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Learning Objectives
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Learning Objectives

1. Geology is the scientific study of the earth. Physical geology is that division of geology concerned with earth materials, changes in the surface and interior of the earth, and the dynamic forces that cause those changes.

2. Earthquakes, like Northridge, reflect the sudden release of energy along faults that respond to plate motions.

3. Not all geologic hazards are immediately apparent. For example, most of the deaths associated with the 1985 eruption of the Nevado del Ruiz volcano in Columbia were caused by a mudflow.

4. Western economic systems depend on abundant supplies of cheap energy.

5. Most geological resources are nonrenewable and their extraction poses potential ecologic damage.

6. Knowledge of geology can enhance appreciation of one's surroundings, such as the scenery produced as mountains are eroded.

7. Earth processes are driven by two heat engines: one that is internal powered by heat from the earth's core; one that is external powered by the sun.

8. The earth's interior comprises three concentric zones: crust (thin, oceanic crust and thicker, continental crust), mantle (solid and thickest zone), and core. Lithosphere is the crust and upper mantle that is broken into plates. Asthenosphere is the soft, "lubricating" layer beneath lithosphere upon which the plates move. Tectonic forces cause vertical and horizontal deformation from forces within the earth.

9. Plate tectonics is a theory that views the earth's lithosphere as broken into plates that are in motion. At mid-oceanic-ridges, plate boundaries are diverging because magma rises from the asthenosphere, pushes the ridge crests apart, and solidifies in the fissures created. Ridges spread at a rate of 1-18 centimeters per year. Transform boundaries occur where plates slide past each other, such as the San Andreas fault. Converging boundaries reflect subduction, where oceanic plates descend into the mantle creating either extrusive or intrusive igneous rocks from melting at depth. Metamorphic rocks may be formed from high-temperature and pressure at subduction zones, if melting does not occur.

10. Rocks formed within the earth are pushed to the surface by tectonic forces. They are unstable and reach equilibrium as new materials formed by the affects of water, solar heating and other surficial processes. Removal of this material, called sediment, by agents of erosion transports it to a site of deposition where it may become sedimentary rock, when lithified.

11. Geology follows the scientific method (see Box 1.3).

12. Geology involves deep time, vastly greater than human lifetimes or even human contemplation. The earth is about 4.5 billion years old. Most geological processes are slow and take place over many million years. Fast, to a geologist, is an event or process completed in a million years or less. Plate motions are relatively fast. Complex life forms have existed on the earth for the past 545 million years. Humans have only been on earth for about 3 million years. Geology follows the scientific method (see Box 1.3).








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