Teaching the Dynamic Earth - GeoScience - Homegeoscience.msc.sa.edu.au/library/dynamic_rock_cycle.pdf · 2010. 6. 5. · Aspects of Unit 9G Environmental Chemistry are also dealt

Teaching the Dynamic Earth

The Dynamic Rock Cycle Contents Page Relevance to National Curriculum at Key Stage 3 and Key Stage 4 ...........................................2 Rock cycle diagram for use in initial plenary (led by Facilitator) ..................................................3 Activity: 1 Weathering – breaking up, or breaking down material at the Earth’s surface 1A Physical weathering - heating and cooling rock chips ...................................................4 1B Physical weathering - results of freeze/thaw weathering ...............................................4 1C Chemical weathering - action of carbonic acid on ground limestone.............................5 2 Erosion & transport – investigating the resistance of rock samples to “erosion” ......................6 3 Deposition – investigating the movement of sand in water......................................................8 4 Compaction and cementation of sediments ..........................................................................10 5 ‘Metamorphism’ - Detecting the distortion .............................................................................12 6 Crystallisation (and melting) - salol .......................................................................................14 7 Extrusive igneous rocks 7A –‘lava’ in the laboratory: the treacle investigation ........................................................16 7B – A volcano in the laboratory: the wax volcano demonstration ....................................20 8 Deformation – make your own folds and faults......................................................................22 Apparatus and materials list......................................................................................................24 Names of common rocks ..........................................................................................................26 Teaching points of workshop activities (in C.A.S.E. terms) .......................................................27

© The Earth Science Education Unit. Copyright is waived for original material contained in this booklet if it is required for use within the laboratory or classroom. Copyright material contained herein from other publishers rests with them.

With the support of:

UK Offshore Operators Association (UKOOA) is the representative organisation for the UK Offshore Oil and Gas Industry. Its 35 members are companies licensed by the Government to explore for and produce oil and gas in UK waters.

The Dynamic Rock Cycle

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The Dynamic Rock Cycle ‘hands-on’ activities on the processes involved

in the rock cycle Objectives: To use the integrating model of the rock cycle as a means of encountering common rocks and Earth-processes in a practical, investigative way.

The National Science Curriculum (2000) Perspective The session is aimed at the following National Science Curriculum statements:

Key Stage 3, Sc3 - 2. Geological changes “Pupils should be taught:

d) how forces generated by expansion, contraction and the freezing of water can lead to the physical weathering of rocks;

e) about the formation of rocks by processes that take place over different timescales, and that the mode of formation determines their texture and the minerals they contain;

f) how igneous rocks are formed by the cooling of magma, sedimentary rocks by processes including the deposition of rock fragments or organic material, or as a result of evaporation, and metamorphic rocks by the action of heat and pressure on existing rocks;

Key Stage 3, Sc3 - 3. Acids and bases

g) how acids in the environment can lead to corrosion of some metals and chemical weathering of rock [for example, limestone]”

Key Stage 4, Sc3 – 2. Changes to the Earth and atmosphere Some of the activities overlap with KS4 requirements, e.g. “2r – how the sequence of, and evidence for, rock formation and deformation is obtained from the rock record.”

Key Stage 3, Sc1 – Scientific enquiry The activities offer scope for developing many of the investigative skills involved in planning, obtaining and presenting evidence, considering evidence and in evaluating it.

Coverage of QCA Scheme of Work Unit 8H The Rock Cycle; 8G Rocks and Weathering – Most of the ‘lessons’ in the QCA Schemes are covered in a similar, or equivalent way in The Dynamic Rock Cycle Workshop. Aspects of Unit 9G Environmental Chemistry are also dealt with.


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ACTIVITY 1: Weathering - breaking up, or breaking down material at the Earth’s surface

Purpose: To consider different types of weathering process. Notes: The apparatus and materials required are: granite chips, 7-10mm across; Bunsen burner, mat, safety goggles and matches; 500ml beaker of water; 2 small chips of several different types of rock, some porous; some non-porous; two shallow plastic containers; deep freeze or freezing compartment of fridge; boiling tube; deionised water; Universal indicator; drinking straw or glass tube; ground limestone (for extension: 4 boiling tubes; 3 bungs for tubes; limestone fragment; granite fragment; pulverised granite. Development of knowledge and understanding: Weathering is investigated by these activities. Weathering loosens solid material and removes dissolved material. It is distinct from erosion – in which solid material is removed.

Demonstration 1A: Weathering - A Physical Example Learning objective: To demonstrate how cycles of heating and cooling can cause a granite chip to break up.

• Carry out a risk assessment. Safety goggles should be worn by all those within range. • Heat a granite chip strongly in the Bunsen flame and then dunk it into a beaker of cold

water (do not drop it to the bottom of the beaker or the glass may crack) • Repeat the process until it crumbles • How many cycles were needed? • How does this represent the ‘real world’? • Where on Earth might activity like this take place? • In what ways is it unrealistic? • Why might you expect a rock containing several minerals to break down by heating and

cooling more quickly than one made of only one mineral?

Demonstration 1B: Weathering - A Physical Example Learning objective: To investigate which rocks are broken down by cycles of freezing and thawing.

• Use two shallow plastic containers. • Get two chips of several different types of rocks and put one of each rock into each

container. Cover each set of rocks with water and put one into a deep freeze. • When frozen, remove the container from the deep freeze and allow the ice to melt. • Compare the two containers. • Replace the one that was frozen before in the deep freeze and freeze it again, then

repeat. • How do the results compare? • Which types of rock broke down most quickly? • Can you explain why? • How does this represent the ‘real world’? • Where on Earth might activity like this take place? • In what ways is it unrealistic? • Why was a plastic container used and not a glass one?


