In what layer of the Earth do tectonic plates float?

Tectonic plates float on the asthenosphere, which is a semi-fluid layer located beneath the lithosphere, primarily within the upper mantle of the Earth. The asthenosphere allows for the movement of tectonic plates because it is composed of solid rock that behaves plastically over geological timescales. This means that while it is solid, it can flow slowly, enabling the rigid plates of the lithosphere above to shift and interact with one another.

The crust, while it constitutes the outermost layer of the Earth, is not directly where the plates float; rather, it is the tectonic plates themselves. The outer core is a liquid layer primarily composed of iron and nickel, which does not support the movement of tectonic plates. Similarly, the inner core is solid and located at the center of the Earth, far removed from the tectonic processes occurring near the surface. This understanding of Earth’s layers is crucial for grasping the dynamics of plate tectonics and the geological activities that result from their movements.