K—Ar dating was instrumental in the development of the geomagnetic polarity time scale.
The initial ratio has particular importance for studying the chemical evolution of the Earth's mantle and crust, as we discussed in the section on igneous rocks.
Lunar rocks also lie on the Geochron, at least suggesting that the moon formed at the same time as meteorites.
Most minerals will lose Ar on heating above o C - thus metamorphism can cause a loss of Ar or a partial loss of Ar which will reset the atomic clock.
Description: Petrology Tulane University Prof. Some examples of isotope systems used to date geologic materials.