3 8 our changing earth (earth science)

and erosion work together to change Earth’s surface?. Vocabulary core crust erosion landform lava magma mantle weathering Picture Credits Every effort has been made to secure permission

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Scott Foresman Science 3.8

Nonfi ction Sequence • Captions

• Diagrams

• Labels

• Glossary

Changes on Earth

ISBN 0-328-13830-4

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Scott Foresman Science 3.8

Nonfi ction Sequence • Captions

• Diagrams

• Labels

• Glossary

Changes on Earth

ISBN 0-328-13830-4

ì<(sk$m)=bdidac< +^-Ä-U-Ä-U

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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?

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

volcano erupts, placing each step in

order Use the words magma and

lava in your description.

What did you learn?

Vocabulary

core

crust

erosion

landform

lava

magma

mantle

weathering

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.

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.

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by Kim Borland

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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!

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Earth from space

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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.

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Cross-section of Earth

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!

Crust

Solid inner core

Mantle

Liquid outer core

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Shapes on Earth’s Surface

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

Rock butte

Waterfall

Desert

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Many landforms are shaped by moving water

Rivers carve out valleys

as they fl ow 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

Mountain lake

Volcano Waves

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Volcanoes and

Earthquakes

This is how a volcano erupts.

Hot ash

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

Magma

Lava

Central

vent

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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 fl ows 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

Ash erupts from Mount

St Helens.

Magma erupts from a vent.

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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

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

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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

Earthquake Damage

1906 San Francisco earthquake

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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

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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

Glaciers

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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.

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The Grand Canyon was created by the Colorado River.

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 mudfl ows

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!

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Glossary

core Earth’s innermost layer

crust the outer layer of Earth that is

made up of different kinds of rock

erosion the movement of weathered

material

landform a solid feature formed on Earth’s

crust

lava hot, melted rock that comes out of

a volcano

magma hot, melted rock beneath Earth’s

surface that is kept under pressure

by gases

mantle the thick layer of Earth between the

crust and the core

weathering any action that breaks rocks into

smaller pieces

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?

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

volcano erupts, placing each step in

order Use the words magma and

lava in your description.

What did you learn?

Vocabulary

core

crust

erosion

landform

lava

magma

mantle

weathering

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).

Corbis; 12 (B) Getty Images.

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

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