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Transcript
Theory of Plate Tectonics
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.
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.
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.
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.
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.
Reading Science Questions
1. What do we call Earth’s outermost layer? ________________________
2. Why do scientists compare the Earth’s crust to a giant jigsaw puzzle?
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3. Pangaea can best be described as:
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4. How is Earth’s crust recycled?
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5. Scientists predict that in another 250 million years, the continents will be located in different
positions. How is this possible?
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6. ___________________ occurs when continental land masses collide with ocean plates or
when two ocean plates collide together.
7. How do earthquakes and tsunamis form?
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