Potassium-argon dating is a method that allows us to calculate the age of a rock, or how long ago it was formed, by measuring the ratio of radioactive argon to radioactive potassium within it. Radioactive potassium (40K – a solid) decays to radioactive argon (40Ar – a gas), at a known rate.

Which of the following is used in radiometric dating?

Uranium–lead radiometric dating involves using uranium-235 or uranium-238 to date a substances absolute age. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years.