The thermosphere is the hottest layer because it

because there is not a lot of anything in that layer so anything that comes into it creates a reaction, heat

Explanation:

Because there are relatively few molecules and atoms in the thermosphere, even absorbing small amounts of solar energy can significantly increase the air temperature, making the thermosphere the hottest layer in the atmosphere"

metamorphism is the change of minerals or geologic texture (distinct arrangement of minerals) in pre-existing rocks (protoliths), without the protolith melting into liquid magma (a solid-state change). the change occurs primarily due to heat, pressure, and the introduction of chemically active fluids. i hoped i !