EARTH SCIENCE TEACHERS ASSOCIATION
*'
NATURE
CONSERVANCY
COUNCIL
Units 11-15
Specially prepared for the Association for Science
Education (ASE)
CONTENTS
Unit 11: The water cycle - a natural recycling process
Unit 12: Which Roadstone?
Unit 13: The Geological Time Scale
Unit 14: 'Who's for a hot tight squeeze in inner space?"
Unit 15: Rock Power! - Geothermal energy resources
The following are also available as single Units from the addresses shown below:
Unit 1:
Unit 2:
Unit 3:
Unit 4:
Unit 5:
Unit 6:
Unit 7:
Unit 8:
Unit 9:
Unit 10:
Will my gravestone last?
Earthquakes - danger beneath our feet
Fluorspar - is it worth mining?
Building sedimentary structures - in the lab and millions of years ago
Waste and the hole-in-the-ground problem
Nuclear waste - the way forward?
Neighbourhood stone watch
Moving ground
Ground water supplies - a modem Jack and Jill story
Astrogeology - and the clues on the moon
"Science of the Earth" Units are obtainable from:
ESTA - Mr Ray Balmer, 3 Ashington Drive, Bury, Lancs., BL8 2TS.
GA - The Geologists' Association, Burlington House, Piccadilly, London, W1 V 9AG.
Geo Supplies Ltd., 16 Station Road, Chapeltown, Sheffield, S30 4XH. Tel: (0742) 455746.
Student Sheet 1
Unit 11: The Water Cycle - a natural recycling process
1.
What is Water?
Water is the only common substance which exists as a solid (ice), liquid (water) and gas (water vapour)
on or near the Earth's surface. Pure water is a compound of hydrogen and oxygen (H20), but most
naturally-occurring water is really a weak solution. For example, water in the oceans contains far
more dissolved substances than water in most rivers. Water is often called "the universal solvent"
because it dissolves many common and important substances and this explains why natural water
is a solution.
Substances which are commonly dissolved in water are calcium, magnesium, sodium, chloride,
hydrogen, carbonate, sulphate,nitrate and phosphate: these substances are ions, but you do not need
to understand the meaning of this for this unit on the water cycle.
1.1
Natural surface water is a weak acid (carbonic acid) because it contains dissolved carbon dioxide.
From where does the water dissolve this carbon dioxide?
The chemistry of natural water changes a lot as it moves from one place to another. For example,
water flowing in a mountain stream dissolves solid material from the stream bed below and gases from
the atmosphere above it. Another example is seawater: it has a different chemistry from river water,
and most ofthe 'salt' which is dissolved in seawater is transported there by rivers. It is therefore not
sensible to speak of "natural water" as if it were the same in all respects and in all places.
1.2
What method would you use to separate solid particles from a water sample?
1.3
You have probably come across the idea of water hardness before. Can you recall what chemical
substances cause hardness of water and under what natural conditions water becomes 'hard'?
1.4
Bearing in mind that the water which evaporates from the oceans into the atmosphere is almost
PURE, try to explain why seawater is a much stronger salt solution than is river water. It might help
to know that, in some parts of the world's oceans, salts precipitate out of solution to form crystals on
the sea bed.
1.5
Collect samples of water from different places: tap water, rain water, distilled water, sea water, pond
water. Remove any solid particles using the method you stated in question 1.2. For each sample,
evaporate a small amount from a large watch glass placed on a beaker (100 ml) which is about half
full of water and which is gently heated from below.
Examine the watch glasses when all the water has been evaporated. Compare the RESIDUES (the
coating left on the watch glass) and suggest explanations for your results.
2.
Introduction to the Water Cycle
It has been estimated that there are about 1.4 million cubic kilometres of water on or near the Earth's
surface, and that 97% ofthis is in the oceans. The atmosphere contains a tiny amount as water vapour
and as cloud droplets.
2.1
Calculate the total AMOUNT of FRESH water (i.e. not in the oceans) on the Earth.
Ofthe fresh water, 75% is stored as ice sheets and glaciers and 25% as liquid water on or below the
land surface.
2.2
Calculate the total AMOUNT offresh LIQUID water on the Earth.
Student Sheet 2
Unit 11: The Water Cycle - a natural recycling process
As you probably know, water in these three states of matter (solid, liquid, gas) is in a continuous state
of movement within the WATER CYCLE (sometimes known as the HYDROLOGICAL CYCLE). The
water cycle is an example of a MODEL because it REPRESENTS and SIMPLIFIES things going on
in the real world.
These real events are very complicated and this model helps us to understand them because it enables
us to study each stage in turn. It isjust like learning about an engine by studying the individual parts.
