The correct answer is - Asthenosphere.
The mantle layer is a solid part of the Earth. It lies just bellow the crust, and it is composed of metals. It is a layer that has very high temperature and pressures, as well as strong convection currents.
The astenosphere is the lower part of the mantle, and it is the densest, and most solid of its layers.
This layer of the Earth is estimated to be 2,900 km thick, and it accounts for incredible 84% of the total volume of the planet.