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Demonstration 1C: Weathering - A Chemical Example Learning objective: To use indicator to investigate the reaction between carbonic acid and limestone.

• Add some Universal indicator to deionised water in a boiling tube (half full). • Make some “carbonic acid” by blowing exhaled air through a straw into the water.

Record the colour of the indicator. • Add a spatula full of ground limestone to the boiling tube, put in the bung and shake

well. • Observe the tube at intervals and look for any change in the colour of the indicator. • What has happened? • Can you explain why? • How does this represent the ‘real world’? • Where on Earth might activity like this take place? • In what ways is it unrealistic? • Why might some rocks be attacked at a faster rate in industrial areas?

Extension 1: Set up a similar activity, using a solid limestone fragment in another boiling tube, and compare the rate of reaction. Extension 2: Set up three boiling tubes, with neutral, deionised water and indicator. Add a small granite chip to one: add the same amount of pulverised granite to the second, and keep the third as a control. Seal each tube tightly with a bung. After several days, the indicator in the pulverised granite tube shows an increase in pH. This is because of hydrolysis of the feldspar mineral in the granite. It is altering to a clay mineral, and releasing KOH.

Weathering: Two Examples of Biological Weathering (Display/Collect Your Own)

• The oyster shell has been bored (!) by marine organisms, and will not survive much longer in one piece.

• Mosses and lichens usually represent the first stages of biological weathering of rocks on the Earth’s surface. (The growth of tree roots along bedding planes and joints also exert powerful forces, which break up rocks.)


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ACTIVITY 2: Erosion and transport

Demonstration 2: Rock Resistance Purpose: To show that rocks erode at different rates and that this can explain the formation of uplands and coastal headlands by the more resistant rock types. Notes: The apparatus and materials required are: expendable rock specimens such as crumbly sandstone (sedimentary), limestone (sedimentary), granite (igneous), basalt (igneous). Four pieces (each of about 50g) of each rock are needed. An alternative is to use locally available rocks of variable resistance. At least 4 plastic containers with wide necks and tops; a mechanic's file; emery paper; goggles; balance; tray; some dilute hydrochloric acid (0.5 M) in a dropper bottle. Caution: corrosive. These activities are done 'dry', to speed up the process and reduce mess. Use three or four different types of rock such as crumbly sandstone, chalk, granite, slate. Some specimens may be destroyed by the activity. The noisy bottle shaking need take only 10 seconds. The debris produced by each rock is easier to compare if each type of rock is shaken in a separate container. The provision of a balance allows quantitative comparisons to be made. By using rocks from the local area you can gain insight into the development of the landscape in your home region. Carry out a risk assessment and wear safety goggles when using acids. Development of knowledge and understanding: Through these activities, pupils come to realise that some rocks resist erosion more than others. Some rocks are attacked faster by physical activity, others by chemical processes. The more resistant rocks will then form upland areas and coastal headlands, whereas the more easily eroded rocks form valleys and bays. The eroded materials are transported away by gravity, water, wind or ice and will eventually become deposited in an accumulation of sediment which may become a sedimentary rock. Acidic waters slowly dissolve calcium carbonate-rich rocks, increasing the calcium and hydrogen carbonate ion content of the water which then flows away. This reaction of acids with rocks is weathering not erosion, because no solid material is carried away. Learning objective: To investigate the relative rates of erosion of rocks by attrition and by chemical action. There are many different ways in which rocks are weathered and eroded in the natural world. It is not always possible to imitate these different ways in the laboratory. We do not have nearly so much time available either! However, we can try. The outlines of some investigations. Before your group does these investigations, think how you can improve them from these outlines to get the most useful information. How can you set up some sort of control, so that you can compare the results with the original rock samples?

Investigation A: Test how much each rock is affected by being bashed against rocks of the same type and other rocks. Use a plastic bottle.

Investigation B: Test how much each rock can resist being worn away, using a file or emery paper.

Investigation C: Test to see which rocks are attacked by acid. Caution: corrosive.

1. Which rocks did you find were the most resistant?


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2. Where on Earth might these processes be occurring naturally? 3. How could these simulations of natural processes be made more realistic? 4. Which rocks are most likely to form hills or headlands in coastal areas?

See ESTA’s “Moulding Earth’s Surface - Landshaping”, for a pupil exercise in prediction, where the results of the above investigations are related to landscapes.


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ACTIVITY 3: Deposition Purpose: To investigate in the lab the processes by which sediment grains are eroded, transported and deposited by flowing water. Notes: The apparatus and materials needed are: a 1m length of guttering (square section guttering is preferred) with two end pieces; clean sand to fill the gutter to within 2cm of the top; rubber tubing to connect to a lab. tap; container such as a large beaker to put in the sink to catch any sediment washed over the end of the gutter – preventing it from blocking the sink; small pieces of gravel. Development of knowledge and understanding: This allows real sedimentary processes to be investigated in the lab. – sediment grains are visibly eroded, transported and deposited in different ways. When these processes have been studied, the study of the gutter can be extended by considering it as a simulation of a river/sea situation.

Demonstration 3: Deposition - in the Stream (This activity is based on ESTA’s “Second-hand Rocks” in “The Science of the Earth 11-14” series.) Learning objective: To observe the processes of erosion, transportation and deposition by flowing water. The gutter provides scope for several investigations into the ways in which sediment is moved in water. Set it up as shown and turn on the tap gently.

1. If you are the first to use the apparatus, notice what happens to the water as it fills up the gutter.


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2. Once it is running uniformly, look carefully for places where erosion is taking place. How is the sand being moved at these spots?

