Origin of Terrestrial Noble Gas

The origins of the noble gas features of the terrestrial planet atmospheres and interiors have defied simple explanations, and so a number of different models have been proposed for volatile sourees and modifieation proeesses. These have often expanded in eomplexity as additional eonstraints have emerged, but all models still have problems. The relevant data for noble gases in the atmospheres and interiors of the terrestrial planets, and the eonstraints these provide, are summarized below. The presently observed volatile states of the planets are the result of aequisition proeesses that refleet the sourees... 

While considerations of the origin of planetary noble gases have been predominantly focused on those presently found in the atmosphere, noble gases still within the Earth provide further constraints about volatile trapping during planet formation. A wide range of noble-gas information for the Earth s mantle has been obtained from mantle-derived materials, and indicates that there are separate reservoirs within the Earth that have distinctive characteristics that were established early in Earth history. These must be included in comprehensive models of Earth volatile history. Also, data are now available for the atmospheres of both Venus and Mars, as well as from the interior of Mars, so that the evolution of Earth volatiles can be considered within the context of terrestrial-planet formation across the solar system. 

Recognition that nontrivial to major fractions of the noble gases in meteorites are exotic components imported into the solar system in presolar grains widens the plausible latitude available to models for the origin of planetary gases, and especially for how closely the noble gas inventories of the major terrestrial planets, including Earth, might be related to those in meteorites. The latter question is related to the broader issue of how uniformly, or otherwise, presolar solids are distributed on a planetary scale, an issue not yet very well explored. 

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