SCIENCE FOR PRIMARY TEACHERS - Open University...Susan Tresman (co-director, Science for Primary...

PS548 SCIENCE FOR PRIMARY TEACHERS

TheOpen University

STUDY COMMENTARY FOR UNITS 5-6: INTO THE EARTH: EARTHQUAKES. SEISMOLOGY AND THE EARTH'S

MAGNETISM

AllAlNMENT TARGETS ADDRESSED IN UNITS fid: AT6, AT9 AND AT1 1 3

COMMENTARY GUIDE 7

1 AN INTRODUCTION TO EARTH SCIENCES 7 AT6: levels 1 to 4; AT9: levels 3 to 5 7 Study notes 7 Teaching notes 7 Key points 13

2 EARTHQUAKE WAVES: WHAT ARE THEY AND HOW DO THEY TRAVEL? 13 AT9: level 5 13 Study notes 13 Teaching notes 14

lnvestigation 1 : Detecting vibrations 14 Key points 15

3 THE EARTH AS A MAGNET 15 AT 1 1 : level 2 15 Study notes 15 Teaching notes 16

Investigation 2: Magnetic field 17 lnvestigation 3: What is a compass? 18 lnvestigation 4: Does a compass always point towards north? 19 lnvestigation 5: Making a compass 19 lnvestigation 6: Making a model of the magnetic Earth 20 Investigation 7: Navigation 21

Key points

4 MODELLING THE EARTH'S INTERIOR AT 6: levels 1 to 4; AT9: levels 3 and 5 Study notes Teaching notes

lnvestigation 8: Building your own volcano lnvestigation 9: Making crystals

Key points

5 ROCK'MAGNETISM (TV PROGRAMME) AT1 1 : levels 1 to 3 Study notes Teaching notes Key points

6 SOME USES OF MAGNETIC AND SEISMIC TECHNIQUES Study notes Teaching notes Key point

DISCUSSION TOPICS

RESOURCES

QUESTIONS

ACKNOWLEDGEMENT

NOTES

SCIENCE FOR PRIMARY TEACHERS: CONTRIBUTORS

Barry Alcock (human biology, Nene College, Northamptonshire) Fiona Allen (reader, Hillside Infants School, Northwood, Middlesex) Bob Allgrove (chemistry, Chichester College of Technology) Matthew Baird (advisory teacher, London Borough of Enfield) Steven Baker (Earth sciences, Droitwich High School) Chris Brown (Earth sciences, consultant author) Sue Browning (advisory teacher, EPSAT, Essex) Andrew Coleman (editor) Hazel Coleman (editor) Chris Culham (advisory teacher, EPSAT, Essex) Carolyn Dale (advisory teacher, Buckinghamshire) Myra Ellis (secretary, electronic publishing, The Open University) Graham Farmelo (physics, The Open University) Stuart Freake (physics, The Open University) David Gamble (county adviser, science, Buckinghamshire) Jack Gill (senior science inspector, Essex) Jackie Hardie (adviser, London Borough of Enfield) Linda Hodgkinson (co-director, Science for Primary Teachers, The Open University) Barbara Hodgson (IET, The Open University) Anne Jones (deputy headteacher, Simpson Combined School, Milton Keynes) Hilary MacQueen (biology, consultant author) Baird McClellan (consultant author) Catherine Millett (chemistry, consultant author) Peter Morrod (chemistry, The Open University) Shelley Nott (illustrator, En-igrna Design) Katharine Pindar (information officer, The Open University) Jane Savage (Institute of Education, University of London) David Sayers (Science INSET co-ordinator, North London Science Centre) Freda Solomon (advisory teacher, London Borough of Enfield) Valda Stevens (biology, consultant author) David Sumner (physics, Tarragon Press) Liz Swinbank (physics, consultant author) Margaret Swithenby (biology, The Open University) Peter Taylor (chemistry, The Open University) Jeff Thomas (biology, The Open University) Susan Tresman (co-director, Science for Primary Teachers, The Open University) Liz Whitelegg (academic liaison adviser, The Open University) Margaret Williams (advisory teacher, Buckinghamshire) Geoff Yarwood (electronic publishing, The Open University)

The Pilot Project for Science for Primary Teachers was made possible by funding from the Department of Education and Science and from National Power plc and Nuclear Electric plc.

The Open University, Walton Hall, Milton Keynes MK7 6AA. First published 1990. Copyright O 1990 The Open University. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, without permission in writing from the publisher or a licence from the Copyright Licensing Agency Limited. Details of such licences (for reprographic reproduction) may be obtained from the Copyright Licensing Agency Ltd., 33- 34 Alfred Place, London WC 1 E 7DP. Printed in the United Kingdom by H. Charlesworth & Co. Ltd, Huddersfield. Further information on this and other Open University courses may be obtained from the Learning Materials Sales Office, The Open University, P.O. Box 188, Walton Hall, Milton Keynes MK7 6DH. ISBN 0 7492 5035 6 1.1

STUDY COMMENTARY FOR UNITS 56

ATTAINMENT TARGET ADDRESSED IN UNITS 5-6

AllAlNMENT TARGET 6: TYPES AND USES OF MATERIALS Pupils should develop their knowledge and understanding of the properties of materials and the way properties of materials determine their uses and form the basis for their classification.

Key Programme of study Level Statement of attainment stage

1 Children should collect, and find similarities Pupils should and differences in, a variety of everyday materials, natural and manufactured, including 1 a be able to describe familiar and unfamiliar cooking ingredients, rocks, air, water and objects in terms of simple properties, for other liquids. They should work with and example shape, colour, texture, and describe change some of these materials by simple how they behave when they are, for example, processes such as dissolving, squashing, squashed and stretched

and transparency, in the characteristics of materials

b be able to group materials according to their characteristics

c know that heating and cooling materials can cause them to melt or solidify or change permanently

Children should work with a number of different everyday materials, grouping them according to their characteristics, similarities and differences. Using secondary sources, they should explore their origins and how materials are used in construction. Properties, such as mass ('weight'), volume, strength, hardness, flexibility, compressibility and solubility should be investigated and measured. Children should explore chemical change in a number of everyday materials, such as mixing plaster of Paris, making concrete and firing clay. They should find out the common use of materials and relate the use to the properties which they have investigated, such as changes brought about by heating and cooling. They should learn about the dangers associated with the use of everyday materials, such as bleach and hot oil.

3 a know that some materials occur naturally while many are made from raw materials

b be able to list the similarities and differences in a variety of everyday materials

4 a be able to make comparisons between materials on the basis of simple properties, strength, hardness, flexibility and solubility

b be able to relate knowledge of these properties to the everyday use of materials

c know that solids and liquids have 'weight' which can be measured and, also, occupy a definite volume which can be measured

d understand the sequence of changes of state that results from heating or cooling ,

e be able to classify materials into solids, liquids and gases on the basis of their properties

5 a know that gases have 'weight'

b be able to classify aqueous solutions as acidic, alkaline or neutral, by using indicators

c be able to give an account of the various techniques for separating and purifying mixtures

SCIENCE FOR PRIMARY TEACHERS

AllAlNMENT TARGET 9: EARTH AND ATMOSPHERE Pupils should develop their knowledge and understanding of the structure and main features of the Earth, the atmosphere and their changes over time.

Key Programme of study Level Statement of attainment stage

1 Children should collect, and find differences and similarities in, natural materials found in their locality, including rocks and soil. They should compare samples with those represented or described at second hand. They should observe and record the changes in the weather and relate these to their everyday activities.

