by Cassandra Jenkins

Scott Foresman Science 3.8

Genre Comprehension Skill Text Features Science Content

Nonfi ction Sequence Captions

Call Outs

Glossary

Changes on Earth

ISBN 0-328-13829-0

Vocabularycore

crust

erosion

landform

lava

magma

mantle

weathering

What did you learn?1. What forces can cause erosion?

2. Name the different layers of Earth.

3. How do volcanoes erupt?

4. In this book you have read about how weathering affects landforms. Write to explain how weathering can change landforms. Use examples from the book to support your answer.

5. Sequence What happens during an earthquake?

Illustrations: 3, 4, 7 Big Sesh StudiosPhotographs: Every effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Unless otherwise acknowledged, all photographs are the property of Scott Foresman, a division of Pearson Education. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R) Background (Bkgd)Opener: David Muench/Corbis; Title Page: Big Sesh Studios; 2 David Muench/Corbis; 5 (BC) Pat OHara/Corbis, (CR) Royalty-Free/Corbis; 6 Photographers Choice/Getty Images; 8 (CR) Spencer Grant/Photo Researchers, Inc., (B) Lloyd Cluff/Corbis; 9 (BL) Ken M. John/Photo Researchers, Inc., (BR) La Prensa Grafica/AP/Wide World Photos; 10 (R) Fred Whitehead/Animals Animals/Earth Scenes, (BR) Jeremy Horner/Corbis; 11 Natural History Museum/DK Images; 12 DK Images; 13 La Prensa Grafica/AP/Wide World Photos; 14 William Manning/Corbis; 15 David Muench/Corbis

ISBN: 0-328-13829-0

Copyright Pearson Education, Inc.

All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permissions, write to: Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

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Changes on Earthby Cassandra Jenkins

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2What are Earths layers?Earths Layers

Earth is divided into three layers. The crust is the

outer layer of Earth. It is made up of different kinds of

rock. The thickness of the crust is different in different

places. The crust is about 37 kilometers (23 miles)

thick under the continents. Compare Earth to a peach.

The crust would be the skin of the peach.

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3

The mantle is below the crust. It is made up of

very hot rocks. It can flow like thick toothpaste.

The core is the innermost layer of Earth. It is made

up of metal. The core is so hot that it could melt. But

it is packed tightly together and stays mostly solid. Its

outer part is a very hot liquid.

Crust

Core

Mantle

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4Shapes on Earths Surface

A landform is a solid feature on Earths crust.

Mountains, hills, and valleys, are landforms. Other

features include bodies of water. There are many

different types of landforms on Earth.

Forces shape these landforms. Moving water is a

strong force. Rivers can act as saws. Sand and pebbles

in the water slowly cut through rock. Flooding rivers

leave silt, sand, and pebbles on their banks. These

things help form valleys.

GlacierValley Plateau

Ocean

Coast

Do you recognize these landforms?

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5

A glacier is a moving body of ice. It slowly moves

downhill. A volcano is an opening in Earths crust.

Hot, melted rock is forced through it. Some mountains

form when pieces of rock are pushed along cracks in

Earths crust. A lake forms when water flows slowly

enough to fill up an area.

Volcano Mountain

LakeRiver

This picture shows a mountain, a kind of landform, and a lake.

Plain

Hill

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6What are volcanoes and earthquakes?How Do Volcanoes Form?

Volcanoes start in the mantle. This is where

magma forms. Magma is hot, partly melted rock that

is under pressure from gases it contains. This pressure

forces it up through Earths crust. The hot material

erupts through an opening in a volcano.

Lava is the material that erupts from a volcano.

Lava has ash, cinders, and hot rock in it. As lava

cools, it becomes new crust.

This lava was once magma inside Earth.

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7

Volcanoes

Magma collects in large pockets. These pockets

are called magma chambers. As magma leaves a

chamber, it moves up a tunnel or vent. Sometimes

magma escapes and erupts from a side vent. But

most magma erupts through a central vent. It erupts

through a bowl-shaped

crater at the top of

the volcano.

Crater Central vent

Side vent

Magma chamber

Side vent

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Earthquakes

Parts of Earths crust can shift suddenly. This causes

the ground to vibrate. This shaking is called an

earthquake. Most earthquakes begin along a fault.

A fault is a large crack in Earths crust.

Earthquake vibrations move as waves through

Earth. They also move up and down. The waves can

cause cracks. They can pile up rubble in areas around

the parts of the crust that moved.

