3 8 changes on earth (earth science)

core crust erosion landform lava magma mantle weathering What did you learn?. Earth’s Layers Earth is divided into three layers.. The crust is the outer layer of Earth.. Crust Core Mant

Trang 1

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

ì<(sk$m)=bdicjg< +^-Ä-U-Ä-U

Earth Science

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

ì<(sk$m)=bdicjg< +^-Ä-U-Ä-U

Earth Science

Trang 2

core

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?

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 Studios

Photographs: 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

O’Hara/Corbis, (CR) ©Royalty-Free/Corbis; 6 ©Photographer’s 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

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

Changes on Earth

Trang 3

What are Earth’s layers?

Earth’s 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

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

Trang 4

Shapes on Earth’s Surface

A landform is a solid feature on Earth’s 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

Glacier

Valley Plateau

Ocean

Coast

Do you recognize

these landforms?

5

A glacier is a moving body of ice It slowly moves downhill A volcano is an opening in Earth’s crust

Hot, melted rock is forced through it Some mountains form when pieces of rock are pushed along cracks in Earth’s crust A lake forms when water flows slowly enough to fill up an area

Volcano Mountain

Lake

River

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

Plain

Hill

Trang 5

What 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 Earth’s 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.

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

Side vent

Magma chamber

Side vent

Trang 6

Parts of Earth’s 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 Earth’s 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

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.

Trang 7

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

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

Trang 8

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

river’s 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

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 aren’t many plants

to hold them down The particles bump into rocks and cause small grains to break

off Slowly the rocks change

Trang 9

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.

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.

Trang 10

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 Earth’s 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

Vocabulary