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Stress and Strain in the Life of a Rock

Stress and Strain in the Life of a Rock
Reading Level
     edHelper's suggested reading level:   high interest, readability grades 3 to 5
     Flesch-Kincaid grade level:   3.43

Vocabulary
     challenging words:    molten, oozed, toll, surface, stress, layer, easily, opposite, likely, mostly, mantle, upper, rocks, folds, upward, fold

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Stress and Strain in the Life of a Rock
By Patti Hutchison 		  
1     The earth's surface is constantly changing. We don't usually see the changes because they happen so slowly. But earth's crust is always being pushed, pulled, folded, and broken. What causes these changes? Stress.
 
2     Earth's crust is made up of plates of rock. These plates move about on the asthenosphere. This is a mostly molten layer of the upper mantle. As they move about, the plates are pushed and pulled. This force is called stress.
 
3     Stress causes the rocks of the crust to slowly change. Their volumes change. Their shapes also change. Stress causes rocks to move up, down, or sideways. They tilt, fold, and even break. This is called deformation.
 
4     There are three main types of stress. One type is called compression. During compression rocks are pushed together. Think of how you used to squeeze mud in your hands. As you pushed the mud together, some oozed out the top and bottom of your hand.
 
5     Rocks are squeezed in the same way by stress. When this happens, rocks are pushed higher and deeper. A rock that was once flat will bulge in the middle as a result of compression.

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