The Theory of Plate Tectonics? Types Three the What Are of Plate Boundaries? Do Tectonic Plates Why Move? R 3TUDY�#OACH 8 Tectonics? 102

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0 1 / 7 1 / Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 33/17/10 5:02:20 PM , or in relation to Earth’s surface slabs of is made of rigid Earth’s Read the two statements below and decide below statements Read the two describes the forces that shape Earth’s that shape Earth’s describes the forces states that tectonic Continents drift across a molten mantle. drift a molten Continents across collide. when continents Mountain ranges can form 5. 6. The word When you blow into a balloon, the balloon expands. Its When you blow into a balloon, Geologists proposed a more complete theory in the late Before Statement After What do you think? do you What column an A in the Before with them. Place or disagree agree whether you read you’ve After disagree. or a D if you the statement with agree if you mind. changed your have see if you to the statements this lesson, reread each other. This new theory suggested that Earth’s surface, This new theory suggested that Earth’s each other. the lithosphere, is divided into large pieces of rock. These pieces are called plates. Each plate moves slowly over Earth’s hot and semiplastic mantle. surface and the rock structures that form as a result. Plate tectonics explains why earthquakes occur and volcanoes earthquakes erupt. When plates separate on the seafloor, result and a mid-ocean ridge forms. When plates come This causes plate can move under the other. one together, earthquakes and creates a chain of volcanoes. When plates can result. earthquakes slide past each other, surface area also increases. As more air is added to the surface area also increases. As more crust if ocean Similarly, balloon, the balloon gets larger. ridges and is never continually forms at mid-ocean surface should be expanding. But destroyed, Earth’s measurements of the planet show that Earth is not getting explained? How can this be larger. The theory of 1960s. It was called plate tectonics theory. tectonicsplate other with respect to each that move rock, or plates, The Plate Tectonics Theory The Tectonics Plate Plate Tectonics TheoryThe of Tectonics Plate

Use the the Use 2 1

d d n i . What is plate What is plate 7 0 4 9 8 8 Key Concept Check Concept Key _ 3 L _ LESSON 3 LESSON Plate Tectonics Tectonics Plate Essentials Reading E CHAPTER 7 CHAPTER What is the theory of plate tectonics? types three the What are of plate boundaries? do tectonic plates Why move? R _ 3TUDY#OACH 8 tectonics? 102

1. State 1. State main heads in this lesson as the main points of your the outline Complete outline. the in with details found lesson. Study the lesson by outline. your reviewing Make an Outline Make Key Key Concepts • • • 1 0 _ 2 1 0 _ 2 3 1 CC132_012_018_RE_L3_889407.indd 12 CC132_012_018_RE_L3_889407.indd 13 1 3 2 _ 0 1 2 _ 0 1 8 _ R E

_ Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. L 3 _ 8 8 9 4 0 asthenosphere interacthelpexplainplatetectonics. the platestomove.Thewaysinwhichlithosphereand is sohot. asthenosphere behaveslikeaplasticmaterialbecauseit (as THEEnuhsfihr).Eventhoughitissolid,the mantle. ThislayerofEarthiscalledtheasthenosphere like thepiecesofagiantjigsawpuzzle. plates arelargepiecesoflithosphere.Thesefittogether ocean ridges.Itisthickbelowcontinents.Earth’s tectonic uppermost mantleformthelithosphere. edn setas lt etnc Plate Tectonics Reading Essentials Tectonic Plates rock layer iscalled the the layerswithinEarth’s interior. smallest plates. Plate isthelargestplate.TheJuandeFucaoneof boundaries arelocatedatmid-oceanridges.ThePacific boundaries areinthemiddleofoceans.Manythese Earth’s majorplatesandtheirboundaries.Noticehowsome relative tooneanother. Lookatthemapabove.Itshows 7 . i n d d The asthenosphereflowsbelowEarth’s plates andenables hotpartofthe Directly belowthelithosphereisavery The lithospherevariesinthickness.Itisthinbelowmid- Earth’s outermostlayersarecoldandrigidcomparedto Earth’s surfaceisdividedintorigidplatesthatmove

