Shift in opinion could do for Earth (6,2,5)
I believe the answer is:
change of heart
'shift' is the definition.
(thesaurus)
'opinion could do for earth' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'earth' is 'heart' which is located in the answer.
This explanation may well be incorrect...
'in' is the link.
Can you help me to learn more?
(Other definitions for change of heart that I've seen before include "Having a different view" , "Profound shift in outlook" , "Attitude alteration" , "Profound alteration in outlook or opinion" , "Switch in opinion" .)