James's contribution to carbon dating (4)
I believe the answer is:
bond
'james's' is the definition.
(James Bond is a fictional spy)
'contribution to carbon dating' is the wordplay.
'contribution to' indicates the answer is hidden within the clue.
'BOND' can be found hidden inside 'carbon dating'.
(Other definitions for bond that I've seen before include "Financial asset" , "Join; secret agent" , "one licensed to kill" , "Valuable asset" , "Fictional agent; join" .)