When we break something down into smaller sections to help us to understand it we call it ANALYSIS,
so in this part ofthe Unit we will ANALYSE the water cycle.
The Water Cycle You Know
You will have come across the water cycle before, possibly several times. It may have been presented
rather like the diagram, Figure 1.
Evaporation
Sea
Underground water movement
Figure 1. The Water Cycle You Know
Although this diagram is correct, it is rather simple for our needs now. In particular, we need to be
aware that there are more stages in the cycle; it is more complicated. Some of the details are best
shown in diagrams. Study these carefully so that you can use them later.
Student Sheet 3
Unit 11: The Water Cycle - a natural recycling process
A Closer Look at theWater Cycle
a) What happens during rain?
Figure 2 shows the water movement during rain.
Some water stays on the surface as puddles, pools, etc., this is surface storage;
some flows downhill as overland flow and eventually reaches streams and rivers;
some flows downward into the soil by infiltration to become soil water.
The soil water moves downwards by deep percolation until it reaches a depth where all the spaces
between the soil particles are filled with water.
The water within this saturated zone is called groundwaterand the surface ofthe groundwater zone
is called the water table.
You can see the water table by looking down a well, the surface ofthe well water is at the water table.
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_-----:--r-.--T ·
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table
r'--t -... Gro~dwate~
Infilt:;=- ~ ~._. _
Deep percolation
Figure 2. Water Movement During Rain.
2.3
When will overland flow be the greatest, during heavy rain, light rain or snow? Explain your answer.
2.4
Plan and describe a way of measuring rates of overland flow.
2.5
When will infiltration be the greatest, during heavy rain, light rain or snow? Explain your answer.
2.6
Plan and describe a way of measuring rates of infiltration.
a) How does water move underground?
Figure 3 shows how water beneath the surface moves. In heavy rain, and for some time afterwards,
the soil water moves downslope as throughflow. Groundwater, however, is always moving because
the water table is never horizontal and the water flows in the direction ofthe slope of the water table.
Where the water table reaches the ground surface, water flows out forming a spring or marsh. Some
groundwater flows directly into stream channels as base flow.
2.7
Would springs at low altitudes or springs at high altitudes tend to have the greatest and most reliable
flow of water? Explain your answer.
Student Sheet 4
Unit 11: The Water Cycle - a natural recycling process
+= _ Soil water
bflow
-------. '. .
~_ :v:~e~t~~~e.
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..,c.... ~.
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.-:- Groundwater fl~W •
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Stream
• Groundwater
. into stream
Figure 3. Water Movement Through and Over the Ground.
2.8
What factors might cause the water table to move up and down?
2.9
Plan and describe a way of measuring changes in the height ofthe water table.
c) How does the water move back into the air?
Figure 4 shows how water is transferred into the air. Providing the air is not too damp, all water at
the earth's surface will lose water to the atmosphere by evaporation.
Water vapour
rI
Transpiration
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Evaporation
\
Transpiration
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Surface water
(surface storage)
Figure 4. Water Movement into the Air.
Soil water
Student Sheet 5
Unit 11: The Water Cycle - a natural recycling process
2.10 Plan and describe a way of measuring rates of evaporation in an area.
Plants need water to survive. They take in water from the soil, through their root systems, by water
uptake. This water passes through the stems and leaves of the plants and is lost into the atmosphere
as water vapour by transpiration.
2.11 Plan and describe a way of measuring how much water a plant gives to the atmosphere by
transpiration.
The water transpired by the plants is then evaporated from the leaves to form water vapour since the
water vapour is produced by both processes, they are often together called evapotranspiration.
During rain, much water falls onto the leaves of plants and most of this later evaporates back into the
atmosphere. By this process of interception the water never reaches the ground.
2.12 How would you expect evaporation and transpiration rates to be affected by warm and cool weather
and by windy and calm conditions?
The water vapour in the atmosphere is an invisible gas. When the atmosphere becomes cooled, it
cannot hold as much water vapour and so some ofthe gas changes (condenses) to liquid water in the
form of minute droplets. Large numbers of these droplets together form clouds. More cooling causes
the clouds to produce rain or some other form of precipitation.
The Water Cycle: Putting it all Together
2.13 Read all this question before you begin.
U se the information and diagrams you have been studying to complete the flow diagram in Data Sheet
1. Some of the stages involve mainly storage of water and these are shown on the diagram in
rectangles (I
Dbut others involve mainly transfer (movement) from one storage zone to another;
these transfer processes are shown as rectangles with curved sides (I
I).
The terms you will need to complete the flow diagram are given and defined on Student Sheets 6 and
7. Storage stages are listed on Sheet 6 and transfer processes on Sheet 7.
Student Sheet 6
Unit 11: The Water Cycle - a natural recycling process
Storage Stages
CLOUDS. Visible liquid water droplets held
up in the atmosphere against gravity by
gentle upward air currents.
