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4.4. Structure of the atmosphere

Structure of the atmosphere

The atmosphere reaches up to 10,000 km high, although more than half of its mass is concentrated in the first 6 km and 75% in the first 11 km. It is not homogeneous because the gases are arranged in it according to their density, the densest being closer to the earth's surface.

Structure according to its chemical composition

  • Homosphere (0 km to 60 km): It is made up of air, a mixture of gases whose main components are nitrogenoxygen, argon, water and CO2.

Activity: Components of Air.

  • Heterosphere (from 60 km to 10,000 km): In this zone, the gases are occupying different layers according to the mass of the atoms. There is a layer of oxygen, another layer of helium, and finally, a layer of hydrogen (lighter atoms).


The troposphere is the lowest layer of the atmosphere, occupying the first 10 - 12 kilometers approximately (less at the poles than at the equator). It contains 80% of the air in the atmosphere.

It is the layer of the atmosphere that is in contact with the earth's surface, where life develops and where meteorological phenomena (winds, rains, etc.) occur.

Most of the oxygen and water vapor are concentrated in the troposphere, so the air has its maximum density. Water vapor is a good thermoregulator that makes the temperatures between day and night not too high and we can survive.

In the troposphere, the temperature decreases with altitude, approximately 6.5 ºC for each kilometer that you climb, reaching as low as -60 ºC .

The boundary of the troposphere with the stratosphere is called the tropopause.


The stratosphere occupies from 12 km to 45 or 50 km in height. It is so called because it is arranged in more or less horizontal strata or layers.

Within the stratosphere, between 15 and 40 km high, is the ozone layer or ozone layer90% of all the ozone in the atmosphere is concentrated here. Ozone is essential for life, as it acts as a protective shield that filters harmful ultraviolet radiation that reaches the Earth. A series of reactions take place that causes the temperature to increase as you go up, and can reach 15 ºC.

Although the ozone layer is essential for our life, pollution has caused a decrease in the thickness of the ozone layer (hole in the ozone layer).

The boundary of the stratosphere with the mesosphere is called the stratopause.


The mesosphere covers from 50 km to 90 km approximately. In this layer, the temperature decreases again with height, and can reach -80ºC, the coldest part of the atmosphere.

The boundary of the mesosphere with the thermosphere is called the mesopause.

Thermosphere or ionosphere

The thermosphere receives this name because, due to the absorption of energy from solar radiation, it can reach a temperature of over 1500 ºC . It is also called the ionosphere because the atoms and molecules that compose it are ionized, that is, with an electrical charge. Gamma rays, X-rays, and ultraviolet radiation coming from the Sun are the cause of this ionization.

This layer covers from 90 km to 500 km approximately.

In the polar zones, many atoms lose electrons and become ionized, releasing energy and giving rise to the northern or southern lights .

It is in the thermosphere that shooting stars are observed, small particles that, upon entering the atmosphere, burn and disintegrate due to friction. Spacecraft also notice this friction when they return to Earth.

This is where the reflection of radio and television waves occurs.

Curiosity: Radio waves

The thermosphere or ionosphere is where the radio waves that are emitted from the Earth's surface are reflected and makes it possible for these waves to travel long distances on Earth.


The exosphere is the transition zone between the Earth's atmosphere and outer space. Here, the gases lose their physicochemical properties until they reach a composition similar to that of space, where there is practically a vacuum and the temperature does not vary. The gases found in the exosphere are the lightest: hydrogen, helium, carbon dioxide, and atomic oxygen.

This layer occupies from 500-580 km up to 10,000 km in height.

The exosphere is where artificial satellites are located.

Answer in your notebook

What function does the ozone layer have?

Interactive Activity: Order the layers of the atmosphere from the lowest to the highest.

Interactive Activity: Layers of the Atmosphere.

Interactive Activity: Who's Who in the Atmosphere?.

Interactive activity: The layers of the atmosphere.

Interactive activity: Match each layer with its corresponding feature.

Interactive activity: Composition of the atmosphere True or false?.

Interactive activity: Dynamics of the atmosphere True or False?.

Interactive Activity: Weather Instruments.

Interactive activity: The layers of the atmosphere.