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Earth Science
by Kelly Kong
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Earth’s Surface
Scott Foresman Science 5.9
ISBN 0-328-13940-8
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Vocabulary
What did you learn?
chemical weathering
1. What are three ways that scientists learn about Earth’s mantle
and core?
core
crust
igneous
mantle
mechanical weathering
Earth’s Changing Surface
by Kelly Kong
2. Is the rate of mechanical weathering the same for all rocks?
Why or why not?
3. Describe two ways that gravity helps cause erosion.
4.
Earth’s plates are always moving.
On your own paper, write to explain how even though plates
move slowly, they can cause huge changes. Provide details
from the book to support your answer.
5.
Summarize Tell how erosion and deposition can
break down and build up land.
metamorphic
plate
sedimentary
Illustrations: 3, 4, 7, 8, 11 Adam Benton; 7 Sharon & Joel Harris
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: ©Bruce Davidson/Nature Picture Library; Title Page: Adam Benton; 2 ©Raymond Gehman/NGS
Image Collection; 5 ©DK Images; 9 (CL) ©William Allen/NGS Image Collection, (BR) Corbis; 10 (TL)
©Larry Stepanowicz/Visuals Unlimited, (BL) ©Wayne Lawler/Ecoscene/Corbis; 13 (T) ©Macduff Everton/
Corbis, Corbis; 14 ©David Lawrence/Corbis; 15 ©Darrell Gulin/Corbis; 16 (BC, CR) ©DK Images;
17 (TL) ©DK Images, (CR) Colin Keats/Courtesy of the Natural History Museum, London/©DK Images,
(BL) Natural History Museum/©DK Images; 19 (TR, TL, CL, CR, BR) ©DK Images; (CL, BL) Colin Keates/
Courtesy of the Natural History Museum, London/©DK Images; 20 (CR) Royal Museum of Scotland/©DK
Images, (BC, BR) ©DK Images; 21 (CL) ©Colin Keats/Courtesy of the Natural History Museum/London/
©DK Images, (BR) ©DK Images; 22 (TR, BC, BL, BC, CL) ©DK Images, (TR) Natural History Museum/©DK
Images; 23 (CL, CR, BC, BL) ©DK Images
ISBN: 0-328-13940-8
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
What is the structure
of Earth?
The Crust
Earth is made up of four different layers. The crust is Earth’s
thin outer layer. There are two types of crust. Continental crust
is found on land and is mostly granite. It is thickest in the
mountains, where it can reach a depth of 75 kilometers.
The crust beneath the ocean floor is called oceanic crust. It
is made of mostly dark green or black rock called basalt. This
crust is about 6 to 11 kilometers thick.
Part of the continental crust is underwater. This is called the
continental shelf. At the edge of the shelf is a steep drop-off,
called the continental slope. At the bottom of this slope is the
continental rise, which is the start of the oceanic crust. This is
less than 100 kilometers from the coast in most places.
Continental rise
Continental shelf
Continental slope
2
3
The Mantle and Core
Below the crust is a thick layer called the mantle. It makes
up most of Earth’s material. The top part of the mantle is solid
hot rock. This part plus the crust above it form the lithosphere.
Deep in the mantle the pressure is very high.
Temperatures range from 360°C to 2,500°C.
Rock in this area is solid, but the heat
and pressure make it flow like a
thick liquid. The hotter rock
floats upward as cooler rock
sinks. This is a convection
current. The lithosphere
floats on top of these
currents.
The center of Earth
is the core, which is
made mostly of iron.
Temperatures in the
core can reach
7,000°C. The inner
core is solid. The
outer core is liquid
that flows in currents.
These currents make
Earth’s magnetic field.
The mantle and the core are so far below Earth’s surface
that scientists cannot get there to study them. They learn about
these layers in different ways. Scientists study rock from the
mantle that comes up through cracks in the crust.
Scientists also learn about
Earth’s layers by measuring
earthquake vibrations with a
tool called a seismograph. As
vibrations move through the
different layers, they change
speed and direction. Some stop
completely when they reach
the outer core. By studying the
vibrations from earthquakes
everywhere, scientists can learn
about Earth’s layers.
