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SCIENCE
F O R
P R I M A R Y
T E A C H E R S
Study Commentary for Unit 27
Study Commentary for Units 28-29
PS548
SCIENCE FOR PRIMARY TEACHERS
TheOpen
University
STUDY COMMENTARY FOR UNlT 27:
EARTH MATERIALS AND PROCESSES
ATTAINMENT TARGETS ADDRESSED
5 TECTONIC AND METAMORPHIC
PROCESSES
IN UNlT 22: AT6 AND AT9
COMMENTARY GUIDE
1 INTRODUCTION
AT6: levels 2 and 4; AT9: level 5
Study notes
Teaching notes
Key points
2 ROCK MATERIALS
AT6: levels 1 to 4
Study notes
Teaching notes
lnvestigation 1 : Making a collection
of rocks
Key points
3 IGNEOUS PROCESSES
AT6: levels 1 to 4; AT9: level 5
Study notes
Teaching notes
Key point
SUPPLEMENT: SOIL
AT9: levels 2 and 3
Study notes
Teaching notes
lnvestigation 4: Are all soils the same?
lnvestigation 5: Do all soils hold the
same amount of water?
Key points
RESOURCES
QUESTIONS
NOTES
AT6: levels 1 to 4; AT9: level 5
Study notes
Teaching notes
Key points
4 SEDIMENTS AND SEDIMENTARY
ROCKS
, AT6: levels 1 to 4; AT9: levels 2.3 and 5
Study notes
Teaching notes
lnvestigation 2: Eroding soap
lnvestigation 3: Can you feel the
difference?
Key points
CENTRE FOR SCIENCE EDUCATION
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-igma 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 1991.
Copyright 63 1991 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 WClE 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 5028 3
1.1
STUDY COMMENTARY FOR UNlT 27
ATTAINMENT TARGETS
ADDRESSED IN UNlT 27: AT6 AND
AT9
ATTAINMENT 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 a
basis for their classification.
Key
stage
1
2
Programme of study
Children should collect, and find similarities
and differences in, a
of everyday
materials, natural and manufactured, including
cooking ingredients, rocks, air, water and
other liquids. They should work with and
change some of these materials by simple
processes such as dissolving, squashing,
pouring, bending, twisting and treating
surfaces.
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.
Level
1
2
Statement of attainment
Pupils should
a be able to describe familiar and unfamiliar
objects in terms of simple properties, for
example shape, colour, texture, and describe
how they behave when they are, for example,
squashed and stretched
a be able to recognize important similarities
and differences, including hardness, flexibility
and transparency, in the characteristics of
materials
be able to group materials according to their
characteristics
know that heating and cooling materials can
cause them to melt or solidify or change
permanently
know that some materials occur naturally
while many are made from raw materials
be able to list the similarities and differences
in a variety of everyday materials
be able to make comparisons between
materials on the basis of simple properties,
strength, hardness, flexibility and solubility
be able to relate knowledge of these properties
to the everyday use of materials
know that solids and liquids have 'weight'
which can be measured and, also, occupy a
definite volume which can be measured
understand the sequence of changes of state
that results from heating or cooling
be able to classify materials into solids,
liquids and gases on the basis of their
properties
know that gases have 'weight'
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
ATTAINMENT 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
stage
1
Programme of study
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.
Level
Statement of attainment
Pupils should
1
know that there is a variety of weather
conditions
be able to describe changes in the weather
2
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
2
Childr en should investigate na
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.
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
4
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 UNIT 27
TABLE 1 Levels of the attainment targets covered in Unit 27
ATs
11
2 13
4
5 16
9 1 1 0 / 1 1 1 2 1 1 3 1 4 / 1 5 16
L
Level 2
L
Level 3
Level 5
Note: a, b, c, etc. refer to the statements of attainment. For the complete
statements, please see pp. 3 and 4.
SCIENCE FOR PRIMARY TEACHERS
COMMENTARY GUIDE
The main ideas introduced and developed in this Unit concern geological cycles
and how rocks are formed and changed. You will learn about the different
elements of the cycles and their contribution. The work builds on the ideas
introduced and taught in Units 5 to 8, and provides some possible explanations
for the origin and formation of the common rock types you have already met.
The topic of soil is not covered directly in Unit 27. At the end of this Study
Commentary you will find a supplementary Section on soil that will enable you
to address AT9. There are Study notes and Teaching notes associated with this
material.
You should study all Sections of the Unit; the Study notes will guide you
through the areas that are most relevant to your needs. There is much
information in this Unit that will be useful for such topics as 'Rocks',
'Materials', 'Volcanoes', 'Water', 'The weather' and 'Change'.
1 INTRODUCTION
Main attainment targets and levels addressed in Section 1: AT6: levels 2
and 4; AT9: level 5
STUDY NOTES
When studying how rocks are formed, we need to be aware of the natural cycles
at work within the Earth. This Unit focuses on one important geological cycle:
the rock cycle. Looking at natural cycles helps us to understand how the Earth
'works'.
TEACHING NOTES
Since this Unit deals with the concept of cycles, we shall take some time here to
explore how you might go about introducing the concept into topic work.
The idea of a 'cycle' of events is not an easy one for young children to
appreciate. They may have been introduced to the idea in terms of an 'energy
chain' or 'food web', but geological cycles present the added difficulty of the
enormous time-scale involved. At this stage the most important requirement is
to foster their interest in Earth sciences, and to ensure that they gain the
understanding and knowledge that is required to meet the necessary programmes
of study; you should not try to teach them the full range of events that make up
a geological cycle. If you wish to embark on work involving some cyclic
phenomena, be aware that young children may not be able to make the necessary
connections to enable them to have a full understanding of a 'cycle' of events;
what will be within their understanding, however, is the consideration of
elements of the cycle as discrete entities.
An obvious cycle to work with is the hydrological, or water, cycle, since this
can bring together work on rocks, weather, life on Earth, change and so on, and
many of the processes involved in the water cycle can be investigated by means
of simple experiments, as the raw materials are readily obtainable. You will
appreciate that when we describe phenomena in terms of cycles, we are
simplifying what really happens; they are an example of the way we use models.
Before children can begin to appreciate the water cycle, they must have an
opportunity to play with, and explore, the properties of water. Make sure that
they get used to pouring water into containers and down piping; they should also
be beginning to understand concepts such as water finding its own level and
flowing downhill. Once children have taken part in activities such as these, they
will derive more benefit from investigations that build on these basic ideas.
STUDY COMMENTARY FOR UNIT 27
Discussions may be prompted by asking open-ended questions such as:
Where do we use water in our homes? Where is it used in school or in the
local community?
What happens to water when it gets very hot? What does it look like? How
do we use it?
What happens to water when it gets very cold? What does it look like? How
do we use it?
What is steam? What is condensation? How can we make steam and
condensation?
Where does water come from? Where does it go?
First-hand observations can help the children to approach these questions. You
could boil a kettle of water in the classroom, and ask the children to watch and
listen to what happens as the water is heated. (CAUTION-Never leave the
children unsupervised in a room where water is boiling.) With careful
supervision, older children could perhaps measure the temperature of the water at
various stages during this heating-up process.
It may be possible for older children to perform simple cooking activities, such
as heating soup or making hot drinks. Again, it is very important that children
are never allowed to perform these activities unsupervised.
Similarly, children can freeze water to make ice-cubes, using a refrigerator in the
school kitchen or staffroom. Ask them to time how long it takes for ice crystals
to start forming, and then how long it takes for hard ice-cubes to form.
Encourage the children to look closely at the ice-cubes, hold them in their hands
and describe what they see when the ice-cubes melt. Again, simple culinary
activities, such as making ice-lollies, could be useful.
The processes of evaporation and condensation are fundamental to an
understanding of the water cycle, and are very difficult concepts for young
children to grasp. When children have had an opportunity to explore water and
some of its properties, you may wish to develop work on these elements of the
water cycle. Some ideas are presented here that could be used to explore
children's understanding of these terms, and suggestions are made about how to
develop their comprehension.
You may consider having a small tank containing water in the classroom. The
children could be invited to write down their ideas about, or observations on, the
water, perhaps illustrating their notes with drawings. At this stage, do not
intervene or attempt to teach them anything about the water. After about a week,
when a variety of items has been collected, the children's .ideas can be explored.
You can then use their own experiences and observations as starting-points for
subsequent work.
If the children have had the opportunity to observe a water tank left in the
classroom, they may have realized that water 'disappears'. This observation can
be used as a starting-point; ask them structured questions, similar to those
suggested below, to set them thinking about what might have happened to it.
Get the children to make handprints by pressing one hand on to a wet cloth and
then on to a paper towel. Ask them to wave the paper towel in the air for a few
moments, to dry it, and then ask them questions such as:
What has happened to the handprint?
