What’s it good for, anyway? Soil Where does it come from? What kinds are there? What’s it good for, anyway? What’s happening to it?

TAKE HOME POINT Soil comes from the physical and chemical breakdown of parent materials, which include bedrock and organic materials such as leaves and animals.

Earth’s surface processes First a definition: Weathering – Physical breakdown and chemical alteration of rock at Earth’s surface

Source: Tom Bean/DRK Photo

Mechanical Weathering Mechanical weathering – breaking of rocks into smaller pieces Four types of mechanical weathering 1. Frost wedging – freezing and thawing of water in cracks disintegrates rocks

Frost Wedging

Evidence of Frost Wedging in Wheeler Park, Nevada Source: Tom Bean/DRK Photo

Rockfall caused by frost wedging

Source: Runk/Schoenberger/Grant Heilman Tree roots growing in rock fractures, plus animal burrows, expose deep rocks to water Source: Runk/Schoenberger/Grant Heilman

Increase in surface area by mechanical weathering

Differential weathering controlled by jointing patterns Definitions: Joints and Faults Deep rock exposed to water

Joint-controlled weathering in igneous rocks

Chemical Weathering Breaks down rock and minerals Important agent in chemical weathering is water Water dissolves and transports ions and molecules The dissolved ions later bond & form the cements in sedimentary rocks

Source: Ramesh Venkatakrishnan

Dissolution Weathered and Unweathered Limestone Boulders Source: Ramesh Venkatakrishnan

Weathering Rates of weathering Others factors affecting weathering Mechanical weathering aids chemical weathering by increasing surface area Others factors affecting weathering Rock characteristics e.g. minerals Marble and limestone easily dissolve in weak acidic solutions -Dissolution

Soils Our food grows in soils. Also very important in recognizing past climates

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 Biotic AND abiotic parts

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 Climate 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 Slope Organisms influence soil properties Also furnish organic matter to the soil (especially plants) Slope Steep slopes have poorly developed soils (due to faster erosion and downslope transport Flatter terrain accumulates soil faster

Variations in soil development due to topography Note location of agriculture

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

Mnemonic: Only Active Educators Become Champions Soil The soil profile O horizon – organic matter A horizon – organic and mineral matter High biological activity (animals live here) Together the O and A horizons make up topsoil E horizon – little organic matter Zone of leaching B horizon – zone of accumulation C horizon – partly altered parent material Mnemonic: Only Active Educators Become Champions

Animal Activities in “A” horizon Source: Runk/Schoenberger/Grant Heilman

Eluviation & Illuviation

Remember the different horizons A E B C Organic Animal Activity Exited Back Crushed Rock Soluble Minerals Soluble Minerals

pedalfer pedocal laterite Evergreen forests Shortgrass tropics

New Jersey State soil ftp://ftp-fc.sc.egov.usda.gov/NSSC/StateSoil_Profiles/nj_soil.pdf

Pedocal with Caliche in the B horizon Organic Activity Leached Accumulation Crushed Rock

Caliche Source: Teaching Collection/University of Washington, Department of Geological Science

Laterite in Sarawak, Borneo Source: Fletcher & Baylis/Photo Researchers, Inc.

Earth’s surface processes Erosion – the physical removal of material by mobile agents like water, wind, ice, or gravity

Soil Erosion Soil erosion Soil characteristics Climate Slope Recycling of Earth materials Natural rates of soil erosion depend on Soil characteristics Climate Slope Type of vegetation

Source: Ramesh Venkatakrishnan Erosion Headed for the Sea Source: Ramesh Venkatakrishnan

Soil 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

Hydrolysis Cleopatra’s Needle, (Egypt) Granite in a Dry Climate Source: New York Public Library, Locan History and Genealogy Division

Hydrolysis Cleopatra’s Needle, (Central Park, NYC) Granite in a Wet Climate Source: Runk/Schoenberger/Grant Heilman