What Is Causing My Silver Jewelery To Tarnish?

margerie103186 asked: I wear several pieces of sterling silver jewelry daily, and have been for years now. I never take off my 2rings or the 2 pairs of earrings in my ears, and wear a necklace and bracelet during the day.
Recently (in the past 2 weeks) my earrings have turned completely black, tarnished. [...]