What is the limitation of potassiumargon dating
Of the naturally occurring isotopes of potassium, 40K is radioactive and decays into 40Ar at a precisely known rate, so that the ratio of 40K to 40Ar in minerals is always proportional to the time elapsed since the mineral formed [ 40K is a potassium atom with an atomic mass of 40 units; 40Ar is an argon atom with an atomic mass of 40 units].
It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar).
Potassium is a common element found in many materials, such as micas, clay minerals, tephra, and evaporites.
Though we know that K-Ar dating works and is generally quite accurate, however, the method does have several limitations.
First of all, the dating technique assumes that upon cooling, potassium-bearing minerals contain a very tiny amount of argon (an amount equal to that in the atmosphere).
The potassium-argon age of some meteorites is as old as 4,500,000,000 years, and volcanic rocks as young as 20,000 years old have been measured by this method.