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Solar System

All the Spheres of the Earth

All the Spheres of the Earth
Reading Level
     edHelper's suggested reading level:   high interest, readability grades 6 to 7
     Flesch-Kincaid grade level:   5.77

Vocabulary
     challenging words:    peridotite, oceanic, argon, basalt, lithosphere, tectonic, dependent, magma, continental, nitrogen, atmosphere, biosphere, hydrosphere, sphere, granite, material

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All the Spheres of the Earth
By Patti Hutchison 		  
1     Do you know that there are four "spheres" that make up our earth? They are: the lithosphere, hydrosphere, atmosphere, and biosphere. These four systems are separate, but they also work together with each other. This is what makes Earth different from the other planets.
 
2     The "sphere" we know best is the lithosphere. This is the land we live on. It is the crust of the earth. It also includes the mantle. This is the solid layer below the crust. There are two kinds of crust. They are the continental crust and the oceanic crust. Continental crust is made of mostly granite. Basalt is the mineral found in most oceanic crust. The upper mantle, closest to the crust, is made of a hard rock called peridotite.
 
3     The lithosphere is made up of huge, solid pieces of rock. These are called tectonic plates. The continental crust is about 150 kilometers thick. The oceanic crust is about 70 kilometers thick. New oceanic lithosphere is always being made. It is made from cooled material from the lower mantle. The lower mantle is the layer of liquid rock or magma far below the earth's surface.
 
4     New lithosphere is made at oceanic ridges. It is younger than continental crust. The oldest oceanic crust is only about 200 million years old. Most continental lithosphere is billions of years old.
 
5     Another "sphere" we know well is the hydrosphere. This is all the water on our planet. It includes all the rivers, lakes, and oceans. The glaciers, groundwater, and water vapor in the air are also considered part of the hydrosphere.

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