For noble gases much more than for other elements, it is impossible to have a coherent appreciation of circumstances on the Earth without a background appreciation of circumstances in the solar system as a whole, or more generally the cosmos at large. This generalization reflects the situation that the original complement of noble gases in the Earth is likely at least partially different from noble gases in other objects in the solar system, and that one cannot adequately understand the unique modifications arising in the Earth's own evolution without understanding the nature of the starting materials. The “cosmochemistry” of the noble gases, based largely but not entirely on the study of meteorites, is a discipline very rich both in data and in competing theories seeking to explain the data. It may also be noted that this is one of the disciplines that has changed dramatically since publication of the first edition of this book. It is not our intention to provide a comprehensive review of noble gas cosmochemistry, which would go considerably beyond our scope; instead, the intention is to focus on aspects most relevant as background to the study of terrestrial noble gases. A number of specific issues and questions in which cosmochemistry is important are raised in Chapter 7.

Cosmic Abundances

The atoms, specifically their nuclei, that comprise the solar system were made in a variety of environments (cf. Woolum, 1988).