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Survey Manual. This is the science that deals with measuring past time and ass geologic events to their proper dates based on geologic data. It is used to date terrestrial rocks and minerals as well as meteorites and lunar samples ranging in age from approximately 2, years to the age of the Solar System 4.
The method is derived from the natural occurrence of the radioactive isotope of potassium, 40 K, which has a dual decay to 40 Ca and 40 Ar and a half—life of 1. Radiogenic 40 Ar ideally accumulates in a mineral over geologic time.
As a result of irradiation, 39 Ar serves as a proxy for potassium since it is produced from 39 K by fast neutron bombardment. After irradiation, argon isotopes are extracted from samples and standards and separately measured on a gas—source mass spectrometer. Isotopic measurements on modern mass spectrometers are highly sensitive and precise.
Thus, very small amounts of material, ranging in size from a single mineral grain to a few millimeters, are analyzed commonly with small associated analytical errors less than 0.
At the U. Search Search. Neutron Irradiations for Argon Isotopic Dating.Ar ar dating range
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