HSES 1eTE C09.qxd 5/16/04 10:08 AM Page 248 Section 9.1 9 .
HSES 1eTE C09.qxd 5/16/04 10:08 AM Page 248Section 9.19.1 Continental Drift1 FOCUSSection Objectives9.19.29.3Describe the hypothesis ofcontinental drift.Evaluate the evidence insupport of continental drift.Identify the main objectionsto Wegener’s hypothesis ofcontinental drift.Key ConceptsWhat is the hypothesis ofcontinental drift?Vocabulary continental driftPangaeaWhat evidence supportedcontinental drift?Reading FocusBuild VocabularyFigure 1 A Curious Fit Thismap shows the best fit of SouthAmerica and Africa at a depthof about 900 meters. The areaswhere continents overlap appearin brown.Inferring Why are there areas ofoverlap?Evidencea. continental puzzleb.?c.?d.?Will California eventually slide into the ocean? Have continentsreally drifted apart over the centuries? Early in the twentieth century,most geologists thought that the positions of the ocean basins and continents were fixed. During the last few decades, however, new data havedramatically changed our understanding of how Earth works.L2AfricaSouth America2 INSTRUCTAn Idea BeforeIts TimeL1Figure 1 Point out the small areas ofbrown and light blue between Africaand South America. Ask: What couldcause the brown-shaded regions ofoverlap? (accumulation of sedimentsdeposited by rivers and stretching of theplates) What do you think the lightblue areas represent? (the continentalshelf)Visual248 Chapter 9HypothesisContinentalDriftAn Idea Before Its Timea. continental puzzleb. matching fossilsc. matching rocks and structuresd. ancient climatesUse VisualsSummarizing Copy the table. Fill it in asyou read to summarize the evidence ofcontinental drift.L2Word Forms Before students read thissection, ask them to write a sentence ortwo describing the meaning of the worddrift. Then have them write a predictionfor what they think continental driftmeans. After students read the section,have them examine their predictions anddiscuss whether their predictions mustbe changed.Reading StrategyReading Strategy248 Chapter 9The idea that continents fit together like pieces ofa jigsaw puzzle came about when better worldmaps became available. Figure 1 shows the twomost obvious pieces of this jigsaw puzzle. However,little significance was given this idea until 1915,when Alfred Wegener, a German scientist, proposed his radical hypothesis of continental drift.Wegener’s continental drift hypothesis statedthat the continents had once been joined to forma single supercontinent. He called this supercontinent Pangaea, meaning all land.Wegener also hypothesized that about 200 million years ago Pangaea began breaking into smallercontinents. These continents then drifted to theirpresent positions, as shown on page 250. Wegenerand others collected much evidence to supportthese claims. Let’s examine their evidence.
HSES 1eTE C09.qxd 5/16/04 10:09 AM Page 249Evidence: The Continental Puzzle Wegener first thoughtthat the continents might have been joined when he noticed the similarity between the coastlines on opposite sides of the South AtlanticOcean. He used present-day shorelines to show how the continents fittogether. However, his opponents correctly argued that erosion continually changes shorelines over time.Q If all the continents were oncejoined as Pangaea, what did therest of Earth look like?A When all the continentsEvidence: Matching FossilsFossil evidence for continental drift includes several fossil organisms found on differentlandmasses. Wegener reasoned that these organisms could not havecrossed the vast oceans presently separating the continents. An example is Mesosaurus, an aquatic reptile whose fossil remains are limitedto eastern South America and southern Africa, as shown in Figure 2.If Mesosaurus had been able to swim well enough to cross the vastSouth Atlantic Ocean, its fossils should be more widely distributed.This is not the case. Therefore, Wegener argued, South America andAfrica must have been joined somehow.The idea of land bridges was once the most widely accepted explanation for similar fossils being found on different landmasses. Mostscientists believed that during a recent glacial period, the lowering ofsea level allowed animals to cross