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14.1 The Vast World Ocean

Reading StrategyBuilding Vocabulary Draw a table similarto the one below that includes all thevocabulary terms listed for the section. As youread the section, define each term in yourown words.

Key ConceptsHow much of Earth’ssurface is covered bywater?

How can the world oceanbe divided?

How does the topographyof the ocean floorcompare to that on land?

What types of technologyare used to study theocean floor?

Vocabulary◆ oceanography◆ bathymetry◆ sonar◆ submersible

How deep is the ocean? How much of Earth is covered by theglobal ocean? What does the ocean floor look like? Humans havelong been interested in finding answers to these questions.However, it was not until relatively recently that these simplequestions could be answered. Suppose, for example, that all ofthe water were drained from the ocean. What would we see?Plains? Mountains? Canyons? Plateaus? You may be surprised tofind that the ocean conceals all of these features, and more.

The Blue PlanetLook at Figure 1. You can see why the “blue planet” or the “waterplanet” are appropriate nicknames for Earth. Nearly 71 per-cent of Earth’s surface is covered by the global ocean. Althoughthe ocean makes up a much greater percentage of Earth’s surfacethan the continents, it has only been since the late 1800s that theocean became an important focus of study. New technologieshave allowed scientists to collect large amounts of data about theoceans. As technology has advanced, the field of oceanographyhas grown. Oceanography is a science that draws on the methodsand knowledge of geology, chemistry, physics, and biology tostudy all aspects of the world ocean.

Vocabulary Term Definition

oceanography a.

bathymetry b.

sonar c.

submersible d. ?

?

?

?

SouthernHemisphere

NorthPole

NorthernHemisphere

SouthPole

Figure 1 The World Ocean These viewsof Earth show the planet is dominated bya single interconnected world ocean.

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FOCUS

Section Objectives14.1 Recognize that most of Earth’s

surface is covered by water.14.2 List Earth’s four main ocean

basins and identify theirlocations.

14.3 Describe the topography ofthe ocean floor and compareit to land.

14.4 Identify and describe threemajor technologies used tostudy the ocean floor.

Build VocabularyWord Parts Before students read thissection, ask them to write the meaningsof the prefix bathy- and the suffix -metry.Then have them write what they thinkthe word bathymetry means. After stu-dents read the section, have them discusswhether their prediction was correct.

Reading Strategya. science that studies all aspects of theworld’s oceanb. measurement of ocean depths andcharting the shape of the ocean floorc. echo sounding to measure ocean depthd. small underwater craft used fordeep-sea research

INSTRUCT

The Blue Planet

One OceanPurpose Students see how Earth’socean basins are connected.

Materials world globe

Procedure Have students point outthe regions on the globe where oceansconnect.

Expected Outcome Students willsee that the Atlantic, Pacific, and IndianOceans connect in the regionsurrounding Antarctica. The Atlanticand Pacific Oceans connectwith the Arctic Ocean.Visual, Logical

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2

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Reading Focus

1

Section 14.1

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Geography of the OceansThe area of Earth is about 510 million square kilometers. Of this total,approximately 360 million square kilometers, or 71 percent, is repre-sented by oceans and smaller seas such as the Mediterranean Sea andthe Caribbean Sea. Continents and islands comprise the remaining 29 percent, or 150 million square kilometers. The world ocean canbe divided into four main ocean basins—the Pacific Ocean, theAtlantic Ocean, the Indian Ocean, and the Arctic Ocean. These oceanbasins are shown in Figure 2.

The Pacific Ocean is the largest ocean. In fact, it is the largest singlegeographic feature on Earth. It covers more than half of the ocean sur-face area on Earth. It is also the world’s deepest ocean, with an averagedepth of 3940 meters.

The Atlantic Ocean is about half the size of the Pacific Ocean, andis not quite as deep. It is a relatively narrow ocean compared to thePacific. The Atlantic and Pacific Oceans are bounded to the east andwest by continents.

The Indian Ocean is slightly smaller than the Atlantic Ocean, butit has about the same average depth. Unlike the Pacific and Atlanticoceans, the Indian Ocean is located almost entirely in the southernhemisphere.

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 theoceans.

What are the four main ocean basins?

