1. Weathering and erosion
How did the Grand Canyon form?

2. Bellringer
In your Science notebook write what you think would happen if you:
- put water on a penny
- put milk on a penny
- put soda on a penny
Write why you think the different liquids will cause a different change.

3. Objectives
Describe how ice, water, wind, gravity, plants, and animals cause mechanical weathering.
Describe how water, acids, and air cause chemical weathering of rocks.

4. Definitions
Weathering – process where rock materials are broken down into smaller pieces by physical or chemical processes.
Mechanical Weathering
Breakdown of rock by physical means
Similar to physical change
Chemical Weathering
Breakdown of rock by chemical means
Similar to chemical change

5. Mechanical Weathering
Ice
The alternate freezing and thawing of soil and rock, called frost action, is a form of mechanical weathering.
Abrasion
Abrasion is the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles.
Wind, Water and Gravity
Wind, water, and gravity carry rocks, causing them to abrade against one another
Rocks shaped by wind blowing sand are called ventifacts.

6. Mechanical Weathering (cont.)
Plants
As a plant grows, the force of the expanding root becomes so strong that it can break a rock apart.
Animals
Almost any animal that burrows causes mechanical weathering by mixing and digging through soil and rock particles.

7. Chemical Weathering Water Acid Precipitation Acids in Groundwater
Even hard rock, such as granite, can be broken down by water. The next slide shows how this can happen.
Acid Precipitation
The high level of acidity in acid precipitation can cause very rapid weathering of rock.
Acids in Groundwater
When acidic groundwater comes into contact with limestone, the limestone is dissolved and forms karst features.

8. Chemical Weathering (Cont.)
Acids in Living Things
Some living things, such as lichens, produce acids that can slowly break down rocks.
Air
Oxygen in the air causes oxidation. Oxidation is the chemical reaction in which an element, such as iron, combines with oxygen to form an oxide.

9. How is sand formed?

10. Examples Mechanical weathering Chemical weathering
Can you think of an example of mechanical or chemical weathering?
Mechanical weathering
rocks
sand
smooth stones
Chemical weathering
rust (Oxidation)
caves
sinkholes

11. Differential Weathering
Differential weathering is a process by which softer, less weather resistant rock wear away and leave harder, more weather resistant rock.

12. Weather and Climate
What do you think would change how fast something weathers?
Does temperature changes (climate) make a difference?
Chemical weathering occurs in warm humid places faster.
How high in the air is it?
Places at higher elevations will have harsher conditions of precipitation.
How steep is the mountain?
Gravity will pull things down the mountain faster.

13. Get into Pairs Answer the following questions in your notebook:
How can plants break down rock?
If I told you there were tiny microscopic organisms that lived on rocks (called lichens) how do you think they cause the rock to break down?
What are the three factors that determine the rate at which rock weathers?