Radio metric dating
So accurate determinations require very pure samples, very accurate and selective detectors, or both.
Weathering and metamorphism are the two most common ways to disturb a system.
Imagine we have an undiscovered element, Parentium, that has a radioactive isotope, Parentium-123, which decays to stable Daughterium-123.
This is the only way Parentium-123 decays, and there is no other source of Daughterium-123.
What radioactive materials actually do is decay according to a law: Decays/Time = K * Number of atoms K is a constant called the decay constant.
Let t stand for time and N(t) stand for the number of atoms at time t .