Geology Reference
In-Depth Information
INTRODUCTION
Throughout this topic, we have emphasized that Earth is a dy-
namic planet, meaning that its internal heat and interacting
systems account for continual change. Some of the interac-
tions among Earth's systems do not take place at the same rate
that they did during early Earth history because the genera-
tion of heat within Earth has diminished. Accordingly, after
Earth formed and differentiated to form a core, mantle, and
crust, plates moved more rapidly, mountain building and con-
tinental accretion took place faster, and volcanism was more
widespread than it is now. Nevertheless, Earth is dynamic and
will remain so into the far distant future. The most important
message from this course is that continual change takes place,
although not always at a rate that we can readily appreciate
from a human lifetime. For example, the Himalaya Moun-
tains in Asia and the Andes Mountains in South America are
actively forming, but the net uplift (uplift minus erosion)
amounts to “only” a few millimeters per year. In the context of
geologic time, though, they are forming quite rapidly.
In this topic, we have investigated the two main subdivisions
of geology: physical geology (Chapters 1-17) and historical ge-
ology (Chapters 18-23). However, few of you will become pro-
fessional geologists, so the question to ask is how will you benefi t
from the information and insights you have gained from this
course? Many of you will enter professions that involve geologic
considerations—engineering, city planning, city or county gov-
ernment, and construction, but even if you do not, geology may
enrich your appreciation of the scenic wonders of our national
parks and monuments, as well as the nature of Earth wherever
you travel. Ten or twenty years from now, you probably will not
remember many specifi c geologic terms such as tombolo , cirque,
anticline , or barchan, but chances are, if you see these features,
you will still have a good idea of how they formed. You may not
remember the precise phrase principle of superposition , but
should you visit the Grand Canyon, you will no doubt fig-
ure out the relative ages of the exposed rock layers. And while
it is unlikely that you will recall the details of the Taconic
and Acadian orogenies, you probably will remember that the
Appalachian Mountains have a long, complex history of plate
collisions, uplift, and erosion.
One objective of this topic, and much of your secondary
education, is to develop your skills as a critical thinker. As op-
posed to simple disagreement, critical thinking involves evalu-
ating the supporting evidence for a particular point of view.
Although your exposure to geology is limited, you do have the
fundamental knowledge needed to appraise why geologists ac-
cept plate tectonic theory, why they think that Earth is 4.6 billion
years old, and why scientists are convinced that the theory of evo-
lution is well supported by evidence. In addition, your abilities as
a critical thinker will probably help you more effectively evaluate
the arguments about global warming, ozone depletion, ground-
water contamination, and many other environmental issues.
such features as faults are well exposed at Earth's surface,
such as mountains regions or where there are deep canyons.
However, geology is everywhere. Remember that in addition
to volcanoes, earthquakes, and mountain building, geologic
processes account for soils, river deltas, caverns, desert dunes,
weathering, and erosion, as well as landforms along shorelines.
In fact, you can see examples nearly everywhere, even in met-
ropolitan areas (
Figure 24.1a) and in the continental interior
(Figure 24.1b). Those of you living near seashores or lake-
shores have the opportunity to observe the interactions among
Earth's systems—wind (atmosphere), water (hydrosphere),
and Earth materials. And the same is true for those of you
who live in arid regions, where the same processes take place
as elsewhere, but wind is also important.
No doubt, you will travel for pleasure or as part of your
chosen profession and see such geologic wonders as the Grand
Canyon, Arizona, the Teton Range and Yellowstone National
Park in Wyoming, the Florida Keys, and the Great Lakes.
Figure 24.1 Geology All Around Us
a This roche moutonnée in Central Park in New York City is some
of the evidence that a continental glacier once covered this area.
This feature is much like the one shown in Figure 14.9a.
GEOLOGY IS ALL AROUND US
Many of the examples of geologic features and phenomena
that we used in this topic come from areas where rocks and
b These rocks are exposed at Black Mesa State Park in western
Oklahoma. In addition to the rocks, which were deposited in a sea
about 90 million years ago, fossil dinosaurs and petrifi ed wood have
been found in these rock layers.
 
Search WWH ::




Custom Search