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Unit 8 Lesson 3 How Do Movements of the Crust
Change Earth?
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Inside the Earth
• Earth is a sphere made up of very different layers.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Inside the Earth
• Earth’s crust is a rocky outer layer made of many
minerals.
• The crust is thinnest under oceans and thickest
under mountains. It makes up only about one
percent of Earth’s mass.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Inside the Earth
• Right below Earth’s crust is the mantle, which is
the thickest layer, making up about two-thirds of
Earth’s mass.
• The mantle contains some liquid rock but is
mostly solid. High heat and pressure in the mantle
cause it to flow like warm plastic.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Inside the Earth
• At the center of Earth is a core made of molten
metal. The inner core is solid iron and nickel. The
outer core is molten, liquid metal.
• The metal core makes up about one-third of
Earth’s mass and is extremely hot.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Plate Tectonics
• Many pieces of Earth’s crust, called plates, fit
together like a jigsaw puzzle. The plates rest on
Earth’s mantle and are always moving.
• The theory that Earth’s crust is divided into
moving plates is called plate tectonics.
• Plates are made from continental crust, oceanic
crust, or a combination of both.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Plate Tectonics
• Certain land features form where plates collide.
Other features form where plates separate.
• Mountain ranges, island chains, and enormous
valleys are possible signs of a plate boundary.
• For example, the Great Rift Valley formed where
the Arabian plate is splitting the African plate into
two new, separate plates.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Plate Boundaries
• Different types of plate motion produce
boundaries that shape different landforms.
• Continental plates moving toward each other push
up mountains.
• Oceanic plates moving toward each other can
cause deep-ocean trenches and volcanic islands to
form.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Plate Boundaries
• Oceanic plates colliding with continental plates
causes mountains and volcanoes to form along
the boundary between the plates.
• When two plates pull apart, new crust forms a rift,
or separation, on both sides of the boundary,
becoming two separate landmasses.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Earthquakes
• A fault is a break in Earth’s crust where rock on
one side can move in relation to rock on the other
side.
• As plates move, pressure increases along a fault,
causing the rock on one side to snap free and
slide past the rock on the other side.
• This release of energy and shaking of the ground
is called an earthquake.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Earthquakes
• The point inside Earth where an earthquake
begins is called the focus.
• The point on Earth’s surface directly above the
focus is called the epicenter, where earthquake
motion is most severe.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Earthquakes
• Scientists use seismographs to detect tremors and
predict if an earthquake is likely to occur.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Measuring Earthquakes
• An earthquake’s magnitude is the amount of
energy it releases.
• The Richter scale measures the magnitude of
earthquakes on a scale from 1 to 10.
• The Richter scale uses the size of waves on a
seismograph to determine an earthquake’s
strength.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Measuring Earthquakes
• An earthquake measuring 6.0 or higher on the
Richter scale can cause heavy damage in
populated areas.
• Scientists have also developed the moment
magnitude scale to more accurately measure the
magnitudes of larger earthquakes.
• This scale, which also assigns numbers between 1
and 10, uses a mathematical formula to calculate
the total energy an earthquake releases.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Volcanoes
• The liquid rock below Earth’s crust is called
magma.
• A volcano is an opening in the crust that allows
magma to reach Earth’s surface.
• Lava is the molten rock that erupts from the
volcano along with ash and hot gases.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Volcanoes
• Shield volcanoes are formed from non-explosive
lava where broad sheets of lava steadily build up.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Volcanoes
• Cinder cone volcanoes are formed from explosive
eruptions where lava explodes into the air and
quickly hardens.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 8 Lesson 3 How Do Movements of the Crust Change Earth?
Volcanoes
• Composite volcanoes are formed from alternating
types of eruptions which produce explosive
eruptions where liquid lava flows.
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