What is the uppermost layer of the Earth's mantle called?

The uppermost layer of the Earth's mantle is indeed called the lithosphere. This layer is composed of the upper portion of the mantle and the overlaying crust. The lithosphere is characterized by its rigidity and is important because it forms the tectonic plates that float on the more fluid asthenosphere beneath it.

This layering is significant as it affects geological processes such as plate tectonics, which can lead to phenomena like earthquakes and volcanic activity. Understanding the lithosphere's role is essential for grasping how the Earth's surface interacts with the internal forces of the planet.

Other layers mentioned, such as the asthenosphere, core, and crust, have distinct properties and functions that separate them from the lithosphere. Therefore, identifying the lithosphere as the uppermost layer of the mantle is crucial in the study of Earth's geology.