Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly (by molar content/volume) 78% nitrogen, (normally inert except upon electrolysis by lightning[1] and in certain biochemical processes of nitrogen fixation), 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and trace amounts of other gases, in addition about 1% water vapor. This mixture of gases is commonly known as air. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

The atmosphere plays a central role for the environmental conditions on Earth. It determines the climate, protects us from harmful UV radiation and ensures the continuation of the water cycle. But, how far-reaching is our knowledge really of what mechanisms and processes are important to the atmosphere and climate? Helmholtz scientists are working in the "Atmosphere and Climate" programme to extend this knowledge.

Humans have a massive impact on the atmosphere and climate through the wide range of various emissions which they produce: The chemical composition of the mantle of air changed substantially in the course of the last century. Helmholtz researchers are inquiring into the interactions taking place between the atmosphere and neighbouring areas, such as the biosphere. In addition, they are studying the make-up of water cycles and are doing research into how the supply of water could be improved. Because people in many countries of the world suffer from their regions having less and less water as a result of climatic changes.
The temperature of the Earth's atmosphere varies with altitude; the mathematical relationship between temperature and altitude varies among six different atmospheric layers:

1. Troposphere: From the Greek word "τρέπω" meaning to turn or mix. The troposphere is the lowest layer of the atmosphere which begins at the surface and extends to between 7 km (4.4 mi) at the poles and 17 km (10.6 mi) at the equator, with some variation due to weather factors. The troposphere has a great deal of vertical mixing due to solar heating at the surface. This heating warms air masses which then rise to release latent heat as sensible heat that further uplifts the air mass. This process continues until all the water vapor is removed. In the troposphere, on average, temperature decreases with height due to expansive cooling.
2. Stratosphere: from the troposphere's 7–17 km range to about 30 km, temperature increases with height. The stratosphere contains the ozone layer. The ozone layer is the part of the Earth's atmosphere which contains relatively high concentrations of ozone. "Relatively high" means a few parts per million—much higher than the concentrations in the lower atmosphere but still small compared to the main components of the atmosphere. It is mainly located in the lower portion of the stratosphere from approximately 15 km to 35 km above Earth's surface, though the thickness varies seasonally and geographically.
3. Mesosphere: from about 50 km to the range of 80 km to 85 km, temperature decreasing with height.
4. Thermosphere: from 80 – 85 km to 640+ km, temperature increasing with height.
5. Ionosphere: is the part of the atmosphere that is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth. It is located in the thermosphere and is responsible for auroras.
6. Exosphere: from 500-1000 km up to 10,000 km, free-moving particles that may migrate into and out of the magnetosphere or the solar wind.

The boundaries between these regions are named the tropopause, stratopause, mesopause, thermopause and exobase.
 
The average temperature of the atmosphere at the surface of Earth is 14 °C.