Earth Materials
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I used the following to cover section 6.4 of the NEAB Modular course (what effect does burning oil and other fossil fuels have on the Earth's atmosphere). It took 1 x 1hr lesson plus homework.
Burning
Burning oil and other fossil fuels produces waste gases. These escape into the atmosphere and can change the environment of living things. This includes humans. The main effects of these waste gases are global warming and acid rain.
Burning (combustion) is a very common type of chemical reaction. The new substances produced when fuels burn are mainly gases. These go into the air, polluting it. When substances burn, they react with oxygen from the air. Reactions with oxygen are called oxidation reactions. Oxidation reactions produce compounds called oxides.
When a substance is burned in air, the elements from which it is made are converted (changed) into their oxides. For example, if a fuel contains sulphur, when the fuel burns, the sulphur becomes sulphur dioxide. Oxides of metals form alkalis, oxides of non-metals form acids.
The high temperatures produced by burning fuels can cause nitrogen and oxygen from the air to react. These produce nitrogen oxides. Sulphur dioxide and nitrogen oxides can harm plants and animals in two ways.
Directly, causing skin irritation and lung disease in animals.By dissolving into rain.
If the water in rivers and lakes becomes too acidic, plants and animals cannot survive. Acidic fumes and acidic rain also damage stonework and metalwork on buildings. This ruins their appearance and weakens them.
For 200 million years, the amounts of various different gases in the air has remained about the same as it is today:
About four fifths nitrogen
About one fifth oxygen
Small amounts of carbon dioxide, water vapour and noble gases.
Now answer the following questions:
1 Most fuels contain carbon and hydrogen. What materials will be formed from these when they are burnt?
2 Most fuels also contain the impurity sulphur. What will this be converted into when the fuel is burnt?
3 Will the fumes from burning fuels be acidic or will they be alkaline?
4 How are nitrogen oxides produced and how can they affect plants and animals?
5 In what ways does acid rain affect humans?
6 What is the main gas in air? Which gas from the air is involved in burning of fuels?
7 What gas is thought to be responsible for causing global warming?
8 Suggest as many practical ways as you can of reducing acid rain and global warming - burn less fuels is not an acceptable answer. How could you personally help to reduce these problems?
9 Write down 6 key words from this sheet and explain why you have chosen each one. Incorporate them into a spider diagram or concept map that summarises the information from this sheet.
I used the following as a homework to teach part of section 6.5 of the same course (candidates should be able to explain, on the basis of evidence, how the current theory of Plate Tectonics superseded the earlier theory). The least well answered part is the final open task in which students write a letter. They tend to be rather vague and do not really support their assertions with evidence.
In Theory …
There have been many theories (ideas) about why the Earth has a wrinkled surface (mountains and ocean tranches). One of the popular ones of the last century was the `Shrinking Earth' theory. It was imagined that the Earth started off as a molten ball of rock material, orbiting the Sun. As this cooled, a skin was formed, much like skin forms on cooling custard! This skin is referred to as the Crust. When things cool down, it is well known that they shrink. This would cause the solid crust to buckle, in the same way that the skin of an apple wrinkles when it has been left for too long without being eaten. The mountain ranges of the Earth were thought to be the wrinkles on the Crust. This idea was well accepted in scientific circles. As with all scientific ideas, eventually someone challenged it. Eventually it was replaced with the `Plate Tectonics' theory, which explains more facts accurately. The shrinking Earth theory would predict that mountain ranges would appear at random, all over the Earth. They are not, they are found only in narrow belts e.g. the Alps or Himalayas. Plate Tectonics predicts that mountains are only found in narrow belts, where two plates collide - this is what is observed. It would predict that mountains would constantly grow higher. They do not, they are eventually worn down e.g. the Scottish mountains are all less than 1500m in height, they were once the size of the alps at about 4000m high. Plate tectonics predicts this since mountains would cease to grow when the plates stop moving in that area. The shrinking Earth theory predicts that volcanoes and Earthquakes would occur at random, all over the surface of the Earth. They do not, they only occur in narrow belts. This is predicted by plate tectonics. Accurate measurements of the positions of countries can now be made using satellite technology. These show that countries are moving around the surface of the Earth. This can not be explained by the shrinking Earth theory. The rocks of Derbyshire contain fossil corals, indicating that tropical conditions once existed here. This can easily be predicted by plate tectonics. India is a sub tropical country. There is evidence that it has been covered in ice, millions of years ago. This is easily explained by plate tectonics.
Now answer the following questions:
Explain in your own words, how the shrinking Earth theory explains the existence of mountain ranges.
What predictions does this theory make about volcanoes and earthquakes?
With reference to the first two questions, why is the plate tectonics theory better?
Which theory best explains the fossil corals in Derbyshire and why?
