Noble Gas Geochemistry
The noble gases - He, Ne, Ar, Kr, and Xe, are unique in their chemical inertness. Their value for Earth science problems arises from their lack of chemical reactivity, systematic variation in physical characteristics (e.g., solubility, diffusivity) with mass, and production by numerous radioactive decay schemes. Well-developed applications of noble gases in the Earth Sciences include geochronometry (using for example the ingrowth of Ar from K decay) and studies of the chemical evolution of the Earth's interior and atmosphere.