IndianOcean

PacificOcean

AtlanticOcean

60˚

30˚

0˚

30˚

60˚

90˚ 0˚30˚60˚120˚150˚ 30˚ 60˚ 90˚ 120˚ 150˚

Arctic Ocean

Distribution of Land and Water

Figure 2

Human-EnvironmentInteraction The fourmain ocean basins are thePacific Ocean, the AtlanticOcean, the Indian Ocean,and the Arctic Ocean. Predicting What is the longitude of theeasternmost point of thePacific Ocean? What is the longitude of thewesternmost point of theAtlantic Ocean?

AnswerPredicting easternmost pointof Pacific: approximately 70°W;westernmost point of Atlantic:approximately 100°W

Geographyof the OceansIntegrate MathGeometry and Projections Explainto students that the map pictured onthis page is a Mercator projection.Because Earth is a sphere, two-dimensional representations of Earthinvariably have some distortion. Onprojections such as this, the degreeof distortion increases with distancefrom the equator. Ask: Where on thisprojection is distortion greatest? (thenorthern and southern extremes, or thepoles) What landmasses do you thinkare the most distorted? (Greenlandand Antarctica) Explain in geometricterms why these landmasses are sodistorted. (Since Earth is a sphere, linesof longitude come closer together asdistance from the equator increases.These lines meet at the poles. To representa spherical body as a two-dimensionalgrid, the lines run parallel rather thanmeeting at the poles, and the featuresbetween them become stretched.)Visual, Logical

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Customize for Inclusion Students

Visually Impaired Provide students with arelief world map or globe. Allow students toexperience the interconnected nature of theworld’s oceans by helping them trace theoutlines of the oceans with their fingers.Students can also compare the sizes of Earth’s

four main ocean basins. This learning tool canbe used by both visually impaired students andtactile learners. (A relief map of the ocean floorcan be used in a similar way to allow studentsto experience deep ocean trenches, ridges,seamounts, and guyots.)

Answer to . . .

Pacific Ocean, AtlanticOcean, Indian Ocean,

Arctic Ocean

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PhilippineTrench

AleutianTrench

KurileTrench

Japan Trench

Mariana Trench

Java (Sunda)Trench

Kermadec Trench

MiddleAmericaTrench

Tonga Trench

East

Pac

ific

Ris

e

Juan deFucaRidge

Hawaiian Is.

Em

peror

Seam

ounts

RyukyuTrench

NorthAmerica

Arctic Ocean

Pacific Ocean

Australia

BeringAbyssal Plain

Eltanin Fracture Zone

BellingshausenAbyssal Plain

Mapping the Ocean FloorIf all the water were drained from the ocean basins, a variety of featureswould be seen. These features include chains of volcanoes, tall mountain ranges, trenches, and large submarine plateaus. Thetopography of the ocean floor is as diverse as that of continents. Thetopographic features of the ocean floor are shown in Figure 3.

An understanding of ocean-floor features came with the develop-ment of techniques to measure the depth of the oceans. Bathymetry

Figure 3 The topographyof the ocean floor is asvaried as the topography ofthe continents. The oceanfloor contains mountainranges, trenches, and flatregions called abyssalplains. Interpreting DiagramsList all of the features youcan identify in the figure.

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Mapping theOcean FloorUse VisualsFigure 3 Have students examine themap showing the topographic featuresof the ocean floor. Ask: In which oceanbasin are most of the oceanictrenches located? (Pacific) Whichocean basins contain oceanic ridges?(Atlantic, Indian) What is the majorundersea geological feature in theAtlantic Ocean? (Mid-Atlantic Ridge)What kind of geological featureis the Hawaiian islands a part of?(a linear chain of undersea volcanoes)

Build Science SkillsPosing Questions Have studentswrite one or more questions they haveabout the characteristics of the oceanfloor. Ask them to formulate eachquestion so that it could be used as thebasis for scientific research. (Samplequestions: Does the chemicalcomposition of seawater vary fromplace to place around the world?What methods can be used toaccurately measure the speed ofocean currents?) After students havewritten their questions, ask them todescribe how they might go aboutanswering their questions. (Sampleanswers: Collect and analyze seawatersamples from a variety of locations.Design an experiment or field study to testdifferent devices used to measure waterspeed.) If necessary, assist students inphrasing their questions so that they canserve as the basis for a scientific inquiry.Verbal, Logical

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Section 14.1 (continued)

On average, the depth of the oceans is morethan four times the elevation of thecontinents. The average elevation of thecontinents is about 840 m above sea level. The

average depth of the oceans is 3729 m. IfEarth’s solid mass were perfectly smooth andspherical, ocean water would cover it all to adepth of more than 2000 m.

