Therefore, unlike the conventional K/Ar technique, absolute abundances need not be measured.
Instead, the ratios of the different argon isotopes are measured, yielding more precise and accurate results.
The reader should be thoroughly familiar with the K-Ar method, as explained in the previous article, before reading any further.
In the previous article I introduced you to K is a stable isotope of potassium, which by definition means that it will not spontaneously undergo decay into another isotope.
Or if we consistently get one date for the steps below (for example) 400°C, and consistently get another date in the steps above 400°C, then it seems as though argon loss occurred as a result of metamorphism at a temperature of about 400°C, with the younger date representing the date of the metamorphism, and the older date representing the formation of the rock; and we can investigate this clue further by looking for other evidence of the metamorphic event.
Potassium can be mobilized into or out of a rock or mineral through alteration processes.
Argon loss and excess argon are two common problems that may cause erroneous ages to be determined.
Argon loss occurs when radiogenic K by a fast neutron reaction) can be used as a proxy for potassium.
So now we know J, and we have measured the R-value of the sample we're actually interested in dating, so we can use these data to solve the equation for t, giving us the age we're looking for.
You will note that this means that we have to be able to date some rocks accurately using some method other than Ar-Ar, so that we can find a standard to use for the determination of J; fortunately we can do this, and geologists have put a lot of effort into identifying rocks which can be accurately dated and used as standards.