Answer:
Erosion
Step-by-step explanation:
Erosion is a natural occurance that whittles away at exposed rock formations in the earth's crust. The most obvious forms or erosion are from water and wind.
For example, a soft porous rock such as sandstone will erode faster than a harder rock like granite. Sandstone is more likely to erode into sand (soil) and slate is more likely to split off as rock fragments.