What is a defining characteristic of the stratosphere?

The defining characteristic of the stratosphere is that it contains the ozone layer. The stratosphere, which is the second layer of Earth's atmosphere, is situated above the troposphere and extends from about 10 to 50 kilometers in altitude. One of its most important features is the ozone layer, which absorbs the majority of the sun's harmful ultraviolet (UV) radiation. This layer of ozone is crucial for life on Earth, as it protects living organisms from the damaging effects of excessive UV exposure, which can lead to skin cancer and other negative health impacts, as well as harm to ecosystems.

In contrast to the stratosphere, the troposphere is the layer where most of Earth's weather occurs, and the temperature generally decreases with altitude in that layer. Although the stratosphere has regions where temperatures actually increase with altitude due to the absorption of UV radiation by ozone, it is not correct to say it has the highest temperatures overall, as that distinction belongs to the thermosphere. While nitrogen is indeed a major component of the stratosphere, it is not a defining characteristic, as nitrogen is abundant throughout the atmosphere. Thus, the presence of the ozone layer is what fundamentally distinguishes the stratosphere from other atmospheric layers.