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Rock stock

The key to teaching earth science effectively is plenty of practical work. Ray Oliver shares his store of fun ideas

When anxious science departments sit round a table dividing up the teaching syllabus for the coming year, someone must draw the short straw. This straw often bears the legend "earth science".

The problem is that few science teachers have direct experience of geology and therefore doubt their ability to deliver worthwhile practical activities. Organising earth science investigations, the famous Sc1, is more daunting still. This attitude overlooks the fun that can be had teaching earth science, and the overlap of content with mainstream science and with geography.

Talking to the geography department may lead to combined practical work, including field trips. The school site and immediate local area will provide examples of crystals under your feet (granite kerbstones), fossils (limestone buildings and paving) and retired lava (black basalt paving blocks). Even garden centres display piles of rock conveniently identified for the amateur rockhound.

The key to teaching earth science successfully must be to incorporate plenty of practical activities, for both key stages 3 and 4. Try some more offbeat experiments but remember, you still need to make a risk-assessment even if the chemical being investigated is jelly.

Geology in the kettle In hard water areas the water supply contains calcium and magnesium minerals. When the water is boiled in the kettle or evaporates around taps, the dissolved minerals reappear as limescale. Link these effects to the natural formation of stalactites and stalagmites in cave systems. Students can compare the effects of leaving pieces of chalk or limestone (calcium carbonate) in distilled water and in acidic soda water. The rock starts to dissolve in acidic water, as with swallow holes and caves formed by naturally acidic rain water containing carbon dioxide from the air.

Volcanic events This smouldering demonstration shows how hot molten material (magma) can burst out at the surface, and escape as a stream of lava. Use a very large sheet of blotting paper to draw the classic outline shape of a volcano. Make a very strong solution of potassium nitrate. Using a paint brush, paint the track of the lava from within the volcano. When dry, this becomes invisible. Clamp the paper vertically and apply a small flame to the base of the lava. The trail of lava shows up as the paper glows and smoulders, just like a firework touch-paper on November 5.

Jelly works For those of a less incendiary nature, jelly can be used to model geological changes. The top of a new lava flow often contains gas bubbles as fluids escape into the air. Place some seltzer tablets at the base of a clear plastic box. Add just enough water to start them fizzing and immediately pour over a layer of partly set jelly representing the lava flow. As the bubbles rise through the glutinous lava, they demonstrate how this type of porous volcanic rock can form. Partly set jelly is an ideal material to simulate lava flows or mudslides on steep slopes. Fix graph paper to a board representing the sloping ground; in this way the students can get quantitative data for their investigations. Variables can include the angle of slope, the viscosity of the jelly and, for the brave, the temperature of the jelly lava. Students can estimate the viscosity of the lava by dropping steel ball bearings into a jar of jelly and timing the descent before using a magnet to retrieve the bearing.

Jelly magnets When molten rocks solidify, any magnetic material within them will line up with the Earth's magnetic field and become fixed permanently in position. These frozen magnetic markers provide evidence for changes to the Earth's magnetic field over time, and in support of the theory of continental drift (palaeomagnetism). Mix some iron filings with partly set jelly ina shallow dish. Place a bar magnet on the overhead projector with the dish on top. Show how moving the magnet - the Earth's field - moves the iron particles within the jelly rock.

Once the jelly rock has set solid, the magnetic markers remain pointing in one direction. They record the direction of the Earth's field on the day the rock formed.

Metamorphic rocks The formation of metamorphic rocks can be simulated using temperature strips (fever strips). When hot igneous rocks move underground they can bake and alter the existing rocks, turning them into new metamorphic rocks, for example limestone to marble. There are bands of changed rocks around the heat source, known as a metamorphic aureole. This is how to show the effect. Place a metal tray on wooden blocks leaving room for a hair-dryer underneath. Place some temperature strips at regular intervals on the tray, starting directly above the hair-dryer. Switch on and monitor the spread of the heat (metamorphism). Tabulate the temperatures and distances from the heat source. An analogy for the changes to rocks as a result of metamorphism might be the change from biscuit mix to the hard, brittle product after leaving the oven.

Icy experiments Try using ice to simulate geological changes. Fill an empty aluminium drinks can to the brim with tap water, together with a filled and sealed plastic bottle. After some hours in the freezer the expansion of water when it freezes, and the associated strong forces, will be obvious. Link this to the ice-shattering of rocks, one of the processes that convert rocks into soils. Make a large slab of coloured ice by freezing a mixture of water and food dye in a tray. Break the slab into pieces representing different ancient continents. Float the continents, originally all in contact, on water in a large container. When the water is heated from the base, convection currents will cause the ice continents to drift apart. Link this experiment to the theory of continental drift and convection currents within the Earth's mantle.

Sun cracks Although students will be familiar with fossils, they may not realise how much hidden evidence rocks contain. When a slab of rock in a quarry shows both fossil footprints and sun cracks, but no fossils, we can still deduce a lot about the ancient environment. Mix a thick slurry of mud and water in a shallow tray. Make the mix thick enough to be able to mark the surface with the shapes of birds' feet or animal footprints. Use a desk lamp or infra-red heater to simulate the effect of the sun. Watch as a polygonal pattern of suncracks appears on the surface of the mud as it contracts. Pour a layer of plaster of Paris on top and leave to set. When lifted out, the underside of the plaster rock retains trace fossils, the sun cracks and footprints, just as with a real sedimentary rock.

Ray Oliver was until recently head of science at The Astley Cooper School, Hemel Hempstead, and is now science publisher for Folens


Science of the Earth, KS34 units. From the Earth Science Teachers Association. Contact: GeoSupplies Ltd, 16 Station Road, Chapeltown, Sheffield S3 5 2X1L.

Down to Earth, quarterly newspaper with ideas, resources and reviews, 49 Station Road, Chapeltown, Sheffield S35 2XE. Tel: 0114 245 5746. Aluminium - A Modem Metal. Extensive resource with much earth science content, from ALFED, Broadway House, Calthorpe Road, Five Ways, Birmingham, B15 ITN.

Holiday Geology Guides, British Geological Survey,Keyworth, Nottingham NG12 5GG.

Inside Science, supplements in the New Scientist magazine Petroleum Geology, RPEducation Service, Visits: Earth Centre, Denaby Main, Doncaster DN12 4EA. National Stone Centre, Porter Lane, Wirksworth, Derbyshire DE4 4LS.

In-service training: UK Offshore Operators Association LtdKeele University. Contact: First Floor, 30 Buckingham Gate, London SWIE 6NX.

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