Unearth dead containing old carbon (6)
I believe the answer is:
locate
'unearth' is the definition.
('locate' can be a synonym of 'unearth')
'dead containing old carbon' is the wordplay.
'dead' becomes 'late' ('late' can be similar in meaning to 'dead').
'containing' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'carbon' becomes 'c' (C is the chemical symbol for carbon).
'o'+'c'='oc'
'late' placed around 'oc' is 'LOCATE'.
(Other definitions for locate that I've seen before include "Pinpoint the position" , "Discover the place where something is" , "Fix position of" , "Find or situate" , "spot" .)