Wiktionary
helium dating
n. (context archaeology English) a method of determining the age of rock that depends on the production of helium during the decay of various radioactive isotopes of uranium and thorium.
Wikipedia
Helium dating
Helium dating may refer to the traditional uranium-thorium dating or uranium-thorium/helium dating.
A relatively new dating method, tritium-helium dating has been developed for determining rates of oxygen utilization in the ocean.