Geological Changes, Rock Type and Soils

Question 1

Define weathering.

1 mark

Answer 1

Weathering is the breakdown of rock in situ.

Question 2

Distinguish between and give examples of physical, chemical and biological weathering.

6 marks

Answer 2

Physical weathering is caused by heat, cold and ice. An example is a rock splitting due to water freezing in a crack.

Chemical weathering is caused by the action of water and air on rocks. An example is acid rain.

Biological weathering is caused by plants and animals. An example is plant roots finding their way into cracks and growing.

Question 3

Describe the formation and give examples of ingeous, sedimentary and metamorphic rocks.

6 marks

Answer 3

Igneous rock forms when lava or magma cools down. Examples include diorite and granite.

Sedimentary rocks are formed from sediment that gets buried deeply and compacted. Examples include sandstone and limestone.

Metamorphic rocks start out as some other kind of rock, but have substantially changed when rocks are subjected to high heat, high pressure and/or hot mineral-rich fluids. An example is marble.

Question 4

What is humus and what is its role in soil?

4 marks

Answer 4

Humus is dark, organic material that forms in soil when plant and animal matter decays.

Its role in soil
Humus contains many nutrients, such as nitrogen, phosphorus and sulfur.
It can make soil more fertile and reduce plant disease.
It makes soil more loose, allowing oxygen to get to the roots of plants.

Question 5

Describe the properties of sandy soils.

6 marks

Answer 5

• Large soil particles - 0.06 to 2 mm
• Large air spaces between particles allow free circulation of air and good drainage
• Warms up quickly and has a long growing season
• Sensitive to droughts
• Often acidic
• Weak structure

Question 6

Describe the properties of clay soils.

4 marks

Answer 6

• Small soil particles - less than 0.002 mm
• Restricted air and water movement, so it can stay wet for a long time
• Contains high levels of nutrients
• Becomes hard in dry conditions

Question 7

Describe the properties of loamy soils.

3 marks

Answer 7

• Made up of a mixture of sand, clay and silt particles
• Good water retention an nutrient holding capacity
• Good drainage