Age dating argon
A demonstration of the method is given using samples of known potassium-argon ages.
Some advantages over the conventional method are that the amount of material required is greatly reduced, no argon-38 “spike” is required and chemical inhomogeneity within a sample is of no consequence.
The other important advantage of Ar-Ar dating is the extra data gained from step heating: instead of heating the irradiated sample to the highest possible temperature all at once, and so releasing all the argon all at once, we can increase the temperature in steps starting at a low temperature. Well, different minerals within the rock will give up their argon at different temperatures, so each step will give us a ratio of K from which these are derived must have appeared in the same ratio in each mineral, because both isotopes of potassium have the same chemical properties.
This means that if the rock cooled rapidly enough that all the minerals in it have the same date, and if there has been no argon loss, and if there is no excess argon added to the system, then the dates we calculate at each step of the heating will be the same date.
Consequently, the amount of it found in rocks is negligible — unless you subject them to an artificial neutron source.
A crucial point to note is that because K are isotopes of the same element, they have the same chemical properties.
In this article we shall explain how this method works and why it is superior to the K-Ar method.
Sample materials included biotite, muscovite, sanidine, adularia, plagioclase, hornblende, actinolite, alunite, dacite, and basalt.
For 18 samples there are no significant differences at the 95% confidence level between the KAr ages obtained by these two techniques; for one sample the difference is 4.3% and is statistically significant.
However, in many instances, the published “ages” have no merit, as they fail the simple statistical tests that should be applied to all such data. In these experiments, a sample is heated in steps of increasing laboratory extraction temperature, until all the argon is released.
The argon released in each step is measured to calculate a “step age” with an associated analytical error.