3. Study where the sand is being moved along the bed. This is known as “transportation” of the sediment. Exactly how is it being moved?

4. Find places where deposition is taking place. Are the newly formed layers of sediment horizontal or inclined? How do they build out into the pool at the end of the gutter?

5. Try changing the flow rate and discuss any differences you spot. 6. Try adding a few pieces of gravel and study the flow around them.

When you have finished, try to match the gutter work to modern sedimentary environments and rock specimens. Would your investigations enable you to say which way former currents flowed?


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ACTIVITY 4: Compaction and cementation of sediments Purpose: To explain that for most sediments to become rocks the grains need to be squeezed together (compacted) and/or glued together (cemented). The extent of the compaction and the strength of the cementation affect the properties of sedimentary rocks. Notes: The apparatus and materials required are: plastic syringe (20cm3), with the nozzle cut off at the end of the barrel; petroleum jelly; tray; goggles; disposable cups and spoons; 250g of dry sand; 10g of powdered clay; 10g of plaster of Paris powder; sample of sandstone (sedimentary); water; apparatus for testing strength of the pellets, e.g. file, variety of masses, heavy ball-bearings, dropper bottle of dilute hydrochloric acid (0.5M). Caution: corrosive. Carry out a risk assessment and wear safety goggles when using acids. Do not let pupils pour plaster of Paris down the sink. Development of knowledge and understanding: The extent of compaction depends upon the type of sediment. Very little compaction takes place when sand is converted to sandstone. In muds and clays, water may initially comprise 80% by volume of the sediment. A great deal of compaction takes place when this is squeezed out. The compaction of sand and mud can be modelled with pennies and matchsticks, respectively, which can be ‘compressed’ between two pieces of wood on an overhead projector. Sands become sandstones when cement crystallises in the pore spaces. The cement is formed from new minerals that crystallise from circulating waters. Pupils simulate part of the sedimentary part of the ‘rock cycle’ by first making a 'rock', then testing the strength of their rock and consequently breaking it up.

Demonstration 4: Sediments into Rocks (This activity is based on ESTA’S “Second-hand Rocks” in the “Science of the Earth 11-14” series.) Learning objective: To simulate the formation of sedimentary rocks and investigate how the properties of the samples of 'sedimentary rocks' so formed are dependent on the extent of their compaction and cementation. Sandstone was once loose sand. The grains of sand have become stuck together in sandstone. Is it something that has happened to the sand, or has something been added to the sand? How has this happened? Try this exercise: it may explain how sand becomes sandstone. HINT - don’t overdo the water! Use a plastic cup for all mixing, before inserting the mixture into the syringe.

1. Put some damp sand in a syringe which has had the nozzle cut off and has been smeared with petroleum jelly on the inside.

2. Put the open end of the syringe on the palm of your hand and press the plunger in hard.


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3. Carefully push the sand pellet out of the syringe onto a piece of paper and leave on one

side. 4. Mix three parts of damp sand with one part clay. 5. Repeat steps 1, 2 and 3 using the sand/clay mix instead of the sand. 6. Repeat the same three steps but this time use a mix of five parts of damp sand and one

part of plaster of Paris powder. 7. Leave your “rocks” to dry. 8. Which of the pellets is most like a rock? Plan an investigation which will give you evidence

to show which is most rock-like. 9. Carry out your investigation. 10. Do your results support your conclusion? 11. How could you improve your investigation if you could do it again? 12. Do you think that sandstone can be formed from sand by pressure alone?


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ACTIVITY 5: Metamorphism Purpose: To consider evidence for the effect of pressure on rocks through observations of the outcomes of a simulated distortion of fossils. Notes: The apparatus and materials required are: modelling material; several cockleshells, or similar shells; 50g of plaster of Paris powder; disposable plastic cups; stirring rod; water. Do not let pupils pour plaster of Paris down the sink. Development of knowledge and understanding: Metamorphic rocks are formed by the action of heat and increased pressure on the original rocks. This activity concentrates on the effects of pressure acting on an original sedimentary rock. If the pressure is intense enough and acts for a long time, the rock recrystallises. Some of the new minerals are platy in shape and become aligned at right angles to the main pressure. This produces new planes along which the rock will split, in preference to the original bedding planes. The new alignment planes, called cleavage planes, are made use of when slate is split for roofing materials. More intense metamorphism will destroy the fossils and form coarser-grained metamorphic rocks.

Demonstration 5: Detecting the distortion (This activity is based on ESTA’s “Hidden Changes in the Earth” in “The Science of the Earth 11-14” series.) Learning objective: To produce distortions in castings of seashells and analyse a distorted seashell casting to predict the relative size and direction of distorting pressures, and to study diagrams to the same effect. Many metamorphic rocks, such as slate, are formed deep below ground, under great pressure. They sometimes contain fossils which have been badly squashed. The results of the squashing gives clues about he directions of the pressures which squeezed the rocks. Work in pairs to make a squashed 'fossil', but do not show other groups what you are doing.

1. Soften the modelling clay. 2. Make a mould by pressing the outside of a shell carefully into the clay. Remember to make

a rim to contain the plaster. 3. Carefully remove the shell, to leave the imprint in the clay. 4. Squeeze the mould so as to change the shape of the shell imprint as shown in the picture

below. First choose whether to squeeze it from top to bottom; from side to side, or whether to apply pressures as shown in the third picture, i.e. shear pressures. Whichever you choose do not distort the shape too much. Remember how you squeezed the mould, it will be important later.