Facts and Figures

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Puerto-RicoTrench

Peru-Chiletrench

South SandwichTrench

Mid-Atlantic Ridge

Mid-IndianR

idg

e

Southwest Indian Ridge

Southeast Indian Ridge

Greenland

Asia

Africa

SouthAmerica

Arctic

Mid-Ocean Ridge

GibbsFracture

Zone

Demerara

Abyssal Plain

St. PaulFracture

Zone

AtlanticOcean

Weddell Abyssal Plain

Red SeaRift

IndianOcean

Key: transform fault

(bathos � depth, metry � measurement) is the measurement of oceandepths and the charting of the shape or topography of the ocean floor.

The first understanding of the ocean floor’s varied topography didnot unfold until the historic three-and-a-half-year voyage of the HMSChallenger. From December 1872 to May 1876, the Challenger expedi-tion made the first—and perhaps still the most comprehensive—study of the global ocean ever attempted by one agency. The 127,500kilometer trip took the ship and its crew of scientists to every ocean

For: Links on oceans

Visit: www.SciLinks.org

Web Code: cjn-5141

Integrate Social StudiesChallenger Expedition Explain tostudents that the journey of the HMSChallenger is considered by many to bethe birth of the science of oceanography.Before the Challenger Expedition,enough information about Earth’s oceanshad been collected to make scientistsand sailors alike realize that an extensiveocean survey would be of great benefit.The success of the expedition inspiredthe launching of many subsequentocean research surveys. Point out tostudents that the expedition took placeduring a time when most ships usedwind and sail for propulsion, andsubmarine cables carried mosttransoceanic communications. Ask: Inwhat ways would data on oceancurrents, prevailing winds, andweather patterns collected byChallenger scientists have been usefulto others? (added to knowledge aboutthe oceans; provided help to sailors andship captains trying to chart the bestcourse for a journey) In what wayswould depth measurements andother data about the nature of theocean bottom have been helpful toothers? (assist companies in makingdecisions about where and how to laysubmarine cables)Verbal

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The Challenger Expedition took data from362 locations scattered throughout theAtlantic, Pacific, and Indian Oceans. Scientiststraveling with the expedition took charge ofdifferent research aspects. Matthew Maury(1806–1873), an American naval officer, wasin charge of charts and instruments. EdwardForbes (1815–1854) was a British biologistwho had already done extensive research inshallower waters around Britain and in the

Aegean Sea. Forbes led the expedition’scollection and analysis of biological specimens.Before the expedition, Forbes had predictedthat life would not be found below about2000 m in the deep sea. Challenger Expe-dition findings proved that life existed at leastas deep as 6000 m; it is now known that lifeexists even at the bottom of the deepest oceantrenches.

Facts and Figures

Answer to . . .

Figure 3 mid-ocean ridges, trenches,abyssal plains, seamounts

Download a worksheet on oceansfor students to complete, and findadditional teacher support fromNSTA SciLinks.

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except the Arctic. Throughout the voyage, they sampled various oceanproperties. They measured water depth by lowering a long, weightedline overboard. Today’s technology—particularly sonar, satel-lites, and submersibles—allows scientists to study the ocean floor ina more efficient and precise manner than ever before.

Sonar In the 1920s, a technological breakthrough occurred with theinvention of sonar, a type of electronic depth-sounding equipment.Sonar is an acronym for sound navigation and ranging. It is alsoreferred to as echo sounding. Sonar works by transmitting sound wavestoward the ocean bottom, as shown in Figure 4A. With simple sonar,a sensitive receiver intercepts the echo reflected from the bottom. Thena 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 energypulse to reach the ocean floor and return. The depths determined fromcontinuous monitoring of these echoes are plotted. In this way a pro-file of the ocean floor is obtained. A chart of the seafloor can beproduced by combining these profiles.

