An atmosphere is a sheet of gases that surround material body or a planet. It is controlled by the gravity of that body. Argon, oxygen and nitrogen form the three main constitutions of the atmosphere.

Earth’s Atmosphere:

About 80 percent of the mass of earth’s atmosphere is contained below 10 km altitude. The atmosphere of earth is mostly composed of many gases including nitrogen, oxygen, carbon dioxide. This helps protect living organisms from genetic damage by solar ultraviolet radiation, solar wind and cosmic rays.

Layers of Atmosphere:

The earth’s atmosphere is divided into layers based on the temperature field. These layers are:

  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere
  • Ionosphere
  • Exosphere

Layers of Atmosphere

Troposphere: It is the undermost layer of the earth’s atmosphere. At the base of the troposphere, the air is warmer. Density and air pressure also decrease with the altitude.

Stratosphere: It is the 2nd layer of the atmosphere. It occurs at an altitude of fifty kilometres.

Mesosphere: It lies beneath troposphere and above the stratosphere. Temperature decreases with the altitude.

Thermosphere: It extends to six hundred kilometres high. Aurora and satellites occur in this layer. It starts just above the mesosphere.

The ionosphere is an abundant layer composed of ionized atoms, molecules and electrons that expand from about forty-eight kilometres above the surface overlapping into the mesosphere and thermosphere.

The exosphere is the upper limit of earth’s atmosphere. It extends from the top of the thermosphere up to 10,000 km.

Gases in Atmosphere:

The atmospheric composition on Earth is largely conducted by the by-products of the life that it nurse.

Gases in Atmosphere

Dry air from earth’s atmosphere contains 0.038 percent of carbon dioxide, 20.95 percent of oxygen, 78.08 percent of nitrogen and 0.93 percent of argon. 

 Atmosphere Gases

Traces of hydrogen, neon, helium, nitrous oxide, ozone and other “noble” gases, but generally a variable amount of water vapour is also present, on average about 1 percent at sea level.

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Practise This Question

A thin tube of uniform cross section is sealed at both ends. It lies horizontally, the middle 5 cm containing mercury and the parts on its two sides containing air at the same pressure P. When the tube is held at an angle of 60 with the vertical, the length of the air column above and below the mercury pellet are 46cm and 44.5cm respectively. Calculate the pressure P in centimeters of mercury. The temperature of the system is kept at 30C.