STREAMS AND LAKES. Streams consist
of water flowing in channels, from the
smallest permanent trickle to the largest
river. Lakes are permanent stores of water
on the Earth's surface, usually fresh water.
Streams and Lakes
GROUNDWATER. Water stored in the rock
in the same way as it is held in a sponge. The
upper limit of the saturated zone is called the
water table.
\
/'
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l
SURFACE STORAGE. Water stored temporarily in depressions on the Earth's
surface, following a rainstorm.
I
Groundwater
/'
'/7
Surface Storage
PLANTS. The vegetation that plays an
important part by transferring water from
the soil to the air by transpiration.
SEAS AND OCEANS. Permanent water
storage in large depressions on the Earth's
surface.
SOIL WATER. Water held in the soil but
the soil is not in a permanently saturated
state.
WATER VAPOUR. Water stored in the atmosphere as the invisible gas.
Student Sheet 7
Unit 11: The Water Cycle - a natural recycling process
Transfer Processes
CONDENSATION. Water changing from
invisible water vapour to visible liquid water
on cooling. Energy is given out by the water.
Breathe on a cold pane of glass; the water
vapour in your breath condenses to water on
the glass.
DEEP PERCOLATION. The seepage of soil
water downwards into the ground water zone.
EVAPORATION. Water changing from the
visible liquid to invisible water vapour on
warming. Energy is taken in by the water.
GROUNDWATER FLOW. The movement of
water within the saturated groundwater zone
in the direction of the downward slope of the
water table.
Overland Flow
THROUGHFLOW. The downslope movement of soil water, usually caused by heavy
rain.
TRANSPIRATION. The loss of water
vapour by the leaves of plants.
WATER UPTAKE. Water taken from the soil
by the root systems of plants.
.
~
INFILTRATION. Water soaking into the soil
or rock from the Earth's surface.
OVERLAND FLOW. Water flowing over the
surface of the soil or rock, usually on its way to
stream channels.
PRECIPITATION.
snow and sleet.
STREAM FLOW.
downslope.
Rainfall, drizzle, hail,
Streams flowing
:L.
"
Transpiration
All the stages of the flow diagram you have just completed involve storage of water to some extent
because a certain volume of water is temporarily stored while it is being transferred from one major
source to another. A particularly difficult stage is the stream itself because it is so obviously
transferring water from one place to another, yet so much water is stored in rivers at anyone time.
Perhaps you should add a curved sided rectangle to the 'streams and lakes' stage.
Where Does Ice Fit In?
Notice that ice is not included by name in this version of the water cycle. Ice does not move as readily
as do water and water vapour, so it tends to get locked up in one stage for long periods, sometimes for
thousands of years. We could include separate stages involving ice, but it is more convenient to
include it with liquid water.
2.14 In which ofthe stages ofthe water cycle would you place each ofthe following?
a.
b.
c.
d.
e.
f.
Ice sheets on land
Frozen rock
Frozen soil
Icebergs
Valley glaciers
Ice crystals in the atmosphere
Student Sheet 8
Unit 11: The Water Cycle - a natural recycling process
2.15 Which stages of the water cycle are mentioned in the T.V. weather forecast, either indirectly or
directly?
2.16 Write a weather forecast or a news item using as many of the water cycle stages as possible. Try to
follow the water cycle through as far as possible and use the correct words if you can. For example,
you could forecast high rainfall for the following day, with high surface storage, especially on
concrete surfaces. This might lead to rapid infiltration but if much of the water fails to infiltrate it
will flow over the surface as overland flow and possibly cause problems for some people .... You could
deliver your talk to the class or record it on audio or video cassette.
3
The Water Cycle at Different Scales
One advantage of the water cycle model is that it can be used at many different scales. The figures
given in section 2 refer to the planet Earth as a whole, but the cycle is often applied to smaller areas
such as continents and islands.
3.1
Imagineyoustandoutin the rain for a few minutes andit then stops
raining and you dry out! Describe the complete water cycle which
includes yourself. You should refer to stages which actually occur
such as overland flow and even stream flow. However, some
stages will probably not apply: you would probably drown ifthere
were any infiltration! You will not be able to include all the stages
of the water cycle, but it must go all the way round from
precipitation to clouds.
Ifyou did task 3.1 you will have described a part ofa very small scale
water cycle. At the other extreme is the general, global water cycle
described in section two. Between these two extremes is the
drainage basin water cycle.
Standing in the Rain
A drainage basin is the area ofland which is drained by one stream and its tributaries, as shown in
Figure 5.
