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).
