The compositional layer that is divided between three mechanical layers is the Earth's crust. The Earth's crust is the outermost layer of the Earth's solid surface and is composed of several distinct mechanical layers, namely the lithosphere, the asthenosphere, and the mesosphere.
1. Lithosphere: The lithosphere is the rigid, outermost mechanical layer of the Earth's crust. It is composed of the uppermost part of the mantle and the crust. The lithosphere is broken into tectonic plates that float and move on the semi-fluid asthenosphere below.
2. Asthenosphere: The asthenosphere is a semi-fluid, plastic-like layer beneath the lithosphere. It is composed of hot, weak, and partially molten rock materials. The asthenosphere allows the tectonic plates of the lithosphere to move and interact with each other.
3. Mesosphere: The mesosphere, also known as the lower mantle, is the deepest mechanical layer beneath the asthenosphere. It is a more rigid and solid layer compared to the asthenosphere. The mesosphere extends from the bottom of the asthenosphere to the Earth's outer core.
Together, these three mechanical layers form the Earth's crust, which is the outermost compositional layer of the Earth.