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Weathering and Soil Formation
Chapter 7
30
Science
7th Grade
12/04/2006

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Term
weathering
Definition
process that breaks down rock and other substances at Earth's surface
Term
erosion
Definition
movement of rock particles by wind, water, ice, or gravity
Term
mechanical weathering
Definition
type of weathering in which rock is physically broken into smaller pieces
Term
abrasion
Definition
the grinding away of rock by rock particles carried by water, ice, wind, or gravity
Term
ice wedging
Definition
wedges of ice in rocks widen and deepen cracks when water seeps through and expands
Term
chemical weathering
Definition
process that breaks down rock through chemical changes
Term
permeable
Definition
a material that is full of tiny, connected air spaces that allow water to seep through it
Term
soil
Definition
loose, weathered material on Earth's surface in which plants can grow
Term
bedrock
Definition
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 up of about equal parts of clay, sand, and silt
Term
soil horizon
Definition
layer of soil that differs in color and texture from the layers above or below it
Term
topsoil
Definition
crumbly, dark brown soil that is a mixture of humus, clay, and other minerals; horizon A
Term
subsoil
Definition
usually constists of clay and other particles washed down from the A horizon, but little humus; B horizon
Term
litter
Definition
the loose layer created when plants shed leaves
Term
decomposers
Definition
organisms that break the remains of dead organisms into smaller pieces and digest them with chemicals
Term
sod
Definition
the 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
management of soil to prevent its destruction
Term
contour plowing
Definition
the practice of plowing fields along the curves of a slope; this helps slow the runoff of excess rainfall and prevents it from washing the soil away
Term
conservation plowing
Definition
plowing that disturbs the soil and its plant cover as little as possible
Term
What factors cause mechanical weathering?
Definition
Freezing and thawing, release of pressure, growth of plants, and actions of animals are all factors of mechanical weathering.
Term
Describe the causes of chemical weathering.
Definition
The causes of chemical weathering are water, oxygen, carbon dioxide, acid rain, and even the actions of living organisms.
Term
What factors affect the rate of weathering?
Definition
The type of rock and the climate both affect the rate of weathering.
Term
Explain why chemical weathering occurs faster in hot, wet climates than in cool, dry climates.
Definition
Chemical reations occur faster at highter temperatures. The same is for chemical weathering.
Term
What role does weathering play in the formation of soil?
Definition
Soil forms as rock is broken down by weathering and mixes with other materials on the surface.
Term
What are the different materials that make up soil?
Definition
Rock particles, minerals, decayed organic material, air, and water are all parts of soil.
Term
How do plants and animals affect the formation and composition of soil?
Definition
When plants and animals die and decay, they form a dark-colored substance called humus which helps soil by creating pockets for air and water. Soil organisms also mix soil and make spaces for air and water.
Term
How do forest soils differ from prairie soils?
Definition
Prairie soils form in cool, dry climates while forest soils form in warm to cool, wet climates. Most prairie soils are very rich but some forest soils lack humus.
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