The atmosphere is an approximately 1,000 km thick layer of air that surrounds the globe. Indispensable for life, it provides us with the air we breathe and acts as a shield, filtering the sun’s harmful rays (the ozone layer) or even lowering the temperature (the greenhouse effect) to control solar heat traps.
The atmosphere is made up of several layers that differ mainly in composition and temperature.
The higher the altitude, the lower the temperature and pressure. So we lose about 6 ° C every 1000 meters. However, heat transfer, meteorological phenomena and ocean currents make it possible to partially homogenize the temperature on the earth’s surface and prevent permanent warming or cooling of some regions.
Essential to life, air is the mixture of gases that make up the atmosphere around the Earth.
Clean air is produced by:
nitrogen or N2 (78%),
Oxygen or O2 (21%),
Rare gases (1%).
This ratio of rarefied gases in the atmosphere controls the main balances of the planet:
Carbon dioxide (CO2) allows to reach a pleasant temperature on the earth’s surface (greenhouse effect),
Stratospheric ozone is a natural filter that protects life on Earth from the harmful action of some of the Sun’s ultraviolet rays.
The Earth and the birth of the atmosphere
The environment doesn’t always have the same makeup. It has evolved to its present structure.
About 5 billion years ago, the so-called primitive atmosphere was devoid of oxygen O2 and therefore does not allow for life as it is today.
It was composed of 80 to 90% water (H2O), 10 to 20% carbon dioxide (CO) and 1 to 4% nitrogen N.
The cooling of the Earth has allowed the oceans to form by condensing water and dissolving carbon dioxide.
The earliest forms of life, aquatic photosynthetic cyanobacteria, appeared about 3 billion years ago.
They used atmospheric carbon dioxide to create. Once this resource was exhausted, some cells produced a new substance: chlorophyll, which made it possible to fix carbon dioxide in the air and transform it into nutrients.
For this transformation, the energy provided by the ambient light is used by these cells which then release oxygen (O); This is photosynthesis.
Life outside the water appeared only 360 million years ago, when the concentration of oxygen was high enough to allow the formation of a protective ozone layer, particularly against UV rays and temperatures favorable to life on the surface of the world. .
Layers of the atmosphere
The atmosphere is made up of 5 different layers which are characterized by their composition and temperature.
layers of atmosphere atmohdf
Troposphere (up to an average altitude of 15 km above the ground)
In this atmospheric region we live in, the temperature drops rapidly with altitude. The troposphere is mainly heated by the absorption of visible and infrared radiation from the ground.
Its thickness is variable: 16 km above the equator and 8 km above the poles and, depending on the season, 13 km in the temperate zone.
The troposphere contains 9/10 of all air mass and almost all water vapor. It is in this layer that most of the meteorological phenomena occur and it is between 0 and 3 km of altitude that the most significant dispersion of pollutants occurs.
Stratosphere (15 to 50km)
The temperature in this region increases with altitude. This heating is caused by the absorption of the sun’s ultraviolet rays by ozone.
The maximum concentration of ozone is in the stratosphere between 25 and 30 km of altitude.
This is the region that has the highest concentration of ozone, which we call the “ozone layer”.
It protects us from the ultraviolet (UV) rays of the sun.
Mesosphere (50 to 85km)
In this region the temperature drops again. This is the transition zone between Earth and space, where meteorites are destroyed.
Thermosphere (85 to 500km)
Due to the release of heat in this region, there is a rapid rise in temperature. The temperature can reach 2000 ° C.
Exosphere (from 500 km)
The temperature in this region is constantly rising.
The separation between the troposphere and the stratosphere is called the “tropopause”. The part between the stratosphere and the mesosphere is called the “stratosphere”. The one between the mesosphere and the thermosphere is called “mesopause”. The one between the thermosphere and the exosphere is called “thermopause”.
These 5 large areas are not waterproof. During severe thunderstorms, for example, ozone infiltration start atmospheric increases ozone concentrations in the troposphere.
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