The asthenosphere is a layer of the Earth's mantle located beneath the lithosphere, which includes the crust and the uppermost part of the mantle. It extends from about 100 kilometers to 700 kilometers below the Earth's surface. This layer is semi-fluid and allows for the movement of tectonic plates, which are large sections of the lithosphere that float on the asthenosphere. The asthenosphere is composed of solid rock that can flow slowly over time due to high temperatures and pressures. This flow is crucial for processes such as plate tectonics, which leads to geological phenomena like earthquakes and volcanic activity. Understanding the asthenosphere helps scientists learn more about the Earth's structure and behavior.