Grade 7 Science Unit 4: The Earth

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Grade 7 ScienceUnit 4 The Earths Crust

• Weathering and Erosion

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Weathering...

• The mechanical and/or chemical breakdown of rock.
• All rocks are exposed to the forces of weathering
  when at or near the surface of the earth.

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2 Types of Weathering

• 1. Mechanical Weathering
• Rocks are simply broken into smaller fragments.
• Most common type is ice wedging (frost action).

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• Movement of plant roots as they grow (root pry).

Roots growing through rock
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• Movement of animals (worms, rodents, ants, etc.)

A burrowing rabbit
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• 2. Chemical Weathering
• Chemical reactions occur with rocks that create
  new substances.
• Acid rain will chemically change rocks like salt,
  gypsum and limestone.

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Statues weathered by acid rain
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• Lichens produce acids which can weather rocks.

Lichens pitting a rock
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Erosion

• The process that loosens and moves weathered rock
  particles (sediment) over the earths surface.
• Eroded materials form the basis of soil.

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Agents of Erosion

• 1. Water in motion Most powerful

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• 2. Meteorological processes (rain and wind)

Created by wind
Erosion by a rain drop
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• 3. Geological processes
• (gravity and glaciers)

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