Drainage
basin outlet
Figure 5. Drainage Basin
Student Sheet 9
Unit 11: The Water Cycle - a natural recycling process
Organisations such as the Water Authorities are constantly measuring water flow and amounts in
drainage basins, and they make regular use ofthe water cycle model. In practice, only certain stages
of the cycle are studied in drainage basins.
3.2
Which stages of the water cycle are likely to be of greatest interest to the Water Authorities?
A drainage basin can be compared with a bank account: it has inputs and outputs and the balance
changes with time. An output is a loss of water from the basin. Also, of course, water is transferred
from one stage to another within the drainage basin.
3.3
List as many inputs and outputs as possible for the surface parts of a drainage basin. Use two
columns.
3.4
What are the main ways by which water is stored in a drainage basin (surface and subsurface)?"
3.5
If the outputs stayed the same over, say, a month and the inputs increased, how would the total
storage change?
3.6
Ifthere were no surface lake or reservoir in this drainage basin, where would the extra storage take
place?
3.7
What might be the one main input and the two main outputs for a typical British drainage basin?
3.8
Suppose you wished to measure each ofthe three stages you named in question 3.7, whereabouts on
the drainage basin would you measure them? You may decide to choose one key point or you may
decide to get a broad picture over the whole basin by measuring the same cycle stage at several places.
Don't worry about equipment at this stage.
4
Water Purification by the Water Cycle
Ground water, soil water and surface water dissolve substances from the rock and soil over which they
pass. When these weak solutions reach the streams the dissolved substances are called the dissolved
load of the stream. Most streams also contain solid particles which can be removed by filtering
(filtration).
4.1
What things are likely to affect the rate at which water dissolves rock and soil material? (Think of
the rock and soil on one hand and the rainfall or water on the other)
This water eventually finds its way to the seas and oceans where it is evaporated to form water
vapour. (Of course, some ofthe water is evaporated on the way). The dissolved substances, however,
remain in the seas and oceans. The clouds formed by later condensation ofthe water vapour then give
rise to rainfall which is much purer than the seawater. This process of purification by evaporation
plus condensation is known as distillation and any equipment which is used for this process in the
lab is called a still. Thus you can see that rain water is a fresh beginning for us in our use of water
and that the water cycle is a natural process of continuous purification of the planet's water reserves.
This idea is taken further in section five.
4.2
What might be the differences between tap water and distilled water? Suggest reasons for these
differences.
4.3
What are the uses of distilled water?
Student Sheet 10
Unit 11: The Water Cycle - a natural recycling process
4.4
In some countries, much ofthe drinking water is produced by large scale distillation ofthe seawater:
they call the process desalination. Suggest possible reasons why Israel is a leading country in this
technology.
4.5
Design your own still, at first as a series oflabelled diagrams. If you use lab equipment, you may be
able to build it in the lab. Remember that heat energy is required for evaporation and that the best
way to cause condensation is to lower the temperature of the water vapour.
5.
The Water Cycle and Us
This section is not simply on water use: it is concerned with the points at which we affect the workings
of the natural water cycle. Water is a major resource. It is a natural substance which is essential
for life itself: human beings are about 80% water! In developing water resources, humans modify and
interrupt the water cycle in many important ways, for example by removing water from its natural
routes, by changing its chemistry or by changing its temperature. Also, these changes are caused at
different scales.
In fact, it is impossible to think of any stage ofthe water cycle that has not been changed in one way
or another, at some location on Earth. In a densely-populated industrialised nation like Britain, the
interruptions are often very easy to see, whether they be beneficial (as with water supply) or
detrimental (as with pollution).
5.1
Build up your own collection of newspaper or magazine cuttings to show how the water cycle has been
affected. You could classify these in various ways, e.g. (a) water supply (b) water chemistry (c)
changes for leisure use.
5.2
The following table shows a few of the ways in which the natural water cycle is interrupted.
Stage
Modification
Precipitation
1.
Under certain conditions, rainfall can be increased by "seeding" clouds with
silver iodide crystals from an aeroplane. This encourages more tiny cloud
droplets to form: these then coalesce into larger drops which then fall under
gravity. Experiments have been done in Australia and the U.S.A.
2.
Greenhouses: these reduce precipitation over small areas.
3.
Increased by irrigation.
Surface Storage 1.
Increased by ploughing.
2.
Increased in depressions on tarmac and concrete surfaces.
1.
Decreased by heavy machinery such as tractors and bulldozers.
2.
Increased by afforestation (planting offorests) which forms a seal over the
soil.
3.
Decreased by urban development.
Overland Flow
1.
As for Infiltration but the opposite in each case (why?)
Soil Water
1.
Decreased by growing crops.
