The K-Ar method is very useful for dating rocks in the range from significantly younger than 100,000 years in favourable cases, to billions (>109) of years. With appropriate samples and careful measurement, very precise and accurate ages can be determined, often with uncertainties of as little as 1% .

How reliable is potassium-argon dating?

Potassium-argon dating is accurate from 4.3 billion years (the age of the Earth) to about 100,000 years before the present. At 100,000 years, only 0.0053% of the potassium-40 in a rock would have decayed to argon-40, pushing the limits of present detection devices.

What is the purpose of potassium-argon dating?

Potassium-argon dating, method of determining the time of origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock. This dating 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.