The Rock Cycle and Pollution of the Atmosphere  (Worksheet 2)

The Rock Cycle and Weathering

Below is a diagram showing the continuous nature of the rock cycle. The rock cycle involves the same particles of rock being broken down and then reformed into new rocks over and over again. This occurs over a very long period of time.


 

The stages of the rock cycle are as follows:

1) During Weathering large rocks are broken down into smaller pieces.

2) Erosion is the wearing down of rock.

3) Transportation is the movement of pieces of rock, usually by rivers and streams but also by wind and glaciers.

4) Deposition occurs when sediment is laid down, as it can no longer be carried along in transportation.


Weathering is the breaking down of large rocks into small rocks and occurs in two ways.
Physical Weathering occurs when rocks are subject to changes in temperature and involves water.
In Freeze-thaw weathering water fills small cracks within rocks. When this water freezes it actually expands (most liquids contract on freezing), widening the crack and eventually breaking the rock apart. This type of weathering is worst in areas where the temperature often varies between just above and just below zero.

Another type of physical weathering involves the effect of the sun. It should be noted that rocks are very poor conductors of thermal energy. During the day the sun gradually heats the rock and the outer layer of rock expands slightly. At night the rock cools down but cannot contract back to its original shape. In this way the rock will eventually be broken down.

Another form of weathering is chemical weathering which involves a chemical reaction. This form of weathering is worst in areas of high pollution and can damage statues, building and gravestones. As rain falls, carbon dioxide in the air dissolves in the rain to form a weak acid, which attacks rock containing calcium carbonate (examples include limestone, chalk and marble).

In heavily polluted areas, other gases such as sulphur dioxide also dissolve in the rain creating an even stronger acid.

Weathering Comprehension

1. What is weathering?
 
2. Which substance is involved in freeze-thaw weathering?
 
3. Which gas dissolves into rainwater creating a mild acid?
 
4. Why is chemical weathering worse in polluted areas?
 
5. What normally carries the eroded rock pieces during transportation?
 
6. What happens during freeze-thaw weathering?
 
7. What effect does the sun have on rocks?
 
8. Which factor is present in all types of physical weathering?
 
9. Which two factors can cause sedimentary rock to change into metamorphic rock over time?
 
10. Which two factors can cause igneous rock to change into sediments over time?
 
11. Which two factors can cause sediments to change into sedimentary rock over time?
 
12. In which process are pieces of rock laid down as sediment?