The pieces become one of the most important substances on Earth—soil. Soil is the ultimate product of weathering. It is the loose, unconsolidated material that makes up the upper layer of Earth’s crust and supports plant life. It is made of broken up rock particles and organic material that comes from decaying plant and animal life.

The time it takes for soil to develop can depend on the rock, because limestone, for example, is easier to weather than, say granite. But in any case, soil develops in four stages. Go through the following interactive to explore the stages of soil development.

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The nature of the soil that develops depends on the nature of the parent material from which it comes and the climatic conditions from which it forms. If there are many mineral nutrients in the parent bedrock, the soil will most likely have the same nutrients. If the parent bedrock is made of only one type of material, the resulting soil will likely have some nutrient deficiencies. The most fertile and productive soils come from a variety of rock materials. They have a wide variety of plant nutrients and are able to support many plants.

Apply the concepts you have learned so far. Look through the following questions, think about them, and then click the question to reveal an answer.

Where do you think soils are the deepest—the deserts or the tropics? Explain your answer.
 

Soils are deeper in the tropics than in the desert. In the tropics, there is sufficient rainfall to allow for lots of chemical weathering and soil development; desert soils tend to be very thin because not as much chemical weathering takes place in desert environments.

Soils have different colors throughout the world. Some are light brown, some are reddish, and others are dark black. What do you think causes differences in soil color?

Color is most often related to the parent material. The color of the rocks gives rise to a similar color of soil. Also, color can be related to the type of weathering the parent material has undergone. Oxidation, for example, causes a red or yellow colored soil. Finally, color may also be related to the amount of decaying plant and animal material in a soil—lots of this gives the soil a dark brown or black color.