14.1 The Vast World Ocean - Mr. Baker's Earth Science Class
HSES 1eTE C14.qxd 5/16/04 12:56 PM Page 394Section 14.114.1 The Vast World Ocean1 FOCUSSection Objectives14.114.214.314.4Recognize that most of Earth’ssurface is covered by water.List Earth’s four main oceanbasins and identify theirlocations.Describe the topography ofthe ocean floor and compareit to land.Identify and describe threemajor technologies used tostudy the ocean floor.Key ConceptsHow much of Earth’ssurface is covered bywater?How can the world oceanbe divided?Vocabulary How does the topographyof the ocean floorcompare to that on land?What types of technologyare used to study theocean floor?Reading FocusBuild VocabularyL2NorthPolea. 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 researchOne OceanFigure 1 The World Ocean These viewsof Earth show the planet is dominated bya single interconnected world ocean.L2Purpose Students see how Earth’socean basins are connected.Materials world globeProcedure 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, Logical394 Chapter 14SouthPoleSouthernHemisphereThe Blue PlanetBuilding 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.Vocabulary ?submersibled.?ow 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 PlanetL22 INSTRUCTReading StrategyHNorthernHemisphereWord 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 students read the section, have them discusswhether their prediction was correct.Reading Strategyoceanographybathymetrysonarsubmersible394 Chapter 14Look at Figure 1. You can see why the “blue planet” or the “waterplanet” are appropriate nicknames for Earth.Nearly 71 percent 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.
HSES 1eTE C14.qxd 5/16/04 12:57 PM Page 395Distribution of Land and Water150 120 90 60 30 0 30 60 90 120 150 Arctic OceanFigure 260 30 PacificOcean0 AnswerPredicting easternmost pointof Pacific: approximately 70 W;westernmost point of Atlantic:approximately 100 WHuman-EnvironmentInteraction The fourmain ocean basins are thePacific Ocean, the AtlanticOcean, the Indian Ocean,and the Arctic Ocean.Predicting What isthe longitude of theeasternmost point of thePacific Ocean? What isthe longitude of thewesternmost point of theAtlantic Ocean?AtlanticOceanIndianOcean30 60 Geographyof the OceansIntegrate MathL2Geometry and Projections Explainto students that the map pictured onthis page is a Mercator projection.Because Earth is a sphere, twodimensional 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, LogicalGeography of the OceansThe 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 andthe Caribbean Sea. Continents and islands comprise the remaining29 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 surface 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?The Ocean Floor395Customize for Inclusion StudentsVisually 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’sfour 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 OceanThe Ocean Floor 395
HSES 1eTE C14.qxd 5/16/04 12:57 PM Page 396Section 14.1 (continued)Arctic OceanMapping theOcean FloorL1Build Science SkillsBeringAbyssal e 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)AleutianTrenchJuan deFucaRidgeNorthAmericaJapan TrenchHawaiianIs.PhilippineTrenchMariana TrenchPacific OceanMiddleAmericaTrenchL2Posing 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, LogicalJava (Sunda)TrenchEastPacific RiseUse VisualsTonga TrenchAustraliaKermadec TrenchEltanin FractureZoneBellingshausenAbyssal PlainFigure 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.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, tallmountain 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 development of techniques to measure the depth of the oceans. Bathymetry396 Chapter 14Facts and FiguresOn 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. The396 Chapter 14average 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.
