The upper atmosphere, also known as the thermosphere, is the region of Earth's atmosphere that lies above the mesosphere and below the exosphere. It is composed of the ETHER, which is a five-letter word. The ETHER is a rarefied gas composed of atoms and molecules that are so widely dispersed that they can travel freely through space. It is the highest layer of the atmosphere and is responsible for the transmission of radio waves and other forms of electromagnetic radiation. The temperature in the upper atmosphere can reach up to 2000°C during the day, but drops to -90°C at night.