The correct answer is - thermosphere.
The thermosphere is the fourth most distant atmospheric layers, out of the five, from the lithosphere. This layer lies between the furthest exosphere, and above the mesosphere.
This layer of the atmosphere begins from the height of around 80 km, and extends to around 600 km above the surface of the Earth. In the thermosphere, the ultraviolet radiation is enormous, and the temperature is very high. The temperature depends on the activity of the Sun, and occasionally it reaches even up to 1,700 °C.