5. Mix up some plaster in an old plastic cup. Place less than 1cm of water in the cup and stir in enough plaster to make a runny cream.

6. Pour the plaster into the distorted mould and leave it to set for a few minutes. 7. Leave any remaining plaster to set in the cup. Wash the stirring rod. 8. When your plaster fossils have set, scratch your initials on the base and then carefully take

your fossil cast out of the modelling material. 9. Pass your fossil on to a nearly group. See if they can work out the directions of the

pressures which you used to distort the fossil. 10. Do the same for theirs. Did you get it right? 11. How could the same distortion have been produced by forces acting in different

directions?


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12. Study each of the drawings below. They show several trilobites found in slates. The top

left is an undistorted trilobite; the other pictures have been distorted by pressures in the Earth.

13. These fossils have been distorted by moderate pressures which have changed the rock from a mudstone to a slate. What would happen to the fossils if the pressures had been much greater?

14. By about how much has each

trilobite been squeezed? By about how much have the surrounding rocks been squeezed? By about how much has the region in which the rocks are found been squeezed? How might this scale of deformation have been caused?


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ACTIVITY 6: CRYSTALLISATION (AND MELTING) Purpose: To explain the effects of heating and cooling on rocks, particularly the observable outcomes of different rates of cooling of molten rocks (magma). Notes: The apparatus and materials required are: Salol (phenyl salicylate), approximately 5g; boiling tube; 250cm³ beaker; 6 microscope slides; teat pipette; goggles; hand lens; hot water; access to a freezer; sheet of coloured paper; samples of igneous rocks of various grain sizes (e.g. granite, gabbro, rhyolite, basalt). Development of knowledge and understanding: Many kilometres below the surface of the Earth the temperature is high enough to cause partial melting. The magma produced rises upwards because it is less dense than the overlying rocks. Crystallisation may take place within intrusions at different levels of the crust or at the surface, if extrusion takes place. Intrusions may subsequently be exposed at the surface by weathering and erosion processes. Igneous rocks form from melts which may exceed 1000 degrees Celsius. This activity models the behaviour of a cooling magma, but at a much lower temperature (around 40 �C). Pupils will discover a link between cooling rates and the sizes of crystals that are produced. The largest crystals of Salol are formed from the slowest cooling melt. Igneous rocks show a similar behaviour so pupils can use the crystal size to predict the relative depths at which the rocks crystallised. Coarse-grained rocks, like granite, are formed by slow cooling at depth, whereas volcanic rocks, like basalt, are fine-grained. Igneous rocks are classified according to their mineral content as well as their crystal size. The Salol crystals provide an insight into the size of crystals as a function of cooling, but they misrepresent real rock textures. Igneous rocks typically contain several minerals which crystallise at different times and rates. Pupils could examine specimens of igneous rock, preferably with polished surfaces, to observe the size, shape and relationships between crystals. Experimental modelling of the crystallisation of two chemicals is described in the book Science of the Earth 11-14: Magma - Introducing Igneous Processes, ESTA.

Demonstration 6: Fast or slow cooling: large or small crystals? (This activity is based on ESTA’s “Magma” in “The Science of the Earth 11-14” series.) Learning objective: To illustrate relationships between the sizes of crystals formed in a melt when it is cooled at different rates. We can find out why the crystals in igneous rocks have different sizes by growing crystals from a melt in the laboratory.

1. Take a piece of paper and label it as shown below. Put a microscope slide on the 'room temperature' part of the paper.


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2. Ask for a pair of microscope slides chilled in a freezer and put one on the paper. Take a

pipette with some melted Salol from a water bath and quickly put a few drops on the slide from the freezer and on the one at room temperature. Place slides of the same temperature on top. Watch what happens.

3. Answer the following questions: (a) On which slide did crystals form first? (b) On which slide did crystals grow fastest? (c) On which slide did the largest crystals form?

4. If you had warm slides, would you expect the crystals: (a) To form straight away or after some time? (b) To grow quickly or slowly? (c) To be large crystals or small crystals? Write down your predictions.

5. Test your ideas by asking for a pair of warm slides. Put one on the paper; add liquid Salol as soon as you can; put the second slide on top and watch carefully. Were you right?

6. Now apply your ideas. Some igneous rocks are made of large crystals, did they cool slowly or quickly? At what rate did fine-grained igneous rocks cool?

7. Some igneous rocks melt and crystallise deep within the crust, whereas others come to the surface in volcanoes. Which of the resulting igneous rocks will have the smallest crystals?


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ACTIVITY 7: EXTRUSIVE IGNEOUS ROCKS Purpose: To explain that the viscosity of lava influences the shape of volcanic landforms and that the viscosity depends on the temperature of the lava and how much water, gas and solids it contains. Notes: The apparatus and materials could include: treacle or syrup; Petri dishes or tiles with 'props' to allow tilting; spatulas or teaspoons and stirring rods; stopclock or watch; ruler; Bunsen burner; camping gas stove or hot water bath; tripod and gauze; boiling tubes with bungs; thermometer, stand, clamps and bosses: teat pipette; syringe; sand; hot soapy water; test tube brushes and cloths; goggles. The least messy way of doing this investigation is if pupils retain the treacle in the boiling tube throughout, by inserting a bung before tipping the tube. Development of knowledge and understanding: Pupils will discover that the viscosity of a liquid can be changed in a variety of ways. The laboratory behaviour of treacle is used to model the characteristics of lava. The violence of volcanic eruptions and the resulting products are shown to be related to the viscosity of the lava. The viscosity of lava and treacle is modified by changes in: temperature; gas content; water content; concentration of solids, e.g. crystals in lava, sand in treacle. Evidence of the gas content is preserved as 'bubbles' in some lavas like pumice; others preserve larger crystals in finer grained background material. Lava viscosity also depends upon the chemical composition of the melt, but this cannot be simulated easily using treacle. The eruptive behaviour of molten rock gives rise to a variety of volcano types and extrusive igneous rocks. Differences in the nature of the original magma and subsequent changes as it rises towards the surface, influence the type of lava erupted. Lava viscosity has a controlling influence on the character of eruptions and the types of volcanoes produced. Low viscosity lavas flow freely from volcanoes to form flat sheets of lava which can cover large areas. As the lava degasses, fire fountains can be produced and you can go and watch or film these as the eruptions are fairly safe. These volcanoes have shallow slopes of 10° or less. High viscosity magmas may just be squeezed out of a vent, but often they solidify in the mouth of a volcano. Then the pressure steadily increases until a catastrophic eruption blasts large blocks of lava and huge volumes of ash into the sky, these fall back to Earth producing steep-sided cones with slopes of 30-40°. Stay well away from this type of eruption.

