Potassium-Argon Dating

K/Ar dating does not work on recent rocks and that's why you will NEVER get accurate dates.

Now that I think about it, WHY DO I NEED TO KNOW THE MECHANICS OF THE DATING PROCESS ANYWAY?

Because it's possible, as the group in your example did, to cast fradulent suspicion on a test procedure by tricking them into performing the test on a sample it's not meant to test.

If you send in cat piss for drug testing, and you get funny results, can you use that to overturn your marijuana conviction? Of course not. Human drug tests work on human urine. When you send them samples that they're not designed to test - like rocks with xenoliths, or with known nonradiogenic argon composition - it's no surprise you get wrong results.

But that's not the test's fault.

If I sent a rock sample to the "best" lab for dating, their results should show the date for the sample in question, or mankinds best attempt to date.

Why? Not all tests can be applied to all samples. Your guys applied the wrong test to the sample. What a surprise, since they've been doing that for years in a fraudulent effort to discredit a procedure not used all that often anymore.

Did those samples contain xenoliths?

Yes. See the links in my previous message.

And why do I find your claim that this "just happened" rather suspect,

He claimed that he had just heard which is something quite different.

since K-Ar dating hasn't been widely used since the 70's?

Depends on what you mean by "widely". It's still used, maybe on the order of 10-15% of all dates. It's low-cost, easy, well-understood, and known to be reliable almost all the time. Often K-Ar dates are cross-checked with other methods to eliminate the possibility of excess argon.

Did they do 40Ar/39Ar dating to eliminate test errors from nonradiogenic argon? If not, why not?

Surely you jest. Ar-Ar wouldn't give them the answer they wanted. But you knew that.

Since that's the most commonly used procedure for dating rocks these days?

The most commonly used procedure these days, over 50% of the cases, is U-Pb concordia-discordia dating, for several reasons. Ar-Ar is widely used but may suffer a decline in usage; new regulations for handling irradiated material post-9/11 make it more cumbersome and expensive.

WHY DO I NEED TO KNOW THE MECHANICS OF THE DATING PROCESS ANYWAY?

If you are going to discuss the dating proces, you need to know enough to understand the answers and figure out who's lying to you. (Hint: its not us).

Try measuring the thickness of a piece of paper with a ruler. The smallest tick marks on the ruler I have are one mm apart, so the smallest length I can measure is 1 mm, much larger than a sheet of paper. Now, if I were just a non-thinking machine, I would report the thickness as "1 mm with an error of 1 mm". Someone dishonest then states that this method of measuring thickness reported a measurement of 1mm (without mentioning the error), and then claims that all thickness measurements are flawed and cannot be trusted. This is similar to the dating of the Mt. St. Helen's rocks by a method that cannot be accurate for very rocks.

This particular Mt. St. Helens example is a bit more complex; I will repeat JonF's link to better discussion for this.

The most commonly used procedure these days, over 50% of the cases, is U-Pb concordia-discordia dating, for several reasons. Ar-Ar is widely used but may suffer a decline in usage; new regulations for handling irradiated material post-9/11 make it more cumbersome and expensive.

Good to know.

See the end of Message 1.