Which layer is primarily involved in the movement of tectonic plates?

The layer primarily involved in the movement of tectonic plates is the lithosphere. The lithosphere encompasses the Earth's crust and the uppermost part of the mantle, forming a rigid layer that floats on the more malleable asthenosphere beneath it. The tectonic plates are sections of the lithosphere that hold the continents and ocean floors.

The movement of these plates is largely driven by the convection currents in the underlying asthenosphere, which allow the rigid lithospheric plates to move. While the asthenosphere does facilitate this movement through its partially molten state, it is the lithosphere itself that consists of the tectonic plates. Thus, those studying Earth's processes must recognize that the lithosphere's structure and interaction with the asthenosphere are crucial for the dynamics of plate tectonics.