GED Science Practice Test: The Structure of the Geosphere

The composition of the earth’s geosphere pictured in the diagram below seems complex.  On the left side of the diagram, you see the three main layers of the earth—the crust, the mantle, and the core—described mostly by their composition. On the right side of the diagram, you see specific layers, described mostly by their structure. The lithosphere is made up of the crust and the upper part of the mantle.  This layer tends to be thinnest under the oceans and in volcanically active continental areas, such as the Western United States. The lithosphere is solid.  The asthenosphere is a liquid layer, made up of molten (liquid) rock that flows very slowly. The lithosphere floats on top of the asthenosphere.  We are mostly concerned with the lithosphere and asthenosphere in this lesson, though it is also interesting to point out that the outer core, the layer of the earth made of liquid iron and nickel that moves, is responsible for creating the earth’s magnetic fields.



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