Download Chapter 1.2 - Planet Earth

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Section 1.2
1.2 A View of Earth
1 FOCUS
Section Objectives
Key Concepts
What are the four major
spheres into which Earth
is divided?
What defines the three
main parts of the solid
Earth?
Which model explains the
position of continents and
the occurrence of
volcanoes and
earthquakes?
Vocabulary
◆
◆
◆
◆
◆
◆
◆
hydrosphere
atmosphere
geosphere
biosphere
core
mantle
crust
Reading Strategy
1.3
Predicting Before you read, predict the
meaning of the vocabulary words. After you
read, revise your definition if your prediction
was incorrect.
1.4
1.5
Vocabulary Term Before You Read After You Read
hydrosphere
a.
?
b.
atmosphere
c.
?
d.
?
?
geosphere
e.
?
f.
?
biosphere
g.
?
h.
?
core
i.
?
j.
?
mantle
k.
?
l.
?
crust
m.
n.
?
?
Reading Focus
Build Vocabulary
Earth’s Major Spheres
The view of Earth shown in Figure 5B should help you see why the
physical environment is traditionally divided into three major spheres:
the water portion of our planet, the hydrosphere; Earth’s gaseous
envelope, the atmosphere; and the geosphere.
Our environment is characterized by the continuous interactions of
air and rock, rock and water, and water and air. The biosphere, which is
made up of all the life-forms on Earth, interacts with all three of these
physical spheres.
Earth can be thought of as consisting of four major
spheres: the hydrosphere, atmosphere, geosphere, and biosphere.
Reading Strategy
B
Figure 5 A View that greeted
the Apollo 8 astronauts as their
spacecraft emerged from behind
th Moon. B Africa and Arabia are
prominent in this image of Earth
taken from Apollo 17. The tan
areas are desert regions. The
bands of clouds over central
Africa are associated with
rainforests. Antarctica, which is
covered by glacial ice, is visible at
the south pole. The dark blue
oceans and white swirling clouds
remind us of the importance of
oceans and the atmosphere.
Introduction to Earth Science
L2
Word Parts Explain to students that
hydro- relates to water and atmosrelates to air. Have them use this
information, along with prior
knowledge, to predict the meaning of
the vocabulary words for this section.
A
view such as the one in Figure 5A provided
the Apollo 8 astronauts with a unique view of
our home. Seen from space, Earth is breathtaking in its beauty. Such an image reminds us that
our home is, after all, a planet—small, self-contained, and in some ways even fragile.
If you look closely at Earth from space, you
may see that it is much more than rock and soil. A
The swirling clouds and the vast global ocean
emphasize the importance of water on our planet.
Describe Earth’s four major
spheres.
Differentiate among the three
parts of the geosphere.
State the value of the theory
of plate tectonics to Earth
Science.
7
L2
Sample answer:
a. ball of water
b. all water on Earth
c. ball of air
d. gaseous envelope surrounding Earth
e. ball of rock
f. solid part of Earth below the
atmosphere and oceans
g. ball of living things
h. all life on Earth
i. center of Earth
j. dense inner sphere
k. ledge
l. less dense middle layer
m. outer envelope
n. light, thin outer layer
2 INSTRUCT
Earth’s Major Spheres
Use Visuals
L1
Figure 5 This image of Earth was taken
by astronauts in space. Ask: Which
of Earth’s features are visible from
space? (oceans, continents, clouds)
What does the color of the land that
is visible tell you about the climate in
those regions? (Brown indicates a desert
climate. Green indicates a wet climate.)
What other Earth features do you
think would be visible from space?
(smoke from forest fires and city lights at
night) Who might find images from
space useful? (meteorologists, geologists,
oceanographers)
Visual, Verbal
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Section 1.2 (continued)
Build Reading Literacy
Hydrosphere Water is what makes Earth unique. All of the water
on Earth makes up the hydrosphere. Continually on the move, water
evaporates from the oceans to the atmosphere, falls back to Earth as
rain, and runs back to the ocean. The oceans account for approximately 97 percent of the water on Earth. The remaining 3 percent is
fresh water and is present in groundwater, streams, lakes, and glaciers.
