Why does the surface of the earth change?
The Earth is very dynamic, and many factors contribute to the changes that occur within or on it's surface.
When it comes to changes on the Earth's surface, the main processes to take into account are plate tectonics and the rock cycle as well as the sea-floor spreading. This processes explain how mountains are built and how the landscape changes through time.
For example, the surface of the earth is composed of plates which are continually moving and colliding with each other. These collisions causes mountains and volcanoes to form on the plate boundaries and thus changes the shape and form of the landmass.