In which layer does all weather activity occur?

All weather activity occurs in the troposphere, which is the lowest layer of Earth's atmosphere. This layer extends from the surface of the Earth up to about 8 to 15 kilometers (5 to 9 miles) in altitude, depending on geographical location and weather conditions. The troposphere contains approximately 75% of the atmosphere's mass, including most of the water vapor, which plays a vital role in weather phenomena such as precipitation, clouds, and storms.

Within the troposphere, temperature generally decreases with altitude, leading to various atmospheric processes that contribute to weather patterns. This layer is characterized by turbulence, mixing, and convection, which are essential for the formation and development of weather systems.

In contrast, the stratosphere, which lies above the troposphere, is more stable and does not have the same kinds of weather activity. The mesosphere, further above, experiences decreasing temperatures and is also not associated with weather. The tropopause, on the other hand, is the boundary between the troposphere and stratosphere and does not itself contain weather phenomena. Therefore, the troposphere is the correct answer due to its direct involvement in all weather-related activities.