In the last few decades, researchers have designed even moresophisticated sonar to map the ocean floor. In contrast to simple sonar,multibeam sonar uses more than one sound source and listeningdevice. As you can see from Figure 4B, this technique obtains a profileof a narrow strip of ocean floor rather than obtaining the depth of asingle point every few seconds. These profiles are recorded every fewseconds as the research vessel advances. When a ship uses multibeamsonar to make a map of a section of ocean floor, the ship travelsthrough the area in a regularly spaced back-and-forth pattern. Not sur-prisingly, this method is known as “mowing the lawn.”

Figure 4 Sonar MethodsA By using sonar, oceanographerscan determine the depth of theocean floor in a particular area. B Modern multibeam sonarobtains a profile of a narrowswath of seafloor every fewseconds.

Outgoing signal

Reflected signal

Sea floor Sea floor

A B

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Build Math SkillsLine Graphs Have students graph sonarresults for a hypothetical transect of theocean bottom. Provide students withthe following time intervals for foursonar data points, each taken 10 kmapart. Sample data: 3.2 s, 5.5 s, 7.2 s,6.4 s. First, have students calculate thedepth for each data point (time/2 �1500 m/s). (3.2 s: 2400 m; 5.5 s: 4125m; 7.2 s: 5400 m; 6.4 s: 4800 m)Second, invite students to graph theirresults, placing distance (km) betweendata points on the x-axis and depth (m)on the y-axis. Have students connecttheir data points to create a line on thegraph. Ask students what the linerepresents. (a rough profile of part of theocean floor)Logical, Visual

Build Science SkillsInferring Remind students of thedifference between sound waves andmicrowaves. Sound waves are producedby vibrating matter. Microwaves are aform of electromagnetic energy. Ask:Which type of wave has more energy?(microwaves) Why can’t sound wavesbe used to gather ocean height datafrom satellites? (Sound waves must havea medium to travel through. Satellitesorbit high in Earth’s atmosphere, wherethere are too few molecules to transmitsound.)Logical, Verbal

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Section 14.1 (continued)

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Satellites Measuring the shape of the ocean surface from space isanother technological breakthrough that has led to a better under-standing of the ocean floor. After compensating for waves, tides,currents, and atmospheric effects, scientists discovered that the oceansurface is not perfectly flat. This is because gravity attracts water towardregions where massive ocean floor features occur. Therefore, moun-tains and ridges produce elevated areas on the ocean surface. Featuressuch as canyons and trenches cause slight depressions.

The differences in ocean-surface height caused by ocean floor fea-tures are not visible to the human eye. However, satellites are able tomeasure these small differences by bouncing microwaves off the oceansurface. Figure 5 shows how the outgoing radar pulses are reflected backto a satellite. The height of the ocean surface can be calculated by know-ing the satellite’s exact position. Devices on satellites can measurevariations in sea-surface height as small as 3 to 6 centimeters. This typeof data has added greatly to the knowledge of ocean-floor topography.Cross-checked with traditional sonar depth measurements, the data areused to produce detailed ocean-floor maps, such as the one previouslyshown in Figure 3.

How do satellites help us learn about the shape ofthe seafloor?

Figure 5 Satellite MethodSatellites can be used to measuresea-surface height. The datacollected by satellites can be usedto predict the location of largefeatures on the seafloor. Thismethod of data collection is muchfaster than using sonar.

Satellite orbitSatellite

Outgoingradar pulses

Return pulsesfrom seasurface

Ocean bottom

Elevation in seasurface height

Build Reading LiteracyRefer to p. 216D in Chapter 8, whichprovides guidelines for this compareand contrast strategy.

Compare and Contrast Afterstudents have read the sections onbathymetric methods, have themcreate a table that compares simplesonar, multibeam sonar, and satellitebathymetry technologies in terms ofdata collection method used and thetype of data obtained. Ask students tosummarize advantages or disadvantagesof each technology with respect to theothers.

