Earth summit's social oddly ignored (7)
I believe the answer is:
topsoil
'earth' is the definition.
(topsoil is a kind of earth)
'summit's social oddly ignored' is the wordplay.
'summit's' becomes 'tops' ('top' can be a synonym of 'summit').
'oddly ignored' indicates alternate letters.
The alternating letters of 'social' are 'oil'.
'tops'+'oil'='TOPSOIL'
(Other definitions for topsoil that I've seen before include "surface of earth" , "Earth's surface" , "Garden's surface layer" , "best part of earth" , "The Good Earth" .)