Although these freshwater sources make up a small fraction of the
total amount of water on Earth, they are quite important. Streams, glaciers, and groundwater are responsible for sustaining life and creating
many of Earth’s varied landforms.
L1
Refer to p. 1D, which provides
guidelines for guided anticipation.
Anticipation Guide Ask students to
respond to the following questions in
writing before they read this section.
Have students check their answers and
make changes as needed after they
finish reading the section. Students
should answer True or False to the
following series of statements:
• The atmosphere contains all of the
water on Earth. (F)
• Groundwater is part of Earth’s
hydrosphere. (T)
• Earth’s atmosphere does nothing to
protect us from the sun’s radiation. (F)
• There is no crust under Earth’s oceans.
(F)
• Earth’s crust is the same thickness
under land as under water. (F)
• The only layer of Earth that is solid is
the crust. (F)
• The biosphere affects all other spheres
of Earth. (T)
Verbal
Figure 6 A On this diagram, the
inner core, outer core, and mantle
are drawn to scale but the
thickness of the crust is
exaggerated by about 5 times.
B There are two types of crust—
oceanic and continental. The
lithosphere is made up of the
crust and upper mantle. Below the
lithosphere are the asthenosphere
and the lower mantle.
A
Earth’s Layers
L2
Lower Mantle
Purpose Provide students with a threedimensional model of Earth’s layered
structure.
Inner
core
Materials hard-boiled egg, knife
Procedure Show students a hardboiled egg. Crack the shell in several
places so pieces of shell can slide a bit
over the white of the egg. Tell students
the shell of the egg represents Earth’s
crust, which is a thin layer, cracked and
broken into plates that can move. Cut
the egg in half. Show students that the
white of the egg represents Earth’s
mantle, and the yolk of the egg
represents Earth’s core.
Expected Outcome Students will be
able to relate the structure of the egg to
the structure of Earth and can use this
representation to create a mental model
of what Earth’s layers look like.
Visual, Logical
8
Chapter 1
Outer
core
0
122
km
0
226
km
Atmosphere A life-sustaining, thin, gaseous envelope called the
atmosphere surrounds Earth. It reaches beyond 100 kilometers above
Earth, yet 90 percent occurs within just 16 kilometers of Earth’s surface. This thin blanket of air is an important part of Earth. It provides
the air that we breathe. It protects us from the sun’s intense heat and
dangerous radiation. The energy exchanges that continually occur
between space, the atmosphere, and Earth’s surface produce weather
and climate.
If Earth had no atmosphere, life on our planet as we know it could
not exist. Many of the processes and interactions that make the surface
such a dynamic place would not occur. For example, without weathering and erosion, the face of our planet might more closely resemble
the moon.
Geosphere Lying beneath both the atmosphere and the ocean is the
geosphere.
Because the geosphere is not uniform, it is divided into
three main parts based on differences in composition—the core, the
mantle, and the crust. Figure 6A shows the dense or heavy inner sphere
that is the core; the less dense mantle; and the lighter, thin crust. The crust
is not uniform in thickness. It is thinnest beneath the oceans and thickest beneath the continents. Figure
Crust 5–70 km
6B shows that the crust and
B
Upper
Mantle
uppermost mantle make up a
Continental
Oceanic
crust
rigid outer layer called the lithocrust
sphere. Beneath the lithosphere,
0
Lithosphere
the rocks become partially
289
km
100
molten, or melted. They are able
to slowly flow because of the
Asthenosphere
200
uneven distribution of heat deep
Upper
within Earth. This region is called
Mantle
300
the asthenosphere. Beneath the
asthenosphere, the rock becomes
660
more dense. This region of Earth
is called the lower mantle.
Depth (km)
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Customize for Inclusion Students
Learning Disabled Have learning disabled
students draw labeled pictures illustrating each
of Earth’s four major spheres: hydrosphere,
atmosphere, geosphere, and biosphere. Be
sure they include Earth’s layers in their sketch
of the solid Earth. They can use Figure 6 as a
guide.
