The Rock Cycle and Weathering
Above 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?
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down for answers
1.
The breaking down of large rocks into smaller pieces.
2.
Water
3.
Carbon Dioxide
4.
Because other gases such as sulphur dioxide dissolve in the rainwater.
5.
Water, wind and glaciers.
6.
Water freezes and expands within cracks in the rocks, causing them to break
apart.
7.
Rock expands in daylight but then tries to contract at night leading to rocks
cracking and breaking off.
8.
A change in temperature.
9 .Heat and pressure
10.
Weathering and erosion
11.
Compaction and cementation
12.
Deposition.
Pollution of the Atmosphere
Two main contributors to pollution are Acid Rain and The Greenhouse Effect.
These are a direct result of the burning of fossil fuels.
Acid Rain
- Fossil fuels contain sulphur, which is a non-metal. Like all non-metals, sulphur
forms an acidic solution when added to water.
- When fossil fuels are burnt, sulphur dioxide is released into the atmosphere and
dissolves in rainwater to produce acid rain.
- Acid rain can damage and even kill trees. It can also harm animals. In
particular, Acid rain causes huge damage to statues and building made of rock
that contains calcium carbonate such as limestone, chalk or marble.
Carbon Dioxide and The Greenhouse Effect
Fossil fuels are also responsible for The Greenhouse Effect. When they are
burnt, carbon dioxide is released into the atmosphere. Some carbon dioxide is
absorbed into the oceans but nevertheless there has been an huge increase in the
level of carbon dioxide in the atmosphere over the last 150 years.
The released carbon dioxide gases trap the heat that has reached the earth from
the sun and prevent it from leaving the atmosphere. This trapped heat leads to
an increase in temperature globally (global warming) and may lead the polar ice
caps to melt and flooding to occur.
This is the Greenhouse Effect.
Pollution True or False Quiz
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