These assumptions include: 1) the initial amount of the daughter isotope is known, 2) neither parent or daughter product has migrated into, or out of, the closed rock system, and 3) decay has occurred at a constant rate over time.
What are the requirements for isotopic dating?
In short, one need only measure the ratio of the number of radioactive parent and daughter atoms present, and the time elapsed since the mineral or rock formed can be calculated, provided of course that the decay rate is known.
Which element is used in radioactive dating?
Potassium-Argon (K-Ar) dating is the most widely applied technique of radiometric dating. Potassium is a component in many common minerals and can be used to determine the ages of igneous and metamorphic rocks.