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Section 14.1
14.1 The Vast World Ocean
1 FOCUS
Section Objectives
14.1
14.2
14.3
14.4
Recognize that most of Earth’s
surface is covered by water.
List Earth’s four main ocean
basins and identify their
locations.
Describe the topography of
the ocean floor and compare
it to land.
Identify and describe three
major technologies used to
study the ocean floor.
Key Concepts
How much of Earth’s
surface is covered by
water?
How can the world ocean
be divided?
Vocabulary
◆
◆
◆
◆
How does the topography
of the ocean floor
compare to that on land?
What types of technology
are used to study the
ocean floor?
Reading Focus
Build Vocabulary
L2
North
Pole
a. science that studies all aspects of the
world’s ocean
b. measurement of ocean depths and
charting the shape of the ocean floor
c. echo sounding to measure ocean depth
d. small underwater craft used for
deep-sea research
One Ocean
Figure 1 The World Ocean These views
of Earth show the planet is dominated by
a single interconnected world ocean.
L2
Purpose Students see how Earth’s
ocean basins are connected.
Materials world globe
Procedure Have students point out
the regions on the globe where oceans
connect.
Expected Outcome Students will
see that the Atlantic, Pacific, and Indian
Oceans connect in the region
surrounding Antarctica. The Atlantic
and Pacific Oceans connect
with the Arctic Ocean.
Visual, Logical
394 Chapter 14
South
Pole
Southern
Hemisphere
The Blue Planet
Building Vocabulary Draw a table similar
to the one below that includes all the
vocabulary terms listed for the section. As you
read the section, define each term in your
own words.
Vocabulary Term
Definition
oceanography
a.
?
bathymetry
b.
?
sonar
c.
?
submersible
d.
?
ow deep is the ocean? How much of Earth is covered by the
global ocean? What does the ocean floor look like? Humans have
long been interested in finding answers to these questions.
However, it was not until relatively recently that these simple
questions could be answered. Suppose, for example, that all of
the water were drained from the ocean. What would we see?
Plains? Mountains? Canyons? Plateaus? You may be surprised to
find that the ocean conceals all of these features, and more.
The Blue Planet
L2
2 INSTRUCT
Reading Strategy
H
Northern
Hemisphere
Word Parts Before students read this
section, ask them to write the meanings
of the prefix bathy- and the suffix -metry.
Then have them write what they think
the word bathymetry means. After students read the section, have them discuss
whether their prediction was correct.
Reading Strategy
oceanography
bathymetry
sonar
submersible
394 Chapter 14
Look at Figure 1. You can see why the “blue planet” or the “water
planet” are appropriate nicknames for Earth.
Nearly 71 percent of Earth’s surface is covered by the global ocean. Although
the ocean makes up a much greater percentage of Earth’s surface
than the continents, it has only been since the late 1800s that the
ocean became an important focus of study. New technologies
have allowed scientists to collect large amounts of data about the
oceans. As technology has advanced, the field of oceanography
has grown. Oceanography is a science that draws on the methods
and knowledge of geology, chemistry, physics, and biology to
study all aspects of the world ocean.
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Distribution of Land and Water
150˚
120˚
90˚
60˚
30˚
0˚
30˚
60˚
90˚
120˚
150˚
Arctic Ocean
Figure 2
60˚
30˚
Pacific
Ocean
0˚
Answer
Predicting easternmost point
of Pacific: approximately 70°W;
westernmost point of Atlantic:
approximately 100°W
Human-Environment
Interaction The four
main ocean basins are the
Pacific Ocean, the Atlantic
Ocean, the Indian Ocean,
and the Arctic Ocean.
Predicting What is
the longitude of the
easternmost point of the
Pacific Ocean? What is
the longitude of the
westernmost point of the
Atlantic Ocean?
Atlantic
Ocean
Indian
Ocean
30˚
60˚
Geography
of the Oceans
Integrate Math
L2
Geometry and Projections Explain
to students that the map pictured on
this page is a Mercator projection.
Because Earth is a sphere, twodimensional representations of Earth
invariably have some distortion. On
projections such as this, the degree
of distortion increases with distance
from the equator. Ask: Where on this
projection is distortion greatest? (the
northern and southern extremes, or the
poles) What landmasses do you think
are the most distorted? (Greenland
and Antarctica) Explain in geometric
terms why these landmasses are so
distorted. (Since Earth is a sphere, lines
of longitude come closer together as
distance from the equator increases.
