Which of the following is not a physical division of the atmosphere?

The exosphere is not considered a distinct physical division of the atmosphere in the same way that the troposphere, stratosphere, and mesosphere are. The troposphere is the lowest layer, where we experience weather and most atmospheric phenomena occur. Above it lies the stratosphere, which contains the ozone layer and is characterized by a temperature increase with altitude. The mesosphere follows, where temperatures decrease with height again.

The exosphere, on the other hand, is often described as the outermost layer of Earth's atmosphere, where it gradually transitions into outer space. While it is an important region in the context of space and atmospheric science, it does not share the same physical characteristics or behaviors as the lower atmospheric layers. The exosphere is characterized by extremely thin air and the presence of very few particles, making it less significant in terms of the atmospheric processes that typically affect weather and climate.

Thus, understanding the physical divisions of the atmosphere involves recognizing that the first three layers are integral to our understanding of weather phenomena, while the exosphere represents a boundary between the atmosphere and outer space, distinct from those traditional layers.