Chapter 6
‘Weathering and Soil’
Study Guide
What is uniformitarianism?
Answer: Uniformitarianism is the principle that states that the geologic processes that operate today also operated in the past. Example: Ancient landforms formed through the same processed observed by scientists today.
What two things break down rocks?
Answer: erosion and weathering
What is erosion?
Answer: Erosion is the process of wearing down and carrying away rocks.
What is weathering?
Answer: Weathering is the process that breaks down rock and other substances from heat, cold, water, ice, and gases.
What are the two types of weathering?
Answer: mechanical weathering and chemical weathering
What is mechanical weathering?
Answer: The type of weathering in which rock is physically broken into smaller pieces is called mechanical weathering.
What are the natural agents of mechanical weathering?
Answer:
1) freezing and thawing
2) release of pressure
3) plant growth
4) actions of animals
5) abrasion
What is abrasion?
Answer: Abrasion is the wearing away of rock by rock particles carried by water, ice, wind, or gravity.
What is chemical weathering?
Answer: Chemical weathering also breaks down rocks, but it does it through chemical changes.
What are the agents of chemical weathering?
Answer:
1) water
2) oxygen
3) carbon dioxide
4) living organisms
5) acid rain
What two important factors determine the rate at which weathering occurs?
Answer:
1) the type of rock
2) the climate
What does permeable mean?
Answer: Permeable means that a material is full of tiny, connected air spaces that allow water to seep through it.
True or False?
Chemical reactions occur faster at higher temperatures. TRUE!!!
Chemical weathering occurs more quickly where the climate is both hot and wet!
What is soil?
Answer: Soil is a mixture of rock particles, minerals, decayed organic material, water, and air.
What is bedrock?
Answer: Bedrock is the solid layer of rock beneath the soil.
What is humus?
Answer: Humus is a dark-colored substance that forms as plant and animal remains decay.
What is fertility of soil?
Answer: Fertility of soil is a measure of how well the soil supports plant growth.
True or False?
Soil that is rich in humus generally has high fertility. TRUE!!!
Sandy soil containing little humus has low fertility. TRUE!!!
What is the best soil for growing most plants?
Answer: loam
What is pH scale?
Answer: A pH scale is a range of values used to indicate how acidic or basic a substance is; expresses the concentration of hydrogen ions in a solution.
A substance with a:
pH less than 4 is STRONGLY ACIDIC!
pH of 7 is NEITHER acidic nor basic (Pure water is an example of this!)
pH greater than 10 is strongly basic
True or False?
Most garden plants grow best in soil with a pH between 6 and 7.5. TRUE!!!
How does soil form?
Answer: Soil forms as rock is broken down by weathering and mixes with other materials on the surface. Soil develops in layers called horizons. A soil horizon is a layer of soil that differs in color, texture, and composition from the layers above or below it.
What is a C Horizon?
Answer: A C Horizon forms as bedrock begins to weather by breaking up into small particles.
What is a B Horizon?
Answer: A B Horizon (subsoil) usually consists of clay and other particles of rock, but little humus. It forms as rainwater washes these materials down from the A Horizon.
What is an A Horizon?
Answer: An A Horizon is made up of topsoil, a crumbly, dark brown soil that is a mixture of humus, clay, and other minerals. Topsoil forms as plants add organic material to the soil, and plant roots weather pieces of rock.
What are decomposers?
Answer: Decomposers are the organisms that break the remains of dead organisms into smaller pieces and digest them with chemicals.
What organisms are considered decomposers?
1) fungi (like mushrooms)
2) bacteria
3) worms
How do animals affect soil?
Answer: mammals such as mice, moles, and prairie dogs break up hard, compacted soil and mix humus with it. Animal wastes contribute nutrients to the soil as well.
What is a natural resource?
Answer: A natural resource is anything in the environment that humans use.
What is one of nature’s most valuable natural resources?
Answer: soil
What are two ways that the value of soil is reduced?
1) loss of fertility through a loss of moisture and nutrients
2) loss of topsoil due to water and wind erosion
What is soil conservation?
Answer: It is the management of soil to limit its destruction.
Name three ways soil can be conserved.
Answer:
1) contour plowing---Farmers plow their fields along the curves of a slope instead of in straight rows. This method helps slow the runoff of excess rainfall and prevents it from washing the soil away.
2) conservation plowing---Dead weeds and stalks of the previous year’s crop are plowed into the ground to help return soil nutrients, retain moisture, and hold soil in place.
3) crop rotation—A farmer plants different crops in a field each year.
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