Carbon dating on the
The learning curve has been long and is far from over today.
With each increment in quality, more subtle sources of error have been found and taken into account.
K-Ar analyses cost several hundred dollars per sample and take a week or two.
A variant of the K-Ar method gives better data by making the overall measurement process simpler.
What simplifies things is that potassium is a reactive metal and argon is an inert gas: Potassium is always tightly locked up in minerals whereas argon is not part of any minerals. So assuming that no air gets into a mineral grain when it first forms, it has zero argon content.
That is, a fresh mineral grain has its K-Ar "clock" set at zero.
These steps help remove as much atmospheric Ar from the sample as possible before making the measurement.
Then the gas sample is cleaned of all unwanted gasses such as H, nitrogen and so on until all that remains are the inert gasses, argon among them.