Children should investigate natural materials (rocks, minerals, soils), should sort them according to simple criteria, and relate them to their uses and origins, -using books and other sources. They should be aware of local distributions of some types of natural materials (sands, soils, rocks). They should observe, through urban or rural fieldwork, how weather affects natural materials (including plants) in their surroundings and how soil develops. They should also consider the major geological events which change the surface of the Earth. They should have the opportunity to make regular, quantitative observations and keep records of the weather and the seasons of the year.

Pupils should

know that there is a variety of weather conditions

be able to describe changes in the weather

know that there are patterns in the weather which are related to seasonal changes

know that the weather has a powerful effect on people's lives

be able to record the weather over a period of time, in words, drawings and charts or other forms of communication

be able to sort natural materials into broad groups according to observable features

be able to describe from their observations some of the effects of weathering on buildings and on the landscape

know that air is all around us

understand how weathering of rocks leads to the formation of different types of soil

be able to give an account of an investigation of some natural material (rock or soil)

be able to understand and interpret common meteorological symbols as used in the media

be able to measure temperature, rainfall, wind speed and direction; be able to explain that wind is air in motion

know that climate determines the success of agriculture and understand the impact of occasional catastrophic events

know that landscapes are formed by a number of agents including Earth movements, weathering, erosion and deposition, and that these act over different time-scales

be able to explain how earthquakes and volcanoes are associated with the formation of landforms

be able to explain the water cycle

- STUDY COMMENTARY FOR UNITS 54

AllAlNMENT TARGET 1 1 : ELECTRICITY AND MAGNETISM Pupils should develop their knowledge and understanding of electric and electromagnetic effects in simple circuits, electric devices and domestic appliances.

Key Programme of study stage

Level Statement of attainment

1 Children should be made aware of some uses of electricity in the classroom and the dangers of misuse. They should experience play activities with a variety of magnetic materials and investigate their effects on a range of materials and for a variety of uses. They should explore the Earth's magnetic field using a compass. They should experience simple activities using bulbs, buzzers, batteries and wires.

2 Children should have the opportunity to construct simple circuits. They should investigate the effects of using different components, of varying the flows of electricity in a circuit and the heating and magnetic effects. They should learn how to record the construction details of a circuit by drawings and diagrams. They should learn about the dangers associated with the use of mains electricity through research of appropriate sources. They should investigate the properties of magnetic and non-magnetic materials. They should begin to investigate simple electronic circuits for measuring, switching and control.

Pupils should

1 a know that many household appliances use electricity but that misuse could be dangerous

2 a know that magnets attract certain materials but not others and can repel each other

b understand the danger associated with the use of electricity, and know appropriate safety measures

3 a know that some materials conduct electricity well while others do not

b understand that a complete circuit is needed for an electrical device, such as a bulb or buzzer, to work

4 a be able to construct simple electrical circuits

5 a be able to describe and record diagrammatically simple electrical circuits that they have made

b be able to vary the flow of electricity in a simple circuit and observe the effects


TABLE 1 Levels of the attainment targets covered in Units 5-6

ATs 1 2 3

Level 5

l e l l l l l l l l l l l l l l l Note: a, b, c, etc. refer to the statements of attainment. For the complete statements, please see pp. 3 to 5.

STUDY COMMENTARY FOR UNITS 5d

COMMENTARY GUIDE This Study Commentary is worth reading carefully as it highlights the main components of this double Unit and sets the contents in context in relation to S 102 as a whole.

The suggestion in the Study Guide that you should have your rock samples and the World Ocean Floor map to hand during the whole of your study of Units 5 to 8 (and indeed later on for Units 27 to 29) is a very good one.

In teaching, there are many applications for skills and knowledge related to Earth sciences that can usefully be integrated into a variety of topic work, for example work on 'Natural hazards', 'Buildings' and 'The Earth beneath our feet'.

The work on rocks and materials that is associated with these Units is useful in developing and reinforcing the skills set out in AT1, such as observing, describing and sorting.

1 AN INTRODUCTION TO EARTH SCIENCES Main attainment targets and levels addressed in Section 1: AT6: levels 1 to 4; AT9: levels 3 to 5

STUDY NOTES This Section starts by pointing out that 'Earth sciences' and 'geology' are not the same thing. Many of you may have been expecting Units 5 to 8 and 27 to 29 to deal with 'traditional geology' and cover such things as rocks and fossils. Indeed there is much geology in them, but in Units 5-6 you will be dealing mainly with the ideas of geophysics, and the processes of science that were introduced in Units 1 and 2, in order to develop a complex model of the interior of the Earth. This may appear to be a somewhat daunting prospect at first sight. However, you will find as you read this Study Commentary that you do not need to get too involved with the mathematical interpretations and explanations of the model. Concentrate on what the geophysics can tell us about the Earth and its internal structure.

You should study this first Section carefully as it introduces you to some important features of the Earth. The AV sequence 'Rocks and rock textures' is important and useful, and guides you through an initial examination of some common rocks and their formation.

Sections 1.5 to 1.7 introduce earthquakes and their effects. How a seismometer works is dealt with in Section 1.7. Scan this Section quickly since all you need to know is that seismometers are instruments used to record an earthquake and determine its location.

TEACHING NOTES This Section includes much important material that can be used extensively in the classroom. Children find much to interest them in the natural environment, so if you base your work on .their local surroundings and build on their experiences, you can ensure that activities involving Earth sciences are both rewarding and enjoyable. Many topics within Earth sciences can be readily integrated with other science disciplines as well as with other areas of the curriculum. As you work through these Units you will recognize the potential of including Earth sciences work in a variety of topics.

Work in Section 1.3.2 'Rocks and rock textures' is relevant to AT6, levels 1 to 4, and AT9, levels 2 and 3, but perhaps more important is that by doing work


on rocks children can develop the skills of observation, description, sorting and classifying, and, perhaps later, interpretation.

The skills of observation and discussion are important ones to develop because they are frequently needed in work involving the natural environment. Even very young children can be taught to observe carefully and describe what they see. From key stage 1 to 2 the children are expected gradually to refine their observations and develop the skills of comparing and sorting; work on the natural environment will enable them to do this.

Even the youngest children come to school with a wealth of experience relating to rocks, stones, sand and soil that they have gained during play activities. It is your task to develop the appropriate skills so that the children can make sense of their observations and experiences and ultimately learn something about the origin of the rocks that we find on Earth.

It is hard to resist making a collection of pebbles while on holiday at the seaside; children are attracted by the variety of pretty colours, their smoothness and the different shapes and sizes. A pebble collection can be an ideal starting- point for work on rocks, giving rise to such questions as:

Are all the stones from the beach the same?

What seems to happen to the colours when the pebbles are dry? Why?

How many different colours can be identified?

Do any of the pebbles have holes in them?

Look for those that have a ridge or band of another colour. Can you pick these out with your eyes shut? Why?

Which pebbles can you rub bits off?

Are there any which sparkle?

Which ones roll best? How can we find out?

Questions such as these will begin to develop children's observation skills and raise their awareness of the wide variety of rocks found on the Earth's surface. Simple sorting activities-perhaps developing and using a key-can lead on from this work, such as grouping together pebbles with similar features, and simple investigations can be carried out, for example investigating how heaviness relates to size. (This could form the beginnings of investigative work on density.)

More exciting observations can be made if the larger pebbles can be broken in half to reveal differences in colour and texture. (Note: A geological hammer and safety goggles are essential here.)

