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题目材料：
In 1644 Descartes described Earth as consisting of a central nucleus of hot primordial fluid surrounded by a solid opaque layer and then succeeding layers of rock, metal, water, and air. Geophysicists still subscribe to the notion of a layered Earth. In the current view, however, Earth possesses a solid inner core and a molten outer core both consisting of iron-rich alloys at enormous temperatures and pressures, followed at about 2.900 kilometers below the surface, by a mantle of solid less dense magnesium-iron silicates; the boundary between the upper and lower mantle lies 670 kilometers below the surface. At 30-50 kilometers below the continental surface (less than 10 kilometers below the seafloor), the Mohorovicic discontinuity marks an additional boundary—that between the mantle and the less dense crust above it.
以上解析由 考满分老师提供。
