Weathering and Soil Formation
Weathering and Soil Formation PREZI LINK
Rocks and Weathering
Weathering is the process that breaks down rock and other substances of Earth's surface.
Heat, cold, water, ice and air all contribute to weathering.
Erosion
Erosion is the removal of rock particles by wind, water, ice, or gravity.
Weathering and Erosion
Weathering breaks down
Erosion removes
Mechanical Weathering
Mechanical weathering is when rocks are physically broken down.
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Freezing & Thawing
a. ICE WEDGING: Water freezes in a crack in a rock, it expands and makes the
crack bigger---breaks the rock
Release of Pressure: As mass gets smaller, pressure decreases---Sediment that was
held together will break
Plant Growth: Roots pry apart cracks in the rock
Animal Actions: Break up rocks by digging
Abrasion: Particles in the air or water scratch the rock
Chemical Weathering
The process where the composition of rocks are changed
1. Water: Dissolves minerals in rock leaving holes and cavities
2. Oxygen: Causes rust on some rocks
3. Carbon Dioxide: Forms carbonic acid in water---causes rain to be acidic leading it to
dissolve rock
4. Living Organisms: Produce weak acids that weather rock---comes from plant roots
and decaying organisms
5. Acid Rain: From burning of fossil fuels---can dissolve rock, especially limestone
Rate of Weathering
Type of Rock & Climate are the most important factors that determine rate of weathering.
How Soil Forms
SOIL is the loose weathered material on earth's surface.
BEDROCK is a solid layer of rock beneath the soil.
How Soil Forms
What is Soil?
Composition
Mixture of rock particles, minerals, decayed organic material, air, water
HUMUS: Decayed organic material in soil; dark in color, forms from plant and animal
remains. It makes soil very fertile.
Texture: Depends on the size of the individual particles.
LOAM: Best soil for growing---made up of equal parts of clay, sand, and silt.
Fertility: Measure of how well the soil supports plant growth
HOW SOIL FORMS:
1. Rock is broken down by weathering and is mixed with other materials on earth’s surface
2. Takes a very long time
3. Develops HORIZONS (Layers)
Horizon A (Topsoil), Horizon B (SubSoil), Horizon C
Soil Types: Classified by climate, plants growing there, and soil composition
Living Organisms:
1. Make Humus: Decomposers break down other organisms.
2. Mix Soil and make spaces for air and water
3. Plants shed leaves to form loose layer on the ground—LITTER
Soil Conservation: management of soil to prevent it’s destruction
Words to know:
Prairie Soil: Once rich with humus because it was covered with tall grass
Sod: Thick mass of roots at the surface---keeps soil in place and allows it to retain it’s
moisture
Natural Resources: Anything in the environment humans can use
1. Contour Plowing: Plowing fields along the curves to help slow the runoff
2. Conservation Plowing: Plowing without disturbing the soil and it’s plant
cover---Mixes dead plants into the soil as you go
3. Crop Rotation: Plant different crops in fields each year to help with minerals
a. Sometimes farmers plant LEGUMES (a type of bean that helps restore
the nutrient supply)