Lichens secrete an acid that dissolves some minerals. Also organic matter is acidic. When water and organic matter mix, they form a slightly acidic solution that breaks down rocks in the soil, like the vinegar in Activity 3. That is why soils in the eastern United States are more acidic than soils in the west. They contain more organic matter.
Eastern topsoil are also generally deeper.
Organic matter is good for plants, it keeps topsoil in its place, keeps soil particles together, retains soil moisture, and speeds up soil formation. It takes between 100 and 500 years for just 1-inch of topsoil to form depending on the type of rocks and climate. In Utah, our topsoil depths range from 1-12 inches. However, topsoils can be several feet deep depending on their location. Because our topsoils are so shallow, farmers, ranchers and others who are charged with caring for the land, must use practices that conserve topsoils and hold them in their place.