Our planet has unique characteristics that ease the development of life. Besides having important water resources, we must add the existence of a gaseous layer adequate for the existence of life that wraps the Earth and maintains its temperature, protects it from cosmic radiation and constitutes an efficient exchange system for solar energy between hot and cold regions. We are talking about the Earth’s atmosphere.
Its formation took place millions of years ago, in the times of primitive Earth, due to several transformations of the surface and the composition of the gases that emanated from it.
The time’s great volcanic activity generated important concentrations of carbon dioxide, water vapor and nitrogen, elements that remained in suspension and formed a precarious and unstable atmosphere thanks to the force of gravity.
Later, the appearance of water on the planet’s surface and the photosynthetic work of the first plants were some of the factors that altered atmospheric composition, finally making up the elements we know today.
Today, the Earth’s atmosphere is made up of 78% nitrogen, 21% oxygen, 0.93% argon, 0.035% carbon dioxide and 0.04% of other gases (among them, helium, neon and water vapor). Although they are established ranges, they change as we ascend from the Earth’s surface towards outer space. The amount of water vapor also varies depending on temperature and relative humidity.
The atmosphere is made up of five layers, each with its own characteristics and functions.
The layer nearest to the Earth’s surface is dubbed troposphere. It is located from sea level up to approximately 10 kilometers high (at the Equator, the distance reaches 19 kilometers, while in the poles it reaches 9). It is the thickest layer of the atmosphere, making up 75% of air’s total weight and containing a great portion of humidity and atmospheric dust. It is also called the “meteorological layer”, because the main meteorological phenomena take place there, like the formation of clouds, rain and storms.
The second atmospheric layer is the stratosphere, which goes up to 50 kilometers high. Constant winds develop here and the masses of air are arranged in strips or strata.
It houses the highest concentration of ozone (O3), variety of oxygen that protects us from harmful ultraviolet radiation coming from the sun.
Also in this sector, commercial flights fly thanks to the absence of meteorological changes and its consequent safety. Next, and up to 80 kilometers high, the mesosphere is located, which has temperatures below –100°C in its upper portion. It is catalogued as a low pressure layer, because the concentration of gases, like nitrogen and oxygen, is lower.
Above 80 kilometers we find the thermosphere or ionosphere, whose name is directly related to this zone’s high temperatures. This phenomenon is due to air molecules absorbing radiation from the sun and that the gases present are ionized. Meteorites that reach Earth are disintegrated in this sector, which decrease in size upon entering into contact with this layer, becoming shooting stars.
The last layer is called exosphere, and it has a considerable amount of gas molecules constantly escaping towards space; this is the only place the gases can escape to, as gravity is not so strong.
The air is very transparent in this zone, there is a great amount of cosmic dust and many meteorological satellites travel through it.
The division between one layer and another are dubbed, respectively, tropopause, stratopause, mesopause and thermopause.
The atmosphere covers and protects the Earth’s entire surface. Commercial airplanes circulate through the layer of the atmosphere that is closest to the Earth, the stratosphere.