Infiltration
Student Sheet 11
Unit 11: The Water Cycle - a natural recycling process
Groundwater
Stream Flow
2.
Decreased by land drainage and urban development.
3.
Increased by irrigation.
4.
Chemically changed by fertilizers (e.g. nitrates).
1.
Decreased by extraction at wells and boreholes.
2.
Increased by pumping water down boreholes to store water for later
extraction.
3.
Chemically changed by fertilizers.
1.
Decreased by extraction from rivers
2.
Decreased by construction of extraction reservoirs.
3.
Flow is controlled by regulating reservoirs.
4.
Flow may be diverted, e.g. as a mill stream.
5.
Chemistry changed by sewage and other industrial waste.
6.
Flow increased by forest clearance (why?)
7.
Increase in river temperature by use for industrial cooling, especially power
stations.
The Water Cycle and Us.
Student Sheet 12
Unit 11: The Water Cycle - a natural recycling process
Write a list of the ways in which the natural water cycle has been modified either in your school
building and grounds or in your house and garden.
5.3
What types of economic activity (e.g. transport, industry, agriculture, quarrying) involve many
interruptions of different stages of the water cycle?
5.4
Consider a catchment which is entirely forested but which is then "clear felled" (all the trees are
removed). Which water cycle stages will be affected the most, and how will they be changed? Suggest
reasons for the changes.
Some schemes, such as the Kielder Scheme in north east England and the Tennessee Valley Authority
in the U.S.A., involve large scale changes, both chemical and physical, to many stages of the water
cycle.
5.5
Select one ofthe cuttings from task 5.1 and analyse the changes to the water cycle which are involved.
Use the correct terminology, and consider changes in ...
(a)
(b)
(c)
(d)
... quantities of water involved (decreases, increases?)
... routes taken by the water (any diversions?)
... chemistry and temperature of the water
... water use
5.6
Find out about one particular example of water cycle interruption in your home area. Your local T.V.
news and newspapers will help. Do the changes involve water quality (chemistry), water quantity
or both? Is there any conflict between different groups of people? Are the people involved aware of
the way the water cycle operates? You could interview local people and present your results as an
audio-tape or as a wall poster.
5.7
When a large surface reservoir is created by damming a stream, how are each of the following stages
changed?
a.
b.
c.
Evaporation
Stream flow
Lake storage
Data Sheet
Unit 11: The Water Cycle - a natural recycling process
I
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1--Seas ~nd ---¥[
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Oceans
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, ____J
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Storage
Transfer
Processes
(--~-~\
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The Water Cycle Shown in a Flow Diagram
The Surface
of the Earth
Student Sheet 1
Unit 12: Which roadstone?
This Unit is about roads and the nature of the materials which are needed to build them satisfactorily.
Much of the Unit is in the form of short numbered questions, followed immediately by the answers. You
will gain most if you do not cheat! Read the Unit a few lines at a time, covering the rest ofthe page with
a piece of card.
1.
Why use rocks to make a road?
In 1741 Jack Metcalfneeded to travel from London to Harrogate, a distance of218 miles. He
refused to go by coach saying he would rather walk because it was quicker. He arrived before
the coach.
1.1
Assuming he walked 20 miles per day how long would it have taken him?
11 days.
1.2
What does that tell us about the speed at which coaches could travel? How long would it take to drive
that distance today if one drove at an average of 50 miles per hour?
4 hours and 19 minutes.
1.3
Think of the entrance to a field into which cattle or people often go. How does it differ from the centre
of the field and why?
The repeated trampling destroys the grass, and the soil is not strong enough to stand the weight of
the cattle or people and so it becomes rough and uneven.
1.4
Does the field surface get most churned up during dry or wet weather?
When the soil is wet it loses much of its strength and so it gets rutted much more easily than when
it is dry.
1.5
Many old lanes, particularly in hilly country are sunken. Why is this?
The people and animals have walked along these lanes for centuries. The grass disappeared, the soil
became churned up and then the rainwater washed the soil away until the bedrock was exposed.
Student Sheet 2
Unit 12: Which roadstone?
1.6
Nowadays we cover our lanes with a 'pavement' (pavement is the technical term for the layers which
make up a road). Why?
a) It protects the soil from erosion.
b) It keeps the underlying soil dry and therefore stronger than if wet.
1.7
If the pavement is to perform these functions what properties must it have?
a) It must be waterproof
b) It must be strong to take the weight of the vehicles
1.8
Look at a piece oftarmac. What is it made of?
a) Rock fragments
b) Bitumen (= tar)
1.9
Which property is given by the bitumen and which by the rock fragments?
The bitumen makes the pavement waterproof and the rock fragments give it strength.
1.10 Why doyounot sink into soft snow if you are
wearing skis or snow shoes but you do if you
are wearing ordinary shoes?
