Geologists have used this method to date rocks as much as 4 billion years old. It is based on the fact that some of the radioactive isotope of Potassium, Potassium-40 (K-40) ,decays to the gas Argon as Argon-40 (Ar-40). Potassium (K) is one of the most abundant elements in the Earths crust (2.4% by mass).

Why is potassium-argon dating used?

The potassium-argon dating method has been used to measure a wide variety of ages. 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.

What is the difference between potassium-argon dating and carbon 14 dating?

Potassium-argon dating Potassium-40 is a radioactive isotope of potassium that decays into argon-40. The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated. K–Ar dating was used to calibrate the geomagnetic polarity time scale.