Chapter 2

The Origins of Soil

(book excerpts)

Physical, chemical, and biological agents, such as wind, running water, ice, temperature changes, gravity, plants, animals, and time, among others perpetually modify the Earth’s crust, changing the parent material into products that are more nearly in equilibrium with the atmosphere, the hydrosphere, and the biosphere. These soil-forming processes are interdependent, each modifying the effectiveness of the others. The types of parent materials and the conditions under which they break down will influence the properties of the soil formed. For example, soils formed from granite are often sandy and infertile whereas basalt under moist conditions breaks down to form fertile, clay soils. The variability in the characteristics of soils such as texture, color, structure, porosity, and chemical and microbiological properties, usually result from the actions of soil-forming processes. Soil formation occurs via a series of changes to the parent material, all of which lead to the formation of layers of soil, also called soil horizons. These layers can then be separated on the basis of the composition and other physical and chemical properties. The formation of soil from parent material is a slow but continuous process.

Click on the following topics for more information on the origins of soil.

Topics Within This Chapter:

  • Formation of Parent Material
  • Igneous Rocks
  • Extrusive Igneous Rocks
  • Intrusive Igneous Rocks
  • Metamorphic Rocks
  • Sedimentary Rocks
  • Weathering of Rocks
  • Physical Weathering
  • Temperature
  • Water, Glacier, Wind, and Organisms
  • Chemical Weathering
  • Soil Development
  • Parent Material
  • Climate
  • Weathering Process Effect on Soil Properties
  • Time
  • Topography
  • Slope and Aspect
  • Soil Biota
  • Soil Profile
  • Master Horizons
  • Soil Horizon O
  • Soil Horizon A
  • Soil Horizon E
  • Soil Horizon B
  • Soil Horizon C
  • Soil Horizon R
  • Vertical Subdivisions
  • Transitional Horizons