The asthenosphere is primarily in a plastic state of matter, which means it can flow slowly over geological time. It is located just below the Earth’s lithosphere, which is the rigid outer layer of the Earth. The asthenosphere is composed of partially molten rock and is capable of deforming and moving, allowing tectonic plates in the lithosphere to drift and interact with one another.
This semi-fluid state is crucial for the movement of tectonic plates because it provides a lubricated layer on which these plates can slide. The temperatures in the asthenosphere range from about 1,200 to 2,000 degrees Celsius, which contributes to its malleable nature. Thus, while it is solid rock, it behaves more like a thick fluid given the high temperatures and pressures present at such depths in the Earth.