Australia has one damaged layer? (5)
I believe the answer is:
ozone
'damaged layer' is the definition.
(the Earth's ozone layer)
'australia has one' is the wordplay.
'australia' becomes 'oz' (informal name for Australia).
'has' means one lot of letters go next to another.
'oz'+'one'='OZONE'
(Other definitions for ozone that I've seen before include "Gas that screens ultraviolet radiation" , "Colourless gas soluble in alkalis and cold water" , "Clean, bracing air" , "Invigorating air of the seaside" , "lively atmosphere" .)