These lines meet at the poles. To represent
a spherical body as a two-dimensional
grid, the lines run parallel rather than
meeting at the poles, and the features
between them become stretched.)
Visual, Logical
Geography of the Oceans
The area of Earth is about 510 million square kilometers. Of this total,
approximately 360 million square kilometers, or 71 percent, is represented by oceans and smaller seas such as the Mediterranean Sea and
the Caribbean Sea. Continents and islands comprise the remaining
29 percent, or 150 million square kilometers.
The world ocean can
be divided into four main ocean basins—the Pacific Ocean, the
Atlantic Ocean, the Indian Ocean, and the Arctic Ocean. These ocean
basins are shown in Figure 2.
The Pacific Ocean is the largest ocean. In fact, it is the largest single
geographic feature on Earth. It covers more than half of the ocean surface area on Earth. It is also the world’s deepest ocean, with an average
depth of 3940 meters.
The Atlantic Ocean is about half the size of the Pacific Ocean, and
is not quite as deep. It is a relatively narrow ocean compared to the
Pacific. The Atlantic and Pacific Oceans are bounded to the east and
west by continents.
The Indian Ocean is slightly smaller than the Atlantic Ocean, but
it has about the same average depth. Unlike the Pacific and Atlantic
oceans, the Indian Ocean is located almost entirely in the southern
hemisphere.
The Arctic Ocean is about 7 percent of the size of the Pacific Ocean.
It is only a little more than one-quarter as deep as the rest of the
oceans.
What are the four main ocean basins?
The Ocean Floor
395
Customize for Inclusion Students
Visually Impaired Provide students with a
relief world map or globe. Allow students to
experience the interconnected nature of the
world’s oceans by helping them trace the
outlines of the oceans with their fingers.
Students can also compare the sizes of Earth’s
four main ocean basins. This learning tool can
be used by both visually impaired students and
tactile learners. (A relief map of the ocean floor
can be used in a similar way to allow students
to experience deep ocean trenches, ridges,
seamounts, and guyots.)
Answer to . . .
Pacific Ocean, Atlantic
Ocean, Indian Ocean,
Arctic Ocean
The Ocean Floor 395
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Section 14.1 (continued)
Arctic Ocean
Mapping the
Ocean Floor
L1
Build Science Skills
Bering
Abyssal Plain
Kurile
Trench
Ryukyu
Trench
r
Empero
unts
Seamo
Figure 3 Have students examine the
map showing the topographic features
of the ocean floor. Ask: In which ocean
basin are most of the oceanic
trenches located? (Pacific) Which
ocean basins contain oceanic ridges?
(Atlantic, Indian) What is the major
undersea geological feature in the
Atlantic Ocean? (Mid-Atlantic Ridge)
What kind of geological feature
is the Hawaiian islands a part of?
(a linear chain of undersea volcanoes)
Aleutian
Trench
Juan de
Fuca
Ridge
North
America
Japan Trench
Ha
wa
iian
Is.
Philippine
Trench
Mariana Trench
Pacific Ocean
Middle
America
Trench
L2
Posing Questions Have students
write one or more questions they have
about the characteristics of the ocean
floor. Ask them to formulate each
question so that it could be used as the
basis for scientific research. (Sample
questions: Does the chemical
composition of seawater vary from
place to place around the world?
What methods can be used to
accurately measure the speed of
ocean currents?) After students have
written their questions, ask them to
describe how they might go about
answering their questions. (Sample
answers: Collect and analyze seawater
samples from a variety of locations.
Design an experiment or field study to test
different devices used to measure water
speed.) If necessary, assist students in
phrasing their questions so that they can
serve as the basis for a scientific inquiry.
Verbal, Logical
Java (Sunda)
Trench
East
Pacif
ic R
ise
Use Visuals
Tonga Trench
Australia
Kermadec Trench
Eltan
in Fra
cture
Z
one
Bellingshausen
Abyssal Plain
Figure 3 The topography
of the ocean floor is as
varied as the topography of
the continents. The ocean
floor contains mountain
ranges, trenches, and flat
regions called abyssal
plains.
Interpreting Diagrams
List all of the features you
can identify in the figure.
Mapping the Ocean Floor
If all the water were drained from the ocean basins, a variety of features
would be seen. These features include chains of volcanoes, tall
mountain ranges, trenches, and large submarine plateaus.
The
topography of the ocean floor is as diverse as that of continents. The
topographic features of the ocean floor are shown in Figure 3.