Where do you think the water has gone?
Do you think you could make the water come back?
How can you make the handprint last longer?
How can you make the handprint disappear more quickly?
SCIENCE FOR PRIMARY TEACHERS
You could ask similar questions about other simple activities, such as washing
their hands and drying them in air, or painting a picture and watching the paint
dry.
The process of condensation, like that of evaporation, is a difficult one for young
children to comprehend. Here are some simple activities to use as starting-points
to help you to assess the children's understanding of it. Put some ice and water
into a tin and then ask the children to look carefully at the outside of the tin.
Again, using structured questions, try to establish the level of their
understanding of the process. Some suggested questions are:
What do you think is on the outside of the tin?
Where do you think it has come from? Get them to make a list of ideas.
Do you think you can make it go away again? Encourage them to develop
ways to try out their ideas.
Can you think of anywhere else you have seen this happen? The children
could make a list of similar occurrences.
A second activity could involve the children breathing on to a mirror and then
looking carefully at what happens. In the discussion that follows, ask them
questions such as:
What happens when you breathe on to a mirror?
What do you think the substance is?
Where has it come from?
Can you make it go away again? Again, encourage them to try out their
ideas.
Where do you think it goes?
The activities arising from these questions should allow you to further the
children's understanding of these complex processes. When children have grasped
the concept of water 'changing state'-that is, from solid to liquid, and liquid to
gas-you can introduce and discuss such ideas as where rain comes from, what
clouds are made of, where rain goes to, and so on. As always, it is important for
children to base their ideas on observations and first-hand experiences rather than
simply repeating facts about the water cycle that are beyond their
comprehension. (Other work involving the water cycle is included in The
Weather..)
Ideas about the rock cycle are best introduced to children after they have studied
rocks in more detail (see Section 2 of this Study Commentary), and will only be
appropriate for older junior children.
KEY POINTS
The existence of natural cycles shows that natural processes do not act
independently but are part of a continuing chain of events. The two cycles
introduced here are the hydrological cycle and the rock cycle.
Geological cycles enable us to understand the way the Earth works. They
represent types of models.
STUDY COMMENTARY FOR UNIT 27
2 ROCK MATERIALS
Main attainment target and levels addressed in Section 2: AT6: levels
1 to 4
STUDY NOTES
This Section provides much information on rocks and minerals that you will
find useful when you come to work on Earth sciences topics in the classroom.
Work through the Section carefully, including the AV sequence and Experiment;
it will stand you in good stead when you read the later Sections.
To work through the AV sequence 'Minerals' you will need to have samples of
the following common rock-forming minerals: quartz, feldspar, mica, calcite and
iron pyrites. Samples of these minerals are readily available from suppliers, and
are included in a Fossil/Mineral Kit that is available from the address given in
the Resources Section at the end of this Study Commentary. The Kit will be
used again in the Study Commentary for Units 28-29, where it is needed for
several activities; you will also find these common minerals useful for many
classroom investigations.
The AV sequence builds on your knowledge and experience of the rocks
introduced in Units 5-6 and helps you to identify the main physical and chemical
properties of some common rock-forming and ore minerals. During the sequence
you will be asked to do a series of tests on the given minerals. As you perform
the tests, you will come to appreciate that each mineral has its own unique set of
physical and chemical properties. Some of these identifying properties are
colour, density and hardness. It is important to realize that no one test will
necessarily be diagnostic for any one mineral, but the information accumulated
from the different tests will enable you to come to some conclusions about the
identification of a mineral and its characteristics.
Section 2.2 gives details about the silicate tetrahedron, which is the basic
building unit of common minerals. As you consider the way that igneous rocks
form, you will find Tables 3 and 4 (on p.9 of the Unit) essential reading; the
information they contain enables us to make predictions about the possible
composition and temperature of crystallization of common minerals and rocks
considered here. Try to remember that quartz (SiO,) has the lowest temperature
of crystallization and, of the common igneous rocks that you will meet, granite
contains the highest percentage, by mass, of SiO,. Peridotite and basalt are both
silica-poor rocks and contain much lower percentages (by mass) of SiO, than
granite, and so have a much higher temperature of crystallization. The
composition of the rock, and in particular the proportion of SiO, controlling the
temperature range of crystallization of magma (Figure 4, on p. 10 of the Unit),
is an important idea; ITQ 1 (on p. 11 of the Unit) will help to reinforce your
understanding of this Section.
The Experiment to investigate the density of rocks and minerals is a useful one
to do, and a way of adapting the method for class use is given in the following
Teaching notes. The results you obtain from the Experiment will also help you
. to revise some of the earlier work on the nature of the Earth's crust (in Units 5
to 8) and density (in Unit 3). SAQs 1 and 2 (on pp. 16-17) should be completed
before you move on to Section 3.
TEACHING NOTES
There are many different kinds of rocks, and dividing them into three main
groups according to how they were formed is a sensible way of coping with the
great variety. You may already have done some work on rock properties and
identification using the ideas introduced in the Study Commentary for Units 5-6.
When children begin to study rocks, an early observation to be made is that each
rock is made up of different materials. In some rocks, such as sandstone, one
SCIENCE FOR PRIMARY TEACHERS
material predominates, whereas others, such as granite, contain many different
materials. The AV sequence introduced criteria for observing and identifying
different minerals, and you can use similar tests to identify rock types. These
'tests' can readily be adapted for use in the classroom and offer an ideal
opportunity to develop skills of scientific enquiry, such as observation, testing
and sorting.
Some of the tests can be used by the children to discover the properties of both
rocks and minerals; others are more appropriate for either rocks or minerals.
What you need to remember is that rocks are made up of minerals, so it is not
appropriate to test rocks for hardness, for example, since the minerals they
contain may well have different hardness values.
To investigate their properties, the children need to make a collection of rocks
and minerals. These could be brought in from home, or collected from local
environments or school trips. However, before the children embark on work
using their own rock samples, it may be appropriate for you to introduce the
tests using known samples; this will enable the children to become familiar with
some of the common rock properties before they tackle more challenging tasks.
A good starting-point is just to get the children to look at the rock andfor
mineral specimens, both with the naked eye and with the aid of a hand lens.
Make sure the children know how to use the hand lenses correctly (see the AV
sequence 'Rocks and rock textures' in Units 5 - 6 ) . Asking them to draw or paint
enlarged versions of what they see will focus the children's attention on colour,
texture and particle size. The rocks could also be sorted using colour: for
example, rocks that are all one colour, rocks that are mainly one colour, rocks
that are two or more colours. (See the Study Commentary for Units 5 - 6 . )
We present a variety of different tests here. You may prefer, however, to
encourage the children to test and rank their collection of rocks and minerals
according to their own criteria, and they may well devise other tests. However,
do remember the message from the AV sequence 'Minerals'-no one test is
necessarily diagnostic for identification purposes, and some tests will be more
useful than others in identifying different minerals; e.g. hardness, rather than
colour and appearance, is a diagnostic test for quartz, whereas colour and
appearance is diagnostic for iron pyrites.
In planning your teaching sequence, you may well decide to introduce minerals
before moving on to work on rocks. As children begin to appreciate that
minerals are frequently seen in their crystalline form, they could be encouraged to
examine everyday materials that have specific and individual crystal structures,
such as sugar, salt and ice. An investigation to grow crystals is given in the
Study Commentary for Units 5-6, and further work on crystals is included in the
chemistry materials. Children can be encouraged to carefully observe crystal
shapes and be aware that crystals are quite common and widespread. Ask them,
for example, where they would expect to find crystals. If they have made crystals
using a variety of chemicals, encourage them to look at their shapes under a
microscope. A collection of different crystals could be made; encourage the
children to record any observations they make-perhaps in a table or by building
models of crystals. These have the added advantage of making attractive
Christmas decorations!
ROCK AND MINERAL TESTING
It is important for children to appreciate that even professional geologists cannot
always name every rock or mineral at first sight. They have to perform tests on
the rock or mineral in question before they can reach any conclusions about what
it might be. A specimen that is particularly difficult to identify may need to be
taken back to the laboratory for further, more sophisticated, tests.
Using different rocks or minerals, encourage the children to think about the sorts
of 'tests' they could use. You may well have to help them with some of the
tests or show them other tests they may not otherwise be aware of. Tests that
could easily be used in the classroom include the following.
STUDY COMMENTARY FOR UNIT 27
Colour Record the different colours in a rock, or the colour(s) of a mineral,
using either paint or coloured pencils. Some children may be able to use the
correct vocabulary to describe the appearance of a rock sample, e.g. dull, shiny,
matt, speckled, etc. If you are able to break the specimens, the children will see
whether the colours inside are the same as or different from those on the outside.
