Just what is soil?

skin of the earth
This is a cutout of the earth, with the critical layer of soil.

Soil has been a defining component of cultures since the beginning of civilization. Some of the first written words were recorded on clay tablets and water was carried in clay pitchers. It provides the base for all buildings (although some may be able to support a skyscraper and some others may not be able to support your weight), it holds the clues of past cultures (to be revealed by archeologists or erosion), it supports the web of life (connecting all ecosystems), provides materials to build houses, is a source of nutraceuticals (definite in the American Heritage Dictionary as a food or naturally occurring food supplement thought to have a beneficial effect on human health), and of course, provides the base for our food, fiber, feed, and even some biofuels.


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The core curriculum standards (2013) adapted by 26 states hasidentified physical sciences; life sciences; earth and space sciences; and engineering, technology, and applications of science as the four main curriculum areas critical for scientific development. Soil fits into ALL of these areas (even SPACE). Soils are complex mixtures of minerals, water, air, organic matter, and countless organisms that are the decaying remains of once-living things. It forms at the surface of land – it is the “skin of the earth.” Soil is capable of supporting plant life and is vital to life on earth.



Soil, as formally defined in the Soil Science Society of America Glossary of Soil Science Terms, is:

1 The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.
2 The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time.

So then, what is dirt?

Dirt is what gets on our clothes or under our fingernails. It is soil that is out of place in our world – whether tracked inside by shoes or on our clothes. Dirt is also soil that has lost the characteristics that give it the ability to support life – it is dead. Soil performs many critical functions in almost any ecosystem (whether a farm, forest, prairie, marsh, or suburban watershed).

For more information

Check out the Soils Overview (PDF) for a printable version of basic soils information. Major role of soils Page tells about the major roles that soils play in our lives. There are many soil properties that help us describe and manage soils. Some of the important physical properties are described on the Physical Properties of Soils Page. Soils can have many different layers. For a description on what soil layers exist, visit the Soil Horizons page.