Answer: Radioactive decay
Radioactive decay is a spontaneous process in which the nucleus of an atom disintegrates, giving way to the emission of radiation and the appearance of a new nucleus, releasing energy in the process.
This process is widely used in radioactive geological dating (also called isotopic dating or radioisotope dating) in which radioactive impurities were selectively incorporated when the fossil materials were formed.
Therefore:
Isotopic dating relies on a process called radioactive decay