The pebbles from the beach can be compared with stones that children have collected from their own gardens or immediate environs, or better still, with stones and rock samples from different parts of the country or the world. You could ask each child to choose a stone or pebhle and describe it in sufficient detail for another child to be able to identify the chosen stone or pebble. Encourage the children to bring back rock samples from holidays, visits and so on, so that you can build up a collection, and they can continue to develop and refine their classification keys.

Get the children to look carefully at some common rock samples, such as granite, sandstone and limestone, and encourage them to describe, in words or drawings or both, exactly what they can see. A hand lens or magnifying glass is useful for this exercise. The children will already be familiar with the idea that many kinds of rock are found on the surface of the Earth; the next stage is to attempt to sort or classify some of these rocks. One way to do this is to help them identify rock 'texture', that is, is the rock made up of tiny particles stuck together, or is it made up of an interlocking mosaic of crystals? Older children can be introduced to the correct terminology for describing what they see, and can be helped to discover which of the rocks are crystalline (igneous) and which are fragmental (sedimentary).


A suggested method of introducing children to the basic principles of rock identification is given below.

ROCK IDENTIFICATION As we have seen, the study of rocks provides opportunities for children to develop skills such as observation, analysis, description and, later, simple interpretation. Rocks can also be used as a means of developing investigatory and problem-solving skills. For rocks to be used in this way, children need to be able to identify them in such a way that the name given to a rock later provides a deeper understanding of the relationship of that rock to the origins and characteristics of rocks in general.

You can help children to identify rocks successfully by guiding them through a series of carefully organized stages such as the following.

Observation and description

All rock identification starts with observation, and children should be given plenty of experience in handling and describing the characteristics of a variety of rock samples. During these activities you can gradually introduce them to concepts that will enable them to distinguish between major rock groups: for example the presence of fossils, and whether the rock is made up of crystals, grains, particles or fragments. They also need to be given the correct vocabulary to describe specific features, such as 'layers', 'banding', 'rounded' or 'hgular'.-A combination of practical activities involving observation, description, comparison and simple experimentation will enable children to understand their own ideas about rocks and test out new ideas. The assignments and work cards produced by the Schools Council Environmental Studies 5-13 Project (see the Resources Section at the end of this Study Commentary) offer many activities and illustrations that focus children's attention on the varieties of colour, composition, hardness, mass, feel, smell and porosity displayed by rocks. Children's understanding of these concepts can be assessed through work- selection activities, and at this stage you should also encourage them to illustrate and make up their own names for individual rocks.

Classifying rocks

Following on from this observational work, ask the children to classify a variety of rocks into a number of subgroups using whatever criteria they choose. Encourage them to record their classifications, together with the criteria, in an appropriate way.

Speculating about the origins of rocks

Ask the children to formulate their own hypotheses about the processes of rock formation from the appearance of given rock hand specimens. Make sure you choose rocks that have clearly different characteristics, for example rocks that contain fossil shells, pebbles, sand or crystals. The Environmental Studies 5-13 Project describes various classroom experiments that can make ideas about the origins of rocks more accessible to young children. Speculating about how rocks are made is a good preparation for the concepts of igneous, sedimentary and metamorphic rocks.

Distinguishing between crystalline and fragmental rocks

The ability to make this distinction is fundamental to rock identification and classification. Thus, once the children have become familiar with the terminology through the above activities, they can practise distinguishing between different types of rock by classifying them into groups of rocks that are made up of crystals (crystalline) and rocks that are made up of fragments or grains (fragmental). At all times, especially for rocks with a fine-grained texture,


the use of a hand lens or microscope should be encouraged. (Do ensure that the children use the hand lens correctly-see the AV sequence 'Rocks and rock textures' in Units 5-6.)

Classifying different types of crystalline rocks

Once the children can identify crystalline rocks, ask them to think about the best ways of subdividing a variety of types of crystalline rocks into different groups. This should give you plenty of opportunities to demonstrate the chief textural characteristics of igneous, sedimentary and metamorphic rocks, which can be used to develop identification keys. The features and appearance of key minerals such as quartz, feldspar and mica can also be introduced at this stage. Observations of differences in hardness between crystalline materials can lead children to distinguish between certain metamorphic rocks (such as quartzite) and chemical sedimentary rocks (such as gypsum and rock salt).

Distinguishing between igneous, sedimentary and metamorphic rocks

As soon as children can successfully distinguish between crystalline and fragmental rocks, and between different types of crystalline rocks, they can move on to identify rocks using a key that assesses their ability to recognize igneous, sedimentary and metamorphic rocks. You should be confident that the children can do this satisfactorily, before they proceed to use a more detailed key.

Work on rock identification can help to develop a broad range of skills in science. It encourages close, detailed observation and analysis; it requires the correct application of key concepts and principles; it depends upon the formation and assessment of hypotheses; and, finally, it helps to consolidate basic knowledge components in Earth sciences. Although younger children will be able to tackle only the early stages, there is no evidence that rock identification cannot be attempted successfully by the majority of older primary pupils, as part of their school science curriculum.

A complete understanding of how each of the major rock types is formed is not required until level 6 of AT9; however, children should be able to appreciate that rocks can be grouped into sets, and as they do further work they will come to understand that the way in which a particular rock has been formed determines which set it belongs to.

A useful and easy way to look at different rocks is on a town walk, looking at the various facing stones of banks, office blocks and so on. After the children

j have learnt how to identify crystalline and fragmental textures in the classroom they will find it interesting to spot these in the facing stones. Topic work on, for example, 'Buildings' will provide opportunities to collect information on local building materials and could develop into investigative work to find out which materials are artificial and which are natural. The emphasis here, though, may be more on brick types and patterns, shapes, structures and work on comparative strengths of various concrete mixes, rather than on natural rocks.

All the activities mentioned help children to develop their observation skills and encourage them to communicate their findings in a variety of ways.

EARTHQUAKES Knowledge and understanding about earthquakes and volcanoes is required in the national curriculum at levels 4 and 5 of AT9; at these levels the wide use of secondary sources is much more appropriate than at earlier levels. Videos, newspaper cuttings and books are essential, and serve both as an initial stimulus and as reference sources for topic work.

You may find it interesting to present the children with the part of Table 3a (on p. 21 of Units 5-6) that relates to the last 30 years (a time period roughly within the lifetime of their parents). The children could identify the places on a


world map or globe and make suggestions as to why the fatalities varied so enormously. It is important for children to know that the magnitude of an earthquake can be measured using a special instrument called a seismometer.

They should also be aware that there are other outward signs of earth tremors, which give an indication of their strength, but not an accurate measurement. The intensity of an earthquake can be measured, from a purely observational point of view, by the extent of the damage it does to buildings and the changes it makes to the nature of the ground. This assessment is made on the Mercalli scale (see Table 2 below), which differs from the Richter scale (see Units 5-6, p. 20) in that it gives the intensity of the disturbance rather than the magnitude.

TABLE 2 Mercalli scale of earthquake intensity

Not felt, except by a few people.

Noticeable indoors; vibration like that of a passing truck.

Hardly felt; some suspended objects swing.

Felt indoors by many, outdoors by a few; dishes, windows and doors rattle.

Felt by most people; dishes and windows broken; objects overturned; trees and poles disturbed.

Felt by all; some furniture moved; cracked plaster; broken chimneys.

People run outdoors; much damage to badly constructed buildings.

