What is the earth's crust

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It is the outermost layer of the earth's surface.  The Earth’s crust is its lightest, most buoyant rock layer. Continental crust covers 41% of the Earth’s surface, though a quarter of that area is under the oceans. The continental crust is 20 to 80 kilometers thick. Its rocks hold four billion years of Earth history. The remainder of the Earth is covered by oceanic crust. The crust is made of relatively light elements, especially silica, aluminum and oxygen. It’s also highly variable in its thickness.  crust is made of relatively light elements, especially silica, aluminum and oxygen. It’s also highly variable in its thickness. 

it should be a. song dynasty’s civil service examination system created an administrative bureaucracy manned by the landed aristocracy.

the viking voyages took place during the middle ages, which was about this time. 500 to 1350. the viking voyages took place during the middle ages, which was about this time.