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SOILS!!! As rocks weather, they combine with organic material to form soil. • What is soil and how is it created (SUMMARIZE!)? • What video clip: Geography Principles: Soil and Vegetation : soil formation Soil • Soil - combination of mineral and organic matter, water, and air • It is that portion of the regolith (weathered rock and mineral) that supports the growth of plants Components in soil that support plant growth Soil • Factors controlling soil formation • Parent material – parent material is the underlying bedrock composition affects soil types Soil • Factors controlling soil formation • Time – Soils get better developed (Thicker, with greater differences between layers) with more time • Climate – Biggest control on soil formation –Key factors are temperature and precipitation Soil • Factors controlling soil formation • Plants and animals – Organisms influence soil properties – Also furnish organic matter to the soil (especially plants) Soil Profile • The soil profile • Soil forming processes operate from the surface downward • Vertical differences are called horizons – zones or layers of soil An idealized soil profile with horizons Soil • The soil profile – O horizon: Organic layers or decaying plant and animal tissue – A horizon: Mineral horizon mixed with humus (dark decayed organic matter) – E horizon: Mineral horizon with less organic matter and certain minerals leak down – B horizon: Mineral horizon in which materials that have leaked from above begin to accumulate – C horizon: unweathered geologic material (sediment; some bedrock) with little sign of soil forming processes – R horizon: Hard, completely unweathered parent material (bedrock); needs blasting or heavy machinery to dig through Mnemonic: Only Active Educators Become Champions Really Remember the different horizons O A Organic Animal Activity Soluble Minerals E B C Exited Soluble Minerals Back Crushed Rock Earth’s surface processes • Erosion – the physical removal of material by mobile agents like water, wind, ice, or gravity Soil Erosion • Soil erosion • Recycling of Earth materials • Natural rates of soil erosion depend on –Soil characteristics –Climate –Slope –Type of vegetation Where Does Our Eroded Soil Go? • Soil erosion • In many regions the rate of soil erosion is significantly greater than the rate of soil formation • Farmers now level fields with lasers to slow loss of topsoil • Terraces • • • • • • • • • • • • • • • Soil makes up the outermost layer of our planet. Topsoil is the most productive soil layer. Soil has varying amounts of organic matter (living and dead organisms), minerals, and nutrients. Five tons of topsoil spread over an acre is only as thick as a dime. Natural processes can take more than 500 years to form one inch of topsoil. Soil scientists have identified over 70,000 kinds of soil in the United States. Soil is formed from rocks and decaying plants and animals. An average soil sample is 45 percent minerals, 25 percent water, 25 percent air, and five percent organic matter. Different-sized mineral particles, such as sand, silt, and clay, give soil its texture. Fungi and bacteria help break down organic matter in the soil. Plant roots and lichens break up rocks which become part of new soil. Roots loosen the soil, allowing oxygen to penetrate. This benefits animals living in the soil. Roots hold soil together and help prevent erosion. Five to 10 tons of animal life can live in an acre of soil. Earthworms digest organic matter, recycle nutrients, and make the surface soil richer.