The in the upper atmosphere prevents some of the sun's ultraviolet radiation from reaching earth.

The answer would be the ozone layer. A layer of ozone in the upper atmosphere absorbs UV radiation and prevents most of it from reaching the Earth. ... This means that more ultraviolet radiation can pass through the atmosphere to the Earth's surface, particularly at the poles and nearby regions during certain times of the year.

I hope that this helped you! Good luck. :)