If the brittle lithosphere consists of individual solid plates of rock and the asthenosphere is a crystal mush that flows very slowly, why don't the tectonic plates just sink to great depths and melt? Select one:

Because the asthenosphere is more dense than the lithosphere

Explanation:

mantle.The tectonic plates just don't plunge in to greater depths because the asthenosphere is denser than the lithosphere and the asthenosphere exist in molten state hence providing a surface on which the tectonic plates can slide over instead of plunging into greater depths

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