Layers of the Earth Based on Physical Properties

Asthenosphere

The asthenosphere lies directly underneath the lithosphere. It is made of the outer portion of the mantle (except for the outermost layer, which is the lithosphere). The asthenosphere is at the right temperature and pressure to allow it to melt. Think of warm tar. I always think of the asthenosphere as "thick and gooey." The asthenosphere is about 200 km thick.

Core

The core is both a compositional change from the mesosphere and a change in physical properties. We've already discussed the composition of the core, but physically, the core is found in two distinct phases: the solid inner core and the liquid outer core. Scientists believe that the earth's magnetic field is caused by the rotation of the earth and the incredible amount of heat in the core that causes the liquid outer core to circulate. Note that the inner core is solid, while the outer core is liquid. Phase changes (solid, liquid, and gas) are physical properties. Water is still water, whether it is a solid (ice), a liquid (water), or a gas (steam). The core of the earth is mainly iron, whether it is a solid or a liquid. The inner core is solid because of the contents of the earth weighing down on it. It is under tremendous pressure.

Lithosphere

The lithosphere is the top layer of the earth. It includes the continental crust and the oceanic crust. It is solid, strong, and rigid. Remember that the lithosphere is a distinct layer based on physical properties, not what it is made of. The lithosphere comprises of the crust and the top of the mantle. It is made up of both granite and basalt from the crust and iron, magnesium, and silicon from the mantle. The lithosphere is about 100 km thick. It's unique in that it is not one whole unit; it is actually several different pieces fused together. As I mentioned earlier, the land actually "floats" on the upper mantle, which is more pliable (flexible or movable) than solid land. The lithosphere is the crust that floats on the more flexible asthenosphere, which will be described next.

Mesosphere

The mesosphere is solid and lies directly underneath the asthenosphere. It is under a high amount of pressure and temperature. The mesosphere is part of the mantle; it extends beneath the asthenosphere to the core, or you could think of it as the innermost part of the mantle.