The thermosphere (or the upper atmosphere) is the height region above 85 km, while the region between the tropospause and the mesopause is the middle atmosphere (stratosphere and mesosphere) where absorption of solar UV radiation generates the temperature maximum near 45 km altitude and causes the ozone layer.he layers are to scale. From Earth's surface to the top of the stratosphere (50 kilometres (31 mi)) is just under 1% of Earth's radius. The thermosphere is the layer of the Earth's atmosphere directly above the mesosphere and directly below the exosphere.