What is Soil - Earth and Environmental is Soil •Soil is a complex ... Effects of Particle Sizes ... •What determines the composition of a soil? •Mostly the bedrock, erosion, organic stuff ...

Download What is Soil - Earth and Environmental  is Soil •Soil is a complex ... Effects of Particle Sizes ... •What determines the composition of a soil? •Mostly the bedrock, erosion,  organic stuff ...

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  • What is Soil

    Soil is a complex mixture of weathered rock, minerals, organic material (both living & decaying), water, and air.

    Different soils have different amounts.

    What might change the amounts?

    On average, soil has the following ratios: 45% minerals & rocks

    25% water

    25% air

    5% organic material

  • How is Soil Produced?

    Weathering of rocks and minerals

    Deposits of sediments washed/blown to the site

    Decomposition/actions of living things.

  • Weathering of Rock

    Weathering is the physical or chemical breakdown of rock into smaller pieces

    These pieces may be large or too small to see!

    Two types of weathering:



  • Mechanical Weathering

    Physical breakdown of rock

    Chemical composition of the rock does not change



    Ice Wedging


    Plant & Animal Activity

  • Exfoliation

    When rocks come to the surface, pressure on them is reduced.

    This can allow cracks to form, and the rocks break apart.

    Example: Granite

  • Ice Wedging

    When water flows into the cracks in rocks & freezes.

    Why does this split the rocks?

  • Abrasion When rocks broken from other processes

    collide and break even more.

    Happens because of gravity, ice, running water, or windwait, how does wind do this?

  • Plant & Animal Activity Plant roots act like ice to split rocks

    Animals, mostly ones that burrow, expose other rocks for further weathering.

  • Chemical Weathering

    Chemical reactions break the minerals in the rock into different materials





    Organic Acids

    Acid Rain

  • Oxidation When elements

    in the rock combine with Oxygen, and break off as new compounds.

    Usually happens in rocks with iron

    Produces a red color

  • Hydrolysis

    When chemicals in the rock react with water, causing some of the minerals to break away from the rock.

    Often happens with metals like Potassium & Aluminum

  • Carbonation When CO2 gets into water it makes Carbonic Acid

    This acid can stick to some minerals and form compounds that are washed away by water.

    This often happens to limestone.

  • Organic Acids

    Some living things produce acids that are released to the environment.

    These acids can make cracks in rocks and start the weathering process.

    Examples: Lichens & mosses

  • Acid Rain

    Nitrogen & Phosphorus from fossil fuels get into the air and combine with rainwater

    This rainwater weathers rock more rapidly than normal rain.

  • Formation of Soil

    When new rock is exposed, soil begins to form.

    This newly exposed rock is known as Bedrock.

  • Formation of Soil Weathering begins to break the bedrock into

    smaller rocks.

    This layer of partially weathered rocks, above the bedrock, is known as Regolith.

  • Soil Characteristics

    The size of soil particles also affects the characteristics of a soil.

    Soils are usually categorized by the amounts of each type of particle that they have.

    Particles are:

    Clay: less than 0.0002mm

    Silt: 0.0002mm 0.05mm

    Sand: 0.05mm 2mm

  • Effects of Particle Sizes

    The size of soil particles affects how much water & air the soil can hold.

    The smaller the particles, the less the soil can hold.

    However, if the soil is made entirely of larger particles, the water will run right through the soil!

    We measure particle sizes by measuring Porosity.

  • Porosity:

    The measure of the volume of pores and distance of pores

  • Effects of Particle Sizes

    Infiltration: the rate at which water from precipitation or other sources flows into the soil

  • Saturation:The amount of water and air

    that can move through soilWater Water

    High permeability Low permeability

  • Soil Profiles

    The formation of soil in different areas produces different layers.

    These layers are called Horizons.

    The composition and depth of horizons is measured by looking at a Soil Profile.

  • Soil Horizons

    O horizon

    Leaf litter

    A horizon


    B horizon


    C horizon



    Mature soil

    Young soil


    Immature soil

  • What changes a Soil Profile?

    What determines the composition of a soil?

    Mostly the bedrock, erosion, & organic stuffbut what determines these?!?


    Climate mostly affects the layers of a soil, but not the materials found in the soil.

    In general, climates that have all 4 seasons have all the layers of soil.

  • Soil Erosion

    What is erosion?

    The movement of weathered materials from one location to another.

    Soisnt this the same as weathering?

    No! Weathering helps to build soil, soil erosion destroys soil.

  • What Causes Soil Erosion?





    Human Actions can speed up the process!

  • Wind Weathering

  • Wind Erosion

  • Gravity Weathering

  • Gravity Erosion

  • Water Weathering

  • Water Erosion

  • Glacier Weathering

  • Glacier Erosion

  • Humans & Erosion

    So, how do humans affect this Soil Erosion thing?

    Development for housing/buildings

    Farmingthis is the big one

  • Humans & Erosion

    Farming can expose a lot of lose soil to erosion.

    This soil is the O and A horizonswhy are these important?

    These contain most of the organic material in the soil, which plants and animals need to survive.

  • Farm Erosion

  • Is Erosion Really a Problem?

    Areas of serious concern

    Areas of some concern

    Stable or nonvegetative areas

  • What can we do to prevent Erosion?

  • Contour Plowing

    Hillsides are plowed in curves that follow the shape of the land.

    Prevents water from flowing straight down.

  • Strip Cropping

    Crops are planted in alternating bands.

    This way, the whole area is not filled with row crops that dont cover all the land.

  • Terracing

    Hills are carved into flat steps.

    This prevents water from flowing rapidly down the hill.

  • Crop Rotation

    Planting a crop to harvest 1 year, and one to leave in place the next year.

    Often combined with strip and contour farming.


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