Internal layers of the Earth based on Physical Properties

• Lithosphere (rock sphere)

The top of the asthenosphere is about 100 km below the surface. Above the asthenosphere, the material is solid, strong and rigid. This layer is called lithosphere. Contains the continental crust of the uppermost part of the mantle.

• Asthenosphere (weak sphere)

A major zone within the upper mantle where temperature and pressure are just the right balance so that part of the material melts. The rocks lose much of their strength and become soft plastic and easily deformed. The thickness is about 200 km.

• Mesosphere

The rock below the asthenosphere is stronger and more rigid than the asthenosphere because the high pressure at this depth offsets the effect of high temperature. The region between the asthenosphere and the core-mantle boundary is called the mesosphere.

• Core

The core of the Earth marks a change in both physical properties and composition. It is composed mostly of iron and is therefore distinctly different from the silicate (rocky) material above. On the basis of physical properties, the core has two distinct parts - a solid inner core and liquid outer core. Heat loss from the core and the rotation of the Earth probably causes the liquid outer core to circulate and generate the Earth's magnetic field.