Study of the earth's surface (9)
I believe the answer is:
geography
'study of the earth's surface' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for geography that I've seen before include "World study" , "Study of earth's topography and man's responses to it" , "Science of the surface of the earth and its inhabitants" , "Scientific study of earth's surface" , "15 down subject" .)