1. Figure 1.6c: The Earth is a compositionally stratified planet with an overall density of 5.5 g/cm3 and has a radius of 6500 km. The major subdivisions are the crust, mantle, outer core and inner core. The earth is in turn surrounded by an atmosphere.

2. Figure 1.11: The earth’s crust is defined as the veneer of rocky material that surrounds the planet. The crust ranges in thickness from 0-10 km beneath the oceans and 33-70 km beneath the continents. The bulk composition of crust beneath the oceans is close to that of basalt, a black rock formed by solidification of volcanic lava, whereas continental crust has an average composition of granite, a light-colored rock formed through crystallization of molten magma deep within the crust.

3. Figure 1.7: Comparison of the composition of the whole earth versus that of the crust.

4. Figure 1.11: The lithosphere encompasses the crust and the top portion of the mantle.

5. The base of the lithosphere is marked by the upper boundary of the asthenosphere or low-velocity zone. The low-velocity zone is a region of partly molten (~3% partial melt) mantle material and is distinguished by a significant reduction in the velocity of seismic waves, particularly shear waves which are attenuated (slowed down) in this region due to the presence of partial melt.

6. Figure 1.11: The rigid lithosphere, gliding over a layer of partly molten asthenosphere, resulted in the lithosphere being broken into a series of independent plates. The boundaries between plates are defined by spreading ridges, trenches and transform faults.

7. Figure 1.12: The surface of the earth can therefore be envisioned as a mosaic of independent plates.

8. Figure 1.14: The boundaries between plates are marked by zones where the plates are either pulling apart (divergent boundary), pushing together (convergent boundary), or slipping past one another (transform boundary).

9. Figure 1.14: Divergent boundaries are generally defined by mid-ocean ridges, lines of mountainous terraine beneath the oceans where extensive undersea volcanism often occurs.

10. Figure 1.16: Convergent boundaries are generally defined as zones where one plate subducts beneath another. Convergent boundaries are often marked by deep-sea trenches and associated explosive volcanism and mountain building.

11. Figure 1.14b: Transform boundaries are often characterized as lines of frequent earthquakes such as occurs along the San Andreas Fault system in California (Fig. 1.17).

12. Figure 19.4: The mantle is composed of peridotite, a dark-green rock composed primarily of Si, O, Mg and Ca.

13. Figure 19.4: The earth’s mantle extends down to 2900 km depth where it meets the outer core, the source of the earth’s magnetic field. The outer core extends from 2900 -5100 km depth and consists mainly of molten Fe. The outer core surrounds the inner core that is composed mostly of solid Fe and Ni.