The uppermost layer of the atmosphere, in which temperature increases as altitude increases, is the:

• A. Troposphere
• B. Stratosphere
• C. Mesosphere
• D. Thermosphere

Answer: (D)

Temperature tends to rise with height in a few atmospheric layers, and knowing how each layer responds to solar energy helps explain why the topmost layer listed is the one described here. In the troposphere, temperature decreases with altitude, which is why air gets cooler as you go up and weather happens there. In the stratosphere, temperature does increase with height due to absorption of ultraviolet light by ozone, but this is below the higher layers. In the mesosphere, temperature again decreases with altitude. In the thermosphere, temperature rises with height because high-energy solar radiation heats the sparse gas molecules there, even though the air is extremely thin. The uppermost layer among these, characterized by increasing temperature with altitude, is the thermosphere.