Support earth and environment (10)
I believe the answer is:
background
'environment' is the definition.
(background is a kind of environment)
'support earth' is the wordplay.
'support' becomes 'back' (to back is to support or endorse).
'earth' becomes 'ground' (synonyms).
'back'+'ground'='BACKGROUND'
'and' acts as a link.
(Other definitions for background that I've seen before include "history" , "(A person's) experience, education, circumstances" , "Reason behind" , "inconspicuous position" , "kind of music" .)