QCA unit 8G - rocks and weathering
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Lesson 1 - What are rocks made of?
Aims: By the end of the lesson, students should be aware that rocks are usually made from a mixture of mineral grains, two main textures can be recognised and how to use experimental evidence and models to explain the texture of different rocks. Development of observational skills.
Outcomes: Students should be able to describe rocks as containing different grains/crystals which fit together, explain that some grain shapes can interlock whilst others can not and relate evidence about porosity to the way that grains fit together. Annotated diagrams to illustrate the two textures and explanation of the textures.
Needs: Small samples of granite and sandstone, plastic beakers, hand lenses, centicubes, polystyrene balls (or table tennis balls), accurate balances, small plastic beakers X2 (to stand on the balances so they do not become wet).
Possible assessment indicators:
Level 4 - simple description and vague diagram of each texture
Level 5 - accurate description plus some explanation of the textures and clear diagrams
Level 6 - as level 5 plus coherent explanation that relates the textures to observations.
Intro: State aims of lesson in terms of outcomes. Ask students what rocks are like, briefly discuss their comments. (No more than 5 min)
Exploring the textures of different rocks. Explain what texture is. The texture of a rock is the size, shape, and arrangement of the grains or crystals in the rock. Give examples for arrangement - two basic textures, either interlocking or have gaps between them. Model these using centicubes and polystyrene balls. Introduce the terms pore and porosity. Show diagrams on OHP
. Ask students how we could investigate the textures of rocks in a practical way - develop the idea of looking and immersion in water. What exactly will we look for? (Gaps using the hand lens, bubbles when the rock is placed in water and an increase in mass as the water soaks into the pores). Remind students about use of the balance. (No more than 10 min)
Activity: Students put title of "Rock Textures" in their exercise books, explain in own words what texture means in the context of rocks, draws two pictures to illustrate the theory of two textures and attempts to draw the real textures of the observed rocks. Ask them to label and explain what they perceive as the key features of the rocks that they have observed and ask them to give evidence to say back up their labelling. (20 min max plus informal homework time)
Close: Several students to state one thing that they have learnt from this lesson.
Lesson 2 - How does rain and temperature cause rocks to weather?
Aims: By the end of the lesson, students should be aware that rocks at the Earth's surface can be damages by the freezing and thawing of water in cracks, by the repeated heating and cooling of rocks and why these things happen.
Outcomes: A story board describing and explaining freeze-thaw and heating-cooling weathering. Students should be able to explain that water absorbed by a rock expands on freezing and that the forces generated are considerable and may cause the rock to crack, that repeated heating and cooling causes stress on rocks that can lead to fragmentation and to describe and justify conditions in which these types of weathering are likely to take place.
Needs: Large beaker, metal tongs, piece of granite
Possible assessment indicators:
Level 4 - able to describe the changes.
Level 5 - as level 4 but can begin to explain that expansion and contraction cause the damage.
Level 6 - as level 5 but can explain in terms of the forces.
Differentiation: Sheet for less able to cut, sequence and stick. Extension - information about the behaviour of water at and around its freezing point.
Intro: Several students give one thing that they learnt in the previous lesson. State aims of this lesson, i.e. by the end, they should be able to describe and explain how water and changes in temperature causes rock to break into fragments. (5 min max)
Activity: Demonstrate the repeated heating and cooling of a small piece of granite. Risk assessment - danger from rock shattering, use a safety screen and issue safety goggles. Summarise what is happening by linking to the heating and cooling topic i.e. large forces are generated by expansion and contraction. Discuss what conditions are most likely to create this type of weathering - answer is parts of the world in which there is a large temperature range over a short time scale e.g. deserts. (about 15 min)
Activity: Show a large piece of sandstone, ask what will happen to the rock when it rains. Focus on the pores filling with water. If the rock were in a mountainous area, what would happen to the water? Freeze. What happens to the volume of water when it freezes? Increases. Evidence? Why is that odd? Most things contract when cooled. What is going to happen to the grains of the sandstone and why? Get pushed apart because of the force generated by the expanding ice. Extend to cracks and thus to the weathering of mountaintops. (5-10 min)
Activity: Students produce a storyboard using an appropriate title to explain how a piece of rock is weathered in a desert and how bits of rock fall off mountaintops. Sometime during the task, set the homework to research how water creates caves, stalactites and stalagmites. Produce a magazine article about it. Use ICT if possible but make sure the work is in your own words. (Max 20 min)
Close: Pupils to give definitions of texture, porous, freeze-thaw and explanations of why some rocks get heavier in the rain and how the two above types of weathering take place. (5 min)
Lesson 3 - What happens to weathered pieces of rock?
Aims: By the end of the lesson, students should be aware that rock fragments become sediment grains which can be transported by water currents and deposited where the flow is slow (has less energy).
Outcomes: Sentences completed and copied into the correct placed on a diagram. Extension - cartoon to illustrate transport of sediments. Students should be able to make predictions about the differences between sediments, in terms of deposition and size of particles, at different points along a river.
Needs: Square section guttering, mixed sizes of sediment (clay, sand, gravel), 600ml beaker for pouring water to form river, large glass trough to collect sediment at bottom of guttering, bucket, pritt, scissors.
Possible assessment indicators:
Level 4 - Can describe that sediment is moved along and deposited by rivers.
Level 5 - Can describe the pattern of movement and deposition.
Level 6 - Can start to relate the energy of the water to the ability of the river to carry and deposit sediment particles. Can produce a cartoon that correctly shows the concepts of the lesson.