Simple Multibeamsonar sonar Satellite

Method Sound Sound Microwaveswaves waves

Type of Ocean Ocean Oceandata floor floor surface height,

depth depth correlated toocean depth

Advan- Simple More Most detailedtages to use detailed of all

Disadvan- Time- Time- Must betages consuming consuming cross-checked

with sonarmeasurements

Verbal, Visual

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Answer to . . .

Satellites bouncemicrowaves off the

ocean surface. Outgoing radar pulsesare reflected back to the satellite andcan be used to detect differences in seasurface height that can be correlatedto seafloor features.

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Section 14.1 Assessment

Reviewing Concepts1. How does the area of Earth’s surface

covered by the oceans compare with the areacovered by land?

2. Name the four ocean basins. Which of thefour ocean basins is the largest? Which islocated almost entirely in the southernhemisphere?

3. How does the topography of the oceanfloor compare to that on land? Name threetopographic features found on the oceanfloor.

4. What types of technology are used tostudy the ocean floor?

5. Describe how sonar is used to determineseafloor depth.

Critical Thinking6. Comparing and Contrasting Compare

and contrast the use of satellites andsubmersibles to collect data about thetopography of the seafloor.

7. Inferring Why is deep-sea exploration anddata collection difficult?

8. Assuming the average speed of soundwaves in water is 1500 meters persecond, determine the water depthin meters if a sonar signal requires4.5 seconds to hit the bottom andreturn to the recorder.

Submersibles A submersible is a small underwater craft used fordeep-sea research. Submersibles are used to collect data about areas ofthe ocean that were previously unreachable by humans. Submersiblesare equipped with a number of instruments ranging from thermometersto cameras to pressure gauges. The operators of submersibles can recordvideo 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. Hedescended to a depth of 923 meters off of Bermuda in a steel spherethat was tethered to a ship. Since that time, submersibles have becomemore sophisticated. In 1960, Jacques Piccard descended in the unteth-ered submersible Trieste to 10,912 meters below the ocean surface intothe Mariana Trench. Alvin and Sea Cliff II are two other manned submersibles used for deep-sea research. Alvin can reach depths of4000 meters, and Sea Cliff II can reach 6000 meters.

Today, many submersibles are unmanned and operated remotelyby computers. These remotely operated vehicles (ROVs) can remainunder water for long periods. They collect data, record video, usesonar, 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 datawithout interruption.

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Build Science SkillsCommunicating Results Havestudents work in small groups toresearch information about submersiblesand the scientists who use them. Haveeach group investigate a different sub-mersible. Possibilities include WilliamBeebe’s sphere, Trieste, Alvin, Sea Cliff II,and Jason. Have the groups orallypresent their findings to the class.

ASSESSEvaluateUnderstandingTo assess students’ knowledge of sectioncontent, have them write a short para-graph comparing the ocean floor toEarth’s landmasses. Have them writeanother paragraph describing howsonar, satellites, and submersibles canbe used to gather data about the deepocean.

ReteachHave students create a timeline thatdescribes how bathymetric techniqueshave changed over the years since theChallenger expedition. Invite students toexplain their timelines and each of themethods shown on their timelines tothe class.

Solution8. 4.5 s/2 � 1500 m/s � 3375 m

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Section 14.1 (continued)

4. sonar, satellites, submersibles5. Sonar works by transmitting sound wavesto the ocean bottom. A receiver interceptsthe echo reflected from the ocean bottomand a clock measures the time it takes for thesound wave to travel to the ocean bottomand back.6. Both are used to find out more about theseafloor’s topography. Satellites use remotesensing to bounce microwaves off the sea

Section 14.1 Assessment

1. Nearly 71 percent of Earth’s surface iscovered by oceans, 29 percent is coveredby land.2. Pacific Ocean, Atlantic Ocean, IndianOcean, Arctic Ocean; Pacific Ocean; IndianOcean3. The topography of the ocean floor isas diverse as that of continents. Three topo-graphic features: mid-ocean ridges, trenches,abyssal plains.

surface to determine differences in height.Submersibles can be manned or unmanned,travel to deep areas, and record data withvideo and other instruments.7. The deep ocean is a harsh environment forhumans—cold, dark, and under high pressure.It is difficult to supply submersibles withpower for continuous use.

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