Download Getting to Know: Plate Tectonics

Getting to Know: Plate Tectonics
Did you know that the North American continent was once joined to Africa? Over hundreds of millions of years ago, the two continents separated and moved to their current positions. The slow separation of the continents is caused by the movement of Earth’s tectonic plates. Many of Earth’s landforms are shaped by the movement of tectonic plates. Plate movement is actually responsible for many natural events and occurrences ranging from volcanic eruptions to the formation of mountains. Without plate tectonics, Earth would not be the place that it is today. What are tectonic plates?
Mountain formation is one result of
plate tectonics.
Earth’s crust is divided into several large tectonic plates that ride on top of slowly moving rock
in the Earth’s mantle. Convection in the mantle causes these plates to move. Tectonic plates
move at extremely slow rates, which is why we cannot feel them moving. However, we can
witness their effects.
Misconception 1: I thought that convection only occurs in fluids such as water and
magma. Is this true?
Convection also occurs in the semisolid rock of the mantle. The mantle consists of
partially molten rock, which is plastic-like in nature. It is not considered a fluid, but it
behaves like a fluid in some ways.
What natural processes do tectonic plates cause?
Tectonic plates are the cause of many natural processes on Earth’s surface. For example, heat
flow and movement of material within Earth causes earthquakes and volcanic eruptions.
Mountains and ocean basins also result from tectonic movement. At the edges of some
tectonic plates, new rock is brought to the surface by internal forces, causing underwater
mountain ranges. Elsewhere, huge underwater trenches are the result of one tectonic plate
sliding under another, causing the rock of the lower plate to dissolve back into the mantle.
Concept: Plate Tectonics
Getting to Know
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How are the rock cycle and tectonics related?
The rock cycle involves the transformation of one type of rock into another. Plate tectonics
are an important part of the rock cycle. Igneous rocks form from hardened magma that rises
from the Earth’s mantle through gaps between the tectonic plates. Over time, this rock erodes
and breaks down. The broken-down pieces of rock deposit as sediment on Earth’s surface. If
conditions are right, sediment becomes compacted, gradually becoming sedimentary rock. As
sedimentary rock is subjected to extreme heat and pressure, it may turn into metamorphic rock.
Eventually, rock that is near a plate boundary may be subducted back into Earth’s mantle. Thus,
plate tectonics is a primary cause of the movement of rock material through the rock cycle.
What are the different types of plate
boundaries?
There are three primary types of plate boundaries: divergent, convergent, and transform. Divergent boundaries are places where two plates are moving away from one another. As they separate, magma rises between them, filling the gap with new rock. Elsewhere, plates are moving toward each other. These are known as convergent boundaries. At convergent boundaries, one plate may be subducted beneath the other, causing it to dissolve into the mantle. These areas often contain a great deal of volcanic activity. Other times, when the plates that are converging contain continents, the two plates push against each other and cause the plates to fold, creating high mountain ranges. The Himalaya are a good example of mountains that formed by the convergence of two continental plates. The third type of plate boundary is known as a transform
boundary. Here, plates are moving past one another. As they
move, the edges of the plates rub against each other.
Sometimes, parts of the edges became stuck; when they
suddenly move again, they release a great deal of force. This
causes the natural events that we know of as earthquakes.
Fault lines are often visible on
Earth’s surface at transform plate
boundaries.
Misconception 2: Do earthquakes occur when plates move apart from each other,
creating huge gaps?
Actually, earthquakes occur because of tectonic plate movement at convergent or
transform boundaries. The movement of the plates against or past one another is what
causes the tremors we feel as earthquakes.
In this lesson, you will learn more about plate tectonics, the rock cycle, and how these
processes produce the variety of landforms found on Earth’s surface.
Concept: Plate Tectonics
Getting to Know
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© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.