8

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Earthquake Damage

How much earthquake damage occurs depends on

how long the crust shakes. It also depends on how

close the earthquake is to the surface. Earthquakes

can happen very close to a city. This causes a lot of

damage to buildings, bridges, pipes, and roads.

An earthquake can cause landslides. Landslides are

downhill movements of rocks and earth. Landslides

can happen on the land or the ocean floor. Landslides

underwater can cause huge waves. Landslides on the

land can bury large areas.

9

Earthquakes can cause damage in cities and in nature.

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What are weathering and erosion?Weathering

Landforms are always changing. This happens

when rocks in landforms break apart. Weathering is

any action that breaks rocks into smaller pieces.

Weathering goes on all the time. It causes changes

over time. Some changes might take a year. Others

could take hundreds of years.

Plants can cause weathering. Their roots grow into

rocks. As the roots grow, they break apart rocks.

10

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11

Water mixed with decayed

material in soil can also cause

weathering. This water changes

the minerals in the rock. The

rock grows weak and starts to

break apart. Water can also seep

in and freeze in the cracks of a

rock. Then the water expands.

Ice pushes against the rock and

breaks it apart over time.

Ice changes rocks in a different

way. Glaciers are huge bodies of

ice. Rocks and ice scrape against

the ground as a glacier moves.

This makes valleys wide and

smooth. Rocks of all sizes drop

to the ground when the glacier

melts. These rocks and soil line

the edges where the glacier used

to be.

Look at how weathering has broken down this boulder into smaller and smaller pieces.

Boulder

Cobble

Pebble

Sand

Silt

Clay

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12

Erosion

Sometimes weathered materials are picked up and

carried away. The movement of weathered materials is

called erosion. Glaciers, gravity, wind, and water can

cause erosion.

Water erosion is the most common form. Rivers move

bits of rock. During floods, mud and sand flow over a

rivers banks. Rainwater washes soil away from hills.

Erosion can make new islands. Rivers carry rocks

and soil to the ocean. They build up over time into

islands. Then wind and waves

change their shape.

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13

In dry places such as deserts, wind often causes

erosion. Wind can pick up dry sand and soil. It blows

them to other places since there arent many plants

to hold them down. The particles bump into rocks

and cause small grains to break

off. Slowly the rocks change.

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Living things can cause erosion. Some squirrels

tunnel through soil. Worms can mix and carry soil to

new places. Groups of ants move soil to make nests.

When an animal tunnels, it allows water and air

into the ground. Then the air and water continue

the erosion.

14

Erosion caused the hole in this cliff.

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Gravity causes erosion by pulling rocks downhill.

This material moves slowly unless the slope is steep.

Weathered material moves very quickly on steep

slopes! The movement of wet soil is called a mudflow.

When rocks slide quickly down a hill, it is called

a rockslide.

15

This hillside eroded. The side of the hill slumped down.

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16

Glossary

core the innermost layer of Earth

crust the outer layer of Earth

erosion the movement of weathered material

landform a solid feature formed on Earths crust

lava molten rock that erupts from a

volcano

magma hot, partly melted rock that is under

pressure

mantle the part of Earth just beneath the crust

weathering any action that breaks rocks into

smaller pieces

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Vocabularycore

crust

erosion

landform

lava

magma

mantle

weathering

What did you learn?1. What forces can cause erosion?

2. Name the different layers of Earth.

3. How do volcanoes erupt?

4. In this book you have read about how weathering affects landforms. Write to explain how weathering can change landforms. Use examples from the book to support your answer.

5. Sequence What happens during an earthquake?

Illustrations: 3, 4, 7 Big Sesh StudiosPhotographs: Every effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Unless otherwise acknowledged, all photographs are the property of Scott Foresman, a division of Pearson Education. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R) Background (Bkgd)Opener: David Muench/Corbis; Title Page: Big Sesh Studios; 2 David Muench/Corbis; 5 (BC) Pat OHara/Corbis, (CR) Royalty-Free/Corbis; 6 Photographers Choice/Getty Images; 8 (CR) Spencer Grant/Photo Researchers, Inc., (B) Lloyd Cluff/Corbis; 9 (BL) Ken M. John/Photo Researchers, Inc., (BR) La Prensa Grafica/AP/Wide World Photos; 10 (R) Fred Whitehead/Animals Animals/Earth Scenes, (BR) Jeremy Horner/Corbis; 11 Natural History Museum/DK Images; 12 DK Images; 13 La Prensa Grafica/AP/Wide World Photos; 14 William Manning/Corbis; 15 David Muench/Corbis

ISBN: 0-328-13829-0

Copyright Pearson Education, Inc.

All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permissions, write to: Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

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