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Build Science Skills
Biosphere The biosphere includes all life on Earth. It is concentrated in a zone that extends from the ocean floor upward for several
kilometers into the atmosphere. Plants and animals depend on the
physical environment for life. However, organisms do more than just
respond to their physical environment. Through countless interactions, organisms help maintain and alter their physical environment.
Without life, the makeup and nature of the solid Earth, hydrosphere,
and atmosphere would be very different.
What are Earth’s four major spheres?
North
American
plate
North
American
plate
Eurasian plate
Caribbean
plate
Juan de
Fuca
plate
African plate
Cocos
plate
Pacific plate
Arabian
plate
Nazca
plate
South
American
plate
Philippine
plate
Pacific
plate
Australian plate
Antarctic plate
Plate Tectonics
You have read that Earth is a dynamic planet. If we could go back in
time a billion years or more, we would find a planet with a surface that
was dramatically different from what it is today. Such prominent features as the Grand Canyon, the Rocky Mountains, and the Appalachian
Mountains did not exist. We would find that the continents had different shapes and were located in different positions from those of today.
There are two types of forces affecting Earth’s surface. Destructive
forces such as weathering and erosion work to wear away high points
and flatten out the surface. Constructive forces such as mountain building and volcanism build up the surface by raising the land and
depositing new material in the form of lava. These constructive forces
depend on Earth’s internal heat for their source of energy.
Convergent plate boundaries
Divergent plate boundaries
Transform plate boundaries
Figure 7 Plate Tectonics There
are currently 7 major plates
recognized and numerous smaller
plates.
Relating Cause and Effect
What is the relationship between
mountain chains and plate
boundaries?
Making Judgments Present groups
with the questions below. Challenge
them to reach a consensus answer to
each question. Once all groups have
finished, have one student in each
group present the results. Ask: How
does the hydrosphere, atmosphere,
and geosphere affect the biosphere?
(Flooding, tornadoes, hurricanes, volcanoes,
and earthquakes have caused loss of life
and habitat.) How do members of the
biosphere affect the geosphere?
(Humans have dug mines into the crusts.
Burrowing animals also affect the solid
Earth, though often in more of a
temporary way.) How do members
of the biosphere affect the
hydrosphere and atmosphere?
(Humans have polluted both water and
air. Human-made dams and those built by
beavers can have a dramatic effect on the
flow of rivers.) Does the biosphere
influence the other spheres more
than the other spheres influence the
biosphere? Explain your answer.
(Students can answer either way as long
as they have solid reasoning to support
their decision. For example, when changes
in the other spheres threaten the biosphere,
humans usually find a way to adjust to the
changes. However, the other spheres are
not always able to respond to human
efforts.)
Verbal
Plate Tectonics
Build Reading Literacy
L1
Refer to p. 362D in Chapter 13, which
provides guidelines for using prior
knowledge.
Introduction to Earth Science
9
Facts and Figures
It is important to note that the “solid Earth” is
not really all solid. The crust, mantle, and inner
core are solid, but the outer core is liquid. In
addition, a tiny part of Earth’s mantle (in the
astherosphere) is molten, which gives rise to
L2
the lava that flows out of volcanoes. Scientists
have inferred the state of matter for each of
Earth’s layers by studying the paths that
seismic waves take through Earth.
Use Prior Knowledge Based on their
previous experiences with words such as
construction and destroy, have students
predict the definitions of the terms
constructive forces and destructive forces.
Help students see this connection and
then check that they understand both
terms by asking them to list some
destructive forces and some constructive
forces.
Verbal
Answer to . . .
Figure 7 Mountain chains are often
found along plate boundaries.
The four major spheres
are the hydrosphere,
atmosphere, geosphere, and biosphere.
Introduction to Earth Science 9
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Section 1.2 (continued)
Convection and Plates
Within the last several decades, a great deal has been learned about
the workings of Earth. In fact, this period is called a revolution in our
knowledge about Earth. This revolution began in the early part of the
twentieth century with the idea that the continents had moved about
the face of the Earth. This idea contradicted the accepted view that the
continents and ocean basins are stationary features on the face of
Earth. Few scientists believed this new idea. More than 50 years passed
before enough data were gathered to transform this hypothesis into a
widely accepted theory.