HSES 1eTE C14.qxd 5/16/04 12:58 PM Page 397Integrate Social StudiesGreenlandPuerto-RicoTrenchChallenger 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)VerbalArctic d SeaRiftidM-AAb Demtlays ernticsa arlP alainedgRiAfricaian Rid g eIndd-MiSt. anOceaneuthSogePeru-Chiletrenchast IndiaL2nRidgeSouth SandwichTrenchWeddell Abyssal PlainKey:(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 expedition 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 oceantransform faultFor: Links on oceansVisit: www.SciLinks.orgWeb Code: cjn-5141The Ocean Floor397Download a worksheet on oceansfor students to complete, and findadditional teacher support fromNSTA SciLinks.Facts and FiguresThe 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 theAegean 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 Expedition 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.Answer to . . .Figure 3 mid-ocean ridges, trenches,abyssal plains, seamountsThe Ocean Floor 397
HSES 1eTE C14.qxd 5/16/04 12:58 PM Page 398Section 14.1 (continued)Build Math SkillsAL1Line 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, VisualBuild Science SkillsBOutgoing signalReflected signalSea floorFigure 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.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, satellites, 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 theL2invention 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 profile 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 surprisingly, this method is known as “mowing the lawn.”Inferring 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, Verbal398 Chapter 14398 Chapter 14Sea floor
HSES 1eTE C14.qxd 5/16/04 12:58 PM Page 399Build Reading LiteracySatellites Measuring the shape of the ocean surface from space isL1Refer to p. 216D in Chapter 8, whichprovides guidelines for this compareand 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 oceansurface is not perfectly flat. This is because gravity attracts water towardregions where massive ocean floor features occur. Therefore, mountains 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 features 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 knowing 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.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.How do satellites help us learn about the shape ofthe SoundwavesSoundwavesMicrowavesType ofdataOceanfloordepthOceanfloordepthOceansurface height,correlated toocean depthAdvantagesSimpleto useMoredetailedMost detailedof allDisadvan- TimeTimeMust betagesconsuming consuming cross-checkedwith sonarmeasurementsSatelliteSatellite orbitVerbal, VisualOutgoingradar pulsesReturn pulsesfrom seasurfaceElevation in seasurface heightOcean bottomFigure 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.The Ocean Floor399Answer to . . .Satellites bouncemicrowaves off theocean surface. Outgoing radar pulsesare reflected back to the satellite andcan be used to detect differences in seasurface height that can be correlatedto seafloor features.The Ocean Floor 399
HSES 1eTE C14.qxd 5/16/04 12:58 PM Page 400Section 14.1 (continued)Build Science SkillsSubmersibles 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 untethered submersible Trieste to 10,912 meters below the ocean surface intothe Mariana Trench. Alvin and Sea Cliff II are two other mannedsubmersibles 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.L2Communicating Results Havestudents work in small groups toresearch information about submersiblesand the scientists who use them. Haveeach group investigate a different submersible. Possibilities include WilliamBeebe’s sphere, Trieste, Alvin, Sea Cliff II,and Jason. Have the groups orallypresent their findings to the class.3 ASSESSEvaluateUnderstandingL2To assess students’ knowledge of sectioncontent, have them write a short paragraph comparing the ocean floor toEarth’s landmasses. Have them writeanother paragraph describing howsonar, satellites, and submersibles canbe used to gather data about the deepocean.L1ReteachHave 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 mSection 14.1 AssessmentReviewing Concepts1.2.3.4.5.How does the area of Earth’s surfacecovered by the oceans compare with the areacovered by land?Name the four ocean basins. Which of thefour ocean basins is the largest? Which islocated almost entirely in the southernhemisphere?How does the topography of the oceanfloor compare to that on land? Name threetopographic features found on the oceanfloor.What types of technology are used tostudy the ocean floor?Describe how sonar is used to determineseafloor depth.Critical Thinking6. Comparing and Contrasting Compareand 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.400 Chapter 14Section 14.1Assessment1. 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 topographic features: mid-ocean ridges, trenches,abyssal plains.400 Chapter 144. 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 seasurface 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.
HSES 1eTE C14.qxd 5/16/04 12:58 PM Page 401Section 14.214.2 Ocean Floor Features1 FOCUSSection ObjectivesKey ConceptsWhat are the three mainregions of the oceanfloor?How do continentalmargins in the AtlanticOcean differ from those inthe Pacific Ocean?How are deep-oceantrenches formed?How are abyssal plainsformed?What is formed at midocean ridges?Vocabulary continental margincontinental shelfcontinental slopesubmarine canyonturbidity currentcontinental riseocean basin floorabyssal plainsseamountsmid-ocean ridgeseafloor spreadingReading Strategy14.5Outlining Before you read, make anoutline of this section. Use the greenheadings as the main topics and the blueheadings as subtopics. As you read, addsupporting details.14.614.7I. Continental MarginsA. Continental ShelfB. Continental Slope?C.List the three main regions ofthe ocean floor.Differentiate between thecontinental margins of theAtlantic and Pacific Oceans.Explain the formation of newocean floor at deep-oceantrenches, abyssal plains, andmid-ocean ridges.?II.?A.Reading FocusBuild VocabularyOceanographers studying the topography of the ocean floor havedivided it into three major regions.The ocean floor regions arethe continental