The asthenosphere is primarily in a solid state, but it behaves like a viscous fluid over geological time scales. This layer is found beneath the Earth’s lithosphere, extending from about 100 km to 410 km below the surface. While the rocks in the asthenosphere are solid, the high temperature and pressure conditions allow them to flow very slowly, which is crucial for the movement of tectonic plates.
This semi-fluid characteristic of the asthenosphere enables it to support the lithosphere above it. The heat from the Earth’s interior causes the rocks to partially melt, which contributes to their ductility and ability to deform. This semi-solid state is essential for key geological processes like earthquakes and volcanic activity, as it facilitates the movement of tectonic plates. Overall, the asthenosphere plays a vital role in the dynamics of the Earth’s interior.