(CAUTION-Take great care to avoid dangerous splinters of rock. Wear safety
goggles and smash the rock under a cloth using a geological hammer.)
Reaction with acid Some minerals react with acid-that is, they fizz. Rocks
that contain the mineral calcium carbonate (CaCO,) fizz and give off a gas when
drops of acid come into contact with the rock. Thus for the mineral calcite
(CaCO,), the 'acid' test is diagnostic. Strong vinegar can be used as the acid in
this test. Calcium carbonate makes up part of rocks such as limestone, chalk and
marble. Test these rocks to see whether they react. Get the children to test
blackboard chalk. Does this contain calcium carbonate? Some animals use this
material to build their shells. Try testing snail shells or sea shells with acid.
Hardness The children can test different minerals for hardness. They will need
to be provided with a variety of items that can be used as 'scratchers', which they
can then arrange into order of hardness, such as:
HARDEST
steel file + penknife blade
SOFTEST
+ brass
nail
+ 2p coin + fingernail
When the children have assembled their collection of scratchers, they could try
using each one to make a scratch on their specimens. They need to know that
making a scratch means that the scratcher actually cuts into a surface rather than
just marking it. How will they record their results? When doing this activity the
children should be thinking about two variables:
the order of hardness of the materials tested; and
the order of hardness of the scratchers.
Encourage the children to think about why it is important for us to know how
hard different rocks are. Engineers and miners, for example, require this
information if they are to construct tunnels or drill wells. Some rocks are easy to
cut into, whereas others are so hard they need special drills with diamonds
embedded in them. The overall hardness of a rock may also tell us something
about its usefulness in the construction industry.
Density The density of a rock or mineral specimen can provide a good clue to
its identification. Get the children to check, say, five or six specimens (rocks or
minerals) that are about the same size. If rocks of the same size have different
masses, then they must have different densities.
Ask the children how they could compare the density of these rocks. By simply
picking up and handling each specimen they should be able to put the rocks in a
rough order of density. They can then check their estimated order by weighing
and recording the mass of each specimen. For some, it may be difficult to
understand that although things can be the same size they can have different
masses. Reinforce this concept by getting them to examine familiar objects
around the home or classroom.
If we wish to compare the density of rocks with greater precision we need to
know their volume (see the Experiment on p. 13 of the Unit), and so calculate
their relative densities. The Experiment can be adapted for use in the classroom.
We can find out the volume of a rock sample by weighing it in water, using a
measuring cylinder and a known volume of water. First, pour some water into
the measuring cylinder and note the water level; then lower the rock specimen
into the water (you will need to tie a piece of thread or thin wire around the
rock). Note the new water level. The rise in the water level gives the volume of
the rock. Repeat this with each of the specimens and record the results.
SCIENCE FOR PRIMARY TEACHERS
To compare the density of each specimen accurately we would have to have
specimens of exactly the same size. Clearly this is not possible. However, we
can work it out as follows.
We know the volume of each specimen (in cm3) and we know its mass (in g).
Now we have to calculate the mass of 1cm3 of the rock. Do this calculation and
record the result.
Now, for each rock specimen, find out for each one how heavy 1 cm3 is, using
the following equation:
Relative density =
mass of rock specimen
mass of an equal volume of water
given that 1 cm3 of water has a mass of 1 g.
This activity is obviously more suitable for older junior children, for whom it
would provide plenty of opportunity to bring in mathematical skills and
concepts.
Permeability Some rocks will allow water to pass through them-these rocks
are said to be permeable. Ask the children to devise a test to investigate whether
the rock specimens are permeable or impermeable.
Magnetism If a rock contains magnetic minerals then the rock will be
magnetic-i.e. it will be attracted to or repelled by magnetic minerals, especially
iron. Test the rock samples using a magnet to see whether they are magnetic.
Record the results.
Cleavage or split Some rocks, such as slate, will cleave or split quite easily
along particular lines. Carefully examine different rocks. Look for signs to see
whether the specimen would split easily in a certain direction. Try to obtain
samples of roofing slates to see how they have been cut.
When the children have been introduced to some or all of these tests they could
perform them on their own collection of rocks and minerals, and keep records of
the results for their own collections. Do ensure that they record where the
specimen was found, when it was found, and who found it. They may also be
able to suggest a possible identification. If all the specimens are logged in this
way, the collection will be of value in that many different children will be able
to use it; the procedure also encourages them to be systematic, and gives them
an opportunity to try their hand at cataloguing.
INVESTIGATION 1: MAKING A COLLECTION
OF ROCKS
To make a rock collection you will need: several egg cartons; some
identification books on rocks; some sticky labels or paper and glue with
which to make labels; and a collection of local rocks.
Collect as many different rock specimens as you can, either from your local
environment, or from further afield; the children could bring them back from
family outings, holidays and so on.
Egg cartons are useful to hold the specimens. Get the children to examine the
rocks closely, and decide on how they will label each specimen. They may
suggest giving them specimen numbers. The place where the specimen was
found is also worth including on the label. Can you suggest why this
information might be important?
When the collection of rock specimens has been labelled, the children could draw
up an identification chart, such as Table 2, on which to record the characteristics
of each rock.
STUDY COMMENTARY FOR UNIT 27
TABLE 2 A suggested chart for recording data on rock characteristics
I
I Specimen 1
/ Specimen 2
1
Specimen 3
crystals
hardness
1 magnetic properties I
I
Older children could use a rock identification book, and try to name the
specimens based on the data they have recorded.
As further rock specimens are added to the collection, other distinguishing
features, such as fossils, may be included on the chart.
Testing rocks and minerals is ideal for small-group work and gives children the
opportunity to do a test, make a decision based on the results of that test, and
classify items accordingly.
KEY POINTS
Minerals are naturally occurring, inorganic materials and represent the most
common solid materials on Earth.
Minerals and combinations of minerals have many different uses: e.g.
silicon in electronics, diamond in jewellery, talc in blackboard chalk,
graphite in lubricants.
Minerals have different properties that are diagnostic for their identificatioh.
Different minerals, like other substances, crystallize at different
temperatures; if the composition of a rock is known, its temperature of
formation can be estimated.
SCIENCE FOR PRIMARY TEACHERS
3 IGNEOUS PROCESSES
Main attainment targets and levels addressed in Section 3: AT6: levels 1 to
4; AT9: level 5
STUDY NOTES
This is an important Section, which deals with the origins and processes of
formation of igneous rocks, and it is perhaps the most demanding Section in this
Unit.
From Units 5-6 you will remember that igneous rocks form from a melt and the
crystal size reflects the rate of cooling of that melt. Units 7-8 introduced the idea
that the source of basaltic magma is the low-speed layer in the upper mantle, and
that within the mantle are convection currents thought to be responsible for
'driving' the plates. Section 3.1 provides a possible explanation for the
mechanism of this 'driving force' of these convection cells-that
is, the
radioactive decay of potassium, thorium and uranium.
Much of this Section is not directly relevant to key stages 1 and 2. However, the
information provided will enable you to deal confidently with questions relating
to the origins and characteristics of igneous rocks.
Allow yourself time to reflect on the concepts introduced in the Section, and
then read through the notes below to reinforce your understanding.
VOLCANOES AND VOLCANIC ROCKS
The way in which magma is erupted out of a volcano varies, depending on the
composition of the magma and its dissolved gas content. Viscosity is the
resistance of a liquid to flow, and lavas of different compositions display different
viscosities. Basaltic lava (silica-poor) has a low viscosity and is usually freeflowing-often at very high speeds (up to 50 km h-'). This type of lava forms
low-angled volcanic cones typical of those found in Hawaii. Lavas rich in silica
(rhyolites) have a viscosity about 103 greater than basaltic lavas, and tend to
form steep-sided cones.
Where there is a high dissolved gas content, the eruption is much more
vigorous: basalt volcanoes display fire fountaining, whereas granitic magma can
suffer violently explosive eruptions as the gas forces its way out of the highly
viscous liquid.
CONSTRUCTIVE PLATE MARGINS AND THE ORIGIN OF
BASALTS
'
At constructive plate margins large quantities of basaltic lava are erupted. This
magma has originated in the mantle. We know that the mantle is composed of
peridotite and that it is likely that the origin of the magma erupted at
constructive margins is the low-speed layer of the upper mantle (see Units 7-8).
We now need to consider how basaltic magma, which forms new oceanic crust at
constructive plate margins, is derived from mantle peridotite. It is generally
thought that basaltic lava is produced by the partial melting of mantle peridotite.
