If you applied an atmosphere to mountains and valleys you would see a lot more difference. The thinner air on top the high mountains will cause them to be colder which affects other local weather including rain and snow formation that will erode them at different rates than flat ground and cause erosion products to accumulate in the valleys. The varying temperatures and weather conditions would then cause different flora and fauna to appear in the different zones and given a billion years you would end up with biomes not too dissimilar to the ones on earth