the narrow Bering Strait betweenAsia and North America. However, if land bridges did exist betweenSouth America and Africa, their remnants should still lie below sealevel. But no signs of such land bridges have ever been found in theAtlantic Ocean.were together, there must alsohave been one huge ocean surrounding them. This ocean iscalled Panthalassa (pan all,thalassa sea). Today all thatremains of Panthalassa is thePacific Ocean, which has beendecreasing in size since thebreakup of Pangaea.Figure 2 Location ofMesosaurus Fossils ofMesosaurus have been found onboth sides of the South Atlanticand nowhere else in the world.Fossil remains of this and otherorganisms on the continents ofAfrica and South America appearto link these landmasses at sometime in Earth’s history.How does the distribution of Mesosaurus fossilsprovide evidence for continental drift?Evidence:Matching FossilsL2Purpose Students compare twogroups of fossils from two continentsto identify those fossils that are commonto both continents.Materials 2 groups of photographs orsamples of fossils, including at least onetype of fossil found in both groupsProcedure Have students examine thetwo groups of fossils. Tell them that thetwo groups were found on differentcontinents. Ask them to identify anyfossils that were found on bothcontinents. Have students infer theimplications of this observation.Expected Outcome Students shouldinfer that the two continents had to beconnected at some point in the pastwhen the organism in the fossil lived.Visual, LogicalAfricaSouth AmericaPlate Tectonics249Customize for Inclusion StudentsVisually Impaired Puzzle pieces of continentscan be made out of sandpaper by gluing amap onto the back of a piece of sandpaperand cutting out the continents. This learningtool can be used by both visually impairedstudents and students who learn tactilely.Remind students who use these pieces that thepiece must be held with the rough side downfor correct geographical orientation of thecontinent.Answer to . . .Figure 1 Areas where there are riversor streams have deposited largeamounts of sediments.Mesosaurus occurs onlyin eastern South Americaand southern Africa.Plate Tectonics 249
HSES 1eTE C09.qxd 5/16/04 10:09 AM Page 250Section 9.1 (continued)Use VisualsBreakup of PangaeaL1ATethysSeaANGAE250 Million Years AgoPangaea consisted of all themajor continents.AL A U R A S I AGONDWAL2PFigure 3 Have students study the mapsshowing the breakup of Pangaea. Ask:In the breakup of Pangaea, whatcontinents appear to have separatedfirst? (North America and Africa) Whatocean began to form when NorthAmerica and Africa separated? (AtlanticOcean) How was India formed? (Indiabroke away from Gondwanaland. It movednorth and eventually collided with Asia.)Visual, LogicalBSome students may think that thecontinents have remained in approximately the same positions since thebreakup of Pangaea. Make transparenciesof the five parts of Figure 3. Superimposethe transparencies two at a time to showstudents the changes. Ask students tocome up to the projection to point outchanges in the location of continentsfrom one transparency to another.Ask which continent has moved thefarthest. (Asia)Visual, LogicalNAL AN DNorthAmerica200 Million Years Ago Therifting that eventually resulted inthe Atlantic Ocean occurred overan extended period of time. Thefirst rift developed betweenNorth America and ntarcticaNorthAmericaEuropeAfricaAsiaC100 Million Years AgoContinued rifting of the southernlandmasses sent India on anorthward journey.IndiaSouthAmericaAustraliaD50 Million Years AgoAustralia began to separatefrom teAfricanplateSouthAmericanplateEPresent A modern map showsthat India has collided withAsia, creating the tic plateFigure 3 Pangaea broke up gradually over aperiod of 200 million years.250 Chapter 9Facts and FiguresRecently, a unique species of purple frogthat lives underground was discovered insouthwestern India. DNA analysis showed thatthe frog was related to a group of frogs thatlive only in the Seychelles Islands off the250 Chapter 9eastern coast of Africa and almost 3000 kmacross the Indian Ocean from India. Biologiststhink that the two frog populations areadditional evidence for continental drift.
