Chapter 26, Problem 5TE

To determine

The reason for the lower part of the lithosphere is rigid.

Answer to Problem 5TE

The inner core of the Earth boils down to temperature, the lithosphere is colder and rigid, while the asthenosphere warms enough to melt into plastic form.

Explanation of Solution

The lithosphere is the external piece of the Earth and it is strong. It is limited by another piece of the upper mantle beneath called the asthenosphere. Even though the stones of the lithosphere are flexible, they are not thick. The asthenosphere is extremely viscous, and the lithosphere-asthenosphere limit is where the researchers mark the distinction in ductility between the two layers of the upper mantle.

The lithosphere is far less flexible than the asthenosphere. The lithosphere-asthenosphere limit is taken at $1300\text{°C}$ . Beneath this temperature, the mantle acts in an inflexible way and over this temperature.

Conclusion:

Therefore, the inner core of the Earth boils down to temperature, the lithosphere is colder and rigid, while the asthenosphere warms enough to melt into plastic form.