Atmosphere

The Earth's atmosphere is a layer of gases surrounding the planet, held in place by gravity. The atmosphere has a mass of approximately 5.15×10^18 kg and is composed of 78% N, 21% O, 0.9% Ar, 0.039% CO₂ and trace amounts of other gases (Ne, He, CH₄, H₂, Kr) as well as water vapor. Earth's atmosphere is structured in layers from the ground up: the troposphere, stratosphere, mesosphere, thermosphere (also known as the ionosphere) and exosphere. About three-quarters of the atmosphere’s mass is concentrated within the troposphere, where its depth ranges from about 18 km at the equator to 7 km at the poles. The ozone layer, which absorbs ultraviolet radiation from the Sun, is located primarily in the stratosphere at altitudes between 15 and 35 km. The Kármán line, situated within the thermosphere at an altitude of 100 km, is widely recognized as the boundary between Earth's atmosphere and outer space. Beyond this, the exosphere extends from about 500 km to as far as 10,000 km, where it interacts with Earth's magnetosphere. Clouds primarily form in the troposphere and are categorized into various types according to their physical structures and formation processes.