Which layer of the atmosphere contains almost all clouds and precipitation?

The troposphere is the lowest layer of the Earth's atmosphere and is where nearly all weather phenomena occur, including clouds and precipitation. This is because the troposphere contains the greatest concentration of water vapor, which is essential for cloud formation and rain. As temperature decreases with altitude in this layer, rising air cools, leading to condensation and the formation of clouds.

In contrast, the stratosphere sits above the troposphere and is characterized by a temperature inversion that prevents significant vertical mixing and cloud formation. The mesosphere, situated above the stratosphere, also has very low water vapor content, making it less conducive to clouds. The thermosphere, the outermost layer of the atmosphere, is extremely thin and lacks the mass necessary for weather development, meaning it does not have clouds or precipitation. Thus, the troposphere is uniquely positioned as the only layer where almost all clouds and precipitation occur, making it the correct answer.