Partial melting is a process in which a mixture-in this case peridotite--does
not 'melt' completely at one specified temperature. Pure substances (if you need
to refresh your memory about what this means, you should refer back to the
chemistry materials) melt at a fixed temperature. Rocks, however, are usually
mixtures and so melt progressively over a range of temperatures. Peridotite
contains mainly olivine, pyroxene and a little feldspar. Feldspar and pyroxene
will start to melt before olivine (refer to Figure 4 on p. 10 of the Unit). So an
early magma of peridotite will tend to have a pyroxene-feldspar compositioni.e. the composition of basalt.
STUDY COMMENTARY FOR UNIT 27
PLUTONIC ROCKS
Plutonic rocks are formed below the surface of the Earth as magma solidifies
after being squeezed, i.e. intruded, into older rocks. You have already seen
examples of plutonic rocks, for example granite and gabbro, and know that their
texture is coarsely crystalline (i.e. they have large crystals) as a result of slow
cooling.
Like the melting process, the crystallization process of rock is far from simple.
The different minerals in a magma crystallize over different temperature ranges.
As minerals are taken out of the magma as a result of crystallization, the magma
gradually changes in chemical composition; the usual effect of this is that the
magma becomes more silica-rich. This process is called fractional crystallization.
DESTRUCTIVE PLATE MARGINS AND THE ORIGIN OF
ANDESITES
At destructive plate margins, the ocean trench represents the place where two
plates are converging, with one plate-which is always an oceanic plate--diving
below the other and eventually becoming resorbed into the mantle. As the slab
of oceanic lithosphere descends into the mantle, it becomes heated, partly by
friction along the Wadati-Benioff zone, and partly by conduction from the
surrounding hotter mantle. The overriding crustal rocks will also be heated.
Partial melting of the subducting plate will occur. Magma will rise through the
overlying plate, often producing plutonic cores to the fold mountains, or perhaps
being erupted as lava.
This process at destructive plate margins involves the down-going plate moving
continuously, but the overriding plate staying in the same position with respect
to the subduction zone beneath it. This means that, with time, more magma will
pass upwards through the same zones in the overriding plate. Remember that the
process of partial melting always takes out the lowest temperature fraction-so
SiO, becomes increasingly concentrated in the 'magma. Thus if peridotite is
partially melted, there is an increase in the silica content of the resultant magma,
thereby producing a basalt. When basalt is partially melted, the resulting magma
will be andesitic and, as the rocks at the base of the crust melt, granitic magma
will be formed. It is important to understand that both partial melting and
fractional crystallization processes have the same overall effect-they produce an
increasingly siliceous material-and that whereas basaltic material can be
resorbed into the mantle, the production of andesitic and rhyolitic magma is a
one-way process: magma of this composition cannot be resorbed back into the
mantle, because its density is too low. It therefore forms a permanent addition to
the crust.
Section 3.6 ends with an explanation of the origin of continents. The Summary
forms a useful list of the main concepts introduced in this Section.
TEACHING NOTES
We have given some suggestions for work on rocks and rock textures in the
Study Commentary for Units 5-6 and in Section 2 of this Study Commentary.
The material is appropriate also for this Section.
If you do any work on volcanoes and volcanic eruptions, this could lead to
exploration of the children's own ideas about the interior of the Earth (see the
Study Commentary for Units 5-6). The effect of insulation may be a useful idea
to investigate here, so that children can appreciate how some things can stay hot
for a very long time.
Children could set up investigations to answer the questions:
Can you find the best material to help keep a hot drink hot for a long time?
Can you make a container that will stop ice-cubes from melting?
SCIENCE FOR PRIMARY TEACHERS
Materials that the children will need to collect, or be provided with, to enable
them to answer these questions include: a stop-watch or timer; a variety of
containers of the same shape, size and material, such as empty cans, plastic pots,
etc.; a collection of materials, such as cotton, cotton wool, nylon, wool, plastic
'bubble' material, thin foam, etc.; rubber bands and sticky tape; sticky labels;
some ice; a kettle with which to make hot drinks; and a thermometer. This work
relates well to that covered in the Study Commentary for Unit 9.
Volcanoes can be studied using secondary sources, such as atlases and other
reference books. This will allow the children to find out where active volcanoes
are found today, and note the differences/similarities in their appearance. Older
children may be interested to discover why volcanoes have different shapes, and
erupt different types of lava. They may well have been on holiday to a volcanic
area and brought back samples of local rock derived from lava. Do not despair if
no one is holidaying in a volcanic area-a local chemist should be able to
supply you with some pumice, which is of volcanic origin.
Carefully supervised cooking activities, such as making fudge and toffee, may
help the children to appreciate the property of viscosity and how this affects the
movement of liquids. (Other practical work involving viscosity is covered in the
chemistry materials.)
Crystalline rocks are frequently used as facing stones for buildings; a local
churchyard will perhaps contain a large variety of rocks that have been made into
headstones. A town or churchyard trail may be an appropriate and enjoyable
activity to develop with the children. It will allow them to use their
observational skills to look at what the local buildings or memorials are made
of, and will also provide an opportunity to practise classifying rocks as either
'crystalline' or 'fragmental'.
KEY POINTS
Magmas are complex chemical mixtures, containing many elements that
become distributed between several minerals as the magmas crystallize. Each
mineral in an igneous rock has crystallized at a different temperature. A
magma crystallizes over a range of temperatures, and does not, in general,
solidify all at once.
Partial melting helps to explain the wide diversity of igneous rocks that
occur in the Earth's crust.
Fractional crystallization is the process by which the minerals crystallizing
out from a melt leave a residual liquid of a different composition.
4 SEDIMENTS AND
SEDIMENTARY ROCKS
Main attainment targets and levels addressed in Section 4: AT6: levels 1 to
4; AT9: levels 2, 3 and 5
STUDY NOTES
This Section is concerned with the formation of sedimentary rocks, and contains
much information that you should find useful in your teaching. The TV
programme 'From Snowdon to the sea' clearly shows the different processes
involved at various stages, as a river flows from source to mouth, and the
different types of sediment that are deposited at each stage.
Sections 4.2 and 4.3 deal with the breakdown or weathering of rocks and the
products of this breakdown. The soil-a product of weathering-is dealt with in
detail in a supplementary Section (see pp. 21-32). The concept of relative
STUDY COMMENTARY FOR UNIT 27
resistance of minerals to weathering is important, because it is this relative
resistance that results in the landscape as we see it.
Sections 4.4 to 4.7 deal with the transportation and subsequent deposition of
weathered material. The nature of the sedimentary rock that is formed as a result
of the accumulation of the products of weathering is, to a large extent,
determined by the method of transportation of these products, together with the
distance over which they have been transported. So by careful examination of a
sedimentary rock, and using data from present-day environments, we can make
deductions about the environmental conditions existing when the sediments were
deposited.
TEACHING NOTES
Many of the ideas and activities relating to the watei cycle that were introduced
in the Teaching notes to Section 1 are also relevant here, and provide startingpoints for thinking about the role of moving water in sediment transportation.
Practical work involving moving water is difficult to set up in the classroom,
although many children will be aware of its action and effects if they have played
at damming part of a river or stream. A visit to a local beach or river would be
invaluable, so that the children could see and feel particles, stones and rocks
being moved by the water. They may also be able to observe the way in which
materials have been laid down in layers, or 'ripples', by the moving water. Some
of the practical activities in exhibitions such as the Launch Pad at the Science
Museum, London, or other interactive science centres, allow children to
experiment with moving water.
Young children may find it hard to appreciate that water is capable of 'wearing
something away'. You could get them to investigate this phenomenon using a
slowly dripping tap and a bar of soap.
INVESTIGATION 2: ERODING SOAP
For this investigation you will need a new bar of soap and a tap that can be
made to drip slowly.
Before the children set up this investigation they need to think about how
they will be able to determine whether any soap has been 'washed away', or
eroded.
Get the children to position a new bar of soap in a sink so that a slow, steady
drip of water splashes on to it from a tap above. The investigation should be
set up before the children go home in the afternoon. Ensure that they make a
careful note of the time they started the investigation, and that no one
touches the tap or soap after it has been positioned. The water should be
allowed to drip all night.
In the morning, the children should record the time the tap is turned off, and
work out the length of time the tap has dripped. They may even be able to
calculate the average number of drips per minute.
The children now need to determine whether any of the soap has been eroded.
One way to do this is to weigh the soap before and after the investigation to
determine how much of its mass has been washed away.
Some suggestions for further investigations in this area are given below.
A shower-head-type spray can be fixed at different heights. The children
could investigate whether changing the velocity of the water drips (i.e.
changing the height of the spray) has an effect on how much soap is eroded.
The results could be compared with those obtained from the dripping tap in
Investigation 2.
Several different soaps could be used, to see whether some soaps are more
resistant than others to the effect of dripping water. How do these harder
SCIENCE FOR PRIMARY TEACHERS
soaps compare in price? The children may be able to make suggestions as to
which brands therefore represent better value.