Scientists can also learn
about the mantle and
core through laboratory
experiments. Materials that are
likely inside Earth are tested
under great heat and pressure.
Material in the mantle
flows in convection currents.
4
5
What causes earthquakes
and volcanoes?
Earth’s Plates
The lithosphere is broken up into large and small sections
called plates. Although you can’t feel it, these plates are
always moving. A plate may include continents, parts of the
ocean floor, or both. Edges of plates are called plate boundaries.
Earth’s plates move as slowly as 1 centimeter per year and
as fast as 24 centimeters per year. Plates can move into, pull
apart from, or grind past each other. These movements change
Earth’s surface. Mountains and valleys can form. Earthquakes
and volcanoes usually happen at plate boundaries.
Plates move for different reasons. Sometimes gravity pulls
part of a plate down into the mantle. This pulls the rest of the
plate with it. Plates also move due to convection currents in
the mantle.
There are three main types of plate boundaries. Converging
plate boundaries are formed where two plates collide. This
can build mountains by folding, tilting, or lifting the crust.
Spreading plate boundaries form when plates separate.
There is a spreading plate boundary in the middle of the
Atlantic Ocean. This ocean is getting wider as the plates move
apart. A ridge has formed at the edges of the plates. It has a
low area running down its middle, which is called a rift valley.
When two plates slide past each other in opposite directions
it is called a sliding plate boundary. Part of California sits on
a sliding plate boundary.
Sliding plate boundary
Converging plate boundary
Spreading plate boundary
6
7
Earthquakes
Volcanoes
Earth’s surface is changed by different kinds of forces.
Constructive forces build new features like mountains.
Destructive forces tear down features. Earthquakes are
destructive forces.
Earthquakes usually happen at faults. These are cracks
in Earth’s crust. As two plates slide past each other, they
sometimes get stuck. Pressure builds up, and in time the plates
break free. They move suddenly, creating the vibrations of an
earthquake. The place where the plates slip is called a focus.
The point on Earth’s surface above a focus is an epicenter.
Energy released in earthquakes can cause destruction, such
as landslides. Most injuries from earthquakes are caused by
buildings falling apart. Earthquakes under the ocean can
produce huge, dangerous waves called tsunamis.
Most volcanoes form near converging plate boundaries.
When one plate slides under another, rock melts into magma.
Sometimes magma breaks through weak spots in the crust to
reach Earth’s surface. The melted rock then flows out as lava.
Gases such as water vapor and carbon dioxide can mix with
lava. Trapped gases can create pressure and cause a volcano to
explode. When this happens, lava can cool in the air and fall
as solid rock or ash.
Volcanoes can also form on the ocean floor. If the volcano
grows high enough to reach the surface, it becomes an island.
This is how the islands of Hawaii were formed. In this case, the
volcano is a constructive force.
Crater
Vent
Epicenter
Fault line
Focus
8
9
What is weathering?
Weathering
Weathering is the process that breaks rocks into smaller
pieces called sediments. There are two types of weathering.
When gravity, ice, or plant roots break up rocks, it is called
mechanical weathering. When chemical processes change
the rocks, it is called chemical weathering.
Mechanical Weathering
Ice wedging occurs when water
freezes in cracks in rocks. When
wind blows dirt from mountains,
the rocks in the mountain are
under less pressure. They expand
at different rates and cracks form.
As cracks grow, water enters them
and freezes. The water expands as
This rock has been
it freezes, breaking the rocks apart.
split by ice wedging.
The rate of mechanical weathering
depends on the type of rock and the conditions. Roots can grow
into cracks in a rock and push the rock apart. This weathering
occurs more quickly in warm, wet conditions, where roots
grow faster. The roots will split soft rocks more quickly than
hard ones.
Chemical Weathering
Chemicals also break down rocks. Raindrops absorb carbon
dioxide from the air. This makes a chemical called carbonic
acid. When rain soaks into some rocks, the carbonic acid
can dissolve parts of them. Caves can form. Fungi and other
organisms can also give off chemicals that change rocks.
