The middle layer
The mesosphere lies between the thermosphere and the stratosphere. “Meso” means middle, and this is the highest layer of the atmosphere in which the gases are all mixed up rather than being layered by their mass.
The mesosphere is 22 miles (35 kilometers) thick. The air is still thin, so you wouldn’t be able to breathe up in the mesosphere. But there is more gas in this layer than there is out in the thermosphere.
Have you ever seen a meteor shower, where meteors burn up and streak across the sky? Some people call them shooting stars. Those meteors are burning up in the mesosphere. The meteors make it through the exosphere and thermosphere without much trouble because those layers don’t have much air. But when they hit the mesosphere, there are enough gases to cause friction and create heat.