Large rain drops, which occur in cooler weather, cause more erosion. Craters
formed by different-sized drops could be measured in fine powder or flour.
Another powerful eroding and transporting force is the wind. Ask the children to
describe what a slight breeze feels like; what does it feel like when the wind is
very strong? Have they seen objects being lifted up by the wind? What sorts of
things can the wind pick up and move about?
The effects of abrasion are likely to be visible at various places around the
school or in the children's local environment. Stone steps often have
indentations in them due to the abrasive effect of foot traffic over many years. If
you have a set of worn steps like this in your school, the children could attempt
to measure the amount of material that has been worn away. They could also
look at the effects of erosion on local buildings; do parts of a building that face
in different directions suffer different amounts of erosion? If you can visit a
churchyard containing old gravestones, they will be able to see the effects of
erosion on several different types of rock. They may be able to make
comparisons of the degree of resistance to erosion of the different types of rocks.
As children come into contact with various types of rock, they will learn to
recognize the 'feel' or texture of the different types. Sandstones, for instance,
generally feel 'sandy' or 'gritty', whereas marble feels very smooth. They may
like to set up an investigation to see whether their friends can recognize rocks
from their texture.
INVESTIGATION 3: CAN YOU FEEL THE
DIFFERENCE?
!
To do this investigation you will need: some specimens of rock that have
different textures, such as sandstone, mudrock and granite (these should all be
of approximately the same size-about 5 cm3); a small cardboard box placed
on its side-a shoe box without a lid works well; and a piece of thick cloth
to cover the box.
Cover the open side of the box with the cloth. (It may be best to use sticky
tape to secure it.) An opening will need to be cut in the piece of cloth so that
someone can put a hand through it and reach into the box. Before securing
the cloth, place all three rock specimens in the box. The children can then
ask their friends (or teachers!) to reach into the box and arrange the rocks into
a sequence by texture-for instance by placing the smoothest to the left and
the most coarse to the right. The children can then check the results of each
person's test and record the data. Encourage them to test at least 10 people.
What other rock specimens could they include in the box?
KEY POINTS
The environment of deposition helps to determine the character and
properties of a sedimentary rock.
The importance of the principle of uniformitarianism is emphasized when
considering sedimentary rocks.
STUDY COMMENTARY FOR UNIT 27
5 TECTONIC AND
METAMORPHIC PROCESSES
Main attainment targets and levels addressed in Section 5: AT6: levels 1 to
4: AT9: level 5
STUDY NOTES
Sections 5.1 to 5.3 deal with the deformation of rocks; Section 5.4is concerned
with metamorphic processes. Faults and joints are common features and are the
result of a rock being subjected to external forces of tension or compression at
relatively low temperatures. Structures produced under tension and compression
differ: normal faults develop under tension and reverse faults under compression.
At higher temperatures, such as the conditions under which metamorphic rocks
form, different structures tend to occur as a result of plastic deformation.
Metamorphic rocks represent the group of rocks that have been changed since
their formation. This 'changing' is due to heat or pressure or, more typically, a
combination of both.
The AV sequence 'Metamorphic rocks' introduces some common metamorphic
rocks, together with their characteristics and conditions of formation, and is well
worth working through. Metamorphism is not an easy concept to understand;
perhaps one way in which it can be appreciated is by thinking about
metamorphic processes with which we are familiar. If your house is built of
brick and roofed with baked clay tiles, then, like most of us, you owe your home
to metamorphism! Both these building materials are produced by working wet
clay into the appropriate shape and firing it in a kiln. This transformation from
soft clay to hard bricks and tiles can be regarded as a type of metamorphism
brought about by heat-reactions have taken place that have resulted in
permanent physical and chemical changes. If the reactions were readily reversible,
the products would be of no value as building materials. In fact, they weather
almost imperceptibly, mainly by mechanical processes, and may take centuries
before they are broken down into separate particles.
In hotter, sunnier climates than ours, bricks are frequently made by allowing the
clay blocks to dry in the Sun. The resulting bricks are quite hard, but need
protection from tropical storms-e.g. by using wide overhanging roofs. Thus it
would seem that a certain minimum temperature must be achieved for
'metamorphic' changes to take place.
So when rocks are heated, under certain conditions, they are changed by
metamorphic processes, but the overall chemical composition of the
metamorphosed rocks is not affected. Apart from some loss of water, there has
been no change in the chemistry of the brick during its firing-new elements
have not been added to the brick, and none have been lost from it.
This everyday analogy illustrates three fundamental aspects of the metamorphism
of-rocks. First, all the changes occur in the solid state, with minimal change of
shape and volume. In metamorphism there is usually no melting of the rocks.
Second, there is usually no significant change in the overall chemical
composition of the rocks-just as nothing is added to or taken from the articles
being fired in the kiln, other than the addition of heat and the loss of water,
along with a little CO, and other less important gases. Third, the original
minerals form new minerals, and this produces a new rock. The chemical
elements that make up the original minerals (clay minerals in our analogy) are
redistributed into new crystal structures.
There are two main kinds of metamorphic process.
Contact metamorphism In this process, surrounding rocks are heated during
intrusion of igneous rocks of younger age. The resulting rocks show changes in
texture and crystallization. The rocks have been 'baked', but there is usually no
SCIENCE FOR PRIMARY TEACHERS
strong directed pressure involved. The manufacture of pottery and bricks is thus
analogous to contact metamorphism.
Regional metamorphism This type of metamorphism affects vast areas, and
the metamorphism of huge volumes of rocks is usually linked with large-scale
tectonic movements. Strong directed pressures are involved with regional
metamorphism.
Temperature and pressure represent important variables in the metamorphic
process: different temperatures and pressures result in different rock types. Figure
1 shows how a mudrock can be changed into different rocks as a result of
increasing temperature and pressure. The degree of metamorphism is referred to
as the metamorphic grade.
mudrock
low-grade
metamorphism
site
J
phyllite
J
schist
gneiss
increasing
temperature
and
pressure
-1
l
I
1
high-grade
metamorphism
FIGURE 1 Sequence of changes affecting a mudrock: an example of metamorphic
grade.
From this Figure we can see that slate is a low-grade metamorphic rock, whereas
gneiss is a high-grade metamorphic rock resulting from much higher
temperatures and pressures.
TEACHING NOTES
Children may have observed folding or faulting either when looking at rocks
along the coast or in photographs. To investigate the processes involved in
producing these structures, Plasticine could be used to make models upon which
lateral pressure can be exerted. Sandwiches using brown and white bread and a
variety of fillings are also fun to use. They have the advantage that buckled 'rock
formations' can be eaten at the end of the lesson! Investigating the properties of
foods such as toffee can help children to understand how the sudden application
of pressure can cause rocks to crack or break, whereas the application of pressure
over a long period can cause them to bend.
Some rocks crack into a characteristic pattern--e.g. the joints in limestone
rocks, which can be studied from photographs or field visits. Substances such as
mud, of which the children will have had experience, can also exhibit this feature
when they dry out.
Two common activities, the firing of clay and cooking, can be of considerable
use in explaining how heat can alter materials. The children could examine clay
or cake ingredients before and after they have been subjected to heat, to see in
what ways the material has changed.
KEY POINT
Metamorphic rocks are rocks that have been changed by heat andlor pressure,
but that have not changed their chemical composition. The original minerals
produce new minerals under these conditions, thus forming a new rock.
Everyday 'metamorphic processes' include baking a cake, and making bricks
and pottery.
. ..).
b
STUDY COMMENTARY FOR UNIT 27
S -
SUPPLEMENT: SOlL
Main attainment target and levels addressed in this Section: AT9: levels 2
and 3
STUDY NOTES
This Section considers factors affecting soil formation and the main goil types
found in Britain.
Soil is essential for many of our activities. It is also a basic part of the natural
environment. Soil, together with the plant life it suppoPts, the rock on which it
lies, and the climate it experiences, forms a finely balanced natwal system.
Depending upon the context, the word 'soil' may have very different meanings.
A simple definition of soil is the material that plants grow in, and which
provides them with physical support and nutrients. There are other more
particular views of soil-engineers, geologists, hydrologists, farmers and
gardeners are all concerned with different aspects or properties of soil. The
geologist, for example, calls this layer the regolith, and regards it as the
weathered material of the underlying bedrock.
When fresh rock is first exposed at the surface of the Earth there is no soil. Soils
are produced by physical and biological agents acting on a parent material. This
may be solid rock or fragmented materials such as glacial deposits. Initially, the
parent material is acted upon (weathered) by climatic factors, such as rainfall and
temperature. Later, when colonized by plants, it is also acted upon by these and
other biological agents. The build-up of organic matter in the soil, from the
breakdown of plant litter, is a particularly important process.
