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How does isotopic dating determine the age of rocks?

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Faux amphibolite — geology A rock formation called “faux amphibolite,” from the Nuvvuagittuq greenstone belt in northern Quebec, dated to 4.28 billion years ago.

Isotopic dating, also known as radiometric dating, determines the age of rocks and minerals by measuring the ratio of radioactive parent isotopes to their stable daughter products. This process relies on the principle of radioactive decay, where unstable parent atoms transform into daughter atoms at a constant, immutable rate known as a half-life.12

Because this decay rate is unaffected by external factors like heat, pressure, or chemical state, scientists can use it as a reliable "atomic clock". By using a mass spectrometer to measure the current abundance of parent and daughter isotopes in a sample, researchers can calculate the time elapsed since the rock or mineral system formed.2

For this method to be accurate, several conditions must be met:
* The system must have remained "closed," meaning no parent or daughter atoms were added or lost since formation.2
* The initial amount of daughter isotopes must be accounted for.2
* The specific decay constant for the isotope pair must be known.2

Different isotopes, such as those in the uranium-lead or potassium-argon systems, are selected based on the age and composition of the geologic material being studied.13