Demonstration 7A: Lava in the laboratory (This activity is based on ESTA’s “Magma” in “The Science of the Earth 11-14” series.) Learning objective: To investigate the relative effects of the factors which influence the runniness of treacle. Magma is a rock which has been heated up so much underground that it has melted and formed a liquid. When magma flows out of the ground from volcanoes it is called lava. Lavas can be very sticky and slow-flowing or they can be runny and fast-flowing. We can find out why some lavas are runny and others are sticky by carrying out some experiments. We cannot bring lava into the laboratory because it is too hot (it may be hotter than 1000 degrees Celsius) and the nearest volcano is too far away. Treacle is a liquid like lava and the runniness of both of these liquids can be changed in similar ways. So we can carry out laboratory experiments on treacle and then use these to understand how lava flows.


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1. Plan a treacle investigation using the sheets overleaf. 2. Carry out your investigation by following your plan. Be sure to clean up afterwards. 3. Do not forget to record your results and to plot them on a graph. 4. Write down what your investigation showed. Were your first ideas right or wrong? 5. Could your investigation have been done better? How? 6. Be ready to tell the rest of the group about your investigation and your results.


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LAVA IN THE LABORATORY: PLAN A TREACLE INVESTIGATION Changing the ‘runniness’ of treacle I think I can change the runniness of the treacle by: (a) making it more runny (two or more ways) ........................................................................................................................................................... ........................................................................................................................................................... (b) making it less runny (at least one way) ........................................................................................................................................................... ........................................................................................................................................................... My ‘runniness’ investigation In my investigation, I am going to make the treacle more/less runny by: ........................................................................................................................................................... ........................................................................................................................................................... I plan to change the ‘runniness’ in steps by: ........................................................................................................................................................... ........................................................................................................................................................... I plan to find out how runny the treacle is at each step by: ........................................................................................................................................................... ........................................................................................................................................................... I will need the following apparatus and materials (use only the apparatus and materials available in the laboratory): ........................................................................................................................................................... ...........................................................................................................................................................


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LAVA IN THE LABORATORY: PLAN A TREACLE INVESTIGATION When the apparatus to test the runniness of the treacle is set up, it will look like this: I will plot the results of my investigation in a table like this: I will use the results from the table to plot a graph like this: I think my results will show that: ........................................................................................................................................................... ........................................................................................................................................................... ...........................................................................................................................................................


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Demonstration 7B: A Volcano in the Laboratory Topic Volcanoes are exciting – hence all the volcano footage on TV. They can be used to fire pupils’ imaginations, and safe analogues of the behaviour of molten rocks can be demonstrated in the school laboratory. This activity consists of a teacher-led demonstration for the whole class. It also demonstrates how ‘rocks’ may form below ‘ground’, as well as on the surface. Prior knowledge Pupils will have seen TV coverage of volcanic eruptions, and may even have spent holidays in volcanic regions. They will also know that temperatures generally rise with depth in the Earth. (This is because of radioactive decay of minerals within the Earth, and the fact that the hundreds of kilometres of overlying rock provide a very good insulator). Starting points/misconceptions to avoid The demonstration can follow the showing of selected video clips of volcanic eruptions. Many pupils (and writers of school textbooks!) believe that there is a universal layer of molten rock lying below the Earth’s crust. They often erroneously equate this imaginary layer with the mantle, which is, in fact solid. Pupils also find it difficult to visualise that some molten rock can set below the Earth’s surface, to form intrusive igneous rocks. Level Either KS3 (11-14 year olds), as a simple demonstration of igneous activity , or can be extended to KS4 (14-16 year olds), with discussion of the structure of the Earth and the physical properties of its layers. It can also be related to plate tectonics. Time The demonstration itself takes about 10 minutes, with discussion to follow. Equipment and safety notes

• One 500ml or 600ml glass beaker • Red candle wax, about 1cm deep, previously melted and poured into the base of the

beaker • Washed sand, in a layer about 1cm deep above the wax • Very cold water to top up the beaker (about three-quarters full) • Bunsen burner, heat proof mat, tripod and gauze, gas supply (or bottled gas burner etc). • Safety screen • The activity is safer than it sounds - the only hazard is a cracked beaker, with some

localised spillage of hot wax: the water remains cold throughout. Activity Pupils watch attentively from behind the safety screen, whilst the teacher applies a strong Bunsen flame to the base of the beaker, on the tripod and gauze. They must not lose concentration, because the “eruption” often happens without much warning, other than an ominous crackling sound as the wax melts! The Bunsen is removed whilst there is still some wax left on the bottom of the beaker.


