1. Bellringer
What processes form igneous rocks? Sedimentary? Metamorphic?

2. Weathering

3. Review:
Weathering – when rocks on or near Earth’s surface break down and change
Erosion – the removal and transport of weathered material from one location to another
Deposition – when the erosion movement slows and drops the weathered material E W D

4. Weathering
Weathering, erosion, and deposition have been happening for millions of years, constantly changing Earth’s surface

5. Weathering
Two types of weathering:
Mechanical (Physical)
Chemical

6. Mechanical Weathering
Mechanical weathering – breaking down rocks and minerals into smaller pieces
Also known as physical weathering because it changes the physical appearance of rocks
Changes the rock’s size and shape, but not its chemical composition
The most common type of weathering in cool and dry climates

7. Mechanical Weathering
Since weathering constantly wears away at rocks, the more a rock has been weathered, the smoother and rounder it will be

8. Mechanical Weathering Agents
1. Freezing temperatures
Frost wedging – when water in rock cracks freezes and expands, making the rocks crack open or break

9. Mechanical Weathering Agents
2. Pressure
Rocks buried underneath other rocks are under a lot of pressure
When that extra weight and pressure are suddenly removed (construction, mining, etc), the relief in pressure can cause cracks that are parallel to the rock surface

10. Mechanical Weathering Agents
Example: exfoliation – outer rock layers are stripped away

11. Mechanical Weathering Agents
3. Tree and Plant Roots – wedge into cracks of rocks and cause them to split

12. Chemical Weathering
Chemical weathering – breaks down rocks into new substances through chemical reactions
Changes the rock’s chemical composition
Most common type of weathering in warm and wet climates

13. Chemical Weathering Agents
Water – can dissolve many minerals in rocks and acts as a medium for chemical reactions to occur
Hydrolysis – the chemical reaction of water with other substances

14. Chemical Weathering Agents
2. Oxygen – combines with minerals and causes chemical reactions
Oxidation – chemical reaction of oxygen with other substances
Example: the oxidation of iron produces rust (Fe3O4 + O2  Fe2O3)

15. Chemical Weathering Agents
3. Carbon Dioxide – mixes with water or water vapor to form carbonic acid

16. Chemical Weathering Agents
Carbonic acid dissolves calcite, a mineral found in limestone, which can create caves where the rock has been eaten away

17. Chemical Weathering Agents
4. Acid rain – rain with a pH < 5.6
Formed when sulfur dioxide (from burning fossil fuels) or nitrogen oxides (car exhaust) are released into the atmosphere and react with water vapor to create sulfuric and nitric acids, respectively

18. Chemical Weathering Agents
Eats away at rocks/minerals
Can kill plants and animals (especially aquatic animals)

19. What Affects Weathering?
1. Climate
Mechanical weathering occurs more quickly in colder places (more ice = more frost wedging)
Chemical weathering occurs more quickly in warm, wet climates because chemical reactions occur more quickly in higher temperatures

20. Mechanical or Chemical?
Montana
Florida
Cool and dry = mechanical
warm and wet = chemical

21. What Affects Weathering?
2. Rock Type and Composition
Sedimentary rocks are more likely to weather than igneous or metamorphic rocks
Why might that be?
Igneous and metamorphic rocks are forged together by high heat and/or pressure
Sedimentary rocks are loosely layered and cemented together

22. What Affects Weathering?
3. Surface Area – how much of the rock is exposed to wind and water
As a rock breaks down into smaller and smaller pieces, the MORE surface area it has
The more area exposed, the more weathering can take place
As rocks are broken down into smaller and smaller pieces, their surface area (SA) and rate of weathering increase.
(low SA) (high SA)

23. What dissolves faster?
Sugar Cubes
Granulated Sugar or

24. Surface area increases as rocks are weathered into smaller pieces

25. What Can Affect Weathering?
4. Topography – materials on sloped surfaces are more likely to weather and erode due to gravity
As rocks roll downslope, they expose more underlying rock, which are then subject to weathering

26. Quiz
I’ll give you 5-10 minutes to look over your notes (Chemistry – Rock Cycle)
Make sure you place your quiz in the correct box

27. Weathering Analysis – look at the images and answer the corresponding questions.
DO NOT WRITE ON THE COLORED PAGES!