The theory that finally emerged, called
plate tectonics, provided geologists with a model to explain how
earthquakes and volcanic eruptions occur and how continents move.
L2
Purpose Students observe how heat
from within Earth can move plates.
Materials hot plate; deep, wide glass
container such as a lasagna pan; diluted
tomato soup; large, thin sponges;
scissors; tongs
Procedure Fill the container about
halfway with tomato soup, and put it
on the hot plate. Slowly heat it until
convection cells form (soup rising in the
center and falling at the edges). While
the soup is heating, cut various rough
plate shapes out of the sponges. Use the
tongs to place the sponges on the
surface of the soup. Have students
observe what happens to the sponges.
(If necessary, review the concept of
convection.) Ask: Why is the soup
moving? (Heat from below creates
convection cells.) Why do the “plates”
move? (The moving soup carried the
plates along with it.) How is the actual
movement of Earth’s plates different
from this demonstration? (The molten
rock in the mantle is solid, and therefore
slower-moving than the soup, and so the
actual plates move much more slowly.)
Safety Caution students not to touch
the hot container or soup.
Expected Outcome The heat will
create convection cells that move the
sponges around.
Visual, Logical
What is the difference between destructive forces
and constructive forces?
According to the plate tectonics model, Earth’s lithosphere is broken
into several individual sections called plates. Figure 7 on page 9 shows
their current position. These plates move slowly and continuously
across the surface. This motion is driven by the result of an unequal
distribution of heat within Earth. Ultimately, this movement of Earth’s
lithospheric plates generates earthquakes, volcanic activity, and the
deformation of large masses of rock into mountains. You will learn
more about the powerful effects of plate tectonics in Chapter 9.
Section 1.2 Assessment
Reviewing Concepts
1.
2.
3.
4.
5.
6.
L2
Have students make posters showing
Earth’s layers and spheres. Students
should label their drawings with the
terms crust, mantle, core, hydrosphere,
biosphere, and atmosphere.
Reteach
L1
Use Figure 7 to review Earth’s plates and
the concept of plate tectonics.
Students’ answers could include
discussions of the hydrosphere (sea level
changes), atmosphere (weather and
climate changes), geosphere (erosion of
topsoil, earthquake occurrence), and
biosphere (evolution of living things).
10
Chapter 1
7. Inferring Using the definitions of spheres as
they occur on Earth, what spheres do you
think are present on Venus?
8. Applying Concepts Describe a situation in
which two or more of Earth’s spheres are
interacting.
9. Classifying Choose an Earth science branch.
List how some of its studies relate to Earth’s
spheres.
Earth’s Spheres You learned in Section 1.1
that Earth is a dynamic planet. Explain
how features in each of Earth’s spheres are
changing over time.
3 ASSESS
Evaluate
Understanding
Critical Thinking
Which of Earth’s spheres do each of these
features belong: lake, meadow, canyon, cloud?
What are the three main parts of the
geosphere?
Why is the solid Earth layered?
The plate tectonics theory explains the
existence and occurrence of what features?
What sort of energy allows the tectonic plates
to move?
Describe an example of how water moves
through the hydrosphere.
10 Chapter 1
Section 1.2 Assessment
1. lake: hydrosphere, meadow: geosphere,
canyon: geosphere, cloud: atmosphere
2. The three main parts of the geosphere are
the core, mantle, and crust.
3. The layers formed because of density differences in the materials that made up early
Earth.
4. Plate tectonics explains mountains,
continents, ocean basins, earthquakes,
and volcanoes.
5. Plate tectonics depends on Earth’s internal
heat.
6. Sample answer: Water in a lake evaporates
into the atmosphere. The water vapor condenses and falls from the clouds into the lake
as rain and the cycle begins again.
7. geosphere, atmosphere
8. Sample answer: waves (hydrosphere)
crashing onto the shore (geosphere); birds
(biosphere) flying in the sky (atmosphere)
9. Sample answer: meteorology: cloud
cover—atmosphere; rain storms—hydrosphere
and atmosphere