4. The Solid Earth: Isotope Geochemistry

Geology (the study of the Earth and the rocks and minerals within it) is the one science that most heavily relies on and is assisted by the use of isotopes as an investigation tool. The recent period of strong and sustained development in geological understanding—starting in the 1950s—coincides with very significant advances in isotope research (and in geophysics), itself strongly dependent on technological advances such as electronics and modern computers. The reason for this quasi-dependence of geology on isotopes (to the point of colloquially equating geochemistry to isotope geochemistry), is that every and each process that occurred in the past and affected a rock and its components also affected the isotopic composition of many elements within the rock. By studying the isotopic composition of a geological sample, we are able to understand not only what processes affected that rock, but also when and under what physical and chemical conditions these processes occurred. As a consequence, isotope geochemistry is very well understood and widely applied. In this chapter, we will briefly examine some of the many applications of isotopes, both stable and radiogenic, in geology.