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Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology.

In terms of atomic weight, it is located between two more stable and far more abundant isotopes (potassium 39 and potassium 41) that make up 93.25% and 6.73% of the Earth total potassium supply respectively.

With a half-life of 1,251 billion years, potassium 40 existed in the remnants of dead stars whose agglomeration has led to the Solar System with its planets.

The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample.

Radioactive elements "decay" (that is, change into other elements) by "half lives." If a half life is equal to one year, then one half of the radioactive element will have decayed in the first year after the mineral was formed; one half of the remainder will decay in the next year (leaving one-fourth remaining), and so forth.

method is based upon the decay of radioactive potassium-40 to radioactive argon-40 in minerals and rocks; potassium-40 also decays to calcium-40.

Thus, the ratio of argon-40 and potassium-40 and radiogenic calcium-40 to potassium-40 in a mineral or rock is a measure of the age of the sample.

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.

Radioactive elements "decay" (that is, change into other elements) by "half lives." If a half life is equal to one year, then one half of the radioactive element will have decayed in the first year after the mineral was formed; one half of the remainder will decay in the next year (leaving one-fourth remaining), and so forth.

method is based upon the decay of radioactive potassium-40 to radioactive argon-40 in minerals and rocks; potassium-40 also decays to calcium-40.

Thus, the ratio of argon-40 and potassium-40 and radiogenic calcium-40 to potassium-40 in a mineral or rock is a measure of the age of the sample.

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.

But it can escape into the surrounding region when the right conditions are met, such as change in pressure and/or temperature.