3 8 our changing earth (earth science)

Genre

Nonfiction

Comprehension Skill

Sequence

Text Features

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Captions
Diagrams
Labels
Glossary

Science Content

Changes on Earth

Scott Foresman Science 3.8

ISBN 0-328-13830-4

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Vocabulary
core
crust
erosion
landform
lava
magma
mantle
weathering

What did you learn?
1. What are the three main layers
of Earth?
2. How are landforms alike and
different?
3. What’s the difference between
magma and lava?
4.

Weathering

by Kim Borland
and erosion work together to

change Earth’s surface. Write to
explain how this works.
5.
Picture Credits
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.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).
Opener: Getty Images; 1 Getty Images; 3 Brand X Pictures; 4 ©Roger Ressmeyer/Corbis; 6 (TL) Digital Vision; 7 (TR)
Getty Images, (CR) Digital Stock; 9 (TL) Getty Images; 10 (CL) ©David Parker/Photo Researchers, Inc., (T) ©Bettmann/
Corbis; 12 (B) Getty Images.
Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson.

ISBN: 0-328-13830-4
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 permission(s), 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

Sequence Describe how a
volcano erupts, placing each step in
order. Use the words magma and
lava in your description.


Forces of Change
When you stand on the ground, Earth feels
solid beneath your feet. But did you know that
our planet is moving and changing all the time?
It’s true! Although you can’t feel it, Earth’s
rocks are constantly pushing, squeezing, and
pulling beneath your feet.
Forces inside Earth and on its surface
change Earth’s rocks. These forces cause
rocks to slowly bend, twist, and turn.

Earth’s rocks are constantly bending,
twisting, and turning.
Some forces change Earth’s surface
quickly. Those forces include earthquakes
and volcanoes. Other forces change Earth’s
surface very slowly. Those
forces include weathering and erosion. Some
forces take a very long time to change Earth!

Earth from space

2

3


Earth’s Layers
Our planet is made up of several layers of
rock. Scientists learn about Earth by studying
these different layers. Scientists study the layers
near Earth’s surface. They also study the layers
deep under the ground.
The crust is the hard, rocky layer that forms
Earth’s surface. Below the crust is the mantle.
The mantle is the thickest layer of Earth. It is
more than two thousand miles thick. It makes up
more than most of Earth’s total volume.
Geologists study
Earth’s crust.

Cross-section of Earth
Crust

Mantle

Liquid
outer
core

Solid inner
core

The innermost layer of Earth is the core. It is
made mostly of iron and nickel. Iron and nickel
are metals. The core has two layers. Those layers
are the outer core and the inner core. The outer
core is a very hot liquid. At Earth’s center is the
inner core. It is solid and hard.
Earth is coolest at the crust. It is hottest at the
core. Earth’s core is about one hundred times
hotter than the hottest desert!

4

5


Shapes on
Earth’s Surface
Desert

A landform is a solid feature
formed on Earth’s crust. Hills,
mountains, valleys, and plains are
landforms. Waterfalls, cliffs, islands,
and caves are landforms too. Even
volcanoes are landforms.
Landforms are of different
shapes and sizes. But all landforms
are alike in one important way.
They are all shaped by natural
forces. Those forces include heat,
wind, water, and ice.

Many landforms are
shaped by moving water.
Rivers carve out valleys
as they flow. Sand and small
rocks carried in rivers wear
away the land. The material
that is worn off gets carried
away. Then it gets left in
new places.

Waves

Volcano

Mountain lake

Rock butte

Waterfall

6

7


Volcanoes and
Earthquakes
Volcanoes can cause rapid changes to Earth’s
landscape. They contain magma. Magma is hot,
molten rock. It sits in pockets called magma
chambers. Gases in the magma create pressure. The
pressure forces the magma through a central vent.
The central vent leads to the top of the volcano.

Central
vent

This is how a volcano erupts.
Hot ash

Lava

Magma

8

Ash erupts from Mount
St. Helens.

Magma erupts from a vent.

When the magma reaches the volcano’s top,
the volcano erupts. Sometimes magma erupts
through side vents. But it usually erupts through
the volcano’s top.
Volcanoes send steam, rocks, and ash into the
air when they erupt. Lava is magma that reaches
the surface. It flows down the slopes and burns
everything in its path. Lava is eight times hotter
than boiling water! When lava cools, it becomes
hard, igneous rock. That rock is a new part of
Earth’s crust.

