ABSTRACT
Earth science involves the study of our planet as a whole, its evolution and origin. Basic issues concern the physical characteristics of the earth and its constituent materials. Our rocky planet is formed of natural, coherent, aggregate masses of solid material. Each rock contains one or more components called minerals. These chemical compounds vary from the utmost in simplicity and purity (e.g., not-so-rare diamonds consist of a network of tetrahedrally linked C atoms in a cubic array) to solid solutions of incredible complexity in structure and chemistry [e.g., hornblende, a common amphibole (Table 1), consists of paired chains of Si04 tetrahedra partially substituted with Al that are cross-linked by various transition metals and other cations in a monoclinic array]. Measure ments of the physical properties of minerals, their stability over pressure and temperature ranges, and their structural phase transformations are central to in terpreting the formation and history of rocks. Because the accessible surface of our planet is but a thin veneer, the mineral samples we observe do not accurately represent the bulk earth (Table 1). Therefore, indirect measurements (e.g., on meteorites) and comparisons of laboratory data on synthetic high-pressure ma terials to seismic studies are used to probe the interior of our planet. Further more, as the earth's surface has changed dramatically over its 4.5-billion year history due to release of heat through volcanism and convection of its interior, comparisons with the surfaces of other rocky moons and planets are useful in that these bodies provide a series of "snapshots" in planetary evolution.
