The isotopic clock is a natural system used in geology and geochronology to measure time based on the radioactive decay of certain chemical elements.
It works because some radioactive isotopes (“parent” isotopes) spontaneously decay into other isotopes (“daughter” isotopes) at a constant, known rate.
When a mineral crystallizes, it incorporates certain radioactive elements into its crystal structure. Over time:
By measuring the ratio between the two, it is possible to calculate how much time has passed since the system was “sealed.”