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Points to bring out (depending on the level of the pupils) • The sand and the water represent the crust of the Earth. • The wax layer represents a layer in the Earth below the crust. (The mantle). • The mantle is solid. It is being heated at a point source. • When the wax melts, it rises, because of its lower density. It represents molten rock,

known as magma. • Some of the wax rises rapidly to the surface, imitating a volcanic eruption. It is very

runny and spreads out evenly over the surface of the water (usually). This represents the way in which some lavas may cover huge areas, arising from fissure eruptions, which are quantitatively more important than the better known individual volcanoes.

• Some of the wax can be seen rising through ‘tubes’ of wax, which insulate it from the surrounding cold water and enable it to reach the surface. This happens in nature too.

• Some of the wax sets very quickly in the cold water, forming grotesque shapes. These represent intrusive igneous rocks. Once the wax has all set, the ‘lava layer’ may be removed and the water poured off, in order to study the shapes of the ‘intrusions’. This is equivalent to the removal of layers of rocks by weathering and erosion.

• Reference can be made to the geological map of the UK. Widespread sheets of lava form the Antrim plateau in Northern Ireland: masses of intrusive igneous rocks are shown as big red blobs in Devon and Cornwall, Southern Uplands of Scotland etc.

• Pupils can be challenged to say which aspects of the model are not consistent with the natural world. The most important one is that the surface eruption set very slowly, whilst the ‘intrusions’ set very quickly. In reality, the reverse would be true, because of the higher ambient temperatures at depth and the insulating properties of several kilometres of rock. Lavas may become solid within days, months or years, whereas a deep-seated intrusion of several tens of cubic kilometres may take millions of years to cool to the ambient temperature. Of course, the wax merely sets: it does not form crystals.

Possible extension

• At KS4, the model can be related to plate tectonic theory. • In reality, complete melting of rocks below ground is seldom achieved. Rocks partially

melt, and the minerals of lowest melting points are the ones which rise (they are also the least dense minerals). This can be shown by preparing a mixture of chopped wax and gravel in a container. When heated, in front of pupils, the wax melts, and rises, whilst the gravel does not. It is possible to do this at the same time as the volcano demonstration, but experience shows that glass beakers tend to be more susceptible to cracking!

• When students study the properties of seismic waves in the Earth, they will appreciate that the mantle is generally solid, with only about 5% of liquid, in between the crystals of the rocks. Localised heating, and/or reduction in pressure, lead to partial melting, but the magma chambers which form are only tens of kilometres across, not mantle wide.

• Studies of the chemistry of igneous rocks show that partial melting of rocks produces three main types of magma, depending upon the nature of the tectonic plate boundary.

Acknowledgements The original idea for the wax volcano model came from Mike Tuke and is described in his ‘Earth Science Activities and Demonstrations’, published by John Murray. Risk assessment Materials: Water, sand, candle wax – all non-toxic Risks: The water remains cold throughout, so poses no risk. A thin layer of wax is melted in a beaker. It could crack the beaker and exude onto the bench, but this is unlikely. If spectators are watching close to the beaker, a safety screen is advisable; viewing from a few feet away poses no risk. The presenter should wear eye protection.


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ACTIVITY 8: Deformation Purpose: To show how faulted rocks at outcrop can provide evidence of the size and direction of the forces which produced the fault. Notes: The apparatus and materials required are: transparent plastic box (e.g. chocolate box or component drawer); spatula or dessertspoon; tray; a piece of board to fit snugly into the box; 500g of dry fine sand; 25g of flour; a photograph of faulted rocks (optional). Only thin layers of flour are needed, sprinkled along the front of the box alone, in order to save flour and to allow the materials to be reused several times. Development of knowledge and understanding: Rocks frequently become fractured during their history, but school laboratory investigations on real rocks are difficult to carry out with any finesse. The activity described uses layers of fine sand and flour which behave like layers of rock. Pupils should appreciate that faulted rocks at the Earth's surface contain clues about the ancient pressures which deformed them. The near-horizontal faults produced by compressional pressures are called thrust faults. More steeply inclined faults are produced by tensional stresses and these can be formed in the same transparent box as in Demonstration 8, by putting the vertical board in the centre of the box, filling one side with sand and flour as before and moving the board gently away. Large scale pressures acting within the lithosphere are caused by plate tectonic movements. Where plates are converging, the compressional stresses produce near horizontal thrust faulting. Where plates diverge, the tensional stresses produce steeper faults, call normal faults.

Demonstration 8: Make your own folds and faults (This activity is based on ESTA’s “Earth’s Surface Features” in “The Science of the Earth 11-14” series.) Learning objective: To simulate the movements which produce faulting in rock structures. When pressures are applied to solid materials they may bend or break. When sands or sandstones bend, folds are produced; when they break, faults are formed. Find out what types of folds and faults are produced by compression by following these instructions.

1. Place the board vertically inside one end of the box. 2. Build up several thin layers of flour and sand. Do not fill it more than half-full. Spread the

flour along the front of the box only.


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3. Very carefully, push the vertical board across the box, so that it begins to compress the

layers. When you notice the layers beginning to bend, stop pushing the board. Hold the board upright and draw a scaled diagram of the result.

4. Continue pushing the layers with the board until the sand is about to overflow the box. Hold the board upright and draw a scaled diagram of the result.

5. Then add arrows to your diagram to show the directions of the forces which were acting whilst you compressed the layers with the board.

6. Are the layers still horizontal, or are they folded? 7. Did one set of layers slide over the rest? If you have been careful, you will have produced

a fault in which layers of rock are pushed up and over other layers. These types of faults are often nearly horizontal.