Because your weight is spread over a larger
area.
Modem roads are designed to transfer the
weight of a vehicle onto a large area of the
underlying soil. A modem road will have
four separate layers.
Name and thickness of Purpose and composition oflayer.
layer
Provides a skid - and wear-resistant surface
for the traffic and protects the lower layers.
Bitumen-bonded aggregate.
Distributes the traffic loads onto the road
base. Bitumen-bonded aggregate.
Main load-bearing layer. Made of rocks
with high crushing strength.
-----------
Sub-base variable
sub-base
-----_.
- - - - - - - Underlying rock
Builds surface up to approximately
the correct level. Made of large
fragments so that water cannot
rise by capillary attraction.
-~~~--~----~----------------------~
Figure 1. Section through a modern road
Student Sheet 3
Unit 12: Which roadstone?
1.11 Which layer has to take the greatest pressure?
The wearing course. For a car the pressure on the top of the sub-base is only about a tenth of that on
the surface.
1.12 Do all the layers need to be waterproof?
No. Only the wearing course.
Most rock types are suitable as aggregate (= broken up rock) for the lower three layers. However the
top layer, the wearing-course, on which the traffic runs, needs to have special properties. The
remainder of this unit concentrates on the wearing-course.
1.13 What properties do you think it should have?
Properties needed by the wearing-course:
a) Strength, to resist the forces imposed by the traffic.
b) Hard wearing., so that it does not get worn away by the movement of the traffic.
c) Skid resistant, so that the traffic can stop safely.
d) Resistant to weathering, so that ice and snow and rain do not cause the pavement to deteriorate.
e) Resistant to stripping, so that the tyres do not pull the rock fragments out.
In addition there are other desirable properties:
Cheap to build and easy to dig up and repair.
No glare from reflection of headlights or low sun.
Light coloured for greater visibility at night.
Quiet running.
Must adjust to changes in temperature.
These other properties will not be considered further.
Many materials might possess the properties listed in a) to e) above, but most road builders use rocks
as the main material for the wearing-course oftheir roads. The next section involves you in examining some common rocks and discovering some of their basic properties.
2.
Which stone?
Your teacher will supply you with a variety of rocks, some of which might make good roadstones:
others certainly would not! Study each ofthem in turn and write down your answers to the questions
which follow.
2.1
Look at the granite.
a) How many different components are there? Use their colours to distinguish them. Write down your
answer. Each component is called a mineral. All rocks except volcanic glasses contain minerals but
often they are too small to see with the naked eye.
The properties of a rock depend on:
the properties of the individual minerals,
the proportion of those minerals,
the way the minerals are held together.
Student Sheet 4
Unit 12: Which roadstone?
Try testing the hardness of the different
minerals in the rock by scratching them with
a steel nail, penknife, or compass point.
~ologists use Mohs' scale of hardness
which ranges from 1 (talc) to 10 (diamond).
Steel has a hardness of just above 5, so those
minerals which are scratched are softer than
hardness 5. Those which are not scratched
have a hardness greater than 5.
I
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, ,
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b) Are most of the minerals in granite harder or softer than steel?
c) Are the minerals firmly held together?
d) Are there any small gaps between the minerals?
2.2
Now look at the sandstone. Rub your finger across the surface and note what happens.
Sandstone is made largely of quartz, so the mineral grains are all hard. Why does it crumble so easily?
Some sandstones are stronger than others, but very few are as strong as granite.
2.3
Now look at the schist. a) Why does schist break up so easily?
b) Is it mostly made of one mineral or are several minerals present?
c) What shape are the pieces that break off?
2.4
Examine the dole rite. a) Try scratching it. b) How does the shape ofthe specimen compare with that
of the schist?
X5
sandstone
granite
Figure 2. Textures of some rocks
3. Back to the road
We shall now look at each ofthe first five properties listed a) to e) on Sheet 3 to find what sort of rock
is most suitable.
Strength
3.1
What are the forces exerted on the wearing-course by the tyres ofthe vehicles? Draw a diagram and
use arrows to show the direction of the force on the road in each of the following cases:
Student Sheet 5
Unit 12: Which roadstone?
a) stationary, b) moving at a steady speed, c) accelerating.
When stationary, there is a vertical downward force due to the weight of the vehicle.
When moving forward at a steady speed, there is also a backward push.
When accelerating, there is a stronger backward push.
3.2
What properties do you think the rock should have in order to resist these forces?
Most of the minerals should be hard so that they are not crushed in any direction.
The minerals should be well held together so that the rock does not crumble or the grains get pulled
or pushed out.
CONCLUSIONS
Most of the minerals in the rock must be hard.
