Geocentric Science

Although the Earth’s surface is composed mostly of water (the layer known as the hydrosphere), the Earth is composed of several distinct layers beneath the Earth’s surface. In the Formation of Earth article, you read about differentiation. The upper image of the Inferred Properties of Earth’s Interior shows the different layers of Earth’s structure:

• Lithosphere (continental and oceanic crust)
• Asthenosphere
• Stiffer mantle
• Outer core
• Inner core

Using the bottom diagram (temperature versus depth), one can determine what the state is of each layer. The solid line represents the actual temperature (the geothermal gradient), and the dotted line represents the melting point. If the solid line is below the dotted line, it indicates that melting has not yet occurred and the material is a solid. However, if the solid line is above the dotted line, it indicates that melting has occurred and the material is a liquid. For example, the temperature of the stiffer mantle (between about 700 to 2900 km below the Earth’s surface) is below the melting point. Therefore, the stiffer mantle is solid. The temperature within the outer core is above the melting point, therefore, the outer core is a liquid.