn't preserve the ratio.