1. Chapter 5- Weathering and Soil
Earth Science
6th Grade

2. Bell work Ch5 L.1
Weathering: the mechanical and chemical processes that change objects on Earth’s surface over time
Mechanical weathering: When physical processes naturally breaks rocks into smaller pieces
Chemical weathering: Changes the materials that are part of a rock into new materials
Oxidation: Combines the element oxygen with other elements or molecules

3. Lesson 1- Weathering How does weathering break down or change rock?
How do mechanical processes break rocks into smaller pieces?
How do chemical processes change rocks?

4. Launch lab (work in pairs)
Each pair gets 12 “rocks” (chocolate candies), 3 plastic cups and a jar with a lid. NO, YOU MAY NOT EAT THE CANDY.
Place four rocks in cup and the other eight in the jar. Fasten lid tightly
Shake jar vigorously 300x
Remove half of the pieces and put them in second plastic cup
Replace lid and shake another 300x
Put remaining pieces in third plastic cup
ANSWER: compare and contrast rocks from each cup. What do you think caused the rocks to change?
TURN IT IN

5. Weathering and its effects
Weathering: the mechanical and chemical processes that change objects on Earth’s surface over time
Also changes Earth’s surface
Break, wear, abrade and chemically alter rocks and rock surfaces
Weathering breaks rocks into smaller and smaller pieces= sediment
Sand, silt and clay (largest=sand, smallest=clay)
Can change chemical makeup of a rock, sometimes makes it easier to break

6. Mechanical Weathering
When physical processes naturally breaks rocks into smaller pieces
Chemical makeup is NOT changed, just change the size

7. Mechanical Weathering
Examples of mechanical weathering
Intense heat (like from forest fire) causes nearby rocks to expand and crack
Ice wedging= water enters cracks in rocks and when the water freezes (at 0C), it expands and that widens the crack.
Abrasion= grinding away of rock by friction of impact. A strong current in a stream can carry rock fragments downstream. Fragments hit each other and grind each other down into smaller and smaller pieces.

8. Mechanical Weathering
Examples of mechanical weathering
Plants= Can grow into the cracks of rocks, roots absorb minerals making the rock weaker. The stems and roots get wider and pushes on the cracks making the rock break.
Animals= animals that live in the soil create holes where water an go and weather rocks. They can also help break down rocks as they dig.

9. Mechanical Weathering
Surface area: increases when something is broken in smaller pieces
Amount of space on the outside of an object
Rate of weathering depends on surface area exposed to environment (for chemical weathering too)
Clay is 100x smaller than sand, so it has an increased surface area
Means that weathering has greater effect. Soil with small particles is affected more than soil with larger particles.

10. Chemical weathering
Changes the materials that are part of a rock into new materials
Changes the composition and the size

11. Chemical weathering Water and chemical weathering
Most substances dissolve in water
Minerals in rocks dissolve slowly in water
Dissolving happens when minerals in a rock break into smaller parts in a solution
Example: salt (sodium chloride) breaks down into individual sodium and chloride ions when dissolved in water

12. Chemical weathering
Dissolving by acid= increases rate of chemical weathering more than rain or water.
Attracts atoms away from rock minerals and dissolves them in acid
Enter air naturally (volcanoes) or form pollutants (burning coal)

13. Chemical weathering
Use pH to tell if a solution is acidic (0-7), basic (7-14) or neutral (7).
Vinegar= 2-3 so it’s an acid
Rain water= 5.6 so it’s slightly acidic. Reacts with carbon dioxide to form weak acid, can dissolve rocks.
Acid rain= 4.5 so it’s more acidic than normal rain. Happens when burning coal produces sulfur oxide which reacts with rain water.

14. Oxidation Combines the element oxygen with other elements or molecules
Usually oxygen comes from the air
Addition of oxygen produces an oxide
Iron oxide is a common oxide= hematite
Aluminum’s oxide= bauxite

15. Oxidation rate
Not all parts of the iron-containing rock oxidize at the same rate
Part exposed to oxygen oxidizes faster than part not exposed to oxygen
Example: Iron oxide- oxidized part turns red (minerals are different than minerals in the center of the rock that are not oxidized)
Right side not oxidized, left side oxidized

16. What affects weathering rate?
Similar rocks can weather at different rates. Why?
Environment helps determine weathering rate
Both types of weathering depend on temperature and water

17. What affects weathering rate?
Mechanical weathering
Occurs fastest in environments with lots of temperature changes
Cycles of freezing and thawing or wetting and drying
Chemical weathering
Occurs fastest in warm, wet places.
Fastest in regions near equator

18. What affects weathering rate?
Rock type
Made of many minerals. Most easily weathered mineral in a rock determines the rate (only as strong as the weakest link)
Low hardness= easier to undergo mechanical weathering
More mechanical weathering= more surface area exposed
More surface area exposed= more chemical weathering
Holes in a rock= easier to weather

19. HOMEWORK Ch5 L.1 Vocabulary words on flash cards
Memorize for quiz
Lesson review questions p.155 #1-10
Outline lesson 1
Quiz!

20. Bell Work Ch5 L.2
Soil: a mixture of weathered rocks, rock fragments, decayed organic matter, water and air
Organic matter: the remains of something that was once alive
Pore: Small holes and spaces in the soil
Decomposition: the process of changing, once-living material into dark-colored organic matter
Parent material: Starting material of soil
Climate: Average weather of an area
Topography: Shape and steepness of the landscape
Biota: All of the organisms that live in the region
Horizon: Layers of soil formed from the movement of the products of weathering

21. Lesson 2- Soil How is soil created? What are soil horizons?
Which soil properties can be observed and measured?
How are soils and soil conditions related to life?

