Fall 2001: PSC2121 Homework Assignments
Solutions due Dec 4, Ch. 22, 23, and 24

Ch. 22:

1. Information about the earth's interior comes primarily from the study of seismic waves (sound vibrations): their speed of travel, reflections, and polarization (transverse or longitudinal).

2. The outer core does not transmit S waves (transverse) and is, therefore, believed to be liquid.

5. From outer to inner the major zones of the earth are crust, mantle, core.

7. A rock is a heterogeneous (non-uniform) mixture of minerals in varying proportions. A mineral is a naturally occurring homogenous (uniform) substance with well-defined chemical composition, crystal structure, and physical properties.

12. The outer core is liquid, the inner core is solid, but close to melting.

13. The inner regions of the earth are denser than outer layers. The core is denser than the mantle.

16. Lava is the molten material (including gases) that flows out of volcanic vents and fissures. Magma is the name for the same material while still below the surface where the gas concentration is higher.

23. Sea floor spreading provides the large forces and energy necessary to move the plates.

24. Molten rock from the mantle rises up along a crack-like valley on the mid-oceanic ridge, then spreads and hardens into new ocean floor. Thus, the ocean floor nearest the mid-oceanic ridge is among the youngest part of the earth's crust.

26. Continents float and slide along the mantle with only a small portion above water level in much the same way that icebergs float mostly submerged on the ocean surface.

27. Convergent plate boundaries occur when two plates come together and the crust is thickened (Himalayas).
Divergent plate boundaries are where new crust is created as plates move away from each other (mid-oceanic ridge).
Transform or Transcurrent boundaries occur when two adjacent plates slide past each other (San Andreas fault).

29. Earthquakes are caused when strain in the crust (due to plate motion and forces) is suddenly released by movement along a fault.

32. Body waves move through the interior of the earth. They may be P waves (fast longitudinal) or S waves (slower transverse). Surface waves move only along the surface of the earth. R (Raleigh) surface waves have an elliptical motion. L (Love) surface waves vibrate horizontally perpendicular to the direction of wave propagation.

34. Since the reactions of chemical weathering usually involve water, they occur most rapidly in a humid environment.

38. Although weathering and erosion smooth the continents, the process is extremely slow and new mountains and features are continually being created.

39. A. (b) B. (c) C. (b) D. (b) E. (c)

Ch. 23:

1. Water covers 71% of the earth's surface as a liquid shell or "hydrosphere".

3. The average depth of the oceans is about 4 km whereas the average height of the continents above sea level is only 0.875 km.

5. More than 99% of the heat entering the sea comes from sunlight which is absorbed near the surface. Heat is also lost from the surface as water evaporates. Below 2 km the temperature of the oceans is just slightly above freezing world-wide. Thus, the oceans provide a large reservoir of cold water.

6. Light traveling through sea water becomes progressively dimmer through absorption and scattering. Less than 50% penetrates below 1 m and only 2% may be present below 30 m.

11. The gently sloping continental shelf extends from the shore out to the steeper continental slope that descends to the deep sea floor.

15. The youngest parts of the ocean floor are near the mid-ocean ridges (diverging plate boundaries) where new ocean floor is being created.

17. The mid-oceanic ridges represent divergent plate boundaries where the plates are being pushed apart, The trenches occur at convergent plate boundaries.

25. A. (c) B. (b) C. (a) D. (c) E. (a)

Ch. 24:

1. Nitrogen (N2 78%) Oxygen (O2 21%) Argon (Ar 1%)

3. Hydrogen and helium are the lightest gases and the earth's gravity is not strong enough to capture them.

7. (a) The "greenhouse effect" refers to the property of water (H2O) and carbon dioxide (CO2) in the atmosphere to allow the passage of visible light through the atmosphere to the earth, but prevent the escape of infrared energy from the earth into space. Like a green house, the atmosphere can trap heat near the earth's surface.
(b) A small rise in temperature at the earth's surface can drastically effect weather patterns and crop growth, melt polar ice caps, and cause substantial rises in ocean water levels that will flood many coastal communities.

8. Ozone absorbs much of the sun's ultraviolet radiation and prevents it from reaching the surface of the earth. UV radiation is dangerous to many forms of life since it causes skin cancer and destroys or alters genetic material.

10. The free electrons and positive ions in the ionosphere provide an electrically conducting shell that can reflect radio waves around the curvature of the earth.

15. The gravitational attraction of the earth causes the densest layers of the atmosphere to be near the surface and the least dense (lightest) to be furthest away. The air pressure at any height represents the weight of all of the atmosphere above that height.

17. At high altitudes the air pressure decreases and the boiling point of water also decreases. Thus, foods cooked in boiling water at high altitudes are cooked at a lower temperature.