Final answer:
The asthenosphere is able to flow due to its plasticity and partial molten state, unlike the brittle lithosphere.
Step-by-step explanation:
The question pertains to the mechanical properties of different layers of Earth, specifically focusing on their ability to flow rather than being brittle. Based on the provided information, the asthenosphere is the layer that is able to flow. The asthenosphere is a part of the upper mantle characterized by plasticity, allowing it to flow, in contrast to the overlying lithosphere which behaves as a rigid, brittle solid.
The lithosphere includes the crust and the uppermost part of the mantle and is prone to breaking rather than flowing. Comparatively, the asthenosphere possesses properties necessary for plastic deformation and can flow due to its partial molten state. This flow is crucial to tectonic plate movements and various geodynamic processes on Earth.