Download 1What Makes Up the Earth?

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What Makes Up the Earth?
LESSON GOALS
You will learn
• three kinds of landforms.
• the earth's three layers.
• about the movement of
plates in the earth's crust.
Imagine taking a trip across the United States. You
could meet many interesting people and see many
famous sights. You would also notice that the shape
of the land changes. Sometimes you could see tall
mountains. Other times you could see flat fields.
Landforms
landform, a shape of the
land, such as a mountain,
plain, or plateau.
A mountain range
Different shapes of land are called landforms.
These pictures show three kinds of landforms:
mountains, plains, and plateaus.
Mountains are parts of the land that rise at least 600
meters above the surrounding land. Mountains are
often found in groups-or.
ranges. The line of
mountains in the picture is a range.
Plains are flat parts of the land. However, plains
are not always completely flat. They often have small
hills. A plateau also is flat. A plateau is flat land that
is higher than the land around it.
A plain
A plateau
The Earth's Three Layers
Landforms are on the surface of the earth. The
picture shows what the inside of the earth looks like.
Notice that the earth is made up of layers. How many
layers do you see? The top layer is the crust. It is 8
to 65 kilometers thick. The crust is made of rocks and
soil. Mountains, plains and plateaus are some
landforms of the crust.
The layer below the crust is the mantle. It is about
2,800 kilometers thick. The mantle is mostly solid
rock. However, some of the rock is partly melted.
The third layer of the earth is the core. It is about
3,500 kilometers thick. The core has two parts. The
outer part is made of melted rock. The inner part of
the core is solid rock.
SCIENCE IN YOUR LIFE
People can see a little
way inside the earth's crust
when they dig mines and
wells. The deepest well
ever dug is 9 kilometers
deep. The deepest mine
goes down about 4
kilometers. However, the
center of the earth is
almost 6,400 kilometers
from the surface.
crust (krust), the top layer
of the earth.
mantle (marr/tl), the
middle layer of the earth.
Layers of the earth
core (kor), the center part
of the earth.
Crust
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Plates That Move
plate, a large section of
rock that makes up part of
the earth's crust.
Look at the picture of the continents. Notice that
many of them seem to fit together like pieces of a
giant jigsaw puzzle. Scientists think that millions of
years ago, the continents were joined in one large
piece of land. Then, the continents broke apart and
moved away from each other. Today, the continents
are still moving.
The continents move because the crust moves. The
crust is made up of large sections of rock-or plates.
The plates move over the melted rock in the earth's
mantle. As the plates move, some of them move
away from each other. Others bump into each other.
Still others slide past each other.
The plates move all the time. People. usually
cannot feel the plates move because the plates move
very slowly. They only move about 2 to 20
centimeters each year.
How continents fit together
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The red lines in the map below are places where
two plates meet. Volcanoes often form near these
places. As plates move, the melted rock under the
plates moves up to the top and forms volcanoes. Most
earthquakes also happen near the edges of plates.
When the plates move past each other, rocks near the
edges bend and break.
The red lines show where
plates meet.
Where two
plates meet
Australia
Lesson Review
1. How are a plain and a plateau different?
2. Describe the three layers of the earth.
3. What causes a continent to move?
4. Challenge! Some plates under the Atlantic Ocean
are moving apart. Why do you think the Atlantic
Ocean is slowly becoming wider?
Study on your own, pages 394-395.
A geyser is an opening in the ground from
which hot water and steam burst out from time to
time. Use books in the library to find out what
causes geysers to erupt. Write a paragraph
explaining what you learn.
EARTH
SCIENCE
FIND OUT
ON YOUR OWN
245
LESSON 1
pages 242-245
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10.
Plateaus and plains are two kinds of __ .
Mountains are often found in groups, or __ .
What is the earth's crust made of?
The mantle of the earth is about
kilometers thick.
What makes up the two layers of the earth's core?
What do scientists think the continents were like millions
of years ago?
The :::I:t that make up the earth's crust move over the
melted rock in the earth's mantle.
The earth's plates move about __ centimeters each year.
When melted rock from under the earth's plates moves
up to the top, a __ forms.
When the earth's plates move past each other, an __
can take place.