Final answer:
The asthenosphere is the layer beneath the lithosphere, known for its viscous behavior, allowing the movement of tectonic plates.
Step-by-step explanation:
The physical layer of Earth located beneath the lithosphere is the asthenosphere. This layer is situated above the Earth's upper mantle and is characterized by its ability to flow slowly over time, much like a soft plastic. This flow allows for the movement of tectonic plates that sit atop it. Unlike the solid and rigid lithosphere, the asthenosphere is less dense and can deform, which is essential for the tectonic activity that shapes our planet's surface.