Related Clues:

• Makeup of a protective layer
• Atmosphere layer
• Layer with a hole
• A layer with a hole
• Thinning layer
• Fresh air
• Contents of a newsworthy layer
• Kind of hole or layer
• Important layer
• O3
• Much-discussed layer
• Lightning byproduct
• Kind of layer protecting the earth
• Layer with a hole in it
• Earth-surrounding layer