The shrinking Earth theory cannot explain why some coastlines that are separated by thousands of km fit together. Nor can it explain the presence of similar rock sequences and fossils that match exactly, even though they are separated by thousands of km. Explain, with the help of diagrams, how these things can be explained by plate tectonics.
Imagine you are a scientist about 40 years ago who is questioning the shrinking Earth theory. Write an imaginary letter to the President of the Royal Society (which is a scientific society) in London (make up an address) suggesting why you feel that the shrinking Earth theory should be changed.
You may find some of the following questions useful for short revision sessions in lessons or as homework. I tend to use them every couple of weeks in a formal session at the start of the final lesson of the week.
Test number 1.
Give the chemical name of limestone, quicklime and slaked lime.
Why is coal placed into a limekiln as well as the limestone?
What is the reaction that happens inside the limekiln? (A description or chemical equation are equally acceptable)
How is slaked lime made?
Describe briefly how cement is manufactured.
What two materials are added to limestone in the glass making process?
Give 3 pieces of evidence that support the theory of continental drift.
Name the layers of the Earth and give an approximate thickness for each.
Test number 2.
What is made in a limekiln? What chemical reaction takes place?
How would you recognise the 3 types of rock? Give one example of each.
How is sedimentary rock made?
Igneous and metamorphic rock both have crystals. How would you tell the difference by looking at them?
Granite has large crystals, basalt has small crystals. What does this tell you about these two igneous rocks?
Give 3 pieces of evidence that support the theory of plate tectonics.
What is thought to make the Earth's plates move?
Test number 3
1 Which types of rock are layered and how would you tell the difference between them?
2 Why are fossils never found in igneous or metamorphic rocks?
3 Link these words to types of rock:
Formed by molten rock cooling down
Made of grains cemented together
Contain fossils
Formed from other rocks by heat and pressure without melting
4 Granite is formed deep in the Earth's crust so it will have larger crystals than a lava such as basalt. Why?
5 Give two examples of each type of rock
6 Link these words to different types of plate boundary:
Ocean trenches
Magnetic stripes
Fold mountain ranges
Volcanoes with runny lava
Large earthquakes
Faulting of rocks
Test number 4
How is oil formed?
What physical property of oil fractions allows them to be separated?
Write down 3 trends in the properties of the fractions of oil e.g. as the boiling point is higher …
Name the 4 fractions, in order, which are used as aeroplane fuel, as fuel for power stations, as a chemical feedstock and finally as a fuel for camping stoves.
What two substances are produced when fractions from oil are burnt? Explain why they are formed.
How is the problem of overproduction and underproduction solved?
What new chemical is produced by the process from Q5 and why is it important.
What is a polymer and what is a monomer? Draw the monomer and polymer repeating unit for poly(ethene).
The following is the text and diagram (drawn by my colleague Richard Toone) that I use to cover oil traps.
Oil Traps.
Oil is formed when sea creatures die and sink to the floor of the ocean. They become buried in sediments . There is not much oxygen down there so they rot anaerobically. Anaerobic is a word which means 'without oxygen'. When creatures die and rot in aerobic (with oxygen) conditions the body completely rots away, nothing is left. However, after millions of years, anaerobic rotting produces what we call oil and natural gas. This gets trapped underground. Humans can find this by careful and expensive exploring. We can then drill down to it and extract it from the ground.
Movements of the Earth's plates causes rocks to bend. In some places they bend upwards. Oil gets trapped in such places, as shown on the diagram. The oil is contained in a layer of porous rock. Porous literally means 'containing pores'. Pores are little holes into which liquids such as oil can seep. There is usually a layer of non porous rock below the layer with the oil in. The oil is less dense (lighter) than the rock and so will gradually seep higher. Where there is oil, there is also water and natural gas. Natural gas is very low density (very light) so it goes to the very top of the trap. Water is denser than oil so it is found at the bottom of the trap. The oil and gas are stopped from escaping to the surface by a layer of non porous rock (obviously - if a rock does not have pores, the oil and gas can not get through). This rock is called 'a caprock' (since it acts as a cap to keep the oil underground). There are often other layers of sedimentary rock in an oil trap e.g. shale. The non porous rock could be something like limestone or mudstone.
Tasks:
Read the sheet carefully. Ask questions about any bits you don't understand.
Stick this sheet into your exercise book.
Stick the diagram of the oil trap into your book, without the list of words from the bottom.
The words from the bottom of the sheet are the labels. Use the information from this sheet to label the oil trap diagram correctly.
Colour each layer in a different colour.
Answer these questions, you will find most of the answers on the sheet.
a From what is oil formed?
b What does anaerobic mean?
c Oil is not formed by creatures which die on land, why not?
d What else is produced when oil is formed?
e What causes rocks to bend into the shape needed to form an oil trap?
f What sort of rock contains oil?
g Oil and gas rise up through rock. Why does this happen?
h Why does the oil and gas not seep all the way to the surface?
i Name a type of rock that could act as a caprock.
