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Guide
to Reading 
If you’ve always thought that the study of Earth
is limited to identifying rocks and minerals, you’re in for some
surprises, starting with this chapter. Geology claims as subject
matter just about anything Earth-related. It’s a very eclectic subject
(composed of a broad selection of topics from many different sources).
With this in mind, begin reading Chapter 1, and note how it very
logically starts at the beginning of everything. Everything is literally
the Universe.
For thousands of years humans have sought to understand
the Universe they’re part of—its beginnings, structure, functioning,
and future. Today we term these studies cosmology. Many of the earliest
ideas were fanciful, revolving around gods and goddesses, though
there were also investigations of a more scientific nature. People
asked the right questions, made careful observations of natural phenomena,
used common sense and ingenuity, and came up with quite accurate
answers to some basic yet profound questions. Human history and this
chapter are both filled with many of these milestones of understanding.
Included in this chapter are discussions of the following:
- the use of parallax to figure distances to stars
- Ptolemy’s belief in an Earth-centered Universe
- the opposing belief in a Sun-centered Universe
- the recognition of Earth as a planet in a solar
system
- the discovery of galaxies, including our own Milky
Way
- Doppler’s explanation of wavelengths and frequencies
altered by moving sources
- the correlation between the Doppler effect and
the red shift of the expanding Universe
- the big bang theory of the beginning of the Universe
- the realization that stars have beginnings, lifetimes,
and deaths
- the process of element formation in stars
- the development of our round Earth and our planetary
system
- the origin of our Moon
After reading all of the above you may feel you’ve
had a crash course in astronomy. In a way you have, but you also
have established a firm foundation for your study of geology.
The chapter continues with an Overview—and an inner
view—of planet Earth. It starts miles high above Earth in the
vacuum of interplanetary space, then zooms you down through Earth’s
magnetic field, magnetosphere, and Van Allen radiation belts,
pausing in the
troposphere to comment on the obvious topography of Earth and the
great amount of hydrosphere covering Earth’s surface. The journey
continues, diving down below the ocean surface and progressing
through
Earth’s crust, mantle, and core.
Most of this section deals with the ocean bottom
and inner earth as preparation for plate tectonics theory, presented
in Chapter 2. The author discusses Earth’s composition (organic chemicals,
minerals, glasses, rocks, metals, melts, and volatiles) and layers
(oceanic and continental crust, the Moho, oceanic and continental
lithosphere, asthenosphere, upper mantle, transition zone, lower
mantle, outer core, and inner core.)
Few humans have visited the ocean bottom, and no
human has physically been more than 2 mi below Earth’s land surface.
How do we know what it’s like inside the Earth? Your author describes
scientists’ efforts to reach deep into Earth and discusses the various
approaches and scientific reasoning that have provided answers to
questions about composition, structure, and conditions within Earth.
These include the use of clues obtained from the study of earthquake
waves, seismic velocities, and meteorites.
There are lots of terms and many numbers involved
in this survey of Earth. Try not to get mired down in lists of rock
types or thickness of layers. Instead concentrate on the thought
processes necessary to analyze something you can neither see nor
touch and on the truly amazing world that exists under your feet.
John Milton’s underworld of the 1600s and Jules Verne’s fanciful
journey of the 1800s were tame compared to the real thing. They imagined
exotic versions of environments on Earth’s surface, all places within
the realm of human experience. The real interior of Earth is beyond
any human’s experience. It’s a place of awesome pressures and temperatures,
much closer than the stars but just as unreachable. Truth can certainly
be stranger than fiction.
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Key Terms
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