What does the lithosphere consist of?

The lithosphere consists of the rigid outer layer of the Earth, which encompasses both the crust and the upper part of the mantle. This layer is characterized by its solid and brittle properties, making it the section of the Earth where tectonic plates exist and interact. The lithosphere is fundamental to our understanding of plate tectonics because it includes the tectonic plates that float on the semi-fluid asthenosphere, allowing for movements that lead to geological phenomena such as earthquakes, volcanic activity, and mountain building.

The other options do not describe the lithosphere. The inner core is a solid sphere of metal at the Earth’s center, the semi-fluid layer beneath the crust refers to the asthenosphere, which is not part of the lithosphere, and the atmosphere surrounds the Earth but does not form part of its geological structure. Understanding that the lithosphere is made up of the crust and the upper mantle helps clarify its role in the Earth's geological processes.