1. Grade 7 Science Unit 4: The Earth’s Crust
Weathering and Erosion

2. 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.

3. 2 Types of Weathering:
1. Mechanical Weathering:
Rocks are simply broken into smaller fragments.
Most common type is ice wedging (frost action).

5. Roots growing through rock
Movement of plant roots as they grow (root pry).
Roots growing through rock

6. Movement of animals (worms, rodents, ants, etc.)
A burrowing rabbit

7. 2. Chemical Weathering:
Chemical reactions occur with rocks that create new substances.
Acid rain will chemically change rocks like salt, gypsum and limestone.

8. Statues weathered by acid rain

9. Lichens produce acids which can weather rocks.
Lichens pitting a rock

10. Erosion
The process that loosens and moves weathered rock particles (sediment) over the earth’s surface.
Eroded materials form the basis of soil.

11. Agents of Erosion:
1. Water in motion: Most powerful

12. 2. Meteorological processes (rain and wind)
Created by wind
Erosion by a rain drop

13. 3. Geological processes (gravity and glaciers)

14. The Dungeons: Bonavista NL