What is the asthenosphere a part of?

The asthenosphere is a component of the upper mantle. It lies just below the lithosphere, which includes the crust and the uppermost portion of the mantle. The asthenosphere is characterized by its semi-viscous, plastic-like properties, allowing for the flow of material and the movement of tectonic plates above it. This region plays a crucial role in the dynamics of plate tectonics, as its ductility facilitates the movement of the rigid plates that float on top. Understanding the asthenosphere is essential for grasping the processes involved in plate interactions, such as subduction, continental drift, and earthquake activity. Its position within the upper mantle distinguishes it from both the crust, which is the outer layer, and the lower mantle, which behaves differently due to higher pressure and temperature conditions.