Land as space for living

            There are many ways in which land is needed to provide space. Land is needed for building homes and cities. It is needed for roads and parks.
            Land is an example of a nonrenewable resource. Unlike a renewable resource, a nonrenewable resource cannot be replaced as it is used up. The processes that have formed a nonrenewable resource, such as land, have for the most part been completed. And land that provides space for a building, for example, basically can't be used for anything else.

Soil for growing things

            In addition to providing living space, land is important in another way. It contains soil that helps support life on the earth. Soil provides a "foothold" for the roots of plants. It supplies nutrients needed for plant growth. It also holds water and air that are needed by plants. Animals and people depend on plants or on animals that eat plants for all of their food.
            There are many kinds of soil. Basically, each kind of soil was formed from the rocky materials of the earth. These materials have been broken down through millions of years. Some soil also contains the decayed remains of plants and animals. The organic part of soil is known as humus.
            The forces that form soil are still at work. However, it takes thousands of years to form 2.5 centimeters (1 inch) of soil! So soil is thought of as a nonrenewable resource.
            The soil over the surface of the earth averages 61 to 91 centimeters (2 to 3 feet) deep. The most fertile of this soil, called topsoil, is usually less than 30 centimeters (1 foot) deep. Many areas of the United States at one time had 23 to 30 centimeters (9 to 12 inches) of fertile topsoil. Through years of use and misuse, the amount has dropped to 15 centimeters (6 inches) or less in many places.