Some rocks are more quickly broken down by chemical
weathering than others. Areas with lots of rain have more
chemical weathering than other areas.
Soil
Soil contains sediment from weathered rocks. It also
contains decayed material from organisms, gases from
air, and water.
Soil can be red, brown, black, or gray. Soil with larger
particles, such as sand, lets water pass through more easily.
Soil with smaller particles, such as clay, holds water better
and feels smooth. Most plants grow best in soil with a lot of
decayed matter.
Topsoil contains a large
amount of decayed
material.
Subsoil is often a different
color than topsoil.
Bedrock is nearly solid
rock that lies below
the subsoil.
10
11
What is erosion?
Erosion and Deposition
Erosion is the movement of materials away from a place.
Deposition is the placing of materials in a new place. Erosion
is a destructive process, while deposition is a constructive one.
Sand dunes, valleys, and deltas are formed by erosion and
deposition together.
Gravity is the main force that causes erosion. Gravity can
cause landslides during earthquakes or after rains. Landslides
often occur on steep slopes with no trees. Tree roots help keep
soil in place.
Gravity also causes rivers to flow. As river water flows
downhill, it picks up sediments. These sediments can wear away
the riverbed. Fast-moving rivers can carry heavier sediments
and erode deep canyons.
This canyon was formed by erosion.
12
Erosion from water happens in other places as well. In the
ocean, currents can erode deep valleys in the continental shelf.
On a farm, rainwater can erode fields. Farmers plow across
fields to stop this erosion. The ruts made by the plow keep the
water from flowing downhill.
When flowing water slows, sediment is deposited. This
happens when rivers reach oceans, lakes, or the bottom of
a hill. When a river enters a lake formed by a dam, it can
cause a problem. The sediment it drops must be dug out.
When a river meets the ocean, the sediment that it drops
can form a delta.
The frozen water in a glacier can cause erosion too. Gravity
pulls glaciers downhill. As they move, they grind rocks beneath
them into sediments. Sediments get carried along by the
moving ice.
This river deposits sediment when it reaches the ocean, forming a delta.
13
Wind Erosion
Wind erosion happens when wind blows dust, soil, or sand.
As wind blows, it can pick up bits of broken rock and carry
them away. Wind erosion can turn rock into amazing shapes,
such as arches and towers.
Sand Dunes
Ocean waves deposit and move sand.
Sand dunes are large, loose piles of sand. The size and shape
of dunes depends on the wind, the sand, and the plants in the
area. Wind pushes sand up one side of a sand dune. When the
sand reaches the edge of the dune’s top, the wind can’t reach it
anymore. It falls straight down because of gravity. This side of
the dune becomes very steep.
Field Erosion
Wave Erosion
The action of waves is a big source of deposition and erosion
along coastlines. As waves crash, rocks can break. Sand and
gravel in the waves can wear down the rocks. Some of the sand
on beaches is formed this way.
Harbors and inlets form when parts of a shoreline erode
faster than others. Harbors are areas protected from waves.
Wave erosion of cliffs can form caves.
When waves hit a beach at an angle, they can move sand.
Sand can form a peninsula called a spit. A spit that forms
across the mouth of a bay is called a baymouth bar. The
enclosed area is called a lagoon. Sandy islands called barrier
islands can form along coastlines and can be moved by erosion.
Sometimes people build barriers across beaches to stop
the movement of sand. This can cause nearby beaches to get
smaller. Governments sometimes have sand dug from the
ocean floor and put on beaches to repair erosion damage.
14
If farm fields become too dry, wind can blow topsoil away.
Farmers prevent topsoil erosion by planting rows of trees. This
prevents some wind from reaching the field. Some farmers
prevent erosion by plowing less, to keep the soil in larger clumps.
Trees at the edge of a field reduce wind erosion by slowing the wind.
15
How are minerals identified?
Properties of Minerals
To a scientist who studies the Earth, minerals are naturally
made solids that can be found in soil and rocks. There are
many different minerals, but just a few of them make up most
of Earth’s rocks.
