Xe isotopes are also promising in tracing mantle dynamics in Earths evolution. The first explicit recognition of non-atmospheric Xe in terrestrial samples came from the analysis of CO-well gas in New Mexico, displaying an excess of I-derived or primitive source Xe and high content in Xe due to the decay of U. At present, the excess of Xe and Xe has been widely observed in mid-ocean ridge basalt (MORBs) and Oceanic island basalt (OIBs). Because Xe receives more fissiogenic contribution than other heavy Xe isotopes, Xe (decay of I) and Xe are usually normalized to Xe when discussing Xe isotope trends of different mantle sources. MORBs Xe/Xe and Xe/Xe ratios lie on a trend from atmospheric ratios to higher values and seemingly contaminated by the air. Oceanic island basalt (OIBs) data lies lower than those in MORBs, implying different Xe sources for OIBs and MORBs.
The deviations in Xe/Xe ratio between air and MORBs show that mantle degassing occurred before I was extinct, otherwise Xe/Xe in the air would be the same as in the mantle. The differences in the Xe/Xe ratio between MORBs and OIBs may indicate that the mantle reservoirs are still not thoroughly mixed. The chemical differences between OIBs and MORBs still await discovery.
To obtain mantle Xe isotope ratios, it is necessary to remove contamination by atmospheric Xe, which could start before 2.5 billion years ago. Theoretically, the many non-radiogenic isotopic ratios (Xe/Xe, Xe/Xe, and Xe/Xe) can be used to accurately correct for atmospheric contamination if slight differences between air and mantle can be precisely measured. Still, we cannot reach such precision with current techniques.