Damage to ordinary buildings; walls may fall; heavy furniture moved.

Much damage; buildings moved; ground cracked; underground pipes broken.

Few buildings still standing; bridges destroyed; cracks in ground; landslips; rails buckled.

Most buildings destroyed; ground cracked; rails bent; many landslides.

Total damage; waves in ground surface; objects thrown into the air.

Magazine and newspaper articles may be available on the most recent earthquake to date and children should be encouraged to discover information about catastrophic events in recent times-where they happened and their effects on the landscape and population.

Reproduced below is an extract from a typical newspaper report of an earthquake that struck the Friuli district of northern Italy on 6 May 1976.

It was just before nine at the end of a warm, still, summer day. Most families in the area were watching television.. . The first shock came at 8.55, a short sharp tremor which rattled a few pots and pans. The second. followed five minutes later, rather stronger, but causing no damage. People began to run on the streets in alarm.

Then, after two more minutes, came the major shock. It lasted fully 55 seconds, destroying whole towns, ravaging country farmhouses, tearing roads and toppling bridges.

To one driver, the road suddenly began to move 'like the seas'; his car was thrown into a field.. . Sides of houses sheared off, leaving upper-floor kitchens, living rooms, bedrooms exposed. A tom and scarred double bed hangs over a severed third floor, pointing to where its occupants were thrown to their deaths. Cars, scarcely visible, are crushed like piles of paper beneath the fallen masonry.

You may be able to find similar newspaper or magazine articles that give an account of an earthquake, perhaps with a map showing the location. From this type of material children can be asked to describe the damage that resulted from the earthquake and their ideas of what the earthquake 'felt' like. Other features such as the length of time that the earthquake lasted can be worked out.


A photograph might form the basis of a similar exercise. Most newspaper articles about earthquakes contain photographs showing both the damage caused by the earthquake and the rescue operations that are taking place. The children could describe the scene shown and think about why the rescue of people is often difficult in areas subject to earthquakes. This may lead the children to question why earthquakes happen at particular locations.

Further projects can incorporate work on areas that suffered damage as a result of the earthquake. The children could make observations and work out a relationship between how far a place is from the earthquake site (Udine, in Friuli) and the kind of damage suffered. Figure l a and b shows two different ways of displaying information gleaned from secondary sources. This work will lead them to realize that the effects of an earthquake are widespread and that, in our example, the area near Udine felt the earthquake so strongly because it was the place on the surface of the Earth directly above where the earthquake occurred

A (epicentre) B

. . , ,

1 do0 500 0 500 1 000 distance away from Udine km

FIGURE 1 Map (a) and bar diagram (b) showing the damage suffered at different distances from the earthquake site.

If your school is near to London it might be possible to arrange a visit to the earthquake simulation exhibit at the Geological Museum (part of the Natural History Museum) in South Kensington, where the children could experience how it might feel to be in an earthquake.


KEY POINTS Observation and the ability to sort and classify information are important skills that need to be taught carefully and reinforced frequently.

By careful observation different rock textures can be recognized and the rocks sorted into groups.

The use of secondary source material provides a good introduction to the study of earthquakes.

EARTHQUAKE WAVES: WHAT ARE THEY AND HOW DO THEY TRAVEL?

I Main attainment target and level addressed in Section 2: AT9: level 5 I

STUDY NOTES. Most of this Section is not of direct use for key stages 1 and 2 and can be read quite quickly. The important concepts are discussed below. However, you should find the TV programme relevant to your own studies, and parts of it may be of use in your class work.

The simple experiment described in Section 2.1 demonstrates that it is a disturbance that travels across the surface of the water and not an object. It is important to understand this because when an earthquake occurs, it is the energy that is transmitted through the rocks-and it is this that causes the damage. For our purposes we need to be aware of two types of seismic waves-P-waves and S-waves. It might be useful to summarize their characteristics.

P-waves, or compression waves, involve a change in volume but no change in shape and are the first to anive after a disturbance.

S-waves, or shear waves, involve a change in shape but volume remains unchanged. S-waves travel more slowly than P-waves.

You may find Section 2.4 quite tough. However, you do not need to work through the mathematical derivation of Equation 9 (p. 31). The main points from the Section are summarized below.

Wave speed depends on two variables: density and elastic modulus. Density = mass/volume (see Unit 3) and wave speed increases as density decreases. This is an inverse relationship.

Elastic modulus is a measure of how the rock distorts when a force is applied to it-in other words, a measure of the rock's compressibility or 'stiffness'. The higher the value of the elastic modulus, the less distortion the rock will undergo for a given applied force. Wave speed is proportional to elastic modulus, that is, as elastic modulus increases, wave speed increases.

If you are finding it difficult to visualize these two variables and their relationship, look back carefully through Section 2.3.

The two relationships you need to remember are given below and on p. 30 of the Unit.

Seismic wave speed increases as density decreases.

Seismic wave speed increases as elastic modulus increases.

S-waves travel more slowly than P-waves because rocks resist compression more effectively than they resist shear. But are both types of wave able to travel through liquids? P-waves can travel through liquids because liquids are quite


difficult to compress. However, you cannot 'shear' a liquid-it is very difficult to change its shape; S-waves therefore cannot travel through liquids. This information will prove very helpful when we come to make predictions about the interior of the Earth.

Section 2.5 is concerned with how waves change their direction as they pass from one medium to another. You will come across this idea again in Unit 10, so it is worth working through the Section carefully. You will see that when a wave passes from a medium of lower to higher seismic wave speed, the direction of the wave changes-the path is bent away from the normal, i.e. the line at right angles to the boundary or interface of the two media. When it passes from a medium of higher to lower seismic wave speed, its path is bent towards the normal.

Take time to understand how waves become 'trapped' within a layer; you will see a direct use of this property when you work through the Study Commentary for Unit 10. For our purposes, the trapping of waves is important because it will tell us something about the properties of this layer. Remind yourself what these properties are.

TEACHING NOTES Work on vibrations will help to intsoduce the concept of 'waves'. You could encourage the children to carry out some simple investigations, such as that suggested in Investigation 1.

INVESTIGATION 1 : DETECTING Vl BRATIONS Drive a metal screwdriver into the soil so that the entire length of the metal end is within the ground (Figure 2). Instruct a friend to thump the ground at a measured distance away from you whilst you listen on the screwdriver handle.

n metal ' screwdriver

FIGURE 2 Detecting vibrations.

From how far away can you hear the thumps?

Does the distance depend on the strength of the thump?

Does the sound you hear travel better in the air or the soil?

When the children are convinced that you can 'hear' or detect vibrations some distance away from where the disturbance occurs, they can be encouraged to think further about earthquakes and their widespread effects.

A diagram such as Figure 3 will give children the correct terminology to use when describing the origin of an earthquake. You can then ask them how it is possible that the effects of earthquakes can be felt at great distances away from the focus.

STUDY COMMENTARY FOR UNITS 5-6

surface of the Earth epicentre

shock waves radiating from the focus

FIGURE 3 Terms used in describing the location of an earthquake.

Using Figure 3, ideas about 'shock' waves and their effects can be investigated. This leads on to the question of why earthquakes happen. A simple answer is that rocks that have been under great stress reach breaking point and make sudden jerking movements along lines or cracks called faults.

KEY POINTS Earthquake waves are only one sort of wave. Light also travels like a wave, as you will discover in Unit 10. All waves have one thing in common: they carry energy. This may be easier to understand after you have studied Unit 9.