22. Launch lab p.158 work in pairs
Place a cup of soil in a jar with a lid
Add a few drops of liquid soap
Add water until almost full
Firmly attach lid
Shake for one minute
Observe contents of jar after 2 minutes, after 5 minutes.
ANSWER: How many different layers did your sample form? What do you think makes up each layer?
TURN IT IN

23. What is soil?
Soil is a mixture of weathered rocks, rock fragments, decayed organic matter, water and air.
Half the volume is solid materials
Life on Earth depends on soil

24. What is soil?
Fragments seen in Ch5. L1 don’t become good soil until animal and plants live in them.
Plants and animals add organic matter to the rock fragments
Organic matter= the remains of something that was once alive

25. Pores Small holes and spaces in the soil
Enable water to flow into/out of the soil
Size depends on particles that make up the soil
As particle size increases= pore size increases
Can have water and air in them, the amount varies.

26. The organic part of soil
Organic part of soil= solid part that was once part of an organism.
Pieces of leaves, dead insects, waste products
Roots die, leaves and twigs fall to the ground and organisms in the soil decompose these materials for food

27. Organic part of soil
Decomposition: the process of changing, once-living material into dark-colored organic matter.
Organic matter gives soil important properties
Dark color of soil absorbs light
Organic matter holds water and provides plant nutrients
Organic material holds minerals together in clusters= keeps pores open for movement of water and air

28. Inorganic part of soil
Inorganic= materials that have never been alive.
Mechanical/chemical weathering of rocks into fragments forms inorganic matter in soil
Classify soil according to size of fragments

29. Inorganic part of soil
Rock fragment sizes= boulders, cobbles, gravel, sand, silt or clay.
Sand- feels rough
Silt- feels smooth
Clay- feels sticky
Large particles have large pores, they drain rapidly. Small pores retain more water in the soil.

30. MiniLab p.159 Observe soil sample, record sizes of particles.
Add a little bit of water to moisten the soil
Rub the moist soil between your fingers
Record observation
Determine if sample is mostly sand, mostly silt or mostly clay based on observations.
ANSWER: what texture does your soil have (when wet/dry)? What other properties did you observe?

31. Formation of soil
Many kinds of soil that form depend on five factors= factors of soil formation
Parent material
Climate
Topography
Biota
Time

32. Parent material Starting material of soil
Rock/sediment that weathers and forms soil
Bedrock= rock that weathers to form soil in the same location where rock was formed.
Soil can be made from rocks that were carried by wind/water to another location
Particle size and type of parent material can determine properties of soil

33. Climate Average weather of an area
Precipitation and daily and average temperatures are measures of climate
Warm, wet climates can form soil quickly
Also places where lots of freezing/thawing occurs make soil quickly

34. Topography Shape and steepness of the landscape.
Determines what happens to the water that reaches the soil surface
Flat landscape= most water is absorbed into soil
Steep landscape= most water runs downhill (can carry soil with it)

35. Biota All of the organisms that live in the region
Help speed up the process of soil formation
Some form passages for water to move through
Most soil organisms involved in decomposition of material that form organic matter

36. Time Weathering is constantly acting on rock and sediment
Soil formation is constant, slow process.
Soil is still young after 1,000 years
Mature soil develops layers
New soil forms on top of old soil
Each layer has its own characteristics

37. Horizons
Layers of soil formed from the movement of the products of weathering
Each layer has characteristics based on the kind of material it contains
Three horizons common to most soils
A-horizon, B-horizon, C-horizon
O-horizon= top organic layer
R-horizon= unweathered bedrock layer

38. Three common horizons A-horizon B-horizon C-horizon
What you see when you dig a shallow hole
Darkest usually because contains most organic matter
B-horizon
Mostly clay deposited from upper layer by water seeping through A layer.
C-horizon
Layer of weathered parent material (rock or sediments)

39. Soil properties and uses
Observing and measuring soil properties
Feeling the soil allows you to estimate how much sand, silt and clay is present
Color is easily observed and shows how much organic matter the soil contains
In the lab:
Determine pH, nutrient content to see if the soil is suitable for farming

40. Soil properties and uses
Soil properties that support life
Nutrients in soil come from decaying and weathering
How well plants grow can tell you about the nutrient content
If add fertilizer, then it doesn’t really matter
Soil formation takes thousands of years so replenishing nutrients takes a long time

41. Soil types and locations
The amount of horizons and amount of weathering depends on location where soil is forming
Not all soil is alike

42. HOMEWORK Ch5 L.2 Vocabulary words on flash cards
Memorize for quiz
Lesson review questions p.165 #1-10
Outline lesson 2
Study for quiz
OPTIONAL Extra Credit p all. You MUST copy down the entire question and the answer. Only answers will not be accepted.

43. Soil lab p
Compare types of rock, climate and topography of Minnesota, Colorado and Florida. Record similarities/differences.
Examine soil profile from each location. Record similarities/differences.
Draw sample profiles and label A,B,C horizons
How does each horizon relate to the factors of soil formation?
Choose one location and model the profile using materials provided. Label location and horizons.
How are soil profiles affected by soil-forming factors?
Were any profiles missing from any locations? Why might one be missing?
Was one of the horizons thicker in any of the profiles? Why?
How does a soil profile relate to soil-forming factors?
TURN THIS IN