Question

what protects the earths atmosphere from suns harmful rays

Answer 1

the atmosphere is to protect and contain earths surface, there is no layer that protects the atmosphere it's self.
i never considered it needing protection itself...
but the Ozone layer is the protective layer within the atmosphere.
From National Geographic,"The ozone layer is one layer of the stratosphere, the second layer of the Earth’s atmosphere. The stratosphere is the mass of protective gases clinging to our planet.

The stratosphere gets its name because it is stratified, or layered: as elevation increases, the stratosphere gets warmer. The stratosphere increases in warmth with elevation because ozone gases in the upper layers absorb intense ultraviolet radiation from the sun."
and the Ozone get's it's name from the Ozone molecule, where oxygen attaches to another oxygen atom, making a thick molecule capable of distorting large amounts of energy.