We use earthquake waves to 'see' inside the Earth-rather like using X-rays to 'see' inside our bodies. We can do this because the speed at which the waves travel through the Earth depends on two properties of the rocks through which they travel: density and elastic modulus. Density you have already met (in Unit 3) and modulus of elasticity is a measure of how the rock distorts when a force is applied to it. So we measure the time taken for earthquake waves to travel from the earthquake, through the Earth, to the receiver. Seismologists can then interpret many such measurements to tell us about some of the properties of the rocks through which the waves have travelled.

A variety of activities can be set up using published materials to encourage children to think about such things as where and why earthquakes happen and what kinds of damage they cause.

THE EARTH AS A MAGNET I Main attainment target and level addressed in Section 3: AT11: level 2 , 1

STUDY NOTES This Section introduces the concept of magnetism and looks at how the Earth behaves as a magnet. Three experiments are included in this Section and it is important that you do these. Experiments 1 and 2 are central to an understanding of the properties of a bar magnet, and Experiment 3 provides an important bridge for work relating to the magnetism of the Earth. The experiments are not difficult to perform and could well be adapted for use in the classroom.


The Earth itself is a magnet-that is why we can use a compass for navigation. In Sections 3.3 and 3.4 there is much detail that you can skip. The main concepts of these two Sections are outlined below.

You are probably familiar with the way a magnetic compass points to the Earth's north magnetic pole, and that in general, this direction does not coincide with the Earth's geographic north pole. The line through the north and south geographic poles is the axis about which the Earth rotates (Unit 1). In the U.K., the compass needle points about 1 lo to the west of geographic or true north. Now try to imagine a compass needle that is free to move in any direction-not just in the horizontal plane, but also the vertical. Such a three-dimensional compass would point downwards as well (see Figure 44, on p. 47 of Units 5-6). From Figure 44 you can see that the compass needle is oriented vertically at the north magnetic (dip) pole (as viewed by someone standing at that pole) and horizontally at the 'magnetic Equator' (again as viewed by an observer standing there). Thus, the orientation of the compass needle in the vertical plane gives an indication of the magnetic latitude, with decreasing inclination of the needle occurring away from the magnetic pole. As Figures 38 and 44 show, the lines of magnetic field direction around the Earth are distributed just as though there were a simple bar magnet at its centre-this is described as a dipole.At this stage, we can think of a model of the Earth's magnetism in terms of a bar magnet.

Section 3.4 describes changes in the Earth's magnetic field strength and direction that have occurred over time. It is possible to detect the location of the magnetic north pole for past periods in the Earth's history by examining the magnetic properties of rocks. This is because most rocks contain very small amounts of magnetic materials. Magnetic grains falling through water will tend to settle on the bottom, oriented like miniature compass needles, and so preserve within the rock the Earth's magnetic field at that time. A similar magnetic field 'fossilization process' occurs when molten material cools.

Experiment 3 in Units 5-6 is a good demonstration of this. On cooling, minerals solidify; as any magnetic minerals cool past their Curie temperature, they will preserve the contemporary magnetic field.

Using a 'fossil' compass of this type, successive positions of the magnetic pole can be determined.

Evidence from rocks containing magnetic minerals shows that there have been changes in the Earth's magnetic field strength and direction over time. This evidence, together with the knowledge that the Earth's interior is extremely hot (i.e. hotter than the-Curie temperature of all known magnetic materials), enables us to reassess our model of the Earth's magnetic source as that of a bar magnet.

If the Earth really had a bar magnet at its core, could we explain magnetic field changes and the presence of magnetism at these extremely high temperatures?

You may well feel that we now need to modify our earlier model. Can you make any suggestions as to how we should modify it?

It is clear that the Earth's magnetism cannot be generated by a solid bar magnet; rather it must be generated by dynamic processes inside the Earth-and possibly must originate in a medium that can vary over time, such as a fluid.

TEACHING NOTES Magnetism is a very hard concept for children to grasp, and one that will be built up over a number of years, but only if children have had plenty of opportunities to explore the properties and effects of magnets.

Magnets may be introduced as part of topic work on 'The home'. For example, you could ask the children whether they know of anything in their homes that uses a magnet. They should be able to think of such items as magnetic cupboard catches, fridge or freezer closures, toys or knife-racks.


Many small magnetic toys are produced very cheaply, and would be fun for the children to look at. Alternatively they could investigate how many paper clips a magnet can pick up. Try comparing different magnets.

Searching for objects in the room that cling to, or are attracted by, a magnet leads children to realize that some materials have magnetic properties and others do not. (CAUTION-take care not to use strong magnets near to items that may be damaged by them, for example watches, TV sets, videotapes and cassette tapes.) We can help children to discover similarities between these by encouraging them to use the skills of AT1: sorting, questioning and investigating.

A variety of investigations can be developed at key stage 1 to enable children to discover that:

some magnets are stronger than others

some parts of a magnet have a stronger force of attraction than other parts

magnets can be made of different materials

magnets have one area that 'pushes' (repels), and another, opposite, area that 'pulls' (attracts)

'like' areas repel and 'unlike' areas attract.

This work can link well with work on forces (see the Study Commentary for Unit 3).

Questions that can be explored through investigations appropriate for work at key stage 1 might include the following.

Which objects will 'stick' to the magnet?

Will magnets always attract each other?

Can you lift one, two, three or more objects using a magnet? Try lifting a variety of objects.

Will magnets work through paper? What about through card?

Can you think of a game you can play with a magnet?

Will magnets work through water?

Can you turn a pin into a magnet? Can you do 'the same thing with a nail?

Do all magnets have the same power?

At key stage 2 children will have some knowledge of the properties of bar magnets and the work can be developed to include magnetic compasses and magnetic fields. Older children could make their own magnetic compass. This could lead on to questions about why such instruments work as they do. They may wish to develop their work to understand that it is the Earth itself that enables a magnetic compass to work, because the planet behaves as if it has a huge bar magnet through its centre. Children can be encouraged to find out more about the magnetic and geographic poles, possibly though topic work on 'Exploring' or 'Navigation'.

Investigations appropriate for key stage 2 will build on the children's knowledge of the properties of magnets. Investigations 2 to 7 may give you some suggestions.

INVESTIGATION 2: MAGNETIC FIELD Issue the children with magnets and paper clips, and show them that when a magnet is brought close to a paper clip the two items are attracted to each other before they touch. Explain that this is because a magnet is surrounded by a special area of space called the magnetic field, which can be shown in the following way.


Use a piece of thin card, some iron filings and a bar magnet. (It helps if you can put the iron filings into an old pepper container or something similar.) Place the magnet on a wooden surface; place the card on top of the magnet; and sprinkle some iron filings on to the card. Gently tap the card. You should see a pattern begin to form. This is the pattern of the magnetic field around the bar magnet.

To make a permanent wall display, you will need to spray the card and filings with clear lacquer.

You could try making other magnetic field patterns by varying the number and position of the bar magnets. Ask questions and make suggestions to stimulate the children's curiosity.

What happens when you put two magnets underneath the card? Place the north poles of two magnets so that they face each other. What magnetic field pattern do they make? Place the south poles so that they face each other. Do they make a similar pattern? What patterns are formed when unlike poles face each other? Try varying the distances between the poles.

Get the children to make magnetic field patterns using horseshoe and circular magnets. Look at all the field patterns. Do they tell you which parts of the magnets are the strongest?

You can also show a magnetic field in three dimensions.

