The zone of hot, partly melted rock that flows and can be deformed is called the asthenosphere. It is a zone in the Earth's mantle that lies under the lithosphere and a part of the upper mantle. It is said to be more hotter the more viscous than the lithosphere. This zone is almost solid in structure although there are parts that are molten. This layer extends for about 100 km to 700 km below the surface. It is involves in the movement of the plate tectonics and the isostatic adjustments. The upper portion of this zone is said to be the part where the lithospheric plates of the crust moves.