Earth summits on fuel (7)
I believe the answer is:
topsoil
'earth' is the definition.
(topsoil is a kind of earth)
'summits on fuel' is the wordplay.
'summits' becomes 'tops' ('top' can be a synonym of 'summit').
'on' means one lot of letters go next to another.
'fuel' becomes 'oil' (I've seen this before).
'tops'+'oil'='TOPSOIL'
(Other definitions for topsoil that I've seen before include "Garden's surface layer" , "where grass grows" , "Upper garden layer" , "The Good Earth" , "Upper layer of earth" .)