Chapter 20 - The Earth's Inner Layers

The Earth is made of several internal layers, some of which are solid, and some of which are liquid. The solid inner core has a radius of 1220 km, and its surface lies 5150 km below sea level. Due to the immense pressure the iron and nickel that make up this solid layer do not melt under the great heat. There is evidence that this solid layer acts like a dynamo, moving much faster then the rest of the earth, effectively driving the rotation of successive earth layers. The liquid outer core is 2250 km thick, and is 2900 km below sea level (less then halfway to the center of the earth). The inner core may be made of the same materials as the solid inner core, but because it is not under as much pressure, the melting point is lower and thus this layer exists in a molten state. The solid lower mantle lies above the liquid outer core, and has a thickness of 2230 km.  Geologists believe that this layer is composed of oxides of iron, magnesium, and silicon. The upper mantle is partially molten and has a thickness of 670 km. The upper mantle interacts directly with the crust of the earth, and at this level is solid, while nearer to he solid lower mantle the upper mantle is in a molten state.