THE SOlL PROFILE
If you dig through the soil down to the upper part of the underlying rock, a
cross-section of the soil is exposed. This is called the soil profile (Figure 2). A
soil profile often has a number of distinct layers, or horizons, characterized by
differences in colour, composition and texture. It is possible to make many
subdivisions and classifications of soil by using these horizons, but we can start
with a simple threefold division-which can be designated by certain letters.
horizon A
(topsoil)
horizon B
(subsoil)
horizon C
(weathering
parent
material)
FIGURE 2
A
so profile is a set of soil horizons.
SCIENCE FOR PRIMARY TEACHERS
Horizon A-sometimes
called topsoil
horizon B-sometimes
called subsoil
horizon C-parent
material.
The parent material underlies the soil. The term 'parent material' includes soft
substances, such as glacial and river deposits, as well as hard rocks, such as
sandstones, limestones and granites.
HORIZON CATEGORIES
Horizon A This comprises the material at the top of the soil profile. It is
usually dark in colour because of the decay of roots in situ and the incorporation
of plant litter from above. It is this horizon that is most affected by the activities
of living things. Most roots are found in this layer, together with plant and
animal life-from the larger animals such as moles and earthworms, to the
microscopic bacteria and fungi.
Horizon B This horizon consists chiefly of altered rock fragments. It contains
very little plant material, although live roots and some plant and animal life
occur. Within this horizon, mineral materials are actively broken down and
altered, plant nutrients released, and the size of the soil particles made smaller.
This horizon also receives material washed down from above, for example, fine
clay particles or iron oxides.
Horizon C This horizon is the parent material from which the soil has
developed. The parent material is often weathered but otherwise little altered. The
depth at which the parent material occurs depends on the nature of the underlying
rock as well as the length of time during which soil formation has been taking
place.
THE ROLE OF WATER IN THE SOIL PROFILE
There is an enormous range of very different soil profiles produced by different
soil processes operating at varying rates and in different combinations. Despite
the diversity of processes involved, the movement of water (i.e. percolation)
through the soil profile represents one of the main factors in its development.
The amount of water retained by the soil depends on the relative rates of input of
water to and loss from it. Factors affecting these rates include quantity and rate of
rainfall, temperature, and soil composition and depth. Water is mainly held
within the soil profile in holes and cracks of varying sizes: some, of very small
diameter, are full of water under most normal conditions; other, larger, holes and
cracks become filled as water percolates through the soil after rainfall. Around
the soil particle a layer of water is held tightly by surface tension and never
released. Capillary water around the particles moves by attraction to other water
molecules.
Water is a major factor in bringing about the rearrangement of weathered material
(see Figure 3), and so producing the distinctive soil profiles. Rearrangement
takes place chiefly via the transfer of material by water through the soil profile.
Most transfers are vertical-upwards and downwards. In the UK, where
precipitation almost always exceeds evaporation, upward movement is mainly
biological, and results from the uptake of water and nutrients by plants. The
downward movement of water, carrying minerals in suspension or solution,
produces the characteristic soil profiles found in Britain. The amount and speed
of water flow through the soil determines both the rate at which the products of
weathering are removed and, in part, the nature of the resulting soil.
-
,
STUDY COMMENTARY FOR UNIT 27
..
d d d d d
d d d d
d d d d
d
d
d
d
d
d
d d
d d
d d d
d
d
d
d
d
d
d
d
d
FIGURE 3 The role of water is important at every stage of the soil-forming
process: (a) when rock is first exposed to the process of weathering; (b) when plant
lie begins to grow on and in the weathered rock; (c) in the rearrangement of material
to produce the soil profile.
In a soil that allows rapid percolation, a high annual rainfall produces a
substantial throughput of water, and hence a substantial potential for moving
material from one part of the soil to another. Much of this water drains freely
out of the soil and through the material below, taking with it dissolved or
suspended material. This process is termed leaching.
Some soils provide clear evidence for the transfer of soil constituents. The
podzol is one such soil commonly found in Britain. In their natural
environment, podzols often occur under heather or coniferous woodland, on
sandy, freely draining, parent materials. They have a very distinctive profile,
which can be divided into four broad horizons from the surface downwards (see
Figure 4).
raw acid humus in
and above the A layer
marked bleached layer
marked black or red-brown
iron-rich horizon
weathering parent
material, e.g. sandstones
FIGURE 4 Podzol soil profile.
Notice that this profile includes a horizon E. This denotes a layer that is usually
depleted of iron oxides; in the podzol profile, horizons E and B should be
considered together, for it is here that the effects of the downward transfer of soil
material by water are clearly seen. Horizon &the eluviated, or leached, layerconsists chiefly of bleached sand grains (that is, sand grains from which the
surface coatings have been removed). In contrast, horizon B often appears to
consist of coated sand grains cemented together by black organic materials andlor
red-brown iron-rich materials. Horizon C is the little-altered parent material from
which the soil has developed.
SCIENCE FOR PRIMARY TEACHERS
The soil-forming process responsible for this type of profile involves the
transfer, by percolating water, of iron, aluminium and organic matter from
horizon E to its deposition in horizon B. This process produces one of the most
visually distinctive soil profiles to be seen in Britain.
SOIL-FORMING FACTORS
Soil is only one part of the natural environment; it interacts with other
components, and so forms an ecosystem. The wide variety of possible
interactions is responsible for the large number of soil types found. In
considering which components of the environment exert a major influence on the
nature and distribution of soils, it is possible to isolate four major factors:
1
parent material
2
climate
3
terrain
4
plants and animals.
In addition to these factors, it is important to take account of how long the
interactions have been taking place. We should perhaps consider time as a fifth
factor.
Parent material
Parent material strongly influences the soil and its properties, particularly during
the early stages of soil development. For example, the weathering of a coarse
sandstone parent material produces a well-drained, coarse sandy soil. In contrast,
a mudrock generally weathers to give a fine-textured soil, which may allow water
to flow through it only very slowly.
Limestone and chalk (predominantly made up of CaCO,) exert a distinctive
influence as they are easily soluble. When they are weathered, much of the
original rock goes into solution and is thus removed, so what remains has often
only a very small mass; consequently soils developed on limestone or chalk are
often shallow, with an organic A .horizon directly overlying weathered parent
material.
Climate
Climate is another important factor to consider in relation to soil formation. On
a world scale, there are broad climatic regions, and it has become traditional to
distinguish complementary soil and vegetation regions which often extend
latitudinally across the globe. On a smaller scale, climate remains of
fundamental importance, and in Britain soil variations occur because of
differences in temperature and rainfall. At this level, the major climatic influence
on soil development is probably rainfall. Rainfall is the major source of soil
water and, as we have seen, the presence of water and its percolation through soil
is an essential process in the development of a soil profile. Climate also has a
marked influence on soils developed from materials of low permeability. When
rainfall is heavy, such soils are likely to become waterlogged, forming gleys or
peats.
Terrain
Terrain influences soil development in a rather complex way, reflecting both the
varying conditions of drainage and water flow within the landscape, and the
patterns of erosion and deposition. If we take an idealized landform developing on
one uniform parent material, the sequence of soils across that landscape reflects
the varying conditions of soil moisture and drainage at each site (see Figure 5).
On the flat crest, the soil is well above the water table-the underground surface
below which the rocks are saturated with water-so water percolates rapidly to
STUDY COMMENTARY FOR UNIT 27
give a soil that is excessively freely drained. Moving downslope from the crest,
over the upper slope convexity, the depth of soil changes, which results in the
water table appearing to move closer to the surface, but drainage is enhanced by
lateral flow, either over or through the soil; these soils are typically freely
drained. This convex part of the slope may also be subject to soil erosion, and
consequently the soil may be shallow. Further downhill, on the middle and lower
slopes, the soil is again influenced by both vertical and lateral movements of
water; but this is an area where material eroded from upslope accumulates, so the
soils are deeper and freely drained. At the slope foot, the water table is likely to
be close to the surface, and there is little gradient to promote lateral flow;
vertical percolation becomes restricted and the soil may be waterlogged for part
or all of its depth. Valley soils are often deep because of the accumulation of
eroded material, and they can often be waterlogged. In some circumstances the
flat valley floor soil may be sufficiently wet to lead to the formation of peat.
V>rn>>>T
e
x
freel dramed
>>
S
freely dramed
>
- zone of transfer
- net accumulation
)) imraz;~l~>>
deep.
freely dramed
waterlogged
)
FIGURE 5 The effect of terrain on soil development.
