[jjk166]

It's worth considering that most of the diversity of environments on earth are really diversity of ecosystems. Strip away the trees and the grass and the topsoil and then Earth would look like a desert wasteland pretty much everywhere.

[yencabulator]

Also, water! The different colors of dirt (containing copper, iron etc) near here are all exposed by water erosion.

[Terr_]

Also, some of the geology is due to biology, especially with respect to erosion. (And oxygen level, I guess.)

Without plants, mountains and valleys etc. would be shaped a little differently, as opposed to "exactly the same but without green on top."