Final answer:
The asthenosphere is located in the upper mantle, below the lithosphere. It is a partially molten layer with the ability to flow, playing a key role in the movement of tectonic plates and various geological processes. The correct answer is option b.
Step-by-step explanation:
The asthenosphere is located in the upper mantle. It is the mechanically weak and partially molten layer beneath the lithosphere that can flow and is involved in plate tectonic movements. The asthenosphere is found below the lithosphere which includes the crust and the rigid upper part of the mantle.
The asthenosphere is significant for a number of geological processes, including the movement of tectonic plates. This is because its mechanical properties allow it to behave plastically under pressure, enabling it to flow like a viscous fluid on geological timescales. This can be observed in the slow convection currents that drive tectonic plate movements, contributing to phenomena such as earthquakes, volcanic activity, and mountain formation.
It is important to distinguish between the asthenosphere and the lithosphere, as they are based on different mechanical properties; the lithosphere includes the crust and upper mantle that behaves as a rigid solid, while the asthenosphere allows for plastic flow.