1 3 de Fuca Pacific

Plate Plate Juan lithosphere. Cocos Plate American North Plate Nazca Plate Thecrustandthesolid, Caribbean Earth’s TectonicPlates Plate The cold andrigidoutermost Scotia PlateScotia American South Plate African Plate Eurasian Plate Arabian Plate Antarctic Plate Plate. called? Earth’s outermost layers S 2. Locate 3. Identify CIENCE objects processed materialsmadeinto ous organic,synthetic,or Common Use without breaking molded orchangingshape Science Use plastic Indo-Australian Visual Check Reading Check Plate U Philippine SE Plate

V capableofbeing Circle theNazca . C anyofnumer- What are OMMON American Pacific Plate North Plate boundary Plate U SE 103 33/17/10 5:02:28PM / 1 7 / 1 0

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forms where two tectonic forms where

forms where two plates collide. two plates collide. forms where When a dense oceanic plate

forms where two tectonicforms where plates

. As they move past each other, the . As they move past each other, A subduction zone is the area where a means “moving apart.” Mid-ocean ridges means “moving apart.” Mid-ocean transform plate boundary plate transform

A Divergent subduction. convergent plate boundary plate convergent divergent plate boundary plate divergent

The San Andreas Fault in California is a transform plate The San Andreas Fault in California A Imagine placing two books side by side. Imagine that Imagine that side by side. placing two books Imagine A Divergent plate boundaries can also exist in the middle Divergent plate boundaries can boundary. boundary. each book is a tectonic plate. The place where the edges of plate. The place where each book is a tectonic How many ways represents a plate boundary. the books meet can You books along a set of boundaries? can you move the push the can You away from each other. pull the books the books past each other. can slide You books together. the same way as you tectonic plates move in much Earth’s books. can move these Convergent Plate Boundaries Plate Convergent BoundaryOcean-to-Continent Transform Plate Boundaries Plate Transform Divergent Plate Boundaries Plate Divergent Plate BoundariesPlate and a less-dense continental plate collide, the oceanic plate subducts, or sinks, under the edge of the continental plate. This creates a deep ocean trench and a line of volcanoes forms on the edge of the continent. This process can also occur when two oceanic plates collide. An older and denser oceanic plate will subduct beneath a younger oceanic plate. A deep ocean trench forms, along with a line of volcanoes. called plates might get stuck and stop moving. Stress builds up plates might get stuck and stop this stress is too great, the where the plates are stuck. When rocks break and suddenly move apart. The result is a rapid release of energy in the form of an earthquake. denser plate descends into Earth along a convergent plate convergent plate boundaries are The two types of boundary. ocean-to-continent and continent-to-continent. plates slide past each other plate in a process buoyant the more The denser plate sinks below separate. separate. At these boundaries, continents pull apart a continent. of African Rift is one example and a rift valley forms. The East of a continental rift. are located along divergent plate boundaries. When the are located along divergent plate ridge, lava erupts. As the lava seafloor spreads at a mid-ocean oceanic crust. As this cools and hardens, it forms new away from each other. process continues, the plates move 4 1

three ways in ways three

d d Tissue Plate n What are the What are i . 7 Divergent 0 Transform Convergent Boundaries 4 9 8 8 Key Concept Check Concept Key _ 3 Reading Check L _ Plate Tectonics Tectonics Plate Essentials Reading E R _ 8 which tectonic plates move. which tectonic plates 104

5. Name Make a layered book to book to Make layered a on the notes your organize types of plate three boundaries. 4. Describe 4. Describe three types of plate three boundaries? 1 0 _ 2 1 0 _ 2 3 1 CC132_012_018_RE_L3_889407.indd 14 CC132_012_018_RE_L3_889407.indd 15 1 3 2 _ 0 1 2 _ 0 1 8 _ R E

_ Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. L 3 _ 8 8 9 4 0 volcanoes occuralongtectonicplateboundaries. collide. Themapbelowshowsthatmostearthquakesand subduction zone.Mountainscanformwheretwocontinents continental rifts.Theyalsoformwhereplatescollidealonga the HimalayasinIndia. dense platefoldsanddeforms,formingmountainssuchas When thishappens,neitherplateissubducted.Theless- boundaries alsoformwhentwocontinentalplatescollide. edn setas lt etnc Plate Tectonics Reading Essentials Evidence for Plate Tectonics Continent-to-Continent Boundary earthquakes canresult. each other, stressbuilds.Whenthissuddenlyreleases, others. Recallthatwhenplatesseparate,collide,orslidepast and volcanoesaremorecommoninsomeplacesthan Positioning System(GPS). plate moves.ThisnetworkofsatellitesiscalledtheGlobal and Earth,itispossibletodeterminehowfastatectonic motion. Bykeepingtrackofthedistancebetweensatellites A network ofsatellitesorbitingEarthisusedtomonitorplate This isaboutthelengthofasmallpaperclip. come togetherat continents m technology wasnotavailabletomeasurehowfastthe 7 . i n d d Volcanoes canalsoformalongamid-oceanridge ofplatetectonicsexplainswhyearthquakes The theory Today, scientistscanmeasurehowfastcontinentsmove. When Wegener proposedthecontinentaldrifthypothesis,

