Potassium dating accuracy
Other methods, such as Isochron dating could potentially be used to show that the data are still consistent with current geological theory. I wrote the first draft thinking the entire range of reported dates represented the error bars on one sample, implying that the perceived dating error was not statistically significant. The study by Funkhouser and Naughton (1968) was on the xenoliths, not on the lava.
The xenoliths, which vary in composition and range in size from single mineral grains to rocks the size of basketballs, do indeed carry excess argon in large amounts.
) My question: Since the real age of the rocks was around 50 years, does this demonstrate that K-Ar dating is inaccurate?
I can think of several possibilities in response to this question: 2 & 3 seem easily falsifiable - anyone else could simply repeat the procedure and see if their results were the same.
Therefore this data cannot be used to falsify K-Ar dating, because it does not violate a prediction of radiometric dating. They come from deep within the mantle and were carried upward to the surface by the lava.
Instead, the hypothetical contamination scenarios proposed by other answers/comments gain support. In the field, they look like large raisins in a pudding, and even occur in beds piled one on top of the other, glued together by the lava.
Geologists avoid dating glassy, polydeformed or very altered rocks with K-Ar, because these are known to sometimes be problematic .
While other answers are correct that the half-life of Potassium-40 is very large, the 0.2 MY error bars indicate that the measurements were accurate enough to establish the "age" with a high degree of certainty.
They sent these rocks to 2 labs and had them dated by potassium-argon dating to be between 270, 000 and 1 million years old.
(see relevant bits of the link - and please ignore all agenda-based stuff in there!
Please respond with and flaws in my reasoning or any additional reasons why the experiment was flawed.
edit 1 above i said Statistically significant disparity in measured ages is inconsistent with the assumptions required to make radiometric dating predictions.An exception is the lava from the 1801 Hualalei flow, which is so badly contaminated by the xenoliths that it is not possible to obtain a completely inclusion-free sample.