An understanding of ocean-floor features came with the development of techniques to measure the depth of the oceans. Bathymetry
396 Chapter 14
Facts and Figures
On average, the depth of the oceans is more
than four times the elevation of the
continents. The average elevation of the
continents is about 840 m above sea level. The
396 Chapter 14
average depth of the oceans is 3729 m. If
Earth’s solid mass were perfectly smooth and
spherical, ocean water would cover it all to a
depth of more than 2000 m.
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Integrate Social Studies
Greenland
Puerto-Rico
Trench
Challenger Expedition Explain to
students that the journey of the HMS
Challenger is considered by many to be
the birth of the science of oceanography.
Before the Challenger Expedition,
enough information about Earth’s oceans
had been collected to make scientists
and sailors alike realize that an extensive
ocean survey would be of great benefit.
The success of the expedition inspired
the launching of many subsequent
ocean research surveys. Point out to
students that the expedition took place
during a time when most ships used
wind and sail for propulsion, and
submarine cables carried most
transoceanic communications. Ask: In
what ways would data on ocean
currents, prevailing winds, and
weather patterns collected by
Challenger scientists have been useful
to others? (added to knowledge about
the oceans; provided help to sailors and
ship captains trying to chart the best
course for a journey) In what ways
would depth measurements and
other data about the nature of the
ocean bottom have been helpful to
others? (assist companies in making
decisions about where and how to lay
submarine cables)
Verbal
Arctic Ridge
cean
Mid-O
Asia
Gibbs
Fracture
Zone
Atlantic
Ocean
Red Sea
Rift
id
M
-A
Ab Dem
tla
ys er
ntic
sa ar
lP a
lai
n
e
dg
Ri
Africa
ian Rid g e
Ind
d-
M
i
St. Paul
Fracture
Zone
South
America
So
w
uth
d
Ri
ian
nd
I
t
es
Indian
Ocean
e
uth
So
ge
Peru-Chile
trench
as
t In
dia
L2
nR
idge
South Sandwich
Trench
Weddell Abyssal Plain
Key:
(bathos ⫽ depth, metry ⫽ measurement) is the measurement of ocean
depths and the charting of the shape or topography of the ocean floor.
The first understanding of the ocean floor’s varied topography did
not unfold until the historic three-and-a-half-year voyage of the HMS
Challenger. From December 1872 to May 1876, the Challenger expedition made the first—and perhaps still the most comprehensive—
study of the global ocean ever attempted by one agency. The 127,500
kilometer trip took the ship and its crew of scientists to every ocean
transform fault
For: Links on oceans
Visit: www.SciLinks.org
Web Code: cjn-5141
The Ocean Floor
397
Download a worksheet on oceans
for students to complete, and find
additional teacher support from
NSTA SciLinks.
Facts and Figures
The Challenger Expedition took data from
362 locations scattered throughout the
Atlantic, Pacific, and Indian Oceans. Scientists
traveling with the expedition took charge of
different research aspects. Matthew Maury
(1806–1873), an American naval officer, was
in charge of charts and instruments. Edward
Forbes (1815–1854) was a British biologist
who had already done extensive research in
shallower waters around Britain and in the
Aegean Sea. Forbes led the expedition’s
collection and analysis of biological specimens.
Before the expedition, Forbes had predicted
that life would not be found below about
2000 m in the deep sea. Challenger Expedition findings proved that life existed at least
as deep as 6000 m; it is now known that life
exists even at the bottom of the deepest ocean
trenches.
Answer to . . .
Figure 3 mid-ocean ridges, trenches,
abyssal plains, seamounts
The Ocean Floor 397
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Section 14.1 (continued)
Build Math Skills
A
L1
Line Graphs Have students graph sonar
results for a hypothetical transect of the
ocean bottom. Provide students with
the following time intervals for four
sonar data points, each taken 10 km
apart. Sample data: 3.2 s, 5.5 s, 7.2 s,
6.4 s. First, have students calculate the
depth for each data point (time/2 ⫻
1500 m/s). (3.2 s: 2400 m; 5.5 s: 4125
m; 7.2 s: 5400 m; 6.4 s: 4800 m)
Second, invite students to graph their
results, placing distance (km) between
data points on the x-axis and depth (m)
on the y-axis. Have students connect
their data points to create a line on the
graph. Ask students what the line
represents. (a rough profile of part of the
ocean floor)
Logical, Visual
Build Science Skills
B
Outgoing signal
Reflected signal
Sea floor
Figure 4 Sonar Methods
A By using sonar, oceanographers
can determine the depth of the
ocean floor in a particular area.