First, find a small clear plastic container. A used shampoo bottle will do well. Sprinkle some iron filings into this container and fill the container with vegetable oil. Replace the lid and mix the oil and filings by. shaking.

Hold the north pole of a bar magnet near to the container. What happens to the iron filings? Does the same thing happen when you hold the south pole of the magnet near to the container?

Shake the container and then hold a bar magnet on each side of it. Notice the magnetic field pattern that is formed.

Encourage the children to try forming different field patterns by using a variety of magnets.

INVESTIGATION 3: WHAT IS A COMPASS? For this investigation you will need a compass, a magnet, a tray partially filled with water, and a circular plastic lid.

Float a magnet (on the plastic lid) in the water tray and turn it so that the magnet lies east-west (see Figure 4). Release the magnet, but do not let the lid touch the side of the tray.

magnet \ plastic lid

tray filled kith water

FIGURE 4 Finding out about a compass.


FIGURE 5 Recording the results.

When the magnet has stopped turning, note note down whether it looks like (a), (b) or (c) of Figure 5.

The children could try this experiment two or three times, and then write a sentence stating what they found.

INVESTIGATION 4: DOES A COMPASS ALWAYS POINT TOWARDS NORTH? Put a magnetic compass on the-floor somewhere in the classroom. (Keep it away from anything made of iron.) Using a piece of chalk, draw (very lightly) an arrow pointing north.

Move the compass to a different part of the room, place it on the floor again, and draw another arrow.

Do all the arrows point in the same direction?

Next, try putting the compass near something made of iron. What happens now?

Record the results.

INVESTIGATION 5: MAKING A COMPASS Making a compass is not difficult and can give children a valuable insight into how these instruments work.

First, hang up a magnet using a long piece of thread fixed with Sellotape. If the magnet starts to spin, leave it for a while until it stops.

When the magnet has stopped spinning, check which way it is pointing and locate north (use a compass).

Move the magnet gently to see if you can make it point a different way. Now mark (e.g. with chalk) the end of the magnet that points north.


FIGURE 6 Making the magnet look like a compass.

To make the magnet look like a compass, first draw an arrow on thin card and cut it out. Carefully remove the Sellotape and thread from around the magnet and stick the magnet on to the card, making sure your marked end is stuck on the arrow head (see Figure 6). You can now reassemble your hanging 'compass', using Sellotape and thread. The children can use the compass to locate north in different areas of the school.

INVESTIGATION 6: MAKING A MODEL OF THE MAGNETIC EARTH You can make a model of the magnetic Earth using an apple, to represent the Earth, and a magnet.

Cut the apple in half through the stalk. Carefully cut out the core and put the magnet in its place, as in Figure 7a. (Note: which way up will you put the magnet?)

Place the two halves together again and put an elastic band around them, as in Figure 7b. The elastic band represents the Equator.

a small magnet inside the apple acts on the compass needle

North Pole

I , magnet inside

compass

rubber b I

South Pole

FIGURE 7 Making a model of the magnetic Earth using an apple.

Get the children to place a compass at different points on the 'Earth' and look at the direction the compass needle is pointing to. What do they notice?

The children could draw diagrams to record their results.

STUDY COMMENTARY FOR UNITS 5d

INVESTIGATION 7: NAVIGATION For this investigation you will need the following: a world map, a compass, some card, some balsa wood, some Blu-Tack, some paper, a pencil, a ruler, and a pair of scissors.

Help the children to make a model boat, as in Figure 8a, using a compass, some balsa wood and some card.

this boat

1 is pointing north

this boat

is pointing east is pointing south-east

FIGURE 8 Using a model boat with compass to navigate.

Ask them to find Southampton on the world map and put the boat there.

Then ask them to choose another port, and write down instructions on how to navigate the boat from Southampton to their chosen destination.

You will need to explain how the compass shows what direction the boat is pointing in (see Figure 8b), and emphasize that they need to look at the scale of the map, so that their instructions can be written in the form:

Travel W for 300 km; then travel S for 150 km.

This investigation could be done in pairs, or groups, with one child, or group of children, writing instructions, and the other child, or group of children, attempting to navigate the chosen route.

When doing work on exploration or navigation children may discover different ways of finding north-and indeed come to understand the importance of being able to find north. Before people discovered magnets, they had to find their way across land and sea using the Sun by day and the stars by night. Two ways of finding north are given below.

1 The Sun always rises somewhere in the east and sets somewhere in the west. Exactly where it rises and sets depends on where you are and on the time of the year (see the Study Commentaries fof Units 1 and 2). Anywhere in the Northern Hemisphere (north of the Equatqr), exactly at midday (half-way between sunrise and sunset), on any day of the year, the Sun is due south. Therefore, if you stand with your back to the Sun at midday you will be facing due north.


2 At night, you can look for Polaris (see Unit 1). To find Polaris, first look for the constellation known as The Plough. If you think of The Plough as a saucepan, the line of stars forming the handle points towards Polaris. Polaris is always due north (see Figure 25 on p. 41 of Unit 1).

KEY POINTS Investigative work involving properties of magnets is an important area of study for key stage 1.

Studying magnetic field patterns helps us to understand and appreciate something of the Earth's magnetism and forms a progression of work for key stage 2.

4 MODELLING THE EARTH'S INTERIOR Main attainment targets and levels addressed in Section 4: AT6: I'evels 1 to 4; AT9: levels 3 and 5

STUDY NOTES This Section is an excellent example of how a scientific model is formulated. It is also interesting to note that we can build up quite a complicated picture of something that we cannot actually see or touch-that is, the Earth below its outer skin, the part that we live on. This is achieved by indirect measurement- a method often used in science.

Although you need not worry too much about understanding the details of the internal structure, you should be able to appreciate that the Earth is layered and that we know this mainly from seismic studies and as a result of loo g at the effects of the Earth's magnetism. '"31 Read Sections 4.1 and 4.2 carefully. They explain how we can modify our simple model of the interior of the Earth using data observed from seismic wave speeds and predicted wave speeds. You should now be able to appreciate that wave speed is dependent on both elastic modulus and density. Neither variable should be considered in isolation. For wave speeds to increase with depth, both density and elastic modulus must increase with depth-but elastic modulus must increase at a faster rate than density.

Section 4.4.1 in particular is likely to produce a degree of panic! However, it can be summarized quite simply as follows. There are two ways of making a magnet: you can use a piece of magnetic material, such as lodestone, or you can cause an electric current to flow in a conductor. The conductor may be a solid (for example a piece of wire) or a liquid (for example a container of molten iron). If the current flows through a specially shaped coil of wire known as a solenoid, the 'pattern' of the magnetic field produced is identical to that produced by a bar magnet. The TV programme 'Magnetic Earth' should help with some of these difficult areas. There is an interesting role-play exercise on electromagnets in the Study Commentary for Unit 9 (see the Teaching notes of Section 9).

The AV sequence in Section 4.5 is important for you to study. It continues the work on looking at rocks, but pays particular attention to igneous rocks, including those that form in volcanoes.

TEACHING NOTES Children may already be aware of the different types of rock that they see on the surface of the Earth (see Section 1 of this Study Commentary), so it may not be too difficult for them to appreciate that there are rocks on the ',outside' and also the 'inside' of the Earth that are of different types.

INSIDE THE EARTH Like a pie, the Earth has a crust. A pie is not all crust, however, and neither is the Earth. It is difficult to tell exactly what the inside of the Earth is like because penetrating it far beyond the crust is extremely difficult and expensive. Even the deepest hole, which is in Texas, is only a pin-prick in the Earth's surface. Nevertheless, it seems that the Earth is made up of layers, as shown .on the front cover of Units 5-6.

