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The calcium-potassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium.
On the other hand, the abundance of argon in the Earth is relatively small because of its escape to the atmosphere during processes associated with volcanism.
The selected size fraction is cleaned in ultrasound and acid baths, then gently oven-dried.
The target mineral is separated using heavy liquids, then hand-picked under the microscope for the purest possible sample.
Young rocks have low levels of The rock samples are crushed, in clean equipment, to a size that preserves whole grains of the mineral to be dated, then sieved to help concentrate these grains of the target mineral.
Developed in the 1950s, it was important in developing the theory of plate tectonics and in calibrating the geologic time scale.
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.
With each increment in quality, more subtle sources of error have been found and taken into account.
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