Download Theory of Plate Tectonics

Maps of Ancient Lands
Plate Tectonics and Large-Scale Interactions
Theory of Plate Tectonics
1  Earth is not like the other planets in the solar
system. Earth has layers, much like an onion.
These layers provide answers to many questions.
Earth's crust, the outermost layer, is not entirely
one piece. It is broken into sections which
resemble a huge jigsaw puzzle. These giant
sections are known as plates. They are
always on the move, creeping along at a snail's
pace. The plates seem to float on top of the
mantle, the layer of Earth composed of partially
melted rock.
2  Have you ever put together a puzzle? The pieces must fit together perfectly in order to form a
picture. Alfred Wegener was a German scientist. Over 100 years ago, he discovered something
fascinating about a map of Earth. Wegener realized that the continents seem to fit together like
the pieces of a jigsaw puzzle. This giant piece of land was called Pangaea. It existed over 250
million years ago. Over time, Pangaea's tectonic plates slowly drifted apart. These plates in
their current positions make our seven continents.
3  Earth's plates are continually being created or recycled. Scientists have studied the ocean floor.
They have discovered ridges of mountains along the bottom of the ocean. These ridges form
where two plates have started to move apart. Molten rock from the underlying mantle oozes
out. Newly formed rock builds up in the space that has been created by the plates' movement.
Plate tectonic theory has also helped scientists explain the deep ocean trenches. These deep
ocean trenches are areas where plates are being recycled. This can happen where two plates
push together. The crust on the edge of one plate is slowly forced under the other. The plate
gets pushed back down into Earth's mantle. It will become molten rock again. This type of area
is known as a subduction zone. It forms when continental land masses collide with ocean
plates, or when two ocean plates collide with each other.
4  On the ocean floor, movement of the plates causes trenches and ridges. Plate movement can
do more than that. It can also form mountains on land. When two continental plates push
together, there is so much force that the plates buckle. Massive mountain ranges are formed.
The friction during crustal movement can sometimes cause earthquakes and tsunamis.
5  The plates on Earth's crust change Earth's surface features in many ways. They had been
pieced together in a giant landmass. The plates slowly moved apart to their current locations.
The plates will continue to move, forming new rocks and recycling the old. Imagine how a map
of Earth might look after another 250 million years of continental drift.
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Maps of Ancient Lands
Plate Tectonics and Large-Scale Interactions
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What analogy does the author use to describe how Earth's continents fit together?
A
The plates on Earth form a picture like a jigsaw puzzle does.
B
The mountains and volcanoes on Earth are pieced together.
C
The plates on Earth fit together like the pieces of a jigsaw puzzle.
D
The plates on Earth are slowly drifting apart.
Which of the following best describes Pangaea?
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
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.
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Maps of Ancient Lands
Plate Tectonics and Large-Scale Interactions
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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
The diagram above illustrates a type of plate boundary. Which crustal feature is most
likely to form at this type of boundary?
A
trench
B
ridges
C
tsunami
D
earthquake
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