The minerals must be tightly held together.
Resistance to wear
As the tyres rub against the road, the surface of some of the tyre and a little bit of the road surface
gets worn a way. This is called abrasion. Abrasion is most effective iflittle grains of sand get between
the tyre and the road surface. The properties which control the abrasion of the wearing-course are
the same as those controlling the strength, that is the hardness of the minerals, and how well they
are held together.
Skid resistance
The surface ofthe road must provide a good
grip for the tyres. If not the traffic will be
unable to stop, or go round corners safely.
3.3
Where, along a road, is a good grip most
important?
At traffic lights, roundabouts, and other
road junctions and corners.
3.4
To prevent skidding should the surface be rough or smooth?
Rough. (see Figure. 3)
b
1 ern
Figure 3. Magnified section of a road surface.
a = micro-texture = relief between minerals in each rock.
b = macro-texture = relief between top of rock fragments and bitumen.
Student Sheet 6
Unit 12: Which roadstone?
3.5
The macro-texture is important in wet and icy weather. Why is this?
Because a thin film of water or ice can lie on the roadway and the rock fragments will stand up above
it. It has been found that rock fragments between 13 and 25mm across are most effective.
If the rock fragments were made of only one mineral the abrasion would flatten and polish the
mineral grains leaving no micro-texture. This would be dangerous because at high speeds the tyres
only touch the rock fragments and so it is their roughness which prevents skidding.
3.6
How can we ensure that the rock fragments do not become polished?
If the rock fragments are made of several minerals of slightly different hardness then they will wear
at slightly different rates and so the surface will never become smooth. The softer mineral will form
pits on the surface.
lcm
road surface
:. 0: 0:
..... ,'.
o
4'
~.~.
' : ..
":
'•
... .: ;:::j:: ··s~~er~l· differ~nt ~iti~~ai~:..\~:·I ~:.
e.: .:. : 0: ~' ..':: .... :.: .... :: eo":: :......-.. : .... ::.:::~.. :~. : ..,:,:...
Figure 4. Effects of abrasion.
Only at low speeds is the macro-texture important in skid resistance.
CONCLUSION
Each rock fragment must be made of two or more minerals of different
hardnesses.
In order to resist skidding, each rock fragment must contain several individual mineral grains.
Because the rock fragments themselves are quite small, this generally means that the mineral
grains in them must be less than 2mm across.
3.7
Look back to sheets 3 and 4, or to the specimens. Is the grain size in granite and dolerite greater or
less than 2mm?
In granite the mineral grains are more than 2mm across so it would not make an ideal roadstone.
Dolerite at least has the correct grain size.
CONCLUSION
The grain size must be less than 2mm.
Which rocks resist weathering?
Weathering is the breakdown of rocks in place. The two important types of weathering are chemical
and physical.
a)
Chemical weathering
3.8
Chemical weathering takes place mainly by acid in the rain or surface water attacking the minerals
in the rock. Put one drop of dilute hydrochloric acid on limestone and on granite. Which is more likely
to be affected by weathering?
Student Sheet 7
Unit 12: Which roadstone?
The limestone. Rain water is ofcourse not nearly as acid as dilute hydrochloric acid. Nonetheless over
a prolonged period the rock would be altered. Even granite will weather given enough time.
3.9
Look at the hardness ofthese minerals. (hardness given on Mohs' scale)
original mineral
feldspar
augite
biotite
hardness
mineral often
produced by
weathering
hardness
6
6
3
kaolin
chlorite
chlorite
2
2
2
Will weathering improve the quality of the
roadstone or not?
No, because the new minerals are softer on
Mohs'scale.
In this country weathering takes place very
slowly and so there is little noticeable change
in the quality of the rock in the lifetime of the
road. However in some climates, weathering
takes place much faster and the quality ofthe
road can change significantly during its lifetime.
3.10 Is chemical weathering likely to be faster in cold dry climates or hot wet ones?
Hot wet ones, because chemical reactions take place faster under those conditions.
Sometimes the rock has already undergone some chemical weathering before it is quarried and it is
important to check that the properties of the rock have not been significantly changed.
b)
Physical weathering
3.11 The most important form of physical weathering in this country is the effect of freezing water
breaking up rocks. How does this happen?
Water expands on freezing and in doing so can exert enormous forces ifthere is no room for expansion.
This is why water pipes burst in frozen houses. Any water that seeps into any holes in the rock becomes
trapped during freezing and so splits the rock open.
3.12 Put the granite and the sandstone into a beaker of water. Watch carefully and explain what happens.
The sandstone bubbles because it contains air between the grains which is displaced by the water.
Nothing happens to the granite.