8. How could you use the same apparatus to find out what happens when sands and sandstones are stretched (put under tension)?


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The Dynamic Rock Cycle Workshop - Apparatus and Materials For each rock cycle specimen tray Photo or photocopy of exposed rocks and sedimentary sequences; small plastic bags of sand and soil; small specimens of: sandstone, mudstone, conglomerate; limestone; slate; schist; gneiss; marble; quartzite; granite; gabbro; basalt with vesicles. For 'The Rock Cycle' around the lab As above, only with larger specimens; 2 x 200ml clear measuring cylinders, red sand, white sand, dessertspoon. For the 'Dynamic Rock Cycle' Activities The following lists are intended to guide those gathering together one set of apparatus for each demonstration. Note: Where 'washed sand' is required, it can be prepared in a large sink by running a hose/tube for 10 minutes into a bucket half-full of sand, and allowing the clay particles to wash away. Fine sand can be sieved out from poorly sorted sand by running it dry through a kitchen sieve. Demonstration 1A: Weathering - A Physical Example Heat & cold: expendable granite chips about 7mm across; Bunsen; heat proof mat; 400ml beaker of cold water; eye protection; tongs. Demonstration 1B: Weathering - A Physical Example Freeze/thaw (exhibit only): 1 plastic container, with several different types of rock, previously soaked in water and repeatedly placed in & out of a freezer; another set up as above, only it is alternately wetted & dried. Demonstration 1C: Weathering - A Chemical Example 2 boiling tubes with bungs; deionised water; Universal indicator; drinking straw; eye protection; limestone chip 7mm or so across; a few grams of ground limestone (garden centre, or grind your own) Demonstration 2: Rock resistance Expendable rock specimens such as crumbly sandstone (sedimentary), chalk (sedimentary), granite (igneous), slate (metamorphic). Four pieces (each of about 50g) of each rock are needed. Alternatively, use locally available rocks of variable resistance. At least 4 plastic containers with wide necks and tops; a mechanic's file; emery paper; goggles; balance; tray; some dilute hydrochloric acid (0.5M) in a dropper bottle. Caution: corrosive. Demonstration 3: Deposition - in the Stream 1m length of plastic gutter (square section), fitted with end stops. (The lower end stop needs a slight ‘v’ shape filing in it to guide outlet water flow); 2m length of rubber tubing; clip to secure tubing to top of gutter; prop for top end of gutter; plastic sheet to protect bench; 1litre beaker or equivalent to catch overflow in sink; washed sand to fill upper 75% of length of gutter to within 2cm or so of rim; access to running water and sink. Demonstration 4: Sediments into rocks Plastic syringe (20cm³), with the nozzle cut off at the end of the barrel; tray; goggles; disposable cups & spoons; 250g of dry sand; 10g of powdered clay (allow a lump of clay to go hard, then file it to powder); 10g of plaster of Paris powder; salt, sugar; etc.; 3 samples of sandstones, 1 cemented by silica, 1 by calcite and 1 by iron compounds; water; apparatus for testing the strength of the pellets, e.g. file, variety of masses, heavy ball-bearings, dropper bottle of dilute hydrochloric acid (0.5M). Caution: corrosive.


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Demonstration 5: Detecting the distortion Modelling material (Plasticene); several cockle shells, or similar shells; 50g of plaster of Paris powder; disposable plastic cups; stirring rod; water. Demonstration 6: Fast or slow cooling: large or small crystals? Salol (phenyl salicylate), approximately 5g; boiling tube; 250cm³ beaker; 6 microscope slides; teat pipette; goggles; hand lens; hot water; access to a freezer; sheet of white paper; samples of igneous rocks of various grain sizes (e.g. granite, gabbro, rhyolite, basalt). Demonstration 7A: Lava in the laboratory A selection from below - exact requirements will depend on the nature of investigations undertaken. Treacle or syrup; Petri dishes or tiles with 'props' to allow tilting; spatulas or teaspoons and stirring rods; stopclock or watch; ruler; Bunsen burner, camping gas stove or hot water bath; tripod and gauze; 3 boiling tubes with bungs; thermometer; stand, clamps and bosses; teat pipette; syringe; sand; hot soapy water; test tube brushes and cloths; goggles. Demonstration 7B: Volcano in the lab One 500ml or 600ml glass beaker; coloured candle wax; clean sand; very cold water; Bunsen; heat proof mat; tripod; gauze; gas supply; eye protection. Demonstration 8: Make your own folds and faults Transparent plastic box (e.g. chocolate box or component drawer); spatula or dessertspoon; tray; a piece of board to fit snugly into the box; 500g of dry fine sand; 25g of flour; a photograph of faulted rocks (optional). Photocopies needed for this workshop Per participant: 'The Dynamic Rock Cycle' booklet Per group: Rock cycle diagram One set: Rock cycle products, processes and rocks labels OHT: The Rock Cycle Sources of worksheets used in ‘The Dynamic Rock Cycle’ Most of the worksheets used at the INSET are taken from "Earth Science for Secondary Teachers", published by the former National Curriculum Council in 1993. This is now out of print, but may still be available in schools. The ESTA equivalent worksheets listed for each activity are available to order from ESTA – see www.earthscienceeducation.com/suppliers/esta.htm for details. The candle wax demonstration is adapted from ‘Earth Science: activities and demonstrations’, by Mike Tuke, published by published by John Murray.


