the atmosphere surrounds the earth as a layer containing a mixture of gases.
the atmosphere is held by the gravitational force of the earth.
though the atmosphere extends beyond 1500 km above the earth , 97 per cent of it lies within a height of 27 km from the earth's surface.
this is because the density of the atmosphere is greater in the lower layers than in the upper layers.
the layers of atmosphere are troposphere , stratosphere , ionosphere , exosphere and mesosphere.
the atmosphere contains oxygen and nitrogen that are essential for the survival of life.
it receives insulation and preserves some amount of heat within the earth to keep it warm.
the ozone layer protects us from harmful and ultraviolet rays.
the water vapour present in it brings about rainfall which supports life on earth.