Although ozone poisonous at the surface, it forms in the stratosphere?

a protective layer

Explanation:

The ozone layer is a relatively thin layer located in the stratosphere that absorbs most of the sun's ultraviolet rays (97-99%). The ozone layer contains a higher concentration of ozone (O₃) than other layers in the atmosphere, approximately 10 parts per million (vs 0.3 parts per million in the rest). It is relatively thin because it is only about 12 miles thick and our whole atmosphere is 300 miles thick.

Without the ozone layer, life would not be able to exist in Earth since UV rays would virtually cook everything (similar to a microwave). The ozone layer was depleting due to the extensive use of chlorofluorocarbons (CFCs) used in refrigeration, and since CFCs were banned its depletion has almost stopped.