B Modern multibeam sonar
obtains a profile of a narrow
swath of seafloor every few
seconds.
except the Arctic. Throughout the voyage, they sampled various ocean
properties. They measured water depth by lowering a long, weighted
line overboard.
Today’s technology—particularly sonar, satellites, and submersibles—allows scientists to study the ocean floor in
a more efficient and precise manner than ever before.
Sonar In the 1920s, a technological breakthrough occurred with the
L2
invention of sonar, a type of electronic depth-sounding equipment.
Sonar is an acronym for sound navigation and ranging. It is also
referred to as echo sounding. Sonar works by transmitting sound waves
toward the ocean bottom, as shown in Figure 4A. With simple sonar,
a sensitive receiver intercepts the echo reflected from the bottom. Then
a clock precisely measures the time interval to fractions of a second.
Depth can be calculated from the speed of sound waves in water—
about 1500 meters per second—and the time required for the energy
pulse to reach the ocean floor and return. The depths determined from
continuous monitoring of these echoes are plotted. In this way a profile of the ocean floor is obtained. A chart of the seafloor can be
produced by combining these profiles.
In the last few decades, researchers have designed even more
sophisticated sonar to map the ocean floor. In contrast to simple sonar,
multibeam sonar uses more than one sound source and listening
device. As you can see from Figure 4B, this technique obtains a profile
of a narrow strip of ocean floor rather than obtaining the depth of a
single point every few seconds. These profiles are recorded every few
seconds as the research vessel advances. When a ship uses multibeam
sonar to make a map of a section of ocean floor, the ship travels
through the area in a regularly spaced back-and-forth pattern. Not surprisingly, this method is known as “mowing the lawn.”
Inferring Remind students of the
difference between sound waves and
microwaves. Sound waves are produced
by vibrating matter. Microwaves are a
form of electromagnetic energy. Ask:
Which type of wave has more energy?
(microwaves) Why can’t sound waves
be used to gather ocean height data
from satellites? (Sound waves must have
a medium to travel through. Satellites
orbit high in Earth’s atmosphere, where
there are too few molecules to transmit
sound.)
Logical, Verbal
398 Chapter 14
398 Chapter 14
Sea floor
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Build Reading Literacy
Satellites Measuring the shape of the ocean surface from space is
L1
Refer to p. 216D in Chapter 8, which
provides guidelines for this compare
and contrast strategy.
another technological breakthrough that has led to a better understanding of the ocean floor. After compensating for waves, tides,
currents, and atmospheric effects, scientists discovered that the ocean
surface is not perfectly flat. This is because gravity attracts water toward
regions where massive ocean floor features occur. Therefore, mountains and ridges produce elevated areas on the ocean surface. Features
such as canyons and trenches cause slight depressions.
The differences in ocean-surface height caused by ocean floor features are not visible to the human eye. However, satellites are able to
measure these small differences by bouncing microwaves off the ocean
surface. Figure 5 shows how the outgoing radar pulses are reflected back
to a satellite. The height of the ocean surface can be calculated by knowing the satellite’s exact position. Devices on satellites can measure
variations in sea-surface height as small as 3 to 6 centimeters. This type
of data has added greatly to the knowledge of ocean-floor topography.
Cross-checked with traditional sonar depth measurements, the data are
used to produce detailed ocean-floor maps, such as the one previously
shown in Figure 3.
Compare and Contrast After
students have read the sections on
bathymetric methods, have them
create a table that compares simple
sonar, multibeam sonar, and satellite
bathymetry technologies in terms of
data collection method used and the
type of data obtained. Ask students to
summarize advantages or disadvantages
of each technology with respect to the
others.
How do satellites help us learn about the shape of
the seafloor?
Simple
sonar
Multibeam
sonar
Satellite
Method
Sound
waves
Sound
waves
Microwaves
Type of
data
Ocean
floor
depth
Ocean
floor
depth
Ocean
surface height,
correlated to
ocean depth
Advantages
Simple
to use
More
detailed
Most detailed
of all
Disadvan- TimeTimeMust be
tages
consuming consuming cross-checked
with sonar
measurements
Satellite
Satellite orbit
Verbal, Visual
Outgoing
radar pulses
Return pulses
from sea
surface
Elevation in sea
surface height
Ocean bottom
Figure 5 Satellite Method
Satellites can be used to measure
sea-surface height. The data
collected by satellites can be used
to predict the location of large
features on the seafloor. This
method of data collection is much
faster than using sonar.