HSES 1eTE C09.qxd 5/16/04 10:09 AM Page 251Build Science SkillsMatching Mountain nce: Rock Types and Structures Anyone who hasworked a jigsaw puzzle knows that the pieces must fit together to forma clear picture. The clear picture in the continental drift puzzle is oneof matching rock types and mountain belts. If the continents existedas Pangaea, the rocks found in a particular region on one continentshould closely match in age and type those in adjacent positions onthe adjoining continent.Rock evidence for continental drift exists in the form of several mountain belts that end at one coastline, only to reappear on alandmass across the ocean. For example, the Appalachian mountainbelt runs northeastward through the eastern United States, ending offthe coast of Newfoundland, as shown in Figure 4A. Mountains of thesame age with similar rocks and structures are found in the BritishIsles and Scandinavia. When these landmasses are fit together as inFigure 4B, the mountain chains form a nearly continuous belt.Figure 4 A The AppalachianMountains run along the easternside of North America anddisappear off the coast ofNewfoundland. Mountains thatare similar in age and structureare found in the British Isles andScandinavia. B When theselandmasses are united as Pangaea,these ancient mountain chainsform a nearly continuous belt.How does the location of mountain chains provideevidence of continental drift?Evidence: Ancient Climates Wegener was a meteorologist,so he was interested in obtaining data about ancient climates to support continental drift. And he did find evidence for dramatic globalclimate changes. Wegener found glacial deposits showing thatbetween 220 million and 300 million years ago, ice sheets coveredlarge areas of the Southern Hemisphere. Layers of glacial till werefound in southern Africa and South America, as well as in India andAustralia. Below these beds of glacial debris lay scratched and groovedbedrock carved by the ice. In some locations, the scratches andgrooves showed that the ice had moved from what is now the sea ontoland. It is unusual for large continental glaciers to move from the seaUsing Models Havestudents use a child’sjigsaw puzzle withseveral large pieces todemonstrate matching rock types andmountain belts as follows. Studentsshould put the puzzle together on apiece of cardboard. After putting ittogether, the puzzle should be coveredwith another piece of cardboard andflipped over. On the back of the puzzle,students should draw lines representinga mountain belt that extends acrossseveral puzzle pieces. Students willunderstand when the puzzle is puttogether how mountain chains formcontinuous belts across land masses.Kinesthetic, VisualBuild Reading LiteracyL1Refer to p. 246D which provides theguidelines for relating cause and effect.Relate Cause and Effect Have students read the section on pp. 251–252about ancient climates as evidencefor continental drift. Ask: Why didWegener believe that the existenceof glaciers in tropical regions of theSouthern Hemisphere was evidence ofcontin the Atlantic Oceanwould have formed at aconstant rate or wouldthat rate have variedover time? Why?EquatorIce massNorthAmericaSouth AfricaAmericaEurasiaTethys SeaAustraliaL3Have students research the followingquestion: Pangaea began to break upand South America and Africa began toseparate 200 million years ago. Whattypes of living organisms were found onEarth when the two continents reachedtheir current positions?IndiaAntarcticaAFigure 5 A The area of Pangaeacovered by glacial ice 300 millionyears ago. B The continents asthey are today. The white areasindicate where evidence of theold ice sheets exists.Interpreting Diagrams Wherewere the continents locatedwhen the glaciers formed?252 Chapter 9252 Chapter 2onto land. It is also interesting that much of the land area that showsevidence of this glaciation now lies near the equator in a subtropicalor tropical climate.Could Earth have been cold enough to allow the formation of continental glaciers in what is now a tropical region? Wegener rejected thisidea because, during this same time period, large tropical swampsexisted in the Northern Hemisphere. The lush vegetation of theseswamps eventually became the major coal fields of the eastern UnitedStates, Europe, and Siberia.Wegener thought there was a better explanation for the ancient climate evidence he observed. Thinking of the landmasses as asupercontinent, with South Africa centered over the South Pole, wouldcreate the conditions necessary to form large areas of glacial ice overmuch of the Southern Hemisphere. The supercontinent idea wouldalso place the northern landmasses nearer the tropics and account fortheir vast coal deposits, as shown in Figure 5.EquatorB