Older children might like to draw a 'slice' of the Earth similar to Figure 66 (p. 8 1 of Units 5-6).

TEMPERATURES INSIDE THE EARTH

The temperature of the material inside the Earth is different at different depths. Table 3 shows the temperatures that are thought to be found at various depths.

TABLE 3 Temperatures thought to be found at different depths inside the Earth

Depth (km) T

Thinking about this sort of information can lead you to pose such questions as:

How much does the temperature of the Earth rise between depths of, say, 30 km and 6 000 km?

Molten iron in a blast furnace reaches a temperature of about 2000 "C. Roughly at what depth does the Earth reach this temperature?

What natural happenings show that the inside of the Earth is hot?

Making a model volcano in clay, papier mdcht or plasticine would help children to appreciate and understand the structure of a volcano and how it 'grows'. In fact, volcanoes can be modelled using a surprising range of materials-an edible variety can be made with mashed potato, using gravy or tomato sauce to represent the lava flows!

Even better volcanoes can be made using modelling clay. Flows of plaster of Paris coloured with poster paint can be poured from the crater; when the plaster of Paris sets it gives a realistic lava flow.

Another way to build a model volcano and create your own volcanic eruption is given in Investigation 8.


INVESTIGATION 8: BUILDING YOUR OWN VOLCANO For this investigation you will need the following: a round flowerpot (about 10-15 cm across), an empty tuna or other small can, a baking sheet, a pair of scissors, some Sellotape, a half-circle of stiff paper (approximately 8 inches in diameter), a paper bag, some vinegar, a tablespoon of powdered paint (red or orange tempera works well), and a tablespoon of baking soda.

bakingrsheet inverted flower pot

FIGURE 9 Building your own volcano.

To build your volcano, first turn the flowerpot upside-down and place it in the middle of the baking sheet (see Figure 9). Pour some vinegar into the empty can until it is almost full. Then pour the vinegar from the can into a jug with a spout and set it aside.

Tape the can to the top of the flowerpot, with the open end of the can facing upwards.

Form the half-circle of paper into a cone shape but do not tape it together yet. Place the cone on the rim of the can and adjust it until it fits tightly. Now tape the sides together. Attach the cone to the can by taping all around the edge where the two meet.

Next, cut off the tip of the cone to make an opening big enough to pour liquids through.

Crumple the paper bag, then smooth it out. Fit it over the pot, can and cone so that it forms a mountain shape and covers your volcano. You can dent and shape the paper to make it look more like a mountain, and perhaps use felt- tipped markers or crayons to add natural features, such as trees and streams.

Cut a small hole in the top of the bag, just above the cone, so that you can see the opening of the cone.

You are now ready to set off a volcanic eruption. As this can be rather messy, it is probably best to take the volcano into the playground for the next stage.

Carefully pour the vinegar through the hole in the cone. First add the powdered paint to the vinegar, and then add the baking soda. Now watch your volcano blow its top!

If children are able to examine pieces of lava, or pumice (easily obtainable from a chemist), and relate this to the model, it-will reinforce their understanding. Work on volcanoes is often covered in TV programmes for schools-the topic provides a marvellous opportunity for children to produce colourful artwork and creative writing.

Work on volcanic eruptions could lead naturally to the study of igneous rocks and crystals.


INVESTIGATION 9: MAKING CRYSTALS You will need a sample of one of the following household substances: salt, sugar, bath salts or Epsom salts.

Put a small amount of water into a clean, transparent container and stir in as much of the substance as you can until no more will dissolve. Pour a tablespoon of this solution into a shallow dish and leave in a warm place to allow the water to evaporate. When there is no water left, use a hand lens or microscope to look at the crystals remaining in the dish. Describe the size and appearance of the crystals.

Do the same investigation again, but this time pour the solution into two dishes. Put one dish in a cool, or cold, area and the other in a warm, or hot, area. When all the water has evaporated look at the crystals. Is there any difference in the size and shape of the crystals in the two dishes?

From their work on volcanoes children should appreciate that liquid material below the Earth's crust may try to escape to the surface. This liquid rock is called magma. When it cools and hardens at, or below, the surface of the Earth it forms igneous rocks, which are crystalline.

Granite is a crystalline, igneous rock. Children may be able to identify the main crystals in a piece of granite: glassy crystals of quartz, shiny dark brownblack plates of mica and larger, slab-like crystals of feldspar. Because granite is tough and long-lasting it is often used in the construction of buildings, bridges and monuments. Look at the buildings in your local area and see if you can find any that are made of crystalline rocks.

The size of the crystals varies between different igneous rocks and provides a clue as to where the rock has cooled. Using the results of your investigations on crystals (Investigation 9), can you make any deductions from the sizes of crystals in rocks? Magma that has cooled quickly forms small crystals-these often cannot be seen by eye. Larger crystals are formed when the magma has cooled slowly. Figure 10 shows a mass of magma that has been forced into crustal rocks. Two points, A and B, have been marked. At which of these points

-do you think the magma cooled quickly? Will the crystals formed be small or large? At which point do you think it cooled slowly? Will the crystals here be -small or large? Can you explain why?

solidified magma

\ .

solidified other rock altered by magma rocks

\ contact with magma A

FIGURE 10 Magma that has been forced into crustal rocks.


KEY POINTS Using seismic wave speeds, we can deduce physical properties such as density, and axial and rigidity moduli, of the interior of the Earth. The use of indirect measurements thus enables us to build up a complex model of the Earth's interior.

Studying volcanoes and their products can help children to appreciate some of the properties and rocks that make up the interior of the Earth.

5 ROCK MAGNETISM (TV PROGRAMME) Main attainment target and levels addressed in Section 5: AT11: levels 1 l to 3

STUDY NOTES The TV programme should help you to visualize some aspects of the magnetism of the Earth more easily. Using a three-dimensional globe puts rather less strain on your imagination than having to look at two-dimensional diagrams!

Although it is not necessary to follow all the details of apparent polar wandering paths, you should appreciate that the study of palaeomagnetism has been critical in working out the positions of the continents as they have moved over the surface of the Earth during geological time. You will learn more about this in Units 7-8, where you will also discover the importance of the fact that the Earth's magnetic field has reversed many times: compass needles have not always pointed to geographic north.

TEACHING NOTES There are no Teaching notes for this Section.

KEY POINTS Palaeomagnetism studies have provided important evidence for establishing positions of continents over geological time.

Evidence of field reversals is a key feature of the self-exciting dynamo model of the Earth's magnetic field.

6 SOME USES OF MAGNETIC AND SEISMIC TECHNIQUES

STUDY NOTES You should find this Section very readable and interesting.


TEACHING NOTES Older children may be interested to know that seismic techniques are used in prospecting for oil and gas.

Work on earthquakes can reveal some interesting ideas about earthquake prediction, which in turn could lead to discussions about the behaviour of animals prior to natural hazards. How do animals know that disaster is about to strike?

KEY POINT Interpretation of seismic data is an important area of study in oil exploration.

DISCUSSION TOPICS How do we know that the Earth is not composed solely of the types of rock that we can see on the surface?

Devise practical investigations for the classroom on the behaviour of magnets and magnetic materials for key stage 1.

Set up a demonstration to show that identical magnetic fields can be produced by bar magnets and solenoids.

