In which layer of the Earth do tectonic plates exist?

The tectonic plates exist primarily in the lithosphere, which is the outermost layer of the Earth. The lithosphere includes the crust and the uppermost part of the mantle. It is rigid and broken into several tectonic plates that float on the semi-fluid asthenosphere beneath it.

This layer is crucial for understanding plate tectonics because it is these tectonic plates that interact with each other, leading to various geological processes, such as earthquakes, volcanic activity, and the formation of mountain ranges. The rigidity of the lithosphere allows for the movement of these plates, which is driven by convection currents occurring in the underlying asthenosphere.

In contrast, the core, while important in Earth's composition, is not involved in the movement of tectonic plates. The crust, although a part of the lithosphere, is not sufficient to define where tectonic plates exist since the lithosphere encompasses both the crust and upper mantle. The asthenosphere, while significant, consists of the semi-fluid layer beneath the lithosphere that allows the tectonic plates to move. Thus, the correct answer highlights the specific layer that encompasses the entire tectonic plate system.