1. Describe how seismic reflection and seismic refraction show the presence of layers within Earth.

When seismic waves encounter a rock of a different density, it may reflect off of that layer, or bend as it travels across the  boundary.  By noting these patterns of reflection and refraction, one can determine the presence and depth of layers within Earth.

2. Sketch a cross section of the entire Earth showing the main subdivisions of Earth's interior and giving the name, thickness, and probable composition of each.

See figure 17.7 on pg. 423

3. What fact make it probable that Earth's core is composed of mostly iron?

Estimations of the density, the existence and composition of iron meteorites, and the presence of a magnetic field on Earth suggest that the core must be made up mostly of iron.

4. Describe the differences between continental crust and oceanic crust.

Oceanic crust is thinner, ~7 km, denser, and composed of basalt-like rock.  Continental crust is thicker (30-50 km) less dense than oceanic crust, and is composed of granite-like rock, covered with sedimentary rock.

6.  Discuss seismic-wave shadow zones and what they indicate about Earth's interior.

For P-waves, there is a shadow zone in Earth ranging in an arc from 103^o to 142^o from the epicenter of the quake.  This shadow zone is explained by the refraction (bending) of P waves when they encounter the core boundary.  S-waves are known to not travel through liquid.  There is an S-wave shadow zone in which S-waves do not occur beyond 103^o from the epicenter

7.  Describe Earth's magnetic field.  Where is it generated?

It is a region of magnetic force that surrounds Earth.  Its invisible lines of magnetic force surround Earth and deflect magnetized objects, such as compass needles.  Earth's magnetic field is strongest at the magnetic poles, where magnetic lines of force appear to leave and enter Earth vertically.

It is likely generated within the liquid metal of the outer core.

    The lithosphere consists of  crust and mantle and is relatively strong and brittle.  The asthenosphere consists of mantle rocks just below the lithosphere, where the rocks appear to have ductile behavior.  It is possible that the asthenosphere represents partial melting of a very small percentage.

Last update 2/24/2005
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