What is the mesosphere made of?
Geological mesosphere is the solid part of the Earth's mantle between asthenosphere and the outer core. The seismic waves travel faster into mesosphere..
Mesosphere is also used in atmospheric classification of layers. It is between stratosphere and thermosphere
Anyway, pressure, temperature and density matter in such classifications.
It is easier to study these variations in the atmosphere, But, beneath land and sea, despite we peaked up the the Everest above and dived deep to the Mariana Trench, in the Pacific, there are limitations in going deep far under sea bottom or the continents.
Only seismology is aiding us to do all these classifications, of the Earth's interior. .