Which layer of the Earth is divided into tectonic plates?

The lithosphere is the outermost layer of the Earth and is divided into tectonic plates. This layer encompasses both the crust and the uppermost solid portion of the mantle. The lithosphere is rigid and brittle, allowing for the formation of tectonic plates that float on the more malleable layer below it, known as the asthenosphere. The movement of these tectonic plates is essential for understanding geological processes such as earthquakes, volcanic activity, and the formation of mountain ranges. The division of the Earth into these plates is fundamental to the theory of plate tectonics, which explains how the plates interact with one another at their boundaries, leading to various geological phenomena.