Which layer of the Earth is responsible for plate movement?

The asthenosphere is the layer of the Earth responsible for facilitating plate movement. It is located beneath the lithosphere, extending from about 100 km to 700 km below the Earth’s surface. This layer is composed of partially molten rock that flows slowly, allowing the rigid plates of the lithosphere, which sit atop it, to move. The heat from the Earth’s interior causes convection currents within the asthenosphere, which ultimately drive the movement of these tectonic plates.

The lithosphere, although critical for supporting the tectonic plates, is not where the actual movement occurs; it's the more fluid nature of the asthenosphere that enables this movement. While the crust is the outermost layer where we live and where tectonic interactions most evidently occur, it is the asthenosphere's semi-fluid characteristics that actually facilitate the motions of plate tectonics. As for the core, while it plays a role in generating heat that influences convection in the mantle, it does not interact with the tectonic plates directly. This understanding clarifies why the asthenosphere is identified as the key layer responsible for plate motion.