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 What Causes Plates to Move?

What Causes Plates to Move?
Reading Level
     edHelper's suggested reading level:   high interest, readability grades 5 to 7
     Flesch-Kincaid grade level:   6.29

Vocabulary
     challenging words:    divergent, lithosphere, oceanic, downward, continuous, circular, continental, material, magma, rates, africa, mantle, core, mass, trench, rate
     content words:    Indian Oceans

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What Causes Plates to Move?
By Patti Hutchison 		  
1     They say a watched pot never boils. But do you know what happens when a pot of water does boil? The water is hotter near the bottom where the heat source is located. The cooler water on top sinks to the bottom. The hotter water on the bottom is pushed to the top. This is a kind of convection current.
 
2     Scientists think convection currents are what cause earth's plates to move. A convection current is caused by differences in temperature. Mantle material close to earth's core is very hot. Mantle material near the lithosphere is cooler.
 
3     The cooler, denser material sinks toward the core. The hot material near the core expands and becomes less dense. It rises and takes the place of the cooler material. The sinking material becomes hotter and rises. This is a continuous circular motion.
 
4     Earth's convection currents can be thousands of kilometers across. But they move very slowly. They flow at rates of a few centimeters per year. Scientists believe this movement of mantle material carries the plates of the lithosphere with it. It causes the plates to move.
 
5     The rising material in this convection current spreads out. It pushes the plates upward and outward. These are divergent boundaries. The material moving downward in the current pulls the plates down with it. These are convergent boundaries.

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