margins, the ocean basin floor, and the mid-oceanridge. The map in Figure 6 outlines these regions for the North AtlanticOcean. The profile at the bottom of the illustration shows the variedtopography. Scientists have discovered that each of these regions has itsown unique characteristics and features.Figure 6 Topography of theNorth Atlantic Ocean BasinBeneath the map is a profile ofthe area between points A and B.The profile has been exaggerated40 times to make the topographicfeatures more distinct.ANorthAmericaMid-oceageridnAMid-ocean ridgeReading StrategyL2C. Continental RiseII. Ocean Basin FloorA. Deep-Ocean TrenchesB. Abyssal PlainsC. Seamounts and GuyotsIII. Mid-Ocean RidgesA. Seafloor SpreadingB. Hydrothermal VentsUse VisualsAfricaOceanbasin floorConcept Map Have students make aconcept map using the term ocean floorfeatures as the starting point. All thevocabulary terms in this section shouldbe used.2 INSTRUCTBContinentalmarginL2Oceanbasin floorContinentalmarginBThe Ocean Floor401L1Figure 6 Point out to students that theprofile shown below the map is a sideview of the ocean floor along the linebetween points A and B on the map.Ask: Why do the topographic featureshave to be exaggerated to make themmore distinct? (The scale of the map isso large that the elevation differencesbetween ocean floor, continental margin,and mid-ocean ridge would not be visible.If the map were 40 times larger, theexaggeration wouldn’t be necessary, butthe map would be too large to print.)Look back at the map of the oceanfloor shown in Figure 3. How woulda profile of the Pacific Ocean basindiffer from this profile of the AtlanticOcean? (The profile of the Pacific Oceanbasin would not show a central mid-oceanridge. Instead, depending on how thetransect line is drawn, it would showtrenches, chains of volcanic islands,or coral atolls.)Visual, LogicalThe Ocean Floor 401
HSES 1eTE C14.qxd 5/16/04 12:59 PM Page 402Section 14.2 (continued)Build Reading LiteracyContinental MarginsThe zone of transition between a continent and the adjacent oceanbasin floor is known as the continental margin.In the AtlanticOcean, thick layers of undisturbed sediment cover the continentalmargin. This region has very little volcanic or earthquake activity.This is because the continental margins in the Atlantic Ocean are notassociated with plate boundaries, unlike the continental margins ofthe Pacific Ocean.In the Pacific Ocean, oceanic crust is plungingbeneath continental crust. This force results in a narrow continental margin that experiences both volcanic activity and earthquakes.Figure 7 shows the features of a continental margin found along theAtlantic coast.L1Refer to p. 392D, which provides theguidelines for this previewing strategy.Preview Have students skim headings,titles of visuals, and boldfaced text forSection 14.2 Ocean Floor Features.Invite them to think in broad termsabout what they will read. Ask: What dothe green section heads have incommon? (They are all parts of the oceanfloor.) What do the blue section headshave in common? (Most are terms forsmaller features of the ocean, usuallyassociated with one of the three parts ofthe ocean.)Visual, LogicalContinental Shelf What if you were to begin an underwaterContinental MarginsIntegrate BiologyL2Sunlight and Ocean Life Explain thatthe ocean bottom along the continentalmargins supports a greater variety ofliving organisms than other regionsof the ocean floor. Tell students thatsunlight penetrates ocean water to anaverage depth of about 300 meters.Ask: What kinds of organisms formthe basis of almost every food chain?(organisms capable of photosynthesis)Why does the continental shelfsupport a greater amount and varietyof life than deeper parts of the oceanfloor? (Sunlight can penetrate to thebottom of at least some parts of thecontinental shelf; algae and other photosynthetic organisms can live on thebottom and serve as the basis for oceanfood chains along the continental shelf.Deeper regions of the ocean floor do notreceive sunlight and so do not supportphotosynthetic organisms that wouldform the basis of food chains.)Logical, VerbalFigure 7 Atlantic ContinentalMargin The continental marginsin the Atlantic Ocean are widerthan in the Pacific Ocean andare covered in a thick layer ofsediment.Explaining Why are continentalmargins in the Pacific Oceannarrower and associatedwith earthquakes andvolcanic activity?journey eastward across the Atlantic Ocean? The first area of ocean flooryou would encounter is the continental shelf. The continental shelf isthe gently sloping submerged surface extending from the shoreline. Theshelf is almost nonexistent along some coastlines. However, the shelfmay extend seaward as far as 1500 kilometers along other coastlines.On average, the continental shelf is about 80 kilometers wide and130 meters deep at its seaward edge. The average steepness of the shelfis equal to a drop of only about 2 meters per kilometer. The slope is soslight that to the human eye it appears to be a horizontal surface.Continental shelves have economic and political significance.Continental shelves contain important mineral deposits, largereservoirs of oil and natural gas, and huge sand and gravel deposits.The waters of the continental shelf also contain important fishinggrounds, which are significant sources of food.Continental marginSubmarinecanyonsAbyssal plainContinental shelfContinental slopeContinental riseOceanic crustContinental crust402 Chapter 14Customize for English Language LearnersTell students that the words abyss and floor areused as synonyms with reference to the deepocean bottom. Explain that the word abyssmeans a “bottomless depth” and historicallyhas been used to describe the unknown.Before humans discovered technologies fordeep sea exploration, the bottom of the ocean402 Chapter 14was considered by many to be the abyssreferred to in many
Figure 1 The World Ocean These views of Earth show the planet is dominated by a single interconnected world ocean. 394 Chapter 14 FOCUS Section Objectives 14.1 Recognize that most of Earth’s surface is covered by water. 14.2 List Earth’s four main ocean basins and identify their locations
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