Cosmogenic isotopes (or cosmogenic nuclides) are rare isotopes created when a high-energy cosmic ray interacts with the nucleus of an in situ atom.  These isotopes are produced within earth materials such as rocks or soil, in Earth's atmosphere, and in extraterrestrial items such as meteorites.  By measuring cosmogenic isotopes, scientists are able to gain insight into a range of geological and astronomical processes.  There are both radioactive and stable cosmogenic isotopes.  Some of these radioisotopes are tritium, carbon-14 and phosphorus-32.