What are plate tectonics and what causes it? By: Mr. D’Angelone.

What are plate tectonics and what causes it?

By: Mr. D’Angelone

By: Mr. D'Angelone 2

Learning Objectives

• Students will name some crustal plates.

• Students will describe the theory of plate tectonics.

• Students will describe the causes of plate tectonics.


Key Terms

• tectonic plate

• theory of plate tectonics

• convection current

• boundary


Tectonic Plates

• Earth's lithosphere is made up of crust and the solid, uppermost part of the mantle.

• The mantle is the layer of rock below the crust.

• The lithosphere is broken up into large pieces called tectonic plates.

• There are 7 large tectonic plates and about 14 smaller ones.

• The largest plate is the Pacific plate.


Tectonic Plates


Floating Plates • Part of the mantle contains rock that flows

like a thick liquid. • This part, called the athenosphere, is just

below the more solid rock of the uppermost mantle.

• Tectonic plates float on the athenosphere like rafts floating on a lake.

• The continents and oceans are carried along on the plates like passengers on a raft.


Theory of Plate Tectonics • Using information that supports seafloor

spreading and continental drift, scientists have developed the theory of plate tectonics.

• The theory of plate tectonics combines the theories of continental drift and seafloor spreading.

• The theory of plate tectonics explains how and why the continents move.

• It states that Earth's lithosphere is broken into plates that float on the upper mantle. The continents move because they are carried along on the moving plates.

What causes plate tectonics?


Convection Currents

• A convection current is the movement of a gas or a liquid caused by differences in temperature and density.

• For example, warm air rises and cool air sinks. When a pan of water boils on a stove, the water near the bottom of the pan heats first. The less dense hot water rises. The cooler and denser water near the top of the pan sinks.


Convection Currents


Inside the Mantle • Scientists think that giant convection currents in

Earth's upper mantle cause the tectonic plates to move.

• The mantle rock close to Earth's core is hot and has some properties of a thick liquid.

• The mantle rock farther from the core is cooler. • The hot mantle rock rises. The cooler mantle

rock sinks. • As the cooler rock moves closer to the core, it

heats up and rises. • The plates are carried along like packages on a

moving conveyor belt or like people on a raft.


Plate Boundaries and Movements

• The place where two plates meet is called a plate boundary.

• Scientists have identified three different kinds of plate boundaries: transform, convergent, and divergent.

• At transform boundaries, two plates slide past each other.

• The movement is not smooth. This sliding movement causes earthquakes.


• At a convergent boundary, the plates move toward each other.

• When oceanic crust meets continental crust, the denser oceanic crust slides under the continental crust.

• This downward movement of the oceanic crust produces a subduction zone

• If two continental plates meet, the crust crumples upward.

• At a divergent boundary, the plates move apart. These plates sometimes form rift valley.


• When oceanic crust meets continental crust at a convergent boundary, a subduction zone forms. This is often an area of volcanic activity.


• When two continental crusts meet at a convergent boundary, they crumple upward. Mountains may be formed.

Mountain Range


• A rift valley may form at a divergent boundary.

Rift Valley


Checking Concepts

1. Which layer of Earth is below the crust?

2. How many large tectonic plates are there?

3. What land feature may be formed when two continental plates meet?

4. At which type of boundary do plates move apart?


Answers

1. Mantle

2. Seven

3. A mountain

4. Divergent

The End

What are plate tectonics and what causes it? By: Mr. D’Angelone.

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