What were CFCs used for?

They are used in the manufacture of aerosol sprays, blowing agents for foams and packing materials, as solvents, and as refrigerants.

When was it discovered that the ozone layer was thinning?

In 1984 Antarctic Survey scientists, Joesph Farman, Brian Gardiner, and Jonathan Shanklin, discovered a recurring Antarctic ozone hole . Their paper was published in Nature, in May 1985, the study summarized data that had been collected by the British Antarctic Survey showing that ozone levels had dropped 10% below normal.