9


1906 San Francisco
earthquake

Earthquake Damage
California’s San Andreas
Fault is more than eight
hundred miles long.

Earthquakes
An earthquake is a natural force that shakes

the ground. Earthquakes happen when pieces of
Earth’s crust rub together along faults, or cracks.
Earthquakes produce waves of vibrations. These
waves move up and down and back and forth.

10

Powerful earthquakes can cause a lot of
damage. Earthquakes that are closer to the surface
cause more damage. The longer an earthquake
lasts, the more damage it can cause. The nearer an
earthquake is to a city, the more buildings will
be damaged.
Earthquakes cause landslides, which also cause
damage. Landslides are rocks and soil that slide
down the side of a hill. They can destroy buildings
and roads. Landslides also happen in the ocean.
There they can create huge, dangerous waves.

11


Weathering
You may not see weathering happen. But
weathering goes on all the time. Weathering is a
process that breaks down rocks on Earth’s surface
into smaller and smaller pieces. Plants, animals,
insects, and other living things can cause
weathering. Water, wind, and ice can cause
weathering too. Sometimes weathering changes

only take a few years. Other times they take
centuries.
Plants are just one cause of weathering. Plants
cause weathering by forcing their roots into cracks
in rocks. As the roots grow, they split the rocks.
Snow-capped mountains

12

Glaciers

Water causes weathering too. Sometimes
water picks up special chemicals from soil. The
chemicals eat away at rocks the water touches.
This is called chemical weathering.
Ice also weathers rocks. Water can get into
cracks. When water freezes into ice, it expands.
This splits rocks apart.
Ice can weather rocks in another way. Glaciers
are huge masses of ice and snow. They scrape the
ground beneath them as they move. This scraping
causes many changes.

13


Erosion
After rock is broken apart by weathering,
the pieces often get carried away. This is called
erosion. Wind, water, glaciers, and gravity all

cause erosion.
Water is always causing erosion. Rivers carry
away bits of rock and leave them in new places.
This forms new islands. Rainwater and ocean
waves also cause erosion.
Deserts lack water. Because of this, most
desert erosion is caused by wind. Deserts have
few plants to block the wind. They also lack plant
roots to hold down soil. This means strong winds
can cause lots of erosion.

These buttes were eroded by the wind.

14

Animals are another cause of erosion.
Worms, squirrels, and ants all dig holes in the
ground. These holes let water and air into the
soil. This causes further erosion.
Gravity causes erosion too. Broken rock and
other materials often fall down hills as mudflows
or rockslides.
Earth is always changing. Most of the time the
changes are small and take a long time. Other
times the changes are big and happen very fast.
Look at the land around you. It may look the
same from day to day. But that land is changing
all the time!

The Grand Canyon was created by the Colorado River.

15


Vocabulary

Glossary
core

What did you learn?

crust
core
Earth’s innermost layer
erosion
landform the outer layer of Earth that is
crust
lava
made up of different kinds of rock
magma
mantle
erosion
the movement of weathered
weathering material

1. What are the three main layers
of Earth?

landform

a solid feature formed on Earth’s
crust

4.

lava

hot, melted rock that comes out of
a volcano

Weathering
and erosion work together to
change Earth’s surface. Write to
explain how this works.

5.

Sequence Describe how a
volcano erupts, placing each step in
order. Use the words magma and
lava in your description.

magma

hot, melted rock beneath Earth’s
Picture Credits
surface that is kept under pressure
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.
by gases

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).
Opener: Getty Images; 1 Getty Images; 3 Brand X Pictures; 4 ©Roger Ressmeyer/Corbis; 6 (TL) Digital Vision; 7 (TR)
Getty Images, (CR) Digital Stock; 9 (TL) Getty Images; 10 (CL) ©David Parker/Photo Researchers, Inc., (T) ©Bettmann/
Corbis; 12 (B) Getty Images.

mantle

the thick layer of Earth between the
crust and the core

Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson.

weathering any action that breaks rocks into
smaller
pieces
Copyright © Pearson Education, Inc.
All Rights Reserved.
Printed in the United States of America.
ISBN: 0-328-13830-4

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 permission(s), 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

16

2. How are landforms alike and
different?

3. What’s the difference between
magma and lava?