1 5 oved. Rememberthatcontinentsmoveapartor speeds ofonlyafewcentimetersperyear. Asia Australia Pacific Ocean P E Acti arth l ate Convergentplate v e

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epicenter America North or America South where? so,plate boundaries?If occur anywhere away from andvolcanoes earthquakes answer.) form? (Circle thecorrect didtheHimalayas boundary ofconvergenttype plate tectonics? tectonics? ofplaterelated to the theory andvolcanoes earthquakes 8. Interpret 7. Explain c. b. a. 6. Identify ocean-to-continent ocean-to-ocean continent-to-continent Visual Check Reading Check Key Concept Check Africa How are Along what Do Europe 105 33/17/10 5:02:51PM / 1 7 / 1 0

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ridge push.

For example, the upstairs floors of For example, the convection.

Recall that mid-ocean ridges are higher than the Convection currents in the mantle produce a Rising mantle material at mid-ocean the potential ridges creates How can something as large as the Pacific Plate move? How can something as large as You learned that the main objection to Wegener’s Wegener’s objection to that the main learned You and in temperature differences by of material caused The circulation to plate tectonic Convection in the mantle is related Convection currents in the mantle produce enormous forces Convection currents in the mantle produce enormous forces are basal massive plates. These forces that can move Earth’s drag, ridge push, and slab pull. Scientists’ opinions differ on is strongest. which force continental drift hypothesis was that he could not explain hypothesis was that he could continental drift now continents move. Scientists how or why Earth’s asthenosphere continents move because the understand that the rigid lithosphere. moves underneath density is called Hot air is less warmer because hot air rises. homes are often As the cold air sinks, the hot air rises. dense than cold air. The warmth for convection comes from radioactive activity. uranium, thorium, and elements inside Earth, such as as solid rock are heated, potassium. When materials such dense. Heated mantle they expand and become less crust. with Earth’s material rises and comes in contact hot mantle material to Thermal energy is transferred from mantle cools, it becomes the colder surface above. As the current. These denser and sinks, forming a convection act like a conveyor belt currents in the asthenosphere it. Therefore, tectonic plates moving the lithosphere above and cooling of mantle move in response to the heating material. Basal Drag Ridge Push Forces Causing Plate Motion Plate Causing Forces Plate Motion Plate Currents Convection surrounding seafloor. Because mid-ocean ridges are elevated, Because mid-ocean surrounding seafloor. gravity pulls the surrounding rocks down and away from the ridge. called the ridge with a force from away for plates to move force on plates that causes motion called basal drag. on plates that causes motion called force Convection currents in the asthenosphere can drag the lithosphere. This is similar to how a conveyor belt moves items at a supermarket. Ridge push moves the lithosphere in opposite directions away from the mid-ocean ridge. 6 What causes 1

What causes d d n i . 7 0 4 9 8 8 Key Concept Check Concept Key _ 3 Reading Check Reading Check L _ force on the bottom of on the bottom force a plate a plate going into the into going a plate mantle movement along a movement mid-ocean ridge Plate Tectonics Tectonics Plate Essentials Reading E R _ 8 c. 106 a. b. 11. Explain

10. Cause and Effect 10. Cause do tectonic plates Why move?

9. Explain 9. Explain ridge push? (Circle the ridge push? (Circle answer.) correct convection? 1 0 _ 2 1 0 _ 2 3 1 CC132_012_018_RE_L3_889407.indd 16 CC132_012_018_RE_L3_889407.indd 17 1 3 2 _ 0 1 2 _ 0 1 8 _ R E

_ Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. L 3 _ 8 8 9 4 0 the table. cloth slidesovertheedge,itwillpullrestofoff tablecloth overtheedgeofatable.Whenenough with aforce called Therefore, itsinks. old andcold,itisdenserthanthesurroundingmantle. zone. Thissinkingplateiscalledaslab.Becausetheslab denser platewillsinkintothemantlealongasubduction edn setas lt etnc Plate Tectonics Reading Essentials A inProgressTheory Slab Pull ago isstillbeingupdated.Severalquestionsremain. volcanoes occurandwhymountainsform. boundaries. Italsohelpsexplainwhyearthquakesand drift andtheformationdestructionofcrustalongplate geology. Itexplainstheconnectionbetweencontinental 7 . i n d d The investigationthatWegener begannearlyacentury in Plate tectonicsisoftensaidtobetheunifyingtheory • • • •

1 7 boundaries. cesses thatoccurwithinthemantleandalong ropy. Itmighthelpscientistsbetterunderstandthepro- in asubductionzone.Thistechnologyiscalledanisot- interest iscreating3-Dimagesofseismicwavevelocities How willscientistsanswerthesequestions?Onetopicof them. measure orobserve rents occurinthemantle.However, thereisnowayto Currently acceptedmodelssuggestthatconvectioncur- What forces actuallydominateplatemotions? active thanscientistsoriginallyunderstood. exist withinplates.Also,themantleismuchmore not perfectlyrigid.Differentthicknessesandweaknesses from plateboundaries?Perhapsitisbecauseplatesare Why dosomeearthquakesandvolcanoesoccurfar system isknowntohaveactivetectonicplates. has platetectonicactivity?Nootherplanetinoursolar Why isEarththeonlyplanetinsolarsystemthat You learnedthatwhentectonicplatescollide,the slab pull. As aslabsinks, itpullsontherest oftheplate Thisissimilartopushinga plate

12. Use Proportions d. c. b. a. answer. to findthe Use proportions plates to spread 1m? How longwillittakethe average rate of2.5cm/y. spreadAtlantic atan Ridge The plates alongtheMid-

plate to travel 3m? How longwould ittakethe slowest, atabout0.7cm/y. Eurasian Plate travels the continue to change? ofplate tectonics theory Explain 13.

2.5 cm Math Skills Cross-multiply andsolve Convert thedistance to Set up a proportion: upaproportion: Set Divide bothsidesby for the sameunit. 2.5 cm. Raig Check Reading x ______2.5 cm asfollows: × x 1 y 1 m

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0 1 / 7 1 / Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 33/17/10 5:03:13 PM END OF LESSON map. forms where two tectonic two forms where ED the process by which the denser plate sinks sinks plate which the denser by the process when the rising mantle material at mid-oceanat material when the rising mantle when a slab sinks and pulls on the rest of the plate of the plate on the rest when a slab sinks and pulls onnect C plates slide past each other plates with a force with a force ridges creates the potential for plates to move away from from away move to plates for potential the ridges creates the ridge with a force below the more buoyant plate when two plates collide plates when two plate buoyant the more below Log on to ConnectED.mcgraw-hill.com ConnectED.mcgraw-hill.com on to Log find this to textbook your and access resources. lesson’s ridge push: slab pull: subduction: boundary: plate transform convergent Plate Boundaries Plate forms where two plates plates two forms where forms where two tectonic two forms where have learned about plate tectonics to complete the concept have learned about plate tectonics 8 the theory that states that Earth’s surface is Earth’s the theory that states that 1

d the cold and rigid outermost rock layer of Earth layer rock and rigid outermost the cold d the circulation of material caused by differences differences by caused of material the circulation n i . 7 0 4 9 8 8 _ 3 L plates separate plates made of rigid slabs of rocks, or plates, that move with move that or plates, made of rigid slabs of rocks, each other respect to in temperature and density in temperature collide collide _ Plate Tectonics Tectonics Plate Essentials Reading E Use what you Review the terms and their definitions in the Mini Glossary. Choose one term and in the Mini Glossary. Review the terms and their definitions own words. explain what it means in your Reread the statements at the beginning of the at the beginning the statements Reread with an A if you column in the After lesson. Fill disagree. or a D if you the statement with agree mind? change your Did you R What do you think _ 8 108 2. plate tectonics: plate 1. divergent plate boundary: plate divergent lithosphere: Mini Glossary convection: boundary: plate convergent 1 0 _ 2 1 0 _ 2 3 1 CC132_012_018_RE_L3_889407.indd 18