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Weathering and Soil Formation
Chapter 7 Key Terms
33
Science
7th Grade
12/04/2006

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Term
weathering
Definition
the process that breaks down rock and other substances at Earth's surface
Term
erosion
Definition
the movement of rock particles by wind, water, ice, or gravity
Term
Mechanical weathering
(physical weathering)
Definition
the type of weathering in which rock is physicaly brokeninto smaller pieces
Term
abrasion
Definition
the grinding away of rock by rock particles carried by water, ice, wind, or gravity (sometimes considered to be a type of erosion)
Term
ice wedging
Definition
when water seeps into cracks in rock and expands when it freezes,breaking rock apart
Term
chemical weathering
Definition
the process that breaks down rock through chemical changes
Term
permeable
Definition
full of tiny, connected air spaces thatallow water to seep through
Term
soil
Definition
the loose, weathered material on Earth's surface in which plants can grow
Term
bedrock
Definition
the solid layer of rock beneath the soil
Term
humus
Definition
a dark-colored substance that forms as plant and animal remains decay
Term
loam
Definition
soil that is made of about equal parts clay, sand, and silt
Term
soil horizons
Definition
a layer of soil that differs in color and texture from the layers above and below it
Term
topsoil
Definition
A crumbly, dark brown soil that is a mixture of humus, clay, and other minerals. Usually the A horizon.
Term
subsoil
Definition
consists of clay and other particles washed down from the topsoil, but little humus, usually the B horison
Term
litter
Definition
organic remains of dead plants
Term
decomposers
Definition
the organisms that break the remains of dead organisms into smaller pieces and digest them with chemicals
Term
sod
Definition
thick mass of tough roots at the surface of the soil
Term
renewable resource
Definition
a resource that is naturally replaced in a relatively short time
Term
Dust Bowl
Definition
an area where wind erosion caused severe loss of topsoil during the 1930s
Term
soil conservation
Definition
the management of soil to prevent its destruction
Term
contour plowing
Definition
the practice of plowing fields along the curves of a slope
Term
conservation plowing
Definition
the practice of disturbing the soil and its plant cover as little as possible,
also called low- or no-till plowing
Term
What factors cause mechanical weathering?
Definition
The type of mechanical weathering will depend on the climate, for example, colder climates will see more ice wedging than others. forested areas will see lots of cracks in rock because of plant growth.
Term
Describe the three causes of chemical weathering.
Definition
Oxygen weathers most metals through the process of oxidation. Water dissolves rock over long periods of time. Acids can also dissolve rocks.
Term
What factors affect the rate of weathering?
Definition
The most important factors that determine the rate at whichweathering occurs are the type of rock and the climate.
Term
Explain why chemical weathering occurs faster in hot , wet climates than in cool, dry climates.
Definition
Wetter climates better provide the water needed for chemical changes. Chemical reactions also occur faster in warmer temperatures.
Term
What role does weathering play in the formation of soils?
Definition
Weathering breaks up rock and allows room for plants, which help beak it down even further.
Term
What are the different materials that make up soil?
Definition
Gravel, sand, silt, and clay make up soil.
Term
How do plants and animals affect the formation and composition of soil?
Definition
Decomposers fertilize the soil by breaking down dead plant remains. Burrowing mammals break up the soil and mix humus with it.
Term
How do forest soils differ from prarie soils?
Definition
Forest soils form in wetter climates, and prarie soils form in drier areas. Prarie soils have lots of humus, forest soils do not.
Term
Explain the importance of soil as one of Earth's resources.
Definition
Everything on Earth depends on soil, whether directly or indirectly.
Term
How did settlers on the Great Plains help create the Dust Bowl?
Definition
People plowed the land. Plowing removed grass from the Great Plains and exposed the soil. In times of drought, the topsoil quickly dried out, turned to dust, and blew away.
Term
What are some techniques that farmers use to conserve soil?
Definition
Farmers conserve soil by using contour plowing and conservation plowing.
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