# 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.

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