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Plate Tectonics

Why are some areas ofJ;al1h's surface very flat while others are full of hillsand valleys? Is the bottom of the ocean flat or does it have its own patternof ridges and valleys? What kind of scientist studies these questions?

Read and examine the information below. Answer the questions that follow.

If you could slice Earth in two like an orange, you'd see that it's made up of severalhuge layers. The outer layer is the crust, where living things exist. Beneath this layer isthe upper mantle, which is also solid. Between the crust and the mantle is a thin boundarylayer called the Moho. Beneath the upper mantle is a hot putty-like layer of mantle. Nextcomes the solid lower mantle, the liquid outer core, and the solid inner core of Earth.

Plate tectonics is a theory that says Earth's crust is made up ofmajor sections calledplates. These plates, which are solid, move very slowly atop the hot putty-like layer of mantle.There are continental plates and oceanic plates. However, each plate usually consists of alandmass and part of a seafloor. Where two or more plates meet is called the plate boundary.How these plates move together and apart creates different kinds of geological events.

Plates can move together, or converge. When an oceanic plate collides with a continentalplate, the oceanic plate sinks under the other plate. The same thing ;.lappens when twooceanic plates collide. Deep sea trenches are formed. When two continental plates collide,they crumple together to form mountain ranges. The Himalaya Mountains are the resultof this kind of plate movement.

Plates also can move apart, or diverge. Breaks in Earth's crust allows volcanic materialcalled magma to spew forth. These breaks in the crust at the bottom of the ocean arecalled mid-ocean ridges. Lava pours out, pushing the plates apart and forming rift valleysat the bottom of the sea. The other kind of plate movement is when two plates slide pastone another. The San Andreas Fault in California is an example of this movement.

Plate tectonics is responsible for earthquakes and volcanoes. Earthquakes are common atplate boundaries, or faultlines, all over Earth's surface. Movement of the plates puts pressureon rocks in the mantle. When they break or snap, energy is released and the ground shakes.Volcanoes also occur at plate boundaries. When plates pull apart, magma can be forced to thesurface and erupt as a volcano. When plates collide and one plate slides under another, thelower plate can melt to create magma. This magma is then forced to the surface as a volcano.

Figure A

Converging Continental PlatesMountains Formed

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Diverging Continental PlatesRift Valley Formed

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Diverging Oceanic PlatesMid-ocean Ridge Formed

Converging Continentaland Oceanic Plates

Deep Sea Trenches and Volcanoes Formed

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the compositionof Earth.

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tectonics.

Converging Oceanic PlatesDeep Sea Trenches and Volcanoes Formed

1. What is .the name of the layer that makes IIII' the slIIrface of Earth?

2. What are the l)ther layers of Earth in order froDnlllpper layers to th~ core?

3. What is the Moho layer?. ' '. -" ",'

/I. What is piate tectonics?

5. What two kinds of plates are there?

6. What does each piate IIIslllally CGlllsist of?

1. What do 1'anlll caRl the piace where !wan or more plates meet?

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Describe themovements ofplates in plate

tectonics.

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16. Think about your answer to the following question. Write your answer on the lines. Beprepared to talk about your answers in a classroom discussion. Why do you thilll< it tookuntil the late 1960's for the theory of plate tectonics to be accepted as true?

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Ideas toRemember

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Plate Tectonics~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~m~~~~~~~~

plate tectonics-a theory that says Earth's crust is made.llP qfIIJ.ajorsectionscalled plates, which move very slQwl:y atop thE\hQtputiy-likelayer of mantle ' " . .

plate boundary-where two 'or more plates meet

converge-move together Qr collide

diVerge-move apart

GuidedPracticeActivity

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Continental andContinental

Continental andContinental

Continental andOceanic

Oceanic andOceanic

Converge

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Appl icationActivity

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Answer the questions or perform the activities below.

21. Look at the diagram of the layers ilnlside Earth. Identify ea~h layer.

2$. What are the three ways in whidl1 plates ~all Imllllve?

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Plate Tectonics~~~~~~~~~~~~~~~~~~~~~~~m~~~~~~~~~~~~~~~~~~~~~~~~~~.Q

Look at each diagram below. Identify the kind of plates shown, how they are moving, and whatthe result will be.

27.

Kind of plates:

Kind of movement:

Result:

28.

Kind «Df plates:

Kind «Df movement:

Result:

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