Minerals can be identified by their properties. Some minerals
have a certain smell. Other minerals make tiny bubbles when
they touch chemicals called acids.
Hardness
Luster
Luster describes the way a mineral’s surface
reflects light. A glassy luster is shiny like
glass. An earthy luster is chalky and dull.
This hematite has a metallic luster.
Shape
Some minerals
have a definite
shape. This pyrite is
shaped like cubes.
Mohs’ scale is used to tell how hard a mineral is.
The scale rates the hardness of minerals from
1 to 10. Diamonds are the hardest minerals.
They have a hardness of 10.
Streak
Streak is the color of a mineral in its
powdered form. To see a mineral’s
streak, you rub it on a hard, rough,
white surface. This is the streak of
hematite.
Magnetism
Magnetite, pictured here
with iron filings,
is strongly magnetic.
Texture
The texture of a mineral describes
the way it feels. This opal has a
smooth texture.
16
17
Using Properties to Identify Minerals
To identify a mineral, scientists observe and compare, using
charts of known minerals. They try to match the mineral they
are studying with a known mineral.
The chart below shows the names and properties of some
common minerals. Use it to identify minerals shown on the
next page.
Mineral
color
texture
smell
luster
hardness
Muscovite
colorless,
light-colored
smooth
no
pearly
22
1
white
Fluorite
colorless,
pink, purple,
green
smooth
no
glassy
4
white
Halite
colorless
smooth
no
glassy
22
1
white
Calcite
white,
colorless,
pale colors
smooth
no
glassy
3
white
Quartz
clear-white
smooth
no
glassy
7
white
Pyrite
gold
smooth
no
metallic
6–7 (for
crystals)
greenishblack
Sulfur
pale to
bright
yellow
gritty
rotten egg
dull to
glassy
12 to 2 2
white
Talc
white,
apple-green,
gray
greasy
no
pearly
1
white
Arsenopyrite
brassy white
or gray
gritty
garlic
metallic
5 2 to 6
black
18
1
1
1
shape
streak
• Smooth texture
• Pearly luster
• Hardness of 2.5
• Forms sheets
• Smooth texture
• Hardness of 2.5
• White streak
• Glassy luster
• Gritty texture
• Dull to glassy
luster
• Smells like a
rotten egg
• White streak
• Greasy texture
• Pearly luster
• Hardness of 1
• White streak
• Gritty texture
• Metallic luster
• Smells like garlic
• Hardness of 5.5 to 6
• Black streak
• Smooth texture
• Glassy luster
• Hardness of 7
• White streak
19
How are rocks classified?
Igneous Rocks
There are three main types of rocks. Each is formed in a
different way. Igneous rocks form when melted rock cools and
hardens. If rock cools slowly, large crystals of minerals form.
If rock cools quickly, small crystals form. Granite is a rock that
cools slowly underground. It has large crystals.
Basalt forms when lava is quickly cooled by ocean water. It
is a dark green or black rock with small crystals. Pumice forms
when lava is quickly cooled by air.
Small holes form where gas was
trapped in lava
as it cooled.
Sedimentary Rocks
Most sedimentary rocks form when bits of rock and other
materials settle on top of each other and harden. The particles
become stuck together by natural chemicals.
Sandstone and conglomerate are sedimentary rocks.
Sandstone is made up of layers of sand. Conglomerate is made
up of larger bits of material pressed together.
Layers of sedimentary rock often hold fossils. Scientists can
learn about a plant or animal and its environment by studying
the rock around it.
Metamorphic Rocks
Basalt
Granite
Conglomerate
Sometimes rocks are changed
after they form. Heat and
pressure can change how
the particles are arranged.
New minerals may also
form. The rocks that are left
by these changes are called
metamorphic rocks. At high
pressure and high temperature,
rock particles may form rough
layers, as seen in gneiss. At low
pressure, thin layers form, as seen
in slate.
Gneiss
Slate
Pumice
20
21
The Rock Cycle
Relative Ages of Rocks
Rocks are always being formed, broken down, or changed.
