Final answer:
The softer layer of the mantle located below the lithosphere is the asthenosphere, known for its plasticity and ability to flow, different from the rigid lithosphere.
Step-by-step explanation:
The layer of the mantle that is made of softer rock, situated right below the lithosphere, is called the asthenosphere. This layer is known for its plasticity, meaning it can flow and move, unlike the rigid and brittle lithosphere above it. The lithosphere comprises both the crust and the uppermost portion of the mantle, while the asthenosphere is the partially molten upper mantle material. The asthenosphere's unique properties are due to the high temperatures and pressures at these depths, which allow the mantle rock to deform and move over time. Understandably, this softer layer plays a crucial role in the movement of Earth's tectonic plates and is integral to the process of mantle convection.