63. Justify the statement that ozone layer is called ‘earth’s protective umbrella.’
Or
How will you explain the formation of the ozone layer in the atmosphere?

The formation of ozone in the stratosphere (11-50 km) occurs in two steps:
First step: The UV radiations coming from the sun have sufficient energy to split the dioxygen into oxygen atoms.
 

Second step: The oxygen atoms react with more dioxygen to form ozone. 
The ozone thus formed on absorbing U.V. radiations dissociate into dioxygen and an oxygen atom. In this process, heat is given out which warms up the stratosphere. 


As a result, this stratosphere is a zone of increasing temperature. In this way 'Ozone cycle' is completed in the stratosphere. 
At an altitude of 25-30 km, we have a layer in which the concentration of ozone is about 10ppm. It is called ozone layer. This region is also called ozonosphere. It does not allow the harmful UV radiations coming from the sun to reach the surface of the earth and thus protects life on the earth. This ozone layer is also called earth protective umbrella.