Element distributed in soil, buried carbon (7)
I believe the answer is:
silicon
'element' is the definition.
(silicon is a kind of element)
'distributed in soil buried carbon' is the wordplay.
'distributed' is an anagram indicator.
'buried' means one lot of letters goes inside another.
'carbon' becomes 'c' (C is the chemical symbol for carbon).
'in'+'soil'='insoil'
'insoil' with letters rearranged gives 'silion'.
'silion' placed around 'c' is 'SILICON'.
(Other definitions for silicon that I've seen before include "Computer chip element" , "Element in sand, quartz" , "Semiconducting element" , "Element occurring in sand" , "Electronic circuit element" .)