Correct Answer:
D. Thermosphere.
The correct answer is Thermosphere. This layer of the atmosphere is aptly named the 'heat sphere' because it experiences extremely high temperatures due to the absorption of high-energy solar radiation, such as X-rays and ultraviolet radiation, by the sparse oxygen and nitrogen molecules. While the individual molecules in the thermosphere possess very high kinetic energy (which we measure as temperature, potentially over 1500°C), the air density is so low that there are few molecules to transfer this heat. Therefore, it would not feel hot to a person, but technically, the temperature is exceedingly high.
- Option A, the Troposphere, is the lowest layer where most weather occurs, and temperature generally decreases with altitude.
- Option B, the Stratosphere, contains the ozone layer, which absorbs UV radiation, causing temperature to increase with altitude, but not to the extreme levels of the thermosphere.
- Option C, the Mesosphere, is characterized by temperatures decreasing with altitude, reaching the coldest temperatures in the Earth's atmosphere.