HSES 1eTE C09.qxd 5/16/04 10:10 AM Page 253Rejecting aHypothesisRejecting a HypothesisWegener’s drift hypothesis faced a great deal of criticism from otherscientists. One objection was that Wegener could not describe a mechanism that was capable of moving the continents across the globe.Wegener proposed that the tidal influence of the Moon was strongenough to give the continents a westward motion. However, physicistsquickly responded that tidal friction of the size needed to move thecontinents would stop Earth’s rotation.Wegener also proposed that the larger and sturdier continentsbroke through the oceanic crust, much like ice breakers cut throughice. However, no evidence existed to suggest that the ocean floor wasweak enough to permit passage of the continents without the oceanfloors being broken and deformed in the process.Most scientists in Wegener’s day rejected his hypothesis. However,a few geologists continued to search for additional evidence of continents in motion.Build Science SkillsQ Some day will the continentscome back together and form asingle landmass?A Yes, but not anytime soon.Based on current plate motions,it appears that the continentsmay meet up again in thePacific Ocean—in about300 million years.Figure 6 Mountain ranges arecommonly formed at plateboundaries. This photographshows part of the CanadianRockies in Banff National Park,Alberta, Canada.Why was Wegener’s hypothesis rejected?Using Tables and Graphs Havestudents make a table listing the reasonswhy Wegener’s hypothesis was criticizedby some people and accepted by others.Intrapersonal, Verbal3 ASSESSEvaluateUnderstandingL1Have students explain in their ownwords why Figure 2 shows evidencefor continental drift.A New Theory Emerges During the years that followedWegener’s hypothesis, major strides in technology enabled scientiststo map the ocean floor. Extensive data on earthquake activity andEarth’s magnetic field also became available. By 1968, these findingsled to a new theory, known as plate tectonics. This theory provides theframework for understanding most geologic processes, such as the formation of the mountains shown in Figure 6.Section 9.1 Assessment1.What is the hypothesis of continentaldrift?2.List the evidence that supporteSouth Africa centered over the South Pole, wouldcreate the conditions necessary to form large areas of glacial ice overmuch of the Southern Hemisphere. The supercontinent idea wouldalso place the northern landmasses nearer the tropics and account fortheir vast coal deposits, as shown in Figure 5.EquatorB
HSES 1eTE C09.qxd 5/16/04 10:10 AM Page 253Rejecting aHypothesisRejecting a HypothesisWegener’s drift hypothesis faced a great deal of criticism from otherscientists. One objection was that Wegener could not describe a mechanism that was capable of moving the continents across the globe.Wegener proposed that the tidal influence of the Moon was strongenough to give the continents a westward motion. However, physicistsquickly responded that tidal friction of the size needed to move thecontinents would stop Earth’s rotation.Wegener also proposed that the larger and sturdier continentsbroke through the oceanic crust, much like ice breakers cut throughice. However, no evidence existed to suggest that the ocean floor wasweak enough to permit passage of the continents without the oceanfloors being broken and deformed in the process.Most scientists in Wegener’s day rejected his hypothesis. However,a few geologists continued to search for additional evidence of continents in motion.Build Science SkillsQ Some day will the continentscome back together and form asingle landmass?A Yes, but not anytime soon.Based on current plate motions,it appears that the continentsmay meet up again in thePacific Ocean—in about300 million years.Figure 6 Mountain ranges arecommonly formed at plateboundaries. This photographshows part of the CanadianRockies in Banff National Park,Alberta, Canada.Why was Wegener’s hypothesis rejected?Using Tables and Graphs Havestudents make a table listing the reasonswhy Wegener’s hypothesis was criticizedby some people and accepted by others.Intrapersonal, Verbal3 ASSESSEvaluateUnderstandingL1Have students explain in their ownwords why Figure 2 shows evidencefor continental drift.A New Theory Emerges During the years that followedWegener’s hypothesis, major strides in technology enabled scientiststo map the ocean floor. Extensive data on earthquake activity andEarth’s magnetic field also became available. By 1968, these findingsled to a new theory, known as plate tectonics. This theory provides theframework for understanding most geologic processes, such as the formation of the mountains shown in Figure 6.Section 9.1 Assessment1.What is the hypothesis of continentaldrift?2.List the evidence that supported thehypothesis of continental drift.3. What was one of the main objections toWegener’s continental drift hypothesis?4. What is Pangaea?Critical Thinking5. Applying Concepts Would the occurrenceof the same