Rocks and mountains change very slowly, but they do change. As soon as a rocky mass is pushed upward, forces of erosion slowly begin to level it again. Wind and rain wear it away, grain by grain. Freezing water expands, enlarging small cracks until the rocks begin to crumble.

Lichens are often the first organisms to colonize the rocks. The dead lichens combined with dust from the air to become soil for mosses and small plants. As plant roots fill the cracks, the rocks break apart and the formation of soil continues. Decomposing plants add a fertile top layer to the soil. Burrowing mammals and insects mix and loosen the soil, which increases the amount of water available to plants.