1. Chapter 2: Weathering and Soil Lesson 1: Rocks and Weathering
Earth’s Surface
Chapter 2: Weathering and Soil
Lesson 1: Rocks and Weathering

2. Breaking Down Rocks
Uniformitarianism: the geologic processes that operate today also operated in the past.
Erosion: the process of wearing down and carrying away rocks.
Weathering: the process that breaks down rock and other substances.

3. Weathering and Erosion
Erosion includes breaking rocks into smaller pieces and the removal of rocks by wind, water, and gravity.
Weathering is caused by heat, cold, water, ice, gas, etc.

4. Mechanical Weathering
Mechanical weathering: rock is physically broken into smaller pieces.
Usually works slowly, but can eventually lead to mountains wearing down.

5. Mechanical Weathering
Agents of mechanical weathering:
Animal actions: burrowing into the soil loosens and breaks apart rocks.
Plant growth: plant roots break into cracks in the rocks and force them to break.

6. Mechanical Weathering
Agents of mechanical weathering:
Release of pressure: as materials are removed from rocks, the pressure on them is reduced until it eventually releases; causes cracking and peeling.

7. Mechanical Weathering
Agents of mechanical weathering:
Abrasion: wearing away of rocks by smaller particles of sand, rock, etc.

8. Mechanical Weathering
Agents of mechanical weathering:
Freezing and thawing: when water freezes in the cracks of rocks, it expands. When it melts, it sinks into the rock. This is also called frost wedging.

9. Chemical Weathering
Chemical weathering: rock is broken down through chemical changes.
New minerals can be formed by the breakdown of rocks.
Example: feldspar changes into clay and into a substance in granite

10. Chemical Weathering Agents of chemical weathering:
Water: water, and the substances in water, can dissolve rocks.
Oxygen: when oxygen and iron combine through water, oxidation (rusting) occurs.

11. Chemical Weathering Agents of chemical weathering:
Carbon dioxide: carbonic acid easily breaks down marble and limestone.
Living Organisms: lichens and plant roots form weak acids to break down rocks.

12. Chemical Weathering Agents of chemical weathering:
Acid rain: pollution causes rain to be even more acidic than it is naturally; this causes very rapid breakdown of rock.
Lady Liberty

13. Weathering Rates Depends mostly on the type of rock and the climate.
Rocks made from minerals that do not dissolve easily will take longer to weather.
Rocks that are more permeable usually weather more quickly.
Permeable: they are full of tiny air-filled holes that allow water to enter the rock.

14. Weathering Rates Climate: the average weather conditions in an area.
Chemical and mechanical weathering both occur more quickly in wet climate.
Chemical reactions occur more quickly at higher temperatures.

15. Chapter 2: Weathering and Soil Lesson 2: How Soil Forms
Earth’s Surface
Chapter 2: Weathering and Soil
Lesson 2: How Soil Forms

16. What is Soil?
Soil: the loose, weathered material on Earth’s surface in which plants can grow.
It is a mixture of rock, minerals, organic material, water, and air.
Bedrock: solid layer of rock beneath the soil; weathers into small particles.

17. What is Soil? Particles of rock are put into categories based on size:
Gravel
Sand
Silt
Clay

18. What is Soil?
Humus: dark-colored substance that forms as plants and animals decay; organic matter.
It contains nutrients that help plants survive; creates space to make soil more permeable.

19. Soil Fertility and Texture
Fertility: how well the soil supports plant growth.
Soil with more humus is usually more fertile.
Texture depends on the size of the particles; the larger the particles, the more coarse the soil.
Loam is the best soil for plants; consists of sand, silt, and clay.

20. Soil pH pH is a measure of how acidic something is.
The pH scale measures acidity on a scale of Plants grow best between 6 and 7.5.
0-4: strongly acidic
4-6: weakly acidic
7: neutral
8-10: weakly basic
11-14: strongly basic

21. Soil Formation Soil forms in layers called horizons.
C horizon: forms as bedrock breaks apart; rocks are broken into small pieces.
B horizon: subsoil – consists of clay and other particles; very little humus.
A horizon: crumbly, dark soil made of humus, clay, and other materials.

22. Living Things Affect Soil
Forming humus: humus is made from the breakdown of living organisms.
Decomposers are organisms that break down decaying organic matter.
Fungi, bacteria, worms, etc.

23. Living Things Affect Soil
Mixing the soil: worms and burrowing animals bring soil from the top down to the bottom layers, and soil from the bottom up to the top layers.
These animals also add waste to the soil, which contribute nutrients to it.

24. Chapter 2: Weathering and Soil Lesson 3: Soil Conservation
Earth’s Surface
Chapter 2: Weathering and Soil
Lesson 3: Soil Conservation

25. Soil Conservation
Natural resource: anything in the environment that humans use.
Soil is a crucial resource to all living beings on Earth.
Soil can take centuries to form, and only about 1/8 of Earth’s soil is suitable for farming.

26. Damaging Soil
When soil loses moisture and/or nutrients, its fertility decreases.
This happened in the 1800s when cotton was exclusively grown on some soils.
Water and wind can easily erode the surface of soil.
Plants help block water from hitting the soil directly.
Wind contributed to the Dust Bowl on the Great Plains.

27. Conserving Soil
Soil conservation: management of soil to limit its destruction.
crop rotation: different crops are planted in a field each year.
some plants (cotton) use up more nutrients than others; other plants (legumes) help to add extra nutrients into the soil.

28. Conserving Soil
Contour plowing: plow fields in curves instead of straight lines; slows water erosion.
Conservation plowing: dead weeds and stalks are plowed into the ground to add nutrients.