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Earth
 Sea-Floor Spreading

Sea-Floor Spreading
Reading Level
     edHelper's suggested reading level:   high interest, readability grades 5 to 7
     Flesch-Kincaid grade level:   5.75

Vocabulary
     challenging words:    asthenosphere, lithosphere, mid-ocean, oceanic, subduction, tectonic, geologist, formation, rift, theory, continental, magma, mantle, dynamic, layer, newly
     content words:    Alfred Wegener, Geologist Harry Hess

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Sea-Floor Spreading
By Patti Hutchison 		  
1     In 1910, Alfred Wegener proposed the theory of continental drift. He believed that the continents were drifting apart. He found evidence to prove his theory. But he could not answer one question. How were the continents moving? He thought they were plowing through the ocean crust. Other scientists knew this could not happen.
 
2     In the 1960's scientists finally found what was missing in Wegener's theory. Geologist Harry Hess finally proved that Wegener was right. The continents are moving apart. Hess believed that sea-floor spreading is the answer to the mystery of continental drift.
 
3     The mid-ocean ridge is found throughout the oceans of the earth. This is a 50,000 mile chain of volcanic mountains in the middle of the ocean. These mountains have a deep crack that runs through them. It is called a rift valley. Sea-floor spreading happens here. It is a slow, regular process. There are no explosive bursts like volcanic eruptions on land.

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