Download Plate Tectonics Reading

8.9AB: Plate Tectonic Theory
Earth and Space
Theory of Plate Tectonics
Lexile 1100L
1
As you may have discovered,
Earth is not just an ordinary
planet in the solar system.
Much like peeling an onion,
Earth’s layers reveal answers to
some interesting mysteries that
have baffled scientists for years.
Earth’s crust, the outer most
layer, is not entirely one piece.
It is broken into sections which
resemble an oversized jigsaw
puzzle. These giant sections,
known as plates, are always on the move, creeping along at a snail’s pace. It is
almost as if the plates float on top of the mantle, the layer of Earth that is
composed of partially melted rock.
2
Have you ever put together a puzzle? The interlocking pieces must fit
together perfectly in order to form a picture. Approximately 100 years ago, a
German scientist named Alfred Wegener discovered something fascinating
about a map of Earth. He realized that the continents seem to fit together like
the pieces of a jigsaw puzzle. The giant piece of land, called Pangaea, existed
over 250 million years ago. Over time, the tectonic plates of which Pangaea
consisted slowly drifted apart. These plates are now in their current positions
on Earth, making up the seven continents as we know them.
1 8.9AB: Plate Tectonic Theory
Earth and Space
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Earth’s plates are continually being created or recycled. By studying the
ocean floor, oceanographers have discovered mountainous ridges along
the bottom of the ocean. These ridges appear to be where two plates
have started to move apart. Molten rock from the underlying mantle
oozes out and fills the space that has been created by the plates’
movement. The theory of plate tectonics has also helped scientists
explain another amazing Earth landform: the deep ocean trenches. These
deep ocean trenches are areas where plates are being recycled. As plates
move apart, forming new crust along one plate edge, the crust on another
edge of the plate is slowly forced back down into Earth’s mantle where it
becomes molten rock again. This type of area, known as a subduction
zone, forms when continental land masses collide with ocean plates or
when two ocean plates collide together.
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Movement of the plates not only causes trenches and ridges on the ocean
floor, but it can also form mountains on land. When two continental
plates push together, there is so much force that the plates buckle,
forming massive mountain ranges. The friction during crustal movement
can sometimes cause earthquakes and tsunamis.
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The plates on Earth’s crust have the power to change Earth’s surface
features in many ways. Having previously been pieced together in a giant
landmass, they slowly moved apart to their current locations. The plates
will continue to move, forming new rocks and recycling the old. In
another 250 million years, as the tectonic plates continue to creep along,
imagine how a map of Earth might look.
2 8.9AB: Plate Tectonic Theory
Earth and Space
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A
B
C
D
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3
Why do scientists compare the
Earth’s crust to a giant jigsaw
puzzle?
The plates on Earth form a
picture like a jigsaw puzzle
does.
The mountains and volcanoes
on Earth are pieced together.
The plates on Earth fit together
like the pieces of a jigsaw
puzzle.
How is Earth’s crust recycled?
A
Earth’s crust is not recycled, only
created.
B
As molten rock seeps out of
weak spots in the crust,
volcanoes are formed.
C
When plates slide past each
other, creating friction, an
earthquake forms.
D
As new crust is created, old
crust is forced down deep inside
Earth’s mantle where it becomes
molten rock again.
The plates on Earth are slowly
drifting apart.
4
Pangaea can best be described as —
A
the seven continents that we
know now.
B
an area on Earth that contains a
ring of volcanoes.
C
a giant landmass that existed
over 250 million years ago.
D
the process by which plates
move.
3 Scientists predict that in another
250 million years, the continents will
be located in different positions.
How is this possible?
A
The tectonic plates on Earth
are continually moving at a
slow rate.
B
The gravity on Earth causes
the continents to move
around.
C
Scientist think that the
continents will move back into
the shape of Pangaea again.
D
All of the above
8.9AB: Plate Tectonic Theory
Earth and Space
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_______ occurs when continental
land masses collide with ocean
plates or when two ocean plates
collide together.
A
Accretion
B
Subduction
C
Jigsawing
D
Recycling
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