What is the firm layer between the crust and the athenosphere?

The firm layer between the crust and the asthenosphere is known as the lithosphere. It encompasses the Earth's crust and the uppermost portion of the mantle, characterized by its rigid and solid nature. The lithosphere is divided into tectonic plates that float on the more ductile asthenosphere beneath it. This structure plays a crucial role in geological processes such as plate tectonics and the formation of various landforms.