They can change from one type to another in any
order. An igneous rock today may become a
metamorphic rock in the future. Sometimes
they stay in the same form for millions
of years. The changes that rocks go
through are called the rock cycle. The
different ways that one type of rock
can become another type of rock are
shown below.
Layers of rock are laid down on top of one another over
time. The layers close to Earth’s surface are younger than
the layers below them. Sometimes the layers get turned
over or bent by earthquakes, volcanoes, or the formation of
mountains. Layers of rock are usually flat. If layers of rock
are broken or tilted, it shows that something has
happened to move the layers. Layers of rock can
show how old one fossil is compared to another.
Fossils found in lower layers are older than those in
upper layers.
in g
Soil
Heat and
Pressure
Igneous
rocks
Melting
th
at
in
g
en
t
io
at
n
Ce
Melting
a
We
g
n
eri
r
he
m
lt
Me
h erin g
e
Magma
at
We
g
W
Co
n
o li
M
el
tin
g
Sedimentary
rocks
Metamorphic
rocks
22
23
Vocabulary
Glossary
chemical
weathering
chemical
weathering
core
core
crust
igneous
crust
mantle
mechanical weathering
What did you learn?
the changing of materials in a
rock by chemical processes
1. What are three ways that scientists learn about Earth’s mantle
and core?
the center part of Earth that
includes the liquid outer core
and the solid inner core
2. Is the rate of mechanical weathering the same for all rocks?
Why or why not?
Earth’s outermost and
thinnest layer
igneous
a type of rock formed when
melted rocks cool and harden
plate
mantle
the layer of Earth between the
crust and the core
metamorphic
sedimentary
mechanical weathering
the breaking down of rock into
smaller pieces by any physical
force or processes such as gravity,
water, wind, ice, or life forms
Illustrations: 3, 4, 7, 8, 11 Adam Benton; 7 Sharon & Joel Harris
Photographs: Every effort has been made to secure
permission
provide
appropriate
credit for
metamorphic
a type
of and
rock
formed
when
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
existing
rock
is changed
Foresman, a division of Pearson Education. Photo locators
denoted
as follows:
Top (T), Centerby
(C),heat
Bottom
(B), Left (L), Right (R) Background (Bkgd)
or
pressure
Opener: ©Bruce Davidson/Nature Picture Library; Title Page: Adam Benton; 2 ©Raymond Gehman/NGS
Image Collection; 5 ©DK Images; 9 (CL) ©William Allen/NGS Image Collection, (BR) Corbis; 10 (TL)
©Larry Stepanowicz/Visuals Unlimited, (BL) ©Wayne Lawler/Ecoscene/Corbis; 13 (T) ©Macduff Everton/
plate
a large
section16of
crust
Corbis, Corbis; 14 ©David Lawrence/Corbis; 15 ©Darrell
Gulin/Corbis;
(BC,Earth’s
CR) ©DK Images;
17 (TL) ©DK Images, (CR) Colin Keats/Courtesy of the Natural History Museum, London/©DK Images,
mantle
(BL) Natural History Museum/©DK Images; 19 (TR,and
TL, CL, upper
CR, BR) ©DK
Images; (CL, BL) Colin Keates/
Courtesy of the Natural History Museum, London/©DK Images; 20 (CR) Royal Museum of Scotland/©DK
Images, (BC, BR) ©DK Images; 21 (CL) ©Colin Keats/Courtesy of the Natural History Museum/London/
sedimentary
aCL)
type
rock
when
©DK Images, (BR) ©DK Images; 22 (TR, BC, BL, BC,
©DK of
Images,
(TR)formed
Natural History
Museum/©DK
Images; 23 (CL, CR, BC, BL) ©DK Images
ISBN: 0-328-13940-8
sediments are pressed and
cemented together
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
24
3. Describe two ways that gravity helps cause erosion.
4.
Earth’s plates are always moving.
On your own paper, write to explain how even though plates
move slowly, they can cause huge changes. Provide details
from the book to support your answer.
5.
Summarize Tell how erosion and deposition can
break down and build up land.