This is a diagram and related photograph of soil layers from bedrock to soil.
A, B, and C represent the soil profile, a notation firstly coined by Vasily Dokuchaev (1846–1903), the father of pedology; A is the topsoil; B is a regolith; C is a saprolite (a less-weathered regolith); the bottom-most layer represents the bedrock.
Surface-water-gley developed in glacial till, Northern Ireland.

Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions:

All of these functions, in their turn, modify the soil and its properties.

Soil is also commonly referred to as earth or dirt; some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.

The pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, and the biosphere.[1] The term pedolith, used commonly to refer to the soil, translates to ground stone in the sense fundamental stone, from the ancient Greek πέδον ground, earth. Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution).[2][3] Accordingly, soil scientists can envisage soils as a three-state system of solids, liquids, and gases.[4]

Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time.[5] It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem.[6]

Most soils have a dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm3, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3.[7] Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic,[8] although fossilized soils are preserved from as far back as the Archean.[9]

Soil science has two basic branches of study: edaphology and pedology. Edaphology studies the influence of soils on living things.[10] Pedology focuses on the formation, description (morphology), and classification of soils in their natural environment.[11] In engineering terms, soil is included in the broader concept of regolith, which also includes other loose material that lies above the bedrock, as can be found on the Moon and on other celestial objects as well.[12]

  1. ^ Chesworth, Ward, ed. (2008). Encyclopedia of soil science (PDF). Dordrecht, The Netherlands: Springer. ISBN 978-1-4020-3994-2. Archived from the original (PDF) on 5 September 2018.
  2. ^ Voroney, R. Paul; Heck, Richard J. (2007). "The soil habitat" (PDF). In Paul, Eldor A. (ed.). Soil microbiology, ecology and biochemistry (3rd ed.). Amsterdam, the Netherlands: Elsevier. pp. 25–49. doi:10.1016/B978-0-08-047514-1.50006-8. ISBN 978-0-12-546807-7. Archived from the original (PDF) on 10 July 2018.
  3. ^ Taylor, Sterling A.; Ashcroft, Gaylen L. (1972). Physical edaphology: the physics of irrigated and nonirrigated soils. San Francisco, California: W.H. Freeman. ISBN 978-0-7167-0818-6.
  4. ^ McCarthy, David F. (2006). Essentials of soil mechanics and foundations: basic geotechnics (PDF) (7th ed.). Upper Saddle River, New Jersey: Prentice Hall. ISBN 978-0-13-114560-3. Retrieved 17 January 2021.
  5. ^ Gilluly, James; Waters, Aaron Clement; Woodford, Alfred Oswald (1975). Principles of geology (4th ed.). San Francisco, California: W.H. Freeman. ISBN 978-0-7167-0269-6.
  6. ^ Ponge, Jean-François (2015). "The soil as an ecosystem". Biology and Fertility of Soils. 51 (6): 645–48. doi:10.1007/s00374-015-1016-1. S2CID 18251180. Retrieved 24 January 2021.
  7. ^ Yu, Charley; Kamboj, Sunita; Wang, Cheng; Cheng, Jing-Jy (2015). "Data collection handbook to support modeling impacts of radioactive material in soil and building structures" (PDF). Argonne National Laboratory. pp. 13–21. Archived (PDF) from the original on 4 August 2018. Retrieved 24 January 2021.
  8. ^ Buol, Stanley W.; Southard, Randal J.; Graham, Robert C.; McDaniel, Paul A. (2011). Soil genesis and classification (7th ed.). Ames, Iowa: Wiley-Blackwell. ISBN 978-0-470-96060-8.
  9. ^ Retallack, Gregory J.; Krinsley, David H.; Fischer, Robert; Razink, Joshua J.; Langworthy, Kurt A. (2016). "Archean coastal-plain paleosols and life on land" (PDF). Gondwana Research. 40: 1–20. Bibcode:2016GondR..40....1R. doi:10.1016/ Archived (PDF) from the original on 13 November 2018. Retrieved 24 January 2021.
  10. ^ "Glossary of terms in soil science". Agriculture and Agri-Food Canada. Archived from the original on 27 October 2018. Retrieved 24 January 2021.
  11. ^ Amundson, Ronald. "Soil preservation and the future of pedology" (PDF). Faculty of Natural Resources. Songkhla, Thailand: Prince of Songkla University. Archived (PDF) from the original on 12 June 2018. Retrieved 24 January 2021.
  12. ^ Küppers, Michael; Vincent, Jean-Baptiste. "Impacts and formation of regolith". Max Planck Institute for Solar System Research. Archived from the original on 4 August 2018. Retrieved 24 January 2021.