Laboratory Manual for Introductory Geology 4e

■ Rotation: The Earth rotates about its axis in 1 day (24 hours or 86,400
seconds).
■ Shape: The Earth is almost, but not quite, a sphere. The Earth’s rotation produces
a slight bulge at the equator: its equatorial radius of 6,400 km (∼4,000 mi) is
21 km (∼15 mi) longer than its polar radius.
■ Temperature: The Earth’s average surface temperature is 15°C (59°F); its core
temperature is about 5,000°C (∼9,000°F).
■ Highest mountain: The peak of Mt. Everest is the Earth’s highest point, at 8,850 m
(29,035 ft) above sea level (and is still rising!).
■ Average ocean depth: 4,500 m (14,700 ft).
■ Deepest part of ocean floor: The bottom of the Mariana Trench in the Pacific Ocean
is the deepest point on the ocean floor, at 11,033 m (35,198 ft) below sea level.
1.4 The Challenges of Studying an Entire Planet
Problems such as submergence along the Maine coast pose challenges to the geologists
who are trying to solve them and the students who are trying to learn about the
Earth. These challenges require us to
■ understand the many kinds of materials that make up the Earth and how
they behave.
■ be aware of how energy causes changes at the Earth’s surface and beneath it.
■ consider features at a wide range of sizes and scales—from the atoms that
make up rocks and minerals to the planet as a whole.
■ think in four dimensions, because geology involves not just the three
dimensions of space but also an enormous span of time.
■ realize that some geologic processes occur in seconds but others take
millions or billions of years, and are so slow that we can detect them only
with very sensitive instruments.
The rest of this chapter examines these challenges and how geologists cope with
them. You will learn basic geologic terminology and how to use tools of observation
and measurement that will be useful throughout your geologic studies. Some concepts
and terms may be familiar from previous science classes.
1.4.1 The Challenge of Scale
Geologists deal routinely with objects as incredibly small as atoms and as incredibly
large as the Appalachian Mountains or the Pacific Ocean. Sometimes we have to
look at a feature at different scales, as in FIGURE 1.6, to understand it fully.
One of the challenges we face in studying the Earth is a matter of perspective:
to a flea, the dog on which it lives is its entire world, but to a parasite inside
the flea, the flea is its entire world. For most of our history, humans have had a
flea’s-eye view of the Earth, unable for many centuries to recognize even the most
basic facts about our planet: that it is nearly spherical, not flat, and that it isn’t the
center of the Universe, or even the Solar System. Nor that as we sit at a desk, we
are actually moving thousands of miles per hour because of the Earth’s rotation
and orbit around the Sun. Exercise 1.7 provides some perspective on the matter
of perspective.
We must cope with enormous ranges in scale involving size (atoms to sand grains
to planets), temperature (below 0°C in the cryosphere and upper atmosphere to
more than 1,000°C in some lavas to millions of degrees Celsius in the Sun), and
1.4 THE CHALLENGES OF STUDYING AN ENTIRE PLANET
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