Passage VI

Earth's interior is divided into 4 primary layers of different chemical composition: the crust, mantle, outer core, and inner core. Figure 1 shows the 4 layers, their depths, and 2 named layer boundaries (Moho and Gutenberg Discontinuity). The lithosphere, asthenosphere, and transition zone boundaries were determined using speed changes in S waves, a type of earthquake wave. Speed changes indicate a phase and/or density change of material inside Earth.

Figure 2 shows how P-wave (another earthquake wave type) and S-wave velocities and density change with depth inside Earth.

Figure 3 shows how Earth's temperature changes with depth.