How would you assess the children's knowledge of magnets before embarking on work involving magnetism for key stage 2?

RESOURCES Down to Earth in the Primary School, a compilation of articles from Geology

Teaching, Association of Teachers of Geology. Dunning, F. W., Adams, P. J., Thackray, J. C., van Rose, S., Mercer, I. F. and

Roberts, R. H. (1981) The Story of the Earth, 2nd edn, HMSO. Earthquakes-Danger Beneath Our Feet, Unit 2, Science of the Earth Series,

Earth Science Teachers Association. Harwood, D. (1987) 'Rock identification: an appropriate'skill for ten to eleven

year olds?', Geology Teaching, 12, 10-13. Kennett, P. and Ross, C. A. (1983) Geophysics, Longman. Mayes, S. (1989) What's Under the Ground? Usbome Starting Point Science. Moving Ground, Unit 8, Science of the Earth Series, Earth Science Teachers

Association. Schools Council Environmental Studies 5-13 Project (1972) Teacher's Guide,

Rupert Hart-Davis. Timms, A. (1989) Volcanoes Activity Book, HMSO. van Rose, S. and Mercer, I. (1974) Volcanoes, HMSO. Whitehead, P. (1989) Reading the Rocks, Earth Science for the National

Curriculum in Science.


QUESTIONS . These questions are designed to test your knowledge and understanding of the Unit material. You should do them after studying the Unit and then check your answers with your tutor.

% explosion

, I 1 , I , sea surface

B

water

sea bed

sediments

FIGURE 1 1 For use with 41-3.

Q1 An explosion just below the sea surface is detected at the sea surface by a ship 6.1 km from the explosion. The first seismic waves to arrive at the ship travel directly in a straight line through the water (path AB in Figure 11) and arrive 3.9 seconds after the explosion. The density of seawater is 1 040 kg m-3.

Select the one item from the list below that is nearest to the value of the axial modulus for seawater.

A 5.0 x 108N m-2 E 7.5 x 109N m-2

B 1.0 x 109Nm-2 F 1.0 x 1010Nm-2

C 2.5 x lo9 N m-2 G 2.5 x 101° N m-2

D 5.0 x lo9 N m-2 H 5.0 x 1010 N m-2

Q2 The second seismic waves to arrive at the ship in Figure 11 arrive 2.1 seconds after the first seismic waves. These second seismic waves have been reflected by the sea bed (path ACB in Figure 11). If the P-wave speed in seawater is 1500m s-I, what is the depth of the sea? Select the one item from the list below that is nearest to the value for the sea depth.

4 3 Part of the seismic waves incident on the sea bed may be refracted into the sediments. The sea bed sediments have a P-wave speed of 2 200 m s-I. If AC in Figure 11 is 4.5 krn, what is the angle of refraction in the sediments? Take the P-wave speed in seawater as 1500 m s-I. Select the one item from the list below that is nearest to the value for the angle of refraction.

D 50" H There will be no refracted wave


Q4 Select from the list below the one position where a normal horizontal- plane compass needle would point to the north geographic pole (the Earth's rotation pole).

A The geomagnetic pole in the north

B The geomagnetic pole in the south

C The north magnetic dip pole

D The south magnetic dip pole

E 100 km from the north geographic pole

F Where the vertical component of the non-dipole field is zero

G On the Equator

H Where the magnetic declination is zero

Q5 The palaeomagnetic north pole for 60-65 Ma rocks from India is 35" N, 80" W, and that for rocks of the same age from the rest of Asia is 70°N, 150°E. Select from the list below two correct deductions that can be made from this information.

A. Asia has not moved relative to the pole between 60-65 Ma and the present time

B India has not moved relative to the pole between 60-65 Ma and the present time

C India has moved a greater distance than Asia between 60-65Ma and the present time

D Asia and India were at the same longitude 60-65 Ma ago

E India was further east than Asia 60-65 Ma ago

F India and Asia must have moved relative to each other and rektive to the pole between 60-65 Ma and the present time

G The Earth's magnetic field must have been reversed to produce these palaeomagnetic pole positions

H India and Asia were joined 60-65 Ma ago but have since moved apart

Q6 This question relates to rock specimen S4, peridotite, which you examined during the AV sequence in Units 5-6. Select six items from Table 4 that are correct for peridotite.

TABLE 4 For use with 4 6

1 sedimentary sedimentary coarse- fine-grained extrusive volcanic relatively relatively rock with rock with grained igneous rock igneous rock igneous rock silica-rich silica-poor fragmental fossils igneous rock rock rock texture

2 has not slow rate of fast rate of low moderate high main rock in main rock in crystallized crystal- crystal- temperature temperature temperature the ocean the from a lization from lization from of formation of formation of formation crust continental magma a magma a magma (below (600- (above

100 OC) 800 O C ) 1 000 OC) crust

3 main rock in plutonic plutonic volcanic main rock in rock has no rock often rock is the mantle equivalent of equivalent of equivalent of mountain volcanic contains meta-

basalt rhyolite gabbro ranges equivalent fossils morphic


Q7 Select from the list below two correct statements about seismic waves.

A A P-wave would take about 30 minutes to reach a recording station at an epicentral angle of 60" if the Earth had uniform seismic properties identical to granite

B Both P-waves and S-waves can travel faster at depth in the Earth, than near the surface

C There is an S-wave shadow zone at epicentral angles between 0" and 103"

D An S-wave would take about 10 minutes to reach a recording station at an epicentral angle of 60" in the Earth

E There is a P-wave shadow zone at epicentral angles between 103" and 180"

F A P- wave with an epicentral angle of 103" just reaches a depth of 2 900 km in the Earth

G The density of rocks increases faster than do the elastic moduli with depth in the Earth

H P-waves at epicentral angles above 142" are faster than predicted by extending the 0-103" P-wave curve

QS Select from the list below two correct statements about the Earth's mantle.

The mantle-core boundary is at 1 050km depth below the Earth's surface

The transition zone in the mantle is at a depth of between 50 and 250 km below the Earth's surface

P-wave speed is reduced in the low-speed layer

S-waves cannot travel in the low-speed layer

The changes in P-wave speed in the transition zone are caused by changes of state from solid to liquid

The changes in P-wave speed in the transition zone are caused by changes in composition

The changes in P-wave speed in the transition zone are caused by phase changes

The P-wave speed everywhere in the mantle is less than 12 km s-'

Q9 Select from the list below two correct statements about the Earth's core.

A Most of the mass of the Earth is in the core

B The top of the core has a greater density than the base of the mantle

C The top of the core has a greater axial modulus than the base of the mantle

D The Earth's magnetic field is produced by electric currents in the inner core

E The Earth's magnetic field is produced by a solid magnet in the outer core

F S-waves can travel in the inner core

G The inner core is composed of iron and sulphur

H The outer core is composed of iron and nickel


Q10 Los Angeles lies on one side of the San Andreas Fault System, and San Francisco, 600km away, lies on the other side. The average rate of horizontal slip along this fault is 3 cm per year. Use this information and Figure 12 in Units 5-6 to decide how long it will be, if at all, before Los Angeles is a suburb of San Francisco. Select the nearest answer from the list below.

D 5Ma H Never, as they will move further apart

ACKNOWLEDGEMENT We wish to thank the pilot group of teachers for their help with the work on magnetism in Section 3.

NOTES

SCIENCE FOR PRIMARY TEACHERS - Open University...Susan Tresman (co-director, Science for Primary...

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