1. The major differences between P and S waves is that P waves push and pull rocks in the direction the wave is traveling while S waves shake the particles at right angles to their direction of travel. Also, P waves can travel through solids, liquids, and gases while S waves can only travel through solids. P waves change the volume of the intervening material while S waves change only the shape of the material that transmits them.
2. The boundary between the crust and mantle (moho) differ from the boundaries that occur at depths of about 400 and 700 kilometers by at the boundary between the crust and the mantle has a sharp decrease in wave velocity which corresponds to the top of the low velocity zone caused by compositional differences while at depths of about 400 and 700 kilometers a bend in the velocity curve (decrease in wave velocity) occurs caused by the minerals that have undergone phase changes.
3. The lithosphere is the solid outer portion of the Earth and includes part of the upper mantle and the crust. The lithosphere is situated above the asthenosphere. The asthenosphere is located directly below the lithosphere at depths of about 100 kilometers and 700 kilometers. In the asthenosphere the velocity of S waves decreases indicating that it consists of partly melted rock.
4. The chemical (mineral) makeup of the inner core is iron, of the outer core is iron and nickel, of the mantle is iron, magnesium, and silicates (peridotite), and of the crust is basalt and granite.
5. It was difficult for seismologists to obtain precise travel-time data before the turn of the century because before the turn of the century seismologists didn’t have instruments that were precise enough to detect the seismic waves.
6. The method first used to accurately measure the size of the inner core was calculated in the 1960s when underground nuclear tests were conducted in Nevada. Because the precise locations and times of the explosions were known, echoes from the seismic waves which bounced off the inner core provided an accurate means of determining its size.
7. The first samples (in place) of the deep-ocean floor were obtained by the development of the deep-sea drilling ship Glomar Challenger.
8. The evidence that Gutenberg used for the existence of the Earth’s central core was the shadow zone could be explained if the Earth contained a core composed of material unlike overlying mantle with a radius of 3420 kilometers.
9. Suppose the shadow zone for P waves was located between 120 and 160 degrees, rather than between 105 and 140 degrees. This would indicate about the size of the core that the core is smaller than what would be with 105 and 140 degrees.
10. The asthenosphere is able to flow like a fluid yet has the ability to transmit S waves which cannot travel through fluids because the asthenosphere consists of partly melted rock that does not prevent but decreases the velocity of S waves.
11. Meteorites are considered important clues to the composition of the Earth’s interior because meteorites are part of the solar system which are assumed to be representative samples.
12. Evidence that is provided by seismology to indicate that the outer core is liquid is that S waves can not propagate through the core and P wave velocities suddenly drop as they enter the core. Other evidence that exists for a molten outer core is the Earth’s magnetic field. The most widely accepted mechanism for explaining the magnetic field requires that the Earth’s core be made of a material which conducts electricity such as iron and is mobile enough that circulation can occur.
13. It is possible for the outer core to be molten when the inner core (which has a higher temperature) is in the solid state because of the elasticity of the inner core material.