Earth’s Atmosphere: Composition and Layers
Earth’s Atmosphere
Origin of the Atmosphere
There are different scenarios. According to the planetesimal theory, the atmosphere was formed by gases emitted by volcanoes as the Earth grew in size and could retain them by the force of gravity. The primitive atmosphere, composed of hydrogen and helium, gradually changed. The current atmosphere formed slowly as our planet cooled, with gases from volcanoes, geysers, and fumaroles. Oxygen was produced by the great primeval forests.
Layers of the Atmosphere
- Troposphere: The first layer, in contact with the Earth’s surface, reaches a height of approximately 7 km at the poles and 15-17 km at the equator. It contains the air that allows the development of life, and meteorological phenomena occur here. Almost all tropospheric water vapor is found in this layer. The temperature decreases by 6.5°C per 1000 meters of altitude and is stable at -60°C at the boundary called the tropopause.
- Stratosphere: Located above the troposphere, it is cloud-free. It extends from the tropopause to 50 km in altitude. The ozone layer is located in this layer, between 20 km and 40 km in height. The lower parts of the stratosphere are used by aviation. The stratosphere ends where the temperature surges; this upper limit is called the stratopause.
- Mesosphere: Located above the stratopause, it extends to 80-90 km in altitude, where the temperature decreases sharply to between -30°C and -110°C. This level is called the mesopause.
- Thermosphere (Ionosphere): A layer formed by ions that reaches up to 600 km in altitude. Ions allow the transmission of electromagnetic waves, which are reflected in this layer and return to Earth, enabling long-distance radio broadcasting.
- Exosphere: The last layer of the atmosphere. Its boundaries are blurred, as it gradually loses the main characteristics of air to reach outer space.
Composition of the Atmosphere
Permanent Gases: Nitrogen, oxygen, argon, neon, helium, krypton, xenon, and radon.
Variable Gases: Water vapor, carbon dioxide, and ozone.
Air also contains nitric and nitrous acid, sulfuric acid, and traces of sulfur, along with variable amounts of impurities like dust, salts, and microorganisms. These, together with flue gases, are contaminants of the atmosphere. Oxygen combines readily with many elements and is necessary for combustion.
Carbon dioxide is present in the air to a small extent; it is produced by animals, combustion, volcanic activity, and some organic decomposition processes.
Nitrogen does not combine easily with other elements but is a constituent of many organic compounds.
Water vapor content is variable, ranging from small quantities to a maximum of 4% in extremely wet conditions.
Ozone is a major oxidant and has a high capacity for the partial absorption of the sun’s ultraviolet radiation, limiting the amount that reaches the Earth’s surface. About 90% of ozone is found between 20 km and 30 km, where it absorbs ultraviolet radiation.
Atmospheric Functions
The atmosphere performs the following functions:
- Maintains a safe temperature on Earth, avoiding abrupt changes that would make our planet uninhabitable.
- Makes combustion and respiration possible, and with it, life itself.
- Transmits sound.
- Spreads light.
- Enables the elevation of light gas balloons through buoyancy.
- Provides resistance.