Which atmospheric layer is closest to Earth's surface?

The troposphere is the atmospheric layer closest to Earth's surface and is essential for life as it contains the majority of the atmosphere's mass, including water vapor and aerosols. This layer extends from the Earth's surface up to about 8 to 15 kilometers (5 to 9 miles) depending on geographic location and weather conditions. Most weather phenomena, such as clouds, rain, and storms, occur within this layer due to its proximity to the Earth's surface and the presence of water vapor that fuels these weather patterns.

In addition to being where weather occurs, the troposphere is characterized by a decrease in temperature as altitude increases, which contributes to the dynamics of our climate and weather conditions. Other atmospheric layers, such as the stratosphere, mesosphere, and thermosphere, are situated above the troposphere and serve different functions, including ozone absorption of UV radiation and the ionization of gases, but they are not where most of the Earth's air and weather systems are found. Thus, the troposphere is fundamental in supporting life on Earth.