Which layer of the atmosphere has the greatest mass and contains nearly all of the Earth's water vapor?

The layer of the atmosphere that has the greatest mass and contains nearly all of the Earth's water vapor is the troposphere. This layer extends from the Earth's surface up to about 8 to 15 kilometers (5 to 9 miles) in altitude, depending on geographic location and weather conditions. The troposphere is crucial for weather patterns and natural phenomena as it contains most of the atmosphere's air, along with the majority of its water vapor.

Since weather systems, clouds, and precipitation occur in this layer, it plays a key role in regulating the climate and supporting life on Earth. The presence of the majority of atmospheric water vapor and the associated weather processes highlight the importance of the troposphere in the study of climate change and environmental patterns. Other atmospheric layers like the stratosphere, mesosphere, and exosphere have significantly less mass and contain minimal water vapor, making them less relevant when discussing Earth's water resources and weather systems.