Ultra violet radiations of the Sun do not reach the

Solution

The ozone layer absorbs 97-99% of the Sun's medium-frequency ultraviolet light (from about 200 nm to 315 nm wavelength), which potentially damages exposed life forms on Earth. Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in low concentrations   throughout   the   Earth's atmosphere. In total, ozone makes up only 0.6 parts per million of the atmosphere.