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Radiometric dating of potassium

This dating method is based upon the decay of radioactive potassium-40 to radioactive argon-40 in minerals and rocks; potassium-40 also decays to calcium-40.Thus, the ratio of argon-40 and potassium-40 and radiogenic calcium-40 to potassium-40 in a mineral or rock is a measure of the age of the sample.The potassium-argon (K-Ar) isotopic dating method is especially useful for determining the age of lavas.Developed in the 1950s, it was important in developing the theory of plate tectonics and in calibrating the geologic time scale.The rock sample to be dated must be chosen very carefully.Any alteration or fracturing means that the potassium or the argon or both have been disturbed.

Ar-Ar analyses cost around 00 per sample and take several weeks.The Ar-Ar method is considered superior, but some of its problems are avoided in the older K-Ar method.Also, the cheaper K-Ar method can be used for screening or reconnaissance purposes, saving Ar-Ar for the most demanding or interesting problems.A precise amount of argon-38 is added to the gas as a "spike" to help calibrate the measurement, and the gas sample is collected onto activated charcoal cooled by liquid nitrogen.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.

The mineral sanidine, the high-temperature form of potassium feldspar, is the most desirable.

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Radiometric dating of potassium introduction

Radiometric dating of potassium

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