The Ocean Floor
399
Answer to . . .
Satellites bounce
microwaves off the
ocean surface. Outgoing radar pulses
are reflected back to the satellite and
can be used to detect differences in sea
surface height that can be correlated
to seafloor features.
The Ocean Floor 399
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Section 14.1 (continued)
Build Science Skills
Submersibles A submersible is a small underwater craft used for
deep-sea research. Submersibles are used to collect data about areas of
the ocean that were previously unreachable by humans. Submersibles
are equipped with a number of instruments ranging from thermometers
to cameras to pressure gauges. The operators of submersibles can record
video and photos of previously unknown creatures that live in the abyss.
They can collect water samples and sediment samples for analysis.
The first submersible was used in 1934 by William Beebe. He
descended to a depth of 923 meters off of Bermuda in a steel sphere
that was tethered to a ship. Since that time, submersibles have become
more sophisticated. In 1960, Jacques Piccard descended in the untethered submersible Trieste to 10,912 meters below the ocean surface into
the Mariana Trench. Alvin and Sea Cliff II are two other manned
submersibles used for deep-sea research. Alvin can reach depths of
4000 meters, and Sea Cliff II can reach 6000 meters.
Today, many submersibles are unmanned and operated remotely
by computers. These remotely operated vehicles (ROVs) can remain
under water for long periods. They collect data, record video, use
sonar, and collect sample organisms with remotely operated arms.
Another type of submersible, the autonomous underwater vehicle
(AUV), is under development. Its goal is to collect long-term data
without interruption.
L2
Communicating Results Have
students work in small groups to
research information about submersibles
and the scientists who use them. Have
each group investigate a different submersible. Possibilities include William
Beebe’s sphere, Trieste, Alvin, Sea Cliff II,
and Jason. Have the groups orally
present their findings to the class.
3 ASSESS
Evaluate
Understanding
L2
To assess students’ knowledge of section
content, have them write a short paragraph comparing the ocean floor to
Earth’s landmasses. Have them write
another paragraph describing how
sonar, satellites, and submersibles can
be used to gather data about the deep
ocean.
L1
Reteach
Have students create a timeline that
describes how bathymetric techniques
have changed over the years since the
Challenger expedition. Invite students to
explain their timelines and each of the
methods shown on their timelines to
the class.
Solution
8. 4.5 s/2 ⫻ 1500 m/s ⫽ 3375 m
Section 14.1 Assessment
Reviewing Concepts
1.
2.
3.
4.
5.
How does the area of Earth’s surface
covered by the oceans compare with the area
covered by land?
Name the four ocean basins. Which of the
four ocean basins is the largest? Which is
located almost entirely in the southern
hemisphere?
How does the topography of the ocean
floor compare to that on land? Name three
topographic features found on the ocean
floor.
What types of technology are used to
study the ocean floor?
Describe how sonar is used to determine
seafloor depth.
Critical Thinking
6. Comparing and Contrasting Compare
and contrast the use of satellites and
submersibles to collect data about the
topography of the seafloor.
7. Inferring Why is deep-sea exploration and
data collection difficult?
8. Assuming the average speed of sound
waves in water is 1500 meters per
second, determine the water depth
in meters if a sonar signal requires
4.5 seconds to hit the bottom and
return to the recorder.
400 Chapter 14
Section 14.1
Assessment
1. Nearly 71 percent of Earth’s surface is
covered by oceans, 29 percent is covered
by land.
2. Pacific Ocean, Atlantic Ocean, Indian
Ocean, Arctic Ocean; Pacific Ocean; Indian
Ocean
3. The topography of the ocean floor is
as diverse as that of continents. Three topographic features: mid-ocean ridges, trenches,
abyssal plains.
400 Chapter 14
4. sonar, satellites, submersibles
5. Sonar works by transmitting sound waves
to the ocean bottom. A receiver intercepts
the echo reflected from the ocean bottom
and a clock measures the time it takes for the
sound wave to travel to the ocean bottom
and back.
6. Both are used to find out more about the
seafloor’s topography. Satellites use remote
sensing to bounce microwaves off the sea
surface to determine differences in height.
Submersibles can be manned or unmanned,
travel to deep areas, and record data with
video and other instruments.
7. The deep ocean is a harsh environment for
humans—cold, dark, and under high pressure.
It is difficult to supply submersibles with
power for continuous use.