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Names of Common Rocks

Sedimentary Sedimentary rock – made of deposited sediment

• conglomerate (cemented pebbles) • sandstone (cemented sand) • mudstone (compressed mud) • shale (compressed mud in thin layers) • clay (compressed mud, but still soft) • limestone (made of calcium carbonate)

Metamorphic Regional metamorphic rock – rock formed from other rock by heat and pressure during mountain-building episodes

• slate (low grade, from mudstone • schist (medium grade, from mudstone) • gneiss (high grade, from mudstone) • marble (low to high grade, from limestone) • metaquartzite (low to high grade, from sandstone)

Thermal metamorphic rock – rock formed from other rock through baking by a nearby molten igneous rock (magma)

• hornfels (from mudstone) • marble (from limestone) • metaquartzite (from sandstone)

Igneous Extrusive igneous rock – from magma extruded from the Earth’s surface (flowing out or being blasted out)

• lava with gas holes (eg. fine grained, dark coloured basalt) Intrusive igneous rock – from magma intruded into the Earth’s crust that cools slowly

• granite (coarse grained, pale coloured, rich in Si, poor in Fe, Mg) • gabbro (coarse grained, dark coloured, rich in Fe, Mg, poor in Si)

Teaching Points of ESEU Workshop Activities: The Dynamic Rock Cycle

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Activity

Pattern (construction)

Challenge (cognitive

conflict)

Explanation of thinking

(metacognition)

Relevance (bridging)

Practical teaching points

1. Weathering

(heating, freezing and chemical)

• The more you heat

and cool it, the weaker it becomes

• Permeable rocks break down by freeze thaw

• Breath -> acid, limestone -> alkaline

• Many minerals vs

monomineralic rocks

• Vesicular basalt doesn’t break down fast

• Reasoning on conflict. Real

world? Where on Earth …? • Reasoning on conflict. Real

world? Where on Earth …? • Real world? Where on Earth

…?

• Takes place in deserts (high

diurnal range), rarely in UK • Takes place in areas that

freeze and thaw, ie not permanently frozen areas

• Going on outside the door • UK rocks mostly attacked by

chemical and biological weathering, physical limited

• Significant danger makes

this into a teacher demo • Needs preparation

beforehand by several cycles of freeze/thaw

2. Erosion and

transportation (rocks with shaker, file, acid, etc)

Toughest rocks are crystalline rocks. Weakest rocks are poorly cemented sedimentary rocks

Limestone crystalline? Tough rock reacts with acid (limestone) so doesn’t fit pattern – why?

Is the test fair? What environment does it simulate?

Hard rocks make hills and headlands (ref. LP3), soft rocks make bays and valleys. All the ups and downs and coastline ins and outs of the UK (and world) explained. When you are going uphill – what does this mean?

Pupils should shake all at the same time. Adding water adds an unnecessary complication

3. Deposition

(gutter)

Process (erosion, transport, deposition) depends on flow rate

How will grain size and/or grain density affect processes?

Three variables (at least) need to be taken into account.

Processes happen in puddles, ponds, seas and the oceans They result in grains sorted by size and density. Cross bedding gives flow direction, eg. Triassic river in the Stoke area flowing north

Difficult for many to see at once – so this may be a circus activity. Be wary of pupils spraying the lab with the rubber tubing

4. Compression

and cementation (syringes)

The tougher the gluing material, the tougher the ‘rock’

Which tests will produce the most effective results? Different tests produce different rankings – why?

Explanation of different rankings

Sandstone cannot be made from sand by compression – some form of glue is necessary. The tougher the ‘glue’ (cement) the tougher the rock – ref. to Activity 2.

Best results if left overnight. Do least destructive tests first.

Teaching Points of ESEU Workshop Activities: The Dynamic Rock Cycle

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5. Metamorphism

(squashed fossils)

Pressure directions can be deduced from type of deformation

Can the same effect be produced by tension as by compression?

What can be deduced from the direction and scale of deformation?

If fossils in N. Wales are compressed N-S by a quarter, then N Wales was compressed N-S by a quarter – what could have done this? (plate containing Scotland colliding with plate containing England)

• Deal with point in some

textbooks that metamorphic rocks don’t contain fossils. Wash out all containers.

6. Crystallisation

(Salol)

Smaller crystals = faster cooling – prediction form this

When it doesn’t work and why

Explanation of observations, ie. why does fast cooling cans smaller crystals?

Coarse igneous rocks cooled slowly (great thicknesses of insulation above) – many thousands of years. Crystals as big as classrooms have been found. Fine grained rocks crystallise quickly over days at the surface (lavas)

Don’t overhear the Salol – 50o is fine – otherwise supercooling more likely. Putting slides on top makes crystallisation easier to see – even on OHP. 2 phase practical used to give 2 chances of getting it right.

7. Extrusion

(treacle)

Viscosity effects of temperature, sand and water content

Slope should not be a variable

How can the changes be explained using the particle model?

Hot, crystal-free, water rich lavas produce flat volcanoes. Cool, crystal-rich, water-poor lava produce steep volcanoes. In steep volcanoes – lava usually crystallises in vent and causes great explosion (eg. describe Krakatoa). Pupils should be nowhere near when this happens.

Keep treacle in test tube (of same temperature) during temperature investigation. Get different groups to investigate different things.

8. Folding/folding

(Ferrero Rocher box)

Compression and tension produce different styles of faults

Similar things found in N. Wales with E-W axes. Explanation? Scotland hitting England and squeezing Wales. Gives some idea of the pressures involved.

Dry sand needed

Documents

Teaching the Dynamic Earth - GeoScience - Homegeoscience.msc.sa.edu.au/library/dynamic_rock_cycle.pdf · 2010. 6. 5. · Aspects of Unit 9G Environmental Chemistry are also dealt