Chapter 2 Weathering and Soil Mechanical Weathering Mechanical weathering affects all rock on Earth’s surface. Release of Pressure As rock erodes, release of pressure causes the outside of the rock to crack and flake off. Freezing and Thawing When water freezes in a crack in a rock, it expands and makes the crack bigger. Animal Actions Burrowing animals like this mole can loosen and break apart rocks and soil. Plant Growth Roots of plants enter cracks in rocks, forcing the cracks farther apart. Abrasion Rock particles carried by wind, water, or ice and wear away exposed rock surfaces like sandpaper on wood.
Chapter 2 Weathering and Soil Mechanical Weathering Mechanical weathering affects all rock on Earth’s surface. Release of Pressure As rock erodes, release.
Dec 15, 2015
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Chapter 2 Weathering and Soil
Mechanical WeatheringMechanical weathering affects all rock on Earth’s surface.
Release of Pressure As rock erodes, release of pressure causes the outside of the rock to crack and flake off.
Freezing and Thawing When water freezes in a crack in a rock, it expands and makes the crack bigger.
Animal Actions Burrowing animals like this mole can loosen and break apart rocks and soil.
Plant Growth Roots of plants enter cracks in rocks, forcing the cracks farther apart.
Abrasion Rock particles carried by wind, water, or ice and wear away exposed rock surfaces like sandpaper on wood.
Chapter 2 Weathering and Soil
Chemical Weathering
WATER (H2O) Water dissolves rock. I can also mix with other
chemicals to dissolve rock quicker.
OXYGEN (O2) Combines with iron to cause rust
CARBON DIOXIDE (CO2) Combines with water to cause
Type of acid rain
LIVING ORGANISMS Grow in cracks in rock and cause additional cracking. Some roots produce weak acids
ACID RAIN Air pollution mixes with water to form sulfur, nitrogen and carbon compounds that cause rapid chemical weathering
Chapter 2 Weathering and Soil
Chemical Weathering
As weathering breaks apart rock, the surface area exposed to weathering increases.
Chapter 2 Weathering and Soil
Chemical or Mechanical?
Reddish soil
Chemical
Rock in a desert breaking because of repeated heating and cooling
Mechanical
Ants making large hills Mechanical
Chapter 2 Weathering and Soil
Rate of Weathering
The most important factors that determine the rate at which weathering occurs are the type of rock and the climate.
Some rocks weather more easily because they are permeable, which means filled with tiny connected air spaces.
Define “permeable” in your notebook, include examples
Chapter 2 Weathering and Soil
Which Weathered Faster?
The graph shows the rate of weathering for two identical pieces of limestone that weathered in different locations.
Chapter 2 Weathering and Soil
Which Weathered Faster?
Time in years
Reading Graphs:
What does the x-axis of the graph represent?
Chapter 2 Weathering and Soil
Which Weathered Faster?
The thickness of stone lost to weathering
Reading Graphs:
What does the y-axis of the graph represent?
Chapter 2 Weathering and Soil
Which Weathered Faster?
Stone A lost about 8.5 millimeters; Stone B lost slightly more than 4 millimeters.
Reading Graphs:
How much thickness did Stone A lose in 1,000 years? How much thickness did Stone B lose in the same period?
Chapter 2 Weathering and Soil
Which Weathered Faster?
Stone A weathered at a faster rate.
Drawing Conclusions:
Which stone weathered at a faster rate?
Chapter 2 Weathering and Soil
Which Weathered Faster?
They were exposed to different climate conditions.
Inferring:
Since the two identical pieces of limestone weathered at different rates, what can you infer caused the difference in their rates of weathering?
Chapter 2 Weathering and Soil
Soil
Loam, a type of soil, is made up of air, water, and organic matter as well as materials from weathered rock.
How is the high percentage of air and water related to the amount of organic matter in the loam?
Organic matter helps create space for air and water.
Chapter 2 Weathering and Soil
Soil
Soil particles range in size from gravel to clay particles too small to be seen by the unaided eye. The sand, silt, and clay shown here have been enlarged.
Chapter 2 Weathering and Soil
The Process of Soil Formation
Soil forms as rock is broken down by weathering and mixes with other materials on the surface. Soil is constantly being formed wherever bedrock is exposed.
Chapter 2 Weathering and Soil
The Process of Soil Formation
Which soil horizon is most similar to bedrock?
Which soil horizon forms last?
Which is most important for growing food?
C
B
A
Chapter 2 Weathering and Soil
Living Organisms in Soil
Some soil organisms make humus, the material that makes soil fertile. Other soil organisms mix the soil and make spaces in it for air and water.
Chapter 2 Weathering and Soil
Soil Damage and Loss-
Wind erosion is one cause of soil loss. For example, wind erosion contributed to the Dust Bowl on the Great Plains. The Dust Bowl ruined farmland in western Oklahoma and parts of the surrounding states. Wind blew dry particles of soil into great clouds of dust that traveled thousands of kilometers.
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