Plants and animals
Weathering and soil development are accelerated by the appearance and growth of
plants on the surface of the bare rock, or on weathered debris. These plants,
which include lichens and mosses, photosynthesize, or 'fix', atmospheric
nitrogen and incorporate it as plant protein. When these plants die, they return a
variety of organic materials to the surface of the weathered rock-this is the first
soil material. By returning organic material to the surface, these first colonizers
of the rock provide both nourishment and a 'foothold' for a succession of plants
and organisms-from lichens and mosses, through grasses and shrubs, and
eventually to trees. This is the beginning of the biogenic cycle, which gives soil
many of its distinctive characteristics. Its importance is not just that it adds plant
material to the soil; in addition, -a large population of soil organisms (e.g.
earthworms, fungi and bacteria) helps break down materials for incorporation
with the weathered minerals. The biological activity of plants and animals-in
particular the action of plant roots, which penetrate the underlying rock and force
it apart-ontributes
greatly to the process of rock disintegration.
SCIENCE FOR PRIMARY TEACHERS
Time
Time is difficult to establish as an independent influence on soil development.
Nevertheless, the time during which the foregoing factors have been interacting
to produce soils will be reflected in the nature of the soils developed. It is often
suggested that the influence of parent material is greatest during the earliest
stages of soil development, but that with time climate may become dominant.
Since most soils in Britain have developed since the end of the last ice age
(about 10000 years ago), it is important to ask how well developed they are, and
how they might change in the future.
HOW DO SOILS DIFFER?
Given the complex interactions between the soil-forming factors, it is not
surprising that there is an enormous range of soils in Britain. Climatic and, as
we have seen, biological factors strongly influence the development of soils and
have led to the formation of four major soil types in Britain: podzol; brown
earth; organic (rendzina is an example of an organic soil); and gley (see Figure
6). The balance between water input and drainage is of major importance in
determining soil type (see Figure 7j.
A
A raw acid humus in
and above the A layer
E marked bleached layer
organic matter well
incorporated in soil
B brown, with good
crumb structure
marked black or red-brown
~ron-richhorizon
brown earth
podzol
A organic matter well
incorporated in soil
A
organic matter well
incorporated in soil
B grey or mottled
profile
C hard limestone
--L'---
rendzina
FIGURE 6 The four main soil types in Britain.
Well-drained soils
Rainfall arriving at the surface of a well-drained soil percolates rapidly through
it, and often carries soluble soil constituents, which may be transferred from one
part of the soil to another, or completely removed. If the process of removal has
been operating for long enough, the soil is described as leached. The rate at
which a leached condition is attained will depend on the nature of the parent
material; in sandy soils it may occur rapidly.
The podzol discussed earlier is a well-drained soil, developing on a sandy parent
material, often under coniferous woodland. Within the upper part of the profile a
distinctive grey 'bleached' horizon (E) is clearly visible. The black or red-brown
layer (B) is evidence of the rapid percolation of water through the profile, and
consequent leaching. Organic matter and iron is removed from the bleached layer
and deposited in the layer beneath.
STUDY COMMENTARY FOR UNIT 27
good
A
9
low input
high input
LEACHED
PODZOL
good drainage
good drainage
.-C
E
-0
D
C
low input
high input
GLEY
PEAT
poor drainage
poor drainage
poor
FIGURE 7 Soil water balance and the formation of soil types.
A brown earth develops under a deciduous forest or grassland area. There is often
no distinct boundary between the A and B, and B and C horizons, and the soil
has a good crumb structure. Horizon A is usually dark brown in colour with
abundant soil organisms. This grades into horizon B, which is lighter in colour
and passes into the weathering parent material. Both acid and calcareous brown
earths occur, depending on the nature of the parent material.
Rendzinas and rankers are generally thin soils with the A horizon developed over
the bedrock. Rendzinas are thin, alkaline, organic soils; rankers are thin, acid,
organic soils.
Waterlogged soils
Many soils are affected by waterlogging periodically and for varying lengths of
time. The cause of waterlogging may be a high groundwater table, slow
percolation of rainfall through the soil, or both. The characteristic features of
waterlogged soils are predominantly grey and bluish-grey colours in the zone of
permanent waterlogging, and a patchwork of grey and bluish-grey colours
together with orange and yellow colours (this patterning is known as mottling)
in the zone where waterlogging occurs for part of the year, or for short periods
throughout the year.
The most extensive waterlogged or seasonally waterlogged soils are gley soils.
Gleys are often waterlogged and anaerobic, with iron present mainly in the greycoloured reduced state-iron(I1); mottling occurs in horizons that dry out and
where some oxygen penetrates and oxidizes iron locally to the red-coloured
state-iron(II1). Peats accumulate under wet conditions.
SOIL TEXTURE
Soil is made up of a range of mineral particles, in some cases intimately mixed
with organic particles. The relative proportions of the different-sized particles
present in a soil determine its texture. Broad categories of soil, such as sand, silt
and clay, are fairly easy to distinguish (Table 3), although a number of
intermediate soil classifications exist. Mixtures of different-sized particles are
known as loams; we can thus refer to, say, sandy loams or clay loams.
SCIENCE FOR PRIMARY TEACHERS
TABLE 3 Size distribution '(in mm)
of the main soil particles
sand
silt
clay
2.0-0.02
0.02-0.002
less than 0.002
Soil texture can be quickly assessed in the field by rubbing a moist sample of
soil between the fingers. The feel of the soil depends to a great extent on the
relative proportions of sand, silt and clay, and is generally described as soil
texture.
Sandy soils feel gritty; the coarse particles can be clearly seen and look like
sandpaper. A moistened silty soil feels smooth and rather soapy. A clayey soil
has a large proportion of fine particles and feels sticky. These three categoriessandy, silty and clayey-are just the broad textural classes. Finer subdivisions
are made to take account of soils with different mixtures of sand, silt and clay.
For example, a soil described as having a sandy clay loam texture will have
approximately 57% sand, 25% clay and 18% silt.
Soil texture refers only to how soils feel to the touch. Soils having the same
texture may look very different. Alternatively soils may look very similar but
have quite different textures.
SOIL STRUCTURE
The components of soil do not usually occur as separate sand, silt or clay
particles, but are normally 'stuck together' and organized into aggregates; the
soil is then described as having structure. Where there is no aggregation, the soil
is' described as structureless.
There are many types of soil structure. Some are produced by the actions of
farmers or gardeners when they artificially break up the soil. These structures are
very irregular in shape and called clods or fragments. Naturally occurring soil
structures have different shapes and sizes, ranging from near ball-like structures
of a few millimetres in diameter (granular or crumby structure) through to large,
vertical, pillar-like structures (columnar or prismatic structure), which may be
more than 20cm long. Structure helps to determine how successful a soil will
be in supporting good plant growth and allowing water to percolate.
Blocky structures result when the soil particles are aggregated into irregular cubelike shapes. This arrangement, with blocky structures of different sizes, results
in a loosely packed soil with large connected holes down through the subsoil.
Soil water percolates freely and plant roots grow easily into the soil to take up
water and plant nutrients (see Figure 8a). Under these conditions crop growth
should be good.
In contrast, platy structures result when the soil particles are aggregated into
plate-like forms, arranged horizontally. These structures are often very compact,
with few vertical holes or cracks. They restrict the free percolation of water from
topsoil to subsoil and, under moist conditions, may produce waterlogging within
the topsoil and restrict plant growth. Plant growth is further restricted when
roots are unable to penetrate platy structures and reach the soil below; the plant
cannot gain access to water and nutrients within the subsoil, and crop growth is
limited (see Figure 8b).
In normal British summers, the water in the topsoil may be insufficient to
satisfy the needs of plants, which may wilt and die. Platy structures occur
naturally within the soil, but they are also produced by the farmer ploughing, or
the gardener digging the soil, when it is wet.
STUDY COMMENTARY FOR UNIT 27
(a)
(b)
FIGURE 8 The effect of soil structure on plant growth. (a) Blocky structure. (b)
Platy structure.
TEACHING NOTES
Soil is an ideal medium for children to work with since it is readily available
almost everywhere. A variety of investigations and topic work can be developed
using soil. Your school may have gardens or grounds, which will be useful
resources, and some children will have access to other gardens; it may also be
possible to involve parents who are keen gardeners.
In work on soil you should encourage the children to think of it as a precious
resource-and one that should not be contaminated or wasted. Research into past
disasters, such as the creation of the dust bowl in the USA, can provide crosscurricular links and reveal the problems that societies have had to face when soil
has been abused. We should not be complacent today, ,since numerous
contemporary examples can be cited of soil contamination spoiling vast areas of
land that previously had been productive. Thus, the study of soil can provide an
opportunity for the discussion of environmental issues.
For younger children, work on soil can involve gathering information about
what soil is and finding out that not all soils look the same. Key stage 2 work
can progress to children finding out, by testing, what soil is made up of, and
how different soils vary.
An early question to ask the children is: what is soil? Some children may know
that soil is made up of different-sized particles and contains decaying plant and
animal material, called humus.
