ABSTRACT
To more completely understand geothermal resources and their distribution on the planet, a review of the Earth’s compositional and physical make-up is necessary. The Earth is compositionally inhomogeneous, consisting of an iron-nickel core, a dense rocky mantle, and a thin, comparatively low-density rocky crust. This compositional diversication developed shortly after our planet formed when more dense material sank to the center and low-density material rose toward the surface. Furthermore, because of this compositional diversity, differences in physical or mechanical properties exist (liquid or molten vs. solid; brittle vs. ductile deformation). Brittle behavior means breaking or fracturing after a threshold level of stress is applied, such as what happens when a glass vase is dropped on a hard surface. Ductile deformation, on the other hand, reects bending without breaking after a material’s yield strength is exceeded, such as bending a metal wire or molding clay. Understanding both the compositional and physical characteristics of the Earth’s interior lays the groundwork for the discussion about plate tectonics in Chapter 4; plate tectonics exerts a fundamental control on the distribution of Earth’s mineral, fossil fuel, and geothermal resources.
