The isotopes the KAr system relies on are Potassium (K) and Argon (Ar).

Potassium, an alkali metal, the Earth's eighth most abundant element is common in many rocks and rock-forming minerals.

Potassium can be mobilized into or out of a rock or mineral through alteration processes.

Due to the relatively heavy atomic weight of potassium, insignificant fractionation of the different potassium isotopes occurs.

However, the Argon, a noble gas, constitutes approximately 0.1-5% of the Earth's present day atmosphere.

Because it is present within the atmosphere, every rock and mineral will have some quantity of Argon.

Argon can mobilized into or out of a rock or mineral through alteration Ar and potassium, there is not a reliable way to determine if the assumptions are valid.

Argon loss and excess argon are two common problems that may cause erroneous ages to be determined.

Argon loss occurs when radiogenic K by a fast neutron reaction) can be used as a proxy for potassium.

Therefore, unlike the conventional K/Ar technique, absolute abundances need not be measured.

Instead, the ratios of the different argon isotopes are measured, yielding more precise and accurate results.