To begin investigative work, children could collect a sample of soil from their
garden or local environment. As with the study of rocks and minerals, beforexhe
children perform any other activity, allow them time to look carefully at their
soil sample, using a hand lens. If you have a variety of soils, encourage them to
describe what they can see; ask whether they can identify any differences and
similarities-and perhaps talk to them about what they think soil is made of and
what we use it for. Their sample may contain clues as to some of the things it is
made of--e.g. small pieces of leaf or twig. Handling the soil will encourage
them to begin thinking about soil texture; they may be able to use the
appropriate vocabulary to describe what their sample feels like, such as smooth,
sticky, damp, gritty, and so on. They may also discover that the smaller the size
of the soil particles, the smoother it feels. Young children could record their
observations as illustrations, using coloured crayons or paints.
If you have access to a bank of sieves-i.e. a series of sieves having differentsized meshes-further analysis can be done to separate the different-sized
particles; comparisons can be made between a variety of soils from different
localities. Older children could weigh each sieve fraction and compile histograms
SCIENCE FOR PRIMARY TEACHERS
for the different soils. When comparing soils, the children will need to think
about how to ensure that their tests are fair, and make careful records of the
results. (Note: Ensure that soils are dry before you carry out any investigations
on them.)
If you are able to obtain soil samples from different localities, older children may
begin to appreciate that there is a relationship between underlying rock type and
soil characteristics. As with rock samples, you could build up display
- - and
resource materials of different soil types.
INVESTIGATION 4: ARE ALL SOILS THE SAME?
Get the children to collect samples of soil from different places in the local
environment, e.g. gardens, parks, fields, woods, waste ground. First, ask
them to look carefully at the soils and say whether they think they are all the
same. Can they devise a test to discover whether their hypothesis is correct?
One method of investigating whether or not soils differ is to put a small
sample of soil into a clean, empty container with a lid, such as a jam jar, and
add water to almost fill the jar. Put the lid on tightly and shake the jar
carefully. Leave the jar undisturbed overnight-r
longer if you can.
After a suitable time has elapsed, ask the children to look carefully at the jar.
Can they see different layers in it? How can they record their observations so
that the different types of soil can be compared? Can they find out what
makes up each layer? Can they identify what is floating on top of the water?
If they examine some of the material that is floating, they should be able to
identify pieces of dead plant material. This makes up the humus in a soil.
When children become more aware that soils differ, they could devise tests to
investigate these differences. Investigation 5 suggests a method of discovering
whether or not all soils hold the same amount of water.
INVESTIGATION 5: DO ALL SOILS HOLD THE
SAME AMOUNT OF WATER?
For this investigation you will need to collect together three known masses
of different soil samples--e.g. sand, clay and loam (a mixture of sand and
clay) or peat; some water; three filters-the top part of a squash bottle with a
piece of muslin over the neck makes a good filter; three containers for the
filters to sit in; a jug; and a stop-watch.
The investigation should be set up as in Figure 9, using known volumes of
water. The children will need to think about whether they should weigh each
soil sample before they begin, and whether they should test an equal quantity
of soil. The same volume of water is poured into each filter; the children can
then time how long it takes for the water to pass through each soil sample.
,
,n
bottle with
bottom
removed
muslin
over
neck
I
n
n
peat
FIGURE 9 Investigating how much water a soil can hold.
STUDY COMMENTARY FOR UNIT 2 7
What does this investigation suggest about the amount of water the different soil
types can hold? Discussions arising from such an investigation could focus on
the suitability of different types of soil for different agricultural activities.
A similar investigation could be done to find out whether different soils contain
different amounts of air. Try using large stones or pebbles, and gravel to
demonstrate that air spaces exist between particles. You can then pour known
volumes of water on to dry sand, clay and loam samples, to discover which soil
sample takes up the most water to fill its air spaces.
At key stage 2 more advanced investigations could include measuring the pH of a
soil and assessing the effect on plant growth of adding different amounts of
fertilizer to the soil.
Children may well have encountered the term 'pH' in previous work, e.g. when
doing investigations on rainwater. The pH value of a soil expresses its degree of
acidity or alkalinity, and is a measure of the hydrogen ion concentration in a
solution (you may wish to refer to the chemistry materials to refresh your
memory about this). Children need to be aware that the scale normally runs from
pH 0 to pH 14, with pH 7 as neutral.
acid soil
neutral soil
alkaline soil
Gardeners and farmers need to know the properties of their soil so that they can
decide which plants will grow best. Working.on a variety of soils, children could
design an investigation to test the pH of a soil sample. (Note: Chemicals in tap
water may affect the results, so it is best to use distilled water to form the soil
solution.) Adding a few drops of Universal indicator to a soil solution in a testtube should enable the children to estimate the pH. To illustrate different soil pH
values it is best to compare, say, a podzol and a rendzina. Small differences in
pH may not be detectable using this method.
If your local soil is acid, the children can find out what methods can be used to
improve the soil by making it less acid-e.g. adding lime to it.
The use of fertilizer gives another opportunity for older juniors to use their
process skills in designing a series of investigations to determine the optimum
level of fertilizer, andtor the 'best' fertilizer, for plant growth. Rapid-cycling
brassicas (see the Resources Section at the end of this Study Commentary) are
ideal plants to use for these investigations. Activities such as these would also
be useful for a class project; small groups of children could work on the different
variables and then combine their results.
Work on the environment may well instigate a discussion about soil erosion or
pollution; the children could carry out experiments on rapid-cycling brassicas
using alum to investigate the effects of chemical pollution, or a heavy
lubricating oil to simulate the effects of an oil spillage.
Throughout this Section, we have stressed the fine balance that exists between
the soil and its environment. In Britain there is considerable evidence of this
balance: we have a wide range of soils, reflecting the often intricate interactions
of environmental factors. In a land as densely populated as Britain it is not
surprising that our activities)have to date been a major influence on soil
development; it appears that this influence will continue and perhaps increase in
degree. In your own locality it may be possible to examine the changes in soil
type that occur across the landscape as one of the natural soil-forming factors
changes. Look at the different soils as you go down a hillslope or as you pass
from grassland to woodland. These soil differences often reflect soil-environment
interactions that have taken place, with only minor alterations, for hundreds or
thousands of years. It is almost impossible, however, not to see the impact of
our activities on the landscape, in agriculture, forestry, urban development or
recreation.
STUDY COMMENTARY FOR UNIT 27
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.
Q1 From the list below, select one pair of rocks in which the second rock
type could not have been derived directly from the first rock type at some stage
in the rock cycle.
+ mudrock
A
Granite
B
C
+ mudrock
Granite + andesite
D
Gneiss
E
Peridotite
+ gabbro
F
Mudrock
+ schist
G
Andesite
+ rhyolite
H
Granite + sandstone
Gabbro
+ granite
Q2 to Q4 The list below contains several statements about a rock, or rocks.
Each statement describes either a characteristic feature of the rock or a stage in its
formation. Note that you may need to select the same statement(s) for more than
one question.
A
The rock formed at depth beneath the Earth's surface
B
Clay minerals are important constituents of this rock
C
The rock was hot at the time of its formation (i.e. more than 600 "C)
D
The rock contains undecomposed olivine as an important constituent
E
The rock has a crystalline texture
F
The rock contains undecomposed amphibole as an important constituent
G The rock is coarse grained
H
The rock contains garnets as an important constituent
Q2 Select one statement that could describe only an igneous rock.
Q3 Select one statement that could describe only a sedimentary rock.
Q4 Select the only two statements that could be used to describe a rhyolite.
Q5 and Q6 Figure 10 shows the variation of temperature with depth in
three continental areas of the USA: the Basin and Range Province, central USA
and the Sierra Nevada. The first two of these are shown also in Figure 25, on
p. 5 1 of Unit 27.
Q5 What is the thermal gradient beneath the Sierra Nevada? From the list
below select the option that is closest to your own.
A
5 "Ckm-l
B
8"Ckm-l
C
12"Ckm-'
D
lS°Ckm-l
SCIENCE FOR PRIMARY TEACHERS
depthkm
FIGURE 10 For use with Q5 and Q6.
Q6 Imagine that thick sequences of mudrocks have been buried to a depth of
4 0 km below each of the areas shown on Figure 10. Below is given a list of
possible rocks or processes that might occur at 40 km depth in these areas today.
Which two statements are correct?
Phyllites beneath the Basin and Range Province
Gneisses beneath central USA
Schists beneath the Sierra Nevada
Phyllites beneath the Sierra Nevada
Schists beneath the Basin and Range Province
Melting of the crustal rocks to produce granitic magmas beneath the Basin
and Range Province
Gneisses beneath the Sierra Nevada
Melting of the crustal rocks to produce granitic magmas beneath central
USA
NOTES