Reading Science: Theory of Plate Tectonics

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's 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.

Which layer of the mantle do the tectonic plates "float" on top of?

• Lithosphere

• Mesosphere

• Asthenosphere

• Outer Core

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. The 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.

Which of the following best describes Pangaea?

• The seven continents that we know now

• An area on Earth that contains a ring of volcanoes

• A giant landmass that existed over 250 million years ago

• The process by which plates move

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Earth's plates are continually being created or recycled. Scientist 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.

Ridges are formed along the ocean floor due to ____ leaving the mantle.

• Steam

• Molten Iron

• Solid Rock

• Molten Rock

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Plate tectonic theory has also helped scientists explain the deep ocean trenches. These deep ocean trenches are areas where the 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 the Earth's mantle. It will become molten rock again. This type of area is known as a subduction zone. They form when continental land masses collide with ocean plates, or when two ocean plates collide together.

When do subduction zones occur?

• Two continental plates collide.

• A continental plate and ocean plate collide.

• Two ocean plates collide.

• On divergent boundaries.

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How is the Earth's crust recycled?

• Earth's crust is not recycled, only created.

• As molten rock seeps out of weak spots in the crust, volcanoes are formed.

• When plates slide past each other, creating friction, an earthquake forms.

• 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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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 sometime cause earthquakes and tsunamis.

The Himalayan mountains were most likely formed due to?

• An ocean plate colliding with a continental plate.

• A volcano erupting near water.

• Two continental plates colliding.

• Two ocean plates colliding.

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The plates on the Earth's crust change Earth's surface features in many ways. They had been 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.

Scientist predict that in another 250 million years, the continents will be in different positions. How is this possible?

• The tectonic plates are continually moving at a slow rate.

• The gravity on Earth causes the continents to move around.

• Scientist think that the continents will move back into the shape of Pangaea again.

• All of the above.

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