Potassium 40 dating range
Potassium 40 dating range - podcast dating
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.
The key is to put the mineral sample in a neutron beam, which converts potassium-39 into argon-39.Variations in this data may point to errors anywhere in the process, which is why all the steps of preparation are recorded in detail.K-Ar analyses cost several hundred dollars per sample and take a week or two.Finally the argon atoms are counted in a mass spectrometer, a machine with its own complexities.Three argon isotopes are measured: Ar is determined by comparison to it.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.
Because Ar has a very short half-life, it is guaranteed to be absent in the sample beforehand, so it's a clean indicator of the potassium content.
The advantage is that all the information needed for dating the sample comes from the same argon measurement. This method is commonly called "argon-argon dating."The physical procedure for K.
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 develping plate tectonics and in calibrating the geologic time scale.
The mineral sanidine, the high-temperature form of potassium feldspar, is the most desirable.