plant fossils in South America andAfrica support continental drift? Explain.L2To assess students’ knowledge of sectioncontent, have them write two or threesentences describing each of the fourlines of evidence for Wegener’scontinental drift hypothesis.ReteachReviewing ConceptsL26. Drawing Conclusions How did Wegenerexplain the existence of glaciers in the southernlandmasses, and the lush tropical swamps inNorth America, Europe, and Siberia?Pangaea was a supercontinent madeup of all the major continents joinedtogether. It began breaking into smallercontinents about 200 million years ago.Pangaea was located near the SouthPole. The southern part of Pangaea,made up of South America, Africa, India,Australia, and Antarctica, had a coldclimate with large continental glaciers.Descriptive Paragraph Write a paragraph describing Pangaea. Include thelocation and climate of Pangaea. Use theequator as your reference for position.Answer to . . .Plate TectonicsSection 9.1Assessment1. a hypothesis that proposes that thecontinents where once joined to formone supercontinent2. matching continental outlines, matchingfossils, matching rocks and structures, ancientclimates3. He could not provide a mechanism toexplain the movement of the continents.4. the supercontinent proposed by Wegener’shypothesis of continental drift2535. Yes, a land plant most likely could not travelacross a large ocean such as the Atlantic. Ifthe plant is found in both Africa and SouthAmerica, those areas had to have been joinedwhen the plant was growing.6. It is difficult to imagine that Earth hadcooled enough to form glaciers in tropicallatitudes, so in order to explain the glaciers,those areas had to have been closer to thepoles than in the present day. Also, the glacialgrooves indicate the ice was coming from anarea that at present is ocean. Large continentalglaciers form only on land, so that area hadto be land.Figure 5 The continents were nearthe South Pole when the glaciersformed.Glaciers in southernSouth America, southernAfrica, India, and Australia are found inareas that now have tropical climates.There is also evidence for tropicalclimates and coal swamps in areas thatare now at higher latitudes, such asnorthern Europe and the northeasternUnited States.He could not provide amechanism for themovement of the continents.Plate Tectonics 253
248 Chapter 9 FOCUS Section Objectives 9.1 Describe the hypothesis of continental drift. 9.2 Evaluate the evidence in support of continental drift. 9.3 Identify the main objections to Wegener’s hypothesis of continental drift. Build Vocabulary Word Forms Before students read this section
civil engineering projects. C01 And C09: CoLLAborATIon For ProgreSS Owing to their synergistic missions, ASTM International Committees C01 and C09 often work closely together to achieve common goals. One notable area of col-laboration is a joint subcom-mittee, C09.48/C01.48 on Performa
Running Water and Groundwater 171 Section 6.3 HSES_1eTE_C06.qxd 5/16/04 9:12 AM Page 171. 172 Chapter 6 Much of the water in soil seeps downward until it reaches the zone of saturation. The zone
Carver HSES is a safe and inclusive space for all students to learn. In association with School District of Philadelphia policies, Carver HSES prohibits all forms of harassment and bullying based on race, gender, religion, ethnic group, sexual orientation, gender identity, or disability. First and foremost, Carver HSES
Budget of a GlacierGlaciers form where more snow falls in winter than can melt during the summer. They constantly gain and lose ice. Snow accumulates, and ice forms at the head of the glacier in the zone of accumulation, shown in Figure 4. Here new snowfall thickens the
recognized impact craters. Friction with Earth’s atmosphere burns up small debris before it reaches the ground. Evidence for most of the craters that formed in Earth’s history has been destroyed by ero-sion or tectonic processes. The formation of an impact crater is modeled in Figure
(metals, nonmetals, and metalloids) Visual, Verbal L1 2 L2 L2 Reading Focus 1 Section 2.1 Download a worksheet on the periodic table for students to complete, and find additional teacher support from
almost 2 meters of snow. 476 Chapter 17 FOCUS Section Objectives 17.1 Compare and contrast weather and climate. 17.2 Explain why seasonal changes occur. Build Vocabulary Word Part Analysis Ask students what the word sphere means. Tell them it’s a three-dimensional object in which all poin
Details:Reading Comprehension Practice Test 8 . Section 33: Sec Thirty Three (319 to 324) Details:Reading Comprehension Practice Test 9 . Section 34: Sec Thirty Four (325 to 334) Details:Comma Practice Test Questions . Section 35: Sec Thirty Five (335 to 355) Details:Grammar Practice Questions . Section 36: Sec Thirty Six (356 to 365) Details:Noun Practice Quiz . Section 37: Sec Thirty Seven .
