Which layer allows tectonic plates to move due to its semi-fluid nature?

The asthenosphere is the layer that allows tectonic plates to move due to its semi-fluid nature. This layer, located just beneath the lithosphere, is composed of partially melted rock that can flow slowly over geological timescales. This flowing characteristic is crucial because it provides the necessary lubrication for the rigid plates of the lithosphere to slide and shift as they drift on the Earth's surface.

The lithosphere comprises the crust and the uppermost part of the mantle, which are relatively rigid and brittle. The core, made up of iron and nickel, lies much deeper within the Earth and does not directly influence the movement of tectonic plates. The crust is the topmost layer where we find land and ocean floors, but it is the asthenosphere beneath that plays the key role in tectonic plate dynamics. Hence, the asthenosphere's semi-fluid properties are essential for the movement and interactions of tectonic plates, leading to phenomena such as earthquakes, volcanic activity, and the formation of mountains.