Plate Tectonic - Plate Tectonics (1)
Pre Lab 

   
OBJECTIVES:
  • Learning that the Earth's outer surface is under stress.
  • Discovering that this stress has made the continents and oceans move through millions of years.
VOCABULARY:
  • continents
  • converge
  • crust
  • diverge
  • earth
  • plates
  • transform
MATERIALS:

Students demonstrate plate motion through movement.


A map of the plates

BACKGROUND:

According to the theory of plate tectonics, the Earth's crust and upper mantle are broken into moving plates of "lithosphere." The lithospheric plates are solid rock. There are several very large plates, each consisting of both oceanic and continental portions. There are a dozen or more smaller plates. The plates average about 80 kilometers (50 miles) in thickness.

All of the plates are moving. They are slow, moving at speeds of centimeters to tens of centimeters per year. They slide along on top of an underlying mantle layer called the asthenosphere, which contains a little magma (molten rock). The plates have been moving for millions and millions of years.

As they move, plates interact at their edges or boundaries. There are three basic directions or types of boundary interactions. In some places, two plates move apart from each other; this is called a diverging plate boundary. Elsewhere two plates move together; this is a converging plate boundary. Finally plates can also slide past each other horizontally. This is called a transform plate boundary.

The movement of the plates generates stress at plate boundaries. The type of stress is different at each type of plate boundary. At converging plate boundaries rocks are squeezed, at diverging plate boundaries they are stretched, and at transform boundaries they are pushed past each other. Because the plates are rigid rock, they resist this motion until they break, creating earthquakes.

PROCEDURE:

In this activity you will introduce the terms of movement of the outer portion of the Earth and explain that these movements cause stress at plate boundaries.

  1. Explain to the class that the Earth's outermost layer is made of rock, and is called the crust. Make sure that the students understand that continental crust or land is mostly above water, and oceanic crust is land that is below water. Illustrate these areas on an inflatable globe. Explain that the crust is the top part of the plates.
      
  2. Explain to the students that the plates are moving. Explain the three types of motion between plates. Introduce the words converge, diverge, and transform (slip/slide) to the class. Have the students repeat the words several times while you demonstrate the motions with your hands. Explain that stress is generated where the plates touch and move past each other, at their boundaries.
      
  3. Have the students illustrate these words with a motor activity. Tell them that they will be able to demonstrate plate movement in other ways during lab.
      
    Have the students stand shoulder to shoulder in two lines facing each other. Have the lines move toward each other. Explain that this is like when two plates move toward each other (this illustrates a CONVERGING plate boundary). Have the lines move away from each other (this illustrates a DIVERGING plate boundary). Have the students in one line take one step to the right while the students in the second line take one step to the left (this illustrates a TRANSFORM plate boundary).

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