JonF
Posts: 634
Joined: Feb. 2005
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| Quote (forastero @ Dec. 08 2011,16:44) | | Quote (JonF @ Dec. 08 2011,08:24) | All of those problems are possible, and are some of the reasons that K-Ar dating isn't used much anymore. Some of those problems are obviated by rational sample selections and processing. Of course, dates can be checked by comparing with other independent methods, and those checks indicate that he possible problems are rare.
In 40Ar/36Ar analyses of historic lava flows, Dalrymple tested whether 26 very young lava flows had excess argon. 18 of them did not. 8 of them had detectable excess argon, but only one had enough to affect an age of a few million years:
"With the exception of the Hualalai flow, the amounts of excess 40Ar and 36Ar found in the flows with anomalous 40Ar/36Ar ratios were too small to cause serious errors in potassium-argon dating of rocks a few million years old or older. However, these anomalous 40Ar/36Ar ratios could be a problem in dating very young rocks. If the present data are representative, argon of slightly anomalous composition can be expected in approximately one out of three volcanic rocks."
So excess argon is rare.
You need to demonstrate that the possible problems are near universal and, if you can do that, explain the consilience between different radiometric techniques and non-radiometric techniques. For example, Are Radioactive Dates Consistent With The Deeper-Is-Older Rule? (his source is available at http://pubs.er.usgs.gov/publica....86110).
Still waiting for some evidence that contamination is a problem. |
What do you mean its not used much any more? The paper says its always used with 40Ar/39Ar, |
No, the paper that you qouted earlier says that "The method most commonly used to date the primary standard is the conventional K/Ar technique. " "Most commonly" is not "always". Why is it that YECs have so much difficulty in distinguishing between "some" and "all"?
K-Ar dating studies have been and are performed on the standards used to calibrate Ar-Ar dating. The number of such stiudies is small compared to the number of Ar-Ar studies and very small compared to the number of U-Pb studies. For some discussion of the various methods used for Ar-Ar standards see How Serious are Errors in Ar40-Ar39 Dates and How Good are Their Monitoring Standards? and the references contained therein and, for example, Fission-track dating calibration of the fish canyon tuff standard in French reactors and A method for intercalibration of U-Th-Pb and 40Ar-39Ar ages in the Phanerozoic. there are lots of others.
| Quote | | Oh and btw, just how do you believe isochrons are calibrated? |
Well, the validity of the methods themselves are "calibrated" by the well-known and well-established laws of physics and chemistry. (Even if the variations you are so fond of posting do actually exist, they do not affect the accuracy of radiometric methods significantly.) There are various tests and physical standards that laboratories interchange to ensure that they are implementing the methods consistently.
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