• Ozone layer in Earth’s stratosphere absorbs most of the ultraviolet radiation of the Sun and thus stops them from reaching Earth’s surface. • The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU). • Ozone depletion (thinning of the ozone layer) is a result of an increase in Chlorofluorocarbons (CFCs) in the Earth’s atmosphere. • International Day for the Preservation of the Ozone Layer is observed on 16th September every year.