Radioactive dating
Radioactive Dating, the calculation of a substance's age by measurement of the radioactive material it contains or of the amount of natural atomic fission that has occurred in the substance. These methods of calculating age are used in geology, anthropology, archaeology, and other fields. Radioactive dating is based on the fact that a radioactive isotope (form) of an element changes into an isotope of another element at a fixed rate. Each radioactive isotope, or radioisotope, has its own rate, expressed in terms of its half-life. The age of a substance, even if it is billions of years old, can be calculated if the substance contains radioisotopes with half-lives that are sufficiently long.