Geology Reference
In-Depth Information
planets evolved from a turbulent, rotating cloud of
material surrounding the embryonic Sun.
Earth consists of three concentric layers—core, man-
tle, and crust—and this orderly division formed dur-
ing Earth's early history.
Plate tectonics is the unifying theory of geology and
this theory revolutionized the science.
The rock cycle illustrates the interrelationships
between Earth's internal and external processes and
shows how and why the three major rock groups are
related.
The theory of organic evolution provides the concep-
tual framework for understanding the history of life.
An appreciation of geologic time and the principle
of uniformitarianism is central to understanding the
evolution of Earth and its biota.
Geology is an integral part of our lives.
all interconnected in such a way that a change in any one of
them affects the others.
We can examine Earth in the same way we view an
automobile—that is, as a system of interconnected compo-
nents that interact and affect each other in many ways. The
principal subsystems of Earth are the
atmosphere
,
biosphere
,
hydrosphere
,
lithosphere
,
mantle
, and
core
(
■
Figure 1.1). The
complex interactions among these subsystems result in a
dynamically changing planet in which matter and energy is
continuously recycled into different forms (Table 1.1). For
example, the movement of plates has profoundly affected
the formation of landscapes, the distribution of mineral re-
sources, and atmospheric and oceanic circulation patterns,
which, in turn, have affected global climate changes.
We must also not forget that humans are part of the
Earth system, and our activities can produce changes with
potentially wide-ranging consequences. When people discuss
and debate such environmental issues as acid rain, the green-
house effect and global warming, and the depleted ozone
layer, it is important to remember that these are not isolated
issues, but are part of the larger Earth system. Furthermore,
remember that Earth goes through time cycles that are much
longer than humans are used to. Although they may have
disastrous short-term effects on the human species, global
warming and cooling are also part of a longer-term cycle that
has resulted in many glacial advances and retreats during the
past 1.8 million years.
Accordingly, we must understand that actions we take
can produce changes with wide-ranging consequences that
we might not initially be aware of. For this reason, an under-
standing of geology, and science in general, is of paramount
importance. If the human species is to survive, we must un-
derstand how the various Earth systems work and interact
and, more importantly, how our actions affect the delicate
balance between these systems.
As you study the various topics covered in this topic, keep
in mind the themes discussed in this chapter and how, like the
parts of a system, they are interrelated. By relating each chap-
ter's topic to its place in the entire Earth system, you will gain a
greater appreciation of why geology is so integral to our lives.
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A major benefi t of the space age has been the ability to look
back from space and view our planet in its entirety. Every as-
tronaut has remarked in one way or another on how Earth
stands out as an inviting oasis in the otherwise black void of
space (see this chapter's opening photograph). We are able to
see not only the beauty of our planet, but also its fragility. We
can also decipher Earth's long and frequently turbulent his-
tory by reading the clues preserved in the geologic record.
A major theme of this topic is that Earth is a complex, dy-
namic planet that has changed continuously since its origin
some 4.6 billion years ago. These changes and the present-
day features we observe result from the interactions among
Earth's internal and external systems, subsystems, and cycles.
Earth is unique among the planets of our solar system in that
it supports life and has oceans of water, a hospitable atmo-
sphere, and a variety of climates. It is ideally suited for life
as we know it because of a combination of factors, includ-
ing its distance from the Sun and the evolution of its interior,
crust, oceans, and atmosphere. Life processes have, over time,
infl uenced the evolution of Earth's atmosphere, oceans, and,
to some extent, its crust. In turn, these physical changes have
affected the evolution of life.
By viewing Earth as a whole—that is, thinking of it as
a system—we not only see how its various components are
interconnected, but also better appreciate its complex and
dynamic nature. The system concept makes it easier for us
to study a complex subject such as Earth because it divides
the whole into smaller components that we can easily un-
derstand, without losing sight of how the components fit
together as a whole.
A
system
is a combination of related parts that inter-
act in an organized manner. An automobile is a good ex-
ample of a system. Its various components or subsystems,
such as the engine, transmission, steering, and brakes, are
Geology
, from the Greek
geo
and
logos
, is defi ned as the study
of Earth, but now must also include the study of the planets
and moons in our solar system. It is generally divided into two
broad areas—physical geology and historical geology.
Physi-
cal geology
is the study of Earth materials, such as minerals
and rocks, as well as the processes operating within Earth and
on its surface.
Historical geology
examines the origin and evo-
lution of Earth, its continents, oceans, atmosphere, and life.
The discipline of geology is so broad that it is subdivided
into numerous fields or specialties. Table 1.2 shows many
of the diverse fi elds of geology and their relationship to the
sciences of astronomy, biology, chemistry, and physics.
Nearly every aspect of geology has some economic or
environmental relevance. Many geologists are involved in
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