Intro: Review weathering, either by asking students for one thing they learnt in the previous lesson or by direct questioning. State the aims of this lesson. (5 min max)
Activity: Modelling a river using guttering and mixture of sand, soil and gravel. Illustrate that faster moving water scours the sediment more effectively, link to the amount of kinetic energy (review knowledge of kinetic energy) the water has. Discuss the ways in which the sediment is transported with questions such as:
Does it dissolve? No. How do students know? Solutions are transparent
Does it roll along?
How else is it carried?
Arrive at the conclusions that particles are transported as a suspension and rolled along, depending on their sizes. Save the glass trough that is used to collect the outwash from the model river for use next lesson. (up to 15 min)
Activity: Extend through discussion to a real river. Consider each stage of maturity and bends/deltas.
Youthful stage - steep, lots of KE, carries all sorts of size from boulder downwards.
Middle age - not so steep, less KE so will carry gravel and smaller, not boulders unless in spate (explain spate)
Old age - meanders, slow flow, low KE so will only carry very small particles.
Bends - slowest part of river is the outside of a bend, get sand banks building up here as there is not enough energy to carry it along.
What happens as rivers enter lakes or the sea? Slows down even more so it drops the sediment (relate again to the kinetic energy of the water) except for the very smallest particles called silt. These only need a little energy to keep them on the move. (5 min)
Close: Students to say one thing that they have learnt about the transport of sediments or weathering from previous lessons.
Lesson 4 - What happens to the weathered pieces of rock as they are transported and when they are deposited?
Aims: By the end of the lesson, students should be aware that weathered particles are denuded by abrasion as they are transported, that water contains dissolved salts that can bind sediments together if the water evaporates. Pressure can drive out water and bind the particles together to form rocks.
Outcomes: Graph of the reduction in mass and diagrams showing the shape at the start and finish of the shaking experiment.
Needs: Plaster cubes, containers to shake the cubes in, balances and beakers to put on the balances, several evaporating basins, sand, sugary water, brine.
Assessment: Informal through questioning of students in lesson.
Intro: Quick quiz at back of exercise book about weathering and transport of sediments. (5 min)
Pose question - what happens to the size of the particles that are transported by rivers? How could we use the available apparatus to obtain evidence for this? Develop the details for the practical. Focus also on the gathering of data that is suitable for graph plotting i.e. measuring the changes in mass of the cubes. Carry out practical.
Collect plaster cube, identify it as yours.
Note the mass.
Prepare the graph (guidance on the board).
Groups of 3-4. Put groups cubes in the container. Lid on.
First person shakes the box 100 times.
Risk assessment - safety goggles and elastic band round the box to prevent cubes from flying out and damaging eyes.
Each person reweighs cube, plots new mass on the graph.
Continue until either the cubes are too small to recognise or until everyone has had two goes.
Waste into bin. (20 min)
Groups decide on conclusions. When is the greatest amount of mass `lost' per shake? Why does this happen? Was the test fair? Are your results reliable? How do you know? (5 min)
Discuss the conclusions. (5 min)
Round front. Context - what happens to weathered bits of rock when they have been deposited? Show the trough of material used for the river demo last time. note the layers where sediment has settled.
Hold up the brine. What is in this container? Develop idea that there could be something dissolved in the water. Evaporate water to illustrate this. Add some sand to tap water. Evaporate this to show the sand grains don't really stick together. Repeat using the sugary water to show that the dissolved salts can bind the sand grains. (15 min)
Now consider the layers in the trough again. What would happen if the water evaporated? Then develop the idea of pressure increasing as more layers are added. Include sea shells in illustration of fossil formation. Come to idea of water being squeezed out. Stuff dissolved in water gets left behind and binds the sediment particles together. (5 min)
Ask one question. Student who answers, picks a "victim" and asks them a question etc. (2 min)
Lesson 5 - sedimentary rocks.
Aims: Sedimentary layers are as a result of distinct episodes of sedimentation and that the grains become cemented together by materials that were dissolved in the water. Pressure squeezes the water out of layers of sediments. Remains of dead organisms can accumulate with the sediments to form fossils. Use evidence from a sequence of rock layers to suggest a sequence of events over time.
Outcomes: Pupils will be able to describe how sediments are changed into rocks by burial and compression. They should also be able to sequence diagrams describing events leading to the formation of sedimentary layers in a cliff.
Needs: Worksheet to support the description of the formation of rocks, cartoon diagrams sheets for sequencing the events relating to the rock layers in a cliff. Pritt, scissors.
Level 4 - able to sequence the sentences with a little help. Require a lot of help to interpret the cliff diagram.
Level 5 - sequence the sentences with no help, need a little help to interpret the cliff section
Level 6 - need no help to do either task correctly
Differentiation: Provision of worksheets for support.
Intro: Last lesson I learned … Pupils write down some points that they remember from the previous lesson. (5 min)
Activity: Review formation of sedimentary rocks (deposition, increased burial, compression, fossils, removal of water and cementation) (10 min)
Pupils make a set of notes e.g. story board, bullet points with diagrams to explain how sedimentary rocks, including fossils were formed. Support sheets
. (20 min)
Activity and homework: Worksheet - Information plus diagram describing the sequence of events leading to the layers formed in a cliff (2 versions, easier and more challenging)
Close: Pupils to state on thing that they have learnt in the lesson. (5 min)
Extension work for the lesson - different types of sedimentary rock from appropriate book (notes and diagrams).