Soil Parent Material

Question 1

What is the first step in soil formation?

Answer 1

When mineral material and organic matter from plants and animals are combined together.

Question 2

What is the general ratio of solids/void space in soils? `

Answer 2

50/50

Question 3

What are the 3 broad classes of rock?

Answer 3

1. Igneous (Molten magma)
2. Metamorphic (Altered by heat and pressure)
3. Sedimentary (Sedimentary deposits)

Question 4

What distinguishes parent material?

Answer 4

Type and/or ratio of the type of mineral quantities.

Question 5

In most cases, rocks are mainly composed of what element?

Answer 5

Silica

Question 6

A higher or lower concentration of silica will cause rocks to break up more quickly at the surface of the earth?

Answer 6

Lower

(Rocks with higher % of Silica are more resistant to breaking up at the climatic conditions of the earth’s surface.)

Question 7

The correct term for the ‘breaking-up’ of soils is?

Answer 7

Weathering

Question 8

What are the two main groups of weathering?

Answer 8

1. Physical
2. Chemical

Question 9

What are the different types of physical weathering?

Answer 9

1. Thermal
2. Mechanical
3. Plant pressure

Question 10

What is the main concept of Thermal Weathering?

Answer 10

Different minerals have varying rates of expansion when exposed to heat. Where these rates differ withing the rock, stress is caused and fracturing can occur in areas of weakness.

Question 11

Explain the second form of thermal weathering in rocks…

Answer 11

Temperature differences within the rock itself (outer and inner sections) can cause exfoliation weathering as the outer layers of the rock are fractured and peeled away.

(AKA ‘onion skin’)

Question 12

Explain the process of ‘frost shattering’ ?

Answer 12

Water can penetrate small cracks in the rocks. When the water freezes, it expands by 10% and the expanding ice forces the cracks to break open.

Question 13

What is the other effect that water infiltration into a rock can have?

Answer 13

Different materials have different rates of swelling and shrinkage. This can initiate stress within the rocks.

Question 14

Biological weathering is…

Answer 14

The process by which plants and animals contribute to the weathering of plants. Either by physical actions of animals or where root growth from plants infiltrates rock and causes damage to its structure.

Question 15

What is the function of exudates in relation to chemical weathering?

Answer 15

Plant roots release exudates that are metabolised by micro-organisms thereby increasing the rate of chemical weathering.

Question 16

Name the (5) types of Chemical Weathering?

Answer 16

1. Hydrolysis
2. Carbonation
3. Hydration
4. Dissolution
5. Oxidation & Reduction

Question 17

What is the most common form of Chemical Weathering?

Answer 17

Hydrolysis

Question 18

Explain the steps of Hydrolysis.

Answer 18

H₂O dissociate into H+ and OH^-

These charged particles attack the bonds that hold minerals together.

This causes disintegration of the rocks and changes the nature of the minerals.

The respiration of biological activity leads to CO₂ being respired. This dissolves in soil water producing a weak acid that attacks minerals.

Question 19

Carbonation is an accelerated form of?

Answer 19

Hydrolysis

Question 20

Explain the process of Carbonation

Answer 20

1. Majority of soil organisms respire Carbon Dioxide.
2. When CO₂ contacts with water, a portion of it dissolves to form carbonic acid.
3. The acid attacks the mineral, degrading it.

Plant roots excrete sugars that are then used and converted to acids by micro-organisms. All acids are rich sources of hydrogen ions; carbonation, therefore, enhances hydrolysis.