Atmosphere | Definition of Atmosphere in Simple Words

Definition of Atmosphere

The earth is surrounded by a huge blanket of air called Atmosphere. It is held to our planet by its gravitational attraction. The air we take in while breathing is actually a mixture of many gases :

  • Oxygen and Nitrogen make up the bulk of the atmosphere.
  •  CO2 and other gases like helium, ozone, argon, and hydrogen are found in lesser quantities.
  • Apart from these gases, small dust particles are also present in the air.

Atmosphere, gases in ain


  • Plants need Nitrogen for their survival. The plants cannot take nitrogen directly from the air but bacteria, that live in the soil and roots of some plants, take nitrogen from the air change it is from so that plants can use it.


  • Human and animals take oxygen from the air to breathe. Green plants produce oxygen during photosynthesis and oxygen content remains constant in the air.

Carbon Dioxide

  • Humans and animals release Carbon Dioxide. Green plants use carbon dioxide to make their food and release oxygen. This perfect balance is upset by the burning of fuels, i.e. coal and oil which add billions of tons of carbon dioxide into the atmosphere each year. The increased volume of  CO2 affects the Earth’s weather and climate.

NOTE: CO2 released in the atmosphere creates a Greenhouse Effect by trapping the heat radiated from the earth, it is called greenhouse gas, without it, the earth would have been too cold to live in. when its level in the atmosphere increases due to factory smoke or car fumes, the heat retained increases the temperature of the earth to be known as Global Warming.


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Layers of the Atmosphere

layers of atmosphere, atmosphere


  • The lowest Layer of atmosphere to be about 13 km high at the equator and 8 km high at the poles. All weather changes such as cloud formation, rain, snow, hail, storm, lightning, and thunder take place in this layer. The boundary between the troposphere and stratosphere is called tropopause, where the temperature stops decreasing.
  • As we go higher in the troposphere, the air gets thinner and the temperature drops to 1°C per 165m. The low of Temperature due to increase in height is known as the lapse rate.


  • Above the layer of Troposphere, Stratosphere extends up to a height of 50 km. This layer creates most ideal conditional for flying aeroplanes due to free from clouds and associates weather phenomenon. Stratosphere contains a layer of ozone gas and this gas protect us from the harmful effect of the Sun’s rays.


  • The Mesosphere is the middle layer of Atmosphere and it’s above the stratosphere, to extend up to 80 km above the Earth’s surface. It is a protective layer as most meteorites from space burn out while passing through this layer due to friction with the atmosphere.
  • The temperature of this layer decreases with height. Menopause is the upper part of this layer and this layer separates Mesosphere from Thermosphere.


  • In Thermosphere, temperature rises very rapidly with increasing height, to extend between 80 – 400 km.
  • The ionosphere is the part of this layer. This layer helps in radio Transmission, i.e. radio waves transmitted from the earth are reflected back to the earth by this layer.


  • The Exosphere is the uppermost layer of the atmosphere. Exobase is the lowest boundary of Exobase and Exosphere extend between 500 – 1000 km. This Layer has very thin air. Light gases like Helium and hydrogen Float into space from here.

Air pressure

atmosphere , Air pressure

  • The pressure exerted by the weight of the atmosphere on the Earth’s is known as Atmospheric pressure. A barometer is used to measure pressure in millibars (MB). usually, the air pressure is around 1013.2 MB at sea level. we do not feel the weight of the atmosphere because we have air inside our bodies, which balances the external air pressure on us keeps us firmly on the ground.
  • Air pressure also varies with temperature. We have low pressure in areas with high temperatures and high pressure in areas with low temperatures. A low-pressure area is where the air is heated and rises up, while a high-pressure area has cold air to sit on the surface.

NOTE: On the moon, there is no air and hence no air pressure Astronauts have to wear special protective space filled with air when they go to the moon. If they did not wear these space suits, the counter-pressure exerted the body of the astronauts would make the blood vessels burst. The astronauts would bleed.

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