Weathering & Soil Notes

Question 1

What is weathering?

Answer 1

The breaking down of rock due to physical and/or chemical changes in the rock as it is exposed to the atmosphere

Question 2

Where does weathering occur?

Answer 2

It occurs at the interface between the atmosphere and the lithosphere

Question 3

What does weathering result in?

Answer 3

Smaller pieces of rock called sediments

Question 4

Physical Weathering Types:

Answer 4

• Frost action
• Plant action
• Pressure unloading

Question 5

Frost action:

Answer 5

Occurs in a cold and moist climate, alternating freezing and melting of water in the rock cracks the rock

Question 6

Plant action:

Answer 6

Plant roots grow into small cracks in the rock and widen them

Question 7

Pressure unloading:

Answer 7

Rock cracks when pressure over the rock is removed

Question 8

What results of physical weathering?

Answer 8

A change in appearance of rock (size, shape, state of matter)

Question 9

What results from chemical weathering?

Answer 9

A change in chemical composition of the rock

Question 10

Types of Chemical Weathering:

Answer 10

• Oxidation
• Acid Reactions
• Hydrolysis

Question 11

Oxidation:

Answer 11

Addition of oxygen to metal, results in rust (iron oxide)

Question 12

Hydrolysis:

Answer 12

Chemical weathering by reaction of water with other substances, when certain minerals are exposed to water they dissolve into ions, water will help any chemical reaction

Question 13

Hydrolysis Example:

Answer 13

Feldspar will chemically weather into clay (kaolinite)

Question 14

Acids:

Answer 14

Gases such as sulfur dioxide, nitrogen dioxide and carbon dioxide will dissolve in rainwater forming acid rain

Question 15

Acid Rain Example:

Answer 15

Calcite will dissolve completely in carbonic acid-thus chemically weather any rock containing this mineral easily

Question 16

Destructive Forces:

Answer 16

• Plate tectonics builds up the earth’s surface, but what goes up must come down
• Once exposed to the air, water or wind, rock will begin its destructive cycle and will weather down

Question 17

How does acid rain form and harm?

Answer 17

• Acid rain forms naturally by volcanic activity or by pollutants
• Acid rain harms any exposed rock, buildings and monuments

Question 18

End result of weathering:

Answer 18

Sediments, including clay, silt, sand, pebbles and cobbles

Question 19

What can affect the rate of weathering?

Answer 19

• Size of sediment
• Type of mineral (hardness, Moh’s scale)
• Temperature
• Humidity (amount of moisture present)

Question 20

How does weathering connect to the rock cycle?

Answer 20

Without weathering, no sedimentary rocks will form

Question 21

What is soil?

Answer 21

A mixture of weathered rock and organic remains (humus)

Question 22

Where does soil form?

Answer 22

Forms at the interface between the atmosphere and the lithosphere

Question 23

How does soil form?

Answer 23

1) Rocks weather
2) Leaching of minerals adds nutrients to lower layers from top layer
3) Biological activity such as decomposition add organic matter (humus) to soil, soil is mixed by earthworms

Question 24

How long does soil take to form?

Answer 24

Takes 500-1,000 years to form

Question 25

Soil horizons:

Answer 25

Horizon A: Topsoil (fertile layer)
Horizon B: Subsoil
Horizon C: Parent rock

Question 26

Types of soil:

Answer 26

1) Residual: stays

2) Transported: moved

Question 27

What measure can be done to conserve soil?

Answer 27

• Soil is a natural resource and must be protected-
• Several methods exist to protect soil such as contour farming, no-till farming, terracing and crop rotation
• These all prevent erosion of the topsoil by wind or water

Question 28

Why is it important to protect soil?

Answer 28

• We need it to sustain ecosystems
• Producers take nutrients from the soil and convert it to food with the help of sunlight
• Basis of the food chain