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253

plate tectonics

OLogy Series
geology
card
253

plate tectonics

OLogy Series
geology

The Earth is always changing. Mountains form and erode away. Volcanoes erupt and grow larger. Earthquakes shift the land. Oceans grow and even continents move. What causes all this activity? The Earth's thin, fragile outer shell is broken into large pieces called "plates." These plates slowly move, floating on a layer of hot mantle below. This movement, or tectonic activity, is constantly changing the surface of the Earth.

Most tectonic activity occurs where two plates meet. Plates can collide, move apart, or slip past each other. A subduction zone is where:

two plates collide and one moves under the other

two plates move apart

two plates collide and fold up

Are you right?

Correct!

A subduction zone is where two plates collide and one moves under the other. The most explosive volcanoes occur above subduction zones where thin, dense oceanic crust moves under thick continental crust.

Plate tectonics helps explain why:

the Earth was once covered with nothing but ocean

all of the Earth's continents were once joined together in one continent

there was once life on Mars similar to life on Earth

Are you right?

Correct!

Today there is a wealth of evidence to support the theory that the continents have joined and broken apart several times. They were also once joined together in a single continent called Pangaea. Plate tectonics helps explain how the continent broke up and slowly separated.

Ed Mathez, Earth scientist

Did you know that plate tectonics even affects climate? That's because the positions of the continents influence the ocean currents and how the winds blow.

Every tectonic plate consists entirely of one type of crust: continental or oceanic.

Fact
or
Fiction
?

Fiction

Most plates consist of both continental and oceanic crust. For example, the North America Plate is made of the North American continent and the western half of the Atlantic Ocean.

The motion of plate tectonics is causing the Atlantic Ocean to grow larger.

Fact
or
Fiction
?

Fact

The two plates that make up the Atlantic Ocean are slowly moving apart. As they do, magma rises from below to create new oceanic crust, and the ocean grows bigger.

Definition: a theory that the Earth's crust and upper part of the mantle is made of large pieces that are moving and changing
When the theory was developed: the 1960s
Number of plates: ten large plates and several smaller plates
Types of plate movement: collision (moving toward each other); slip (moving past each other); spread (moving away from each other); subduction (one plate sliding under another)

Image credits: courtesy of AMNH; Ed Mathez: courtesy of AMNH.