What is the atmosphere?
We explain what an atmosphere is and what the importance of the Earth’s atmosphere is. Layers and characteristics of the atmosphere.
The atmosphere plays a vital role in protecting the planet and therefore life.
We call atmosphere the more or less homogeneous ball of gases concentrated around a planet or celestial star and held in place by the action of gravity.
On some planets, composed mostly of gas, this layer can be particularly dense and deep.
The Earth’s atmosphere is about 10,000 km away from the surface of the planet, and contains in different layers the gases necessary to preserve the stable planetary temperature and allow the development of life.
The air currents present in it are closely related to the hydrosphere (the set of planetary water), and affect each other.
Our atmosphere can be divided into two large regions: homosphere (the lower 100 km) and heterosphere (from 80 km to the outer edge), according to the variety of gases that make up each, much more varied and homogeneous in the first, and stratified and differentiated in the second.
The origin and evolution of the atmosphere date back to the very beginnings of the planet, in which a thick layer of primeval gases remained around the planet, consisting mostly of hydrogen and helium from the solar system.
However, the gradual cooling of the Earth and the very later appearance of life were changing the atmosphere and varying its content to reach what we know today, through processes such as photosynthesis and chemosynthesis or respiration.
Characteristics of the atmosphere
The Earth’s atmosphere is made up of various types of gases, the highest percentage of which accumulates in the first 11 km of altitude (95% of the air is in its initial layer) and whose total is around 5.1 x 1018 kg.
The main gases that integrate it (in the homosphere) are nitrogen (78.08%), oxygen (20.94%), water vapour (between 1 and 4% at surface level) and argon (0.93%). However, other gases are present in minority quantities, such as carbon dioxide (0.04%), neon (0.0018%), helium (0.0005%), methane (0.0001%), among others.
The heterosphere is composed of differentiated layers of molecular nitrogen (80-400 km), atomic oxygen (400-1100 km), helium (1100-3500 km) and hydrogen (3500-10,000 km).
Atmospheric pressure and temperature decrease with altitude, so the outer layers are cold and sparsely dense.
Layers of the atmosphere
The mesosphere is the coldest zone in the atmosphere, reaching -80 °C.
The Earth’s atmosphere is composed of the following layers:
- Troposphere. The initial layer, in contact with the earth’s surface, where most atmospheric gases accumulate. It reaches 6 km in height at the poles and 18 km in the rest of the planet, being the warmest layer of all, despite the fact that in its outer limits the temperature reaches -50 °C.
- Stratosphere. It ranges from 18 to 50 km high, in various gaseous layers. One of them is the ozonosphere, where solar radiation impacts on oxygen, forming ozone molecules (O3) that constitute the known “ozone layer”. This process generates heat, so that the stratosphere registers a considerable increase in temperature up to -3 °C.
- Mesosphere. The middle layer of the atmosphere, between 50 and 80 km high, is the coldest zone in the whole atmosphere, reaching -80 °C.
- Ionosphere or thermosphere. It ranges from 80 to 800 km in altitude and has very little dense air that allows drastic temperature fluctuations depending on the intensity of the sun: it can record temperatures of 1500 °C during the day and fall dramatically at night.
- Exosphere. The outer layer of the atmosphere, which ranges from 800 to 10,000 km in altitude, is relatively undefined, little more than the transit between the atmosphere and outer space. There, the lightest elements of the atmosphere, such as helium or hydrogen, escape.
Importance of the atmosphere
The atmosphere plays a vital role in the protection of the planet and therefore also of life.
Its density deviates or attenuates the forms of electromagnetic radiation coming from space, as well as possible meteorites and objects that could impact its surface, most of which dissolves by rubbing with gases upon entering it.
On the other hand, in the stratosphere is the ozone layer (ozonosphere), an accumulation of this gas that prevents the direct access of solar radiation to the earth’s surface, thus keeping the temperature of the planet stable.
At the same time, the mass of gases prevents the rapid dispersion of heat into space, in what is called the “greenhouse effect“.
Finally, the atmosphere contains the indispensable gases for life as we know it, and plays a vital role in perpetuating the water cycle of evaporation, condensation and precipitation of water.