Sandstone has lots of gaps between the grains called pores. It has a high porosity . Granite, on the
other hand, consists of interlocking grains with essentially no gaps between them. It has a very low
porosity and can absorb only a very little water.
Student Sheet 8
Unit 12: Which roadstone?
3.13 What would be the effect of soaking each rock
and then freezing it? Try it. If you have a
freezer and a tolerant mother take home a
piece of porous sandstone and a piece of
granite. Soak them in water for one or two
days and then put them in polythene bags
and place them in the freezer each evening
and take them out each morning. Which one
disintegrates first?
3.14 So porous rocks make poor roadstone. Would a high porosity be a problem if you were building a road
in the tropics?
No, because providing you were not too high above sea level there would not be any frosts.
CONCLUSION
The roadstone must have a low porosity if it is to be used in an area where
there are likely to be frosts.
Stripping
This is not what you think! Stripping is the
term used by engineers when the tyres pull
rock fragments from the wearing-course.
The individual rock fragments must stay
embedded in the bitumen. That means that
the rock fragments must bond or stick firmly
to the bitumen.
\
I
3.15 Will the bitumen stick best to
1
2
3
4
a clean rough surface
a glassy surface
a wet surface
a dusty surface
Think about trying to remove chewing gum from wood and from glass.
The bitumen will bond best to a rough surface. It will not stick satisfactorily to glassy surfaces,or to
wet or dusty surfaces. So the rock must not be glassy and the rock fragments must be clean and dry
when mixed with the bitumen.
3.16 Will dolerite or flint make the stronger bond with bitumen?
Dolerite, because it has a rough surface.
Student Sheet 9
Unit 12: Which roadstone?
Flint was used to make the first 50 km of the M1 when it was built, but it had to be replaced because
too many windscreens got broken as the tyres pulled the stones out of the road surface.
CONCLUSION
Glassy rocks are not suitable as roads tone.
Summary of properties and conclusions
Strength and resistance to wear
a) most of the minerals in the rock must be hard.
b) the minerals must be tightly held together.
Skid resistance
c) Each rock fragment must be made of two or more minerals of different hardness.
d) The grain size of the minerals must be smaller than 2mm.
Resistance to weathering
e) The rock must have a low porosity.
Stripping
f) The roadstone must not be glassy.
Now refer back to your preliminary examination of a road surface or a piece of tarmac and see how
many of the criteria in Section 3 are met in the case you have studied.
4.
Getting the rock right.
Now that you have investigated the properties which are needed for a good wearing-course
roadstone, you are in a position to decide which of many different rock types are likely to be most
useful. The following extract from the Sunday Times (February 1985) shows how important this is:"One of the biggest and most experienced firms of consulting engineers in Scotland is facing a multimillion pound lawsuit after advising a Scottish Council to build a roadstone quarry, which has since
proved to be virtually useless."
4.1
Assuming that you have some or all of the specimens listed on Data Sheet 1, try the following
observations and enter your results on the sheet.
For each sample:
a) Measure and record its grain size (if it is too fine to measure, put <0.5mm)
b) Determine, or look up, which minerals it contains and list them.
c) Determine, or look up, the hardness of each mineral and write it beside the mineral name.
If you do not have the specimens, or if you do not know much basic geology, use the information in
Tables 1 and 2 to help you.
d) Now complete your research by putting a tick where the rock satisfies each criterion for roadstone
and a cross where it does not.
Student Sheet 10
Unit 12: Which roadstone?
Minerals
grain size mm
Igneous rocks
Granite
feldspar, quartz, mica
>2
Gabbro
Dolerite
Basalt
feldspar, augite
feldspar, augite
feldspar, augite
>2
0.5 - 2
<0.5
mica
mica
>2
<0.5
quartz
calcite
clay minerals
quartz, feldspar, clay minerals
quartz
0.1 - 2
variable
<0.1
<2
very fine to glassy
Metamorphic rocks
schist
slate
Sedimentary rocks
sandstone
limestone
shale or clay
greywacke
flint
Table 1. Mineral Composition of some rocks
Augite
Calcite
Clay minerals
Feldspar
Mica
Quartz
5.5
3
2.5
6
2.5
7
Table 2. Hardness of some minerals (on Mohs' Scale)
5.
Where does your roadstone come from?
5.1
Look at the map (Figure 5) showing the outcrops of rocks suitable for coating with bitumen for use as
wearing-course roadstone. In which parts of the British Isles are they found?
Mainly in western 'upland' Britain because that is where the older and consequently harder rocks are
found.
5.2
Which part of Britain is likely to need the most roadstone?
The southeast, because it has the greatest number of roads and the heaviest traffic and needs
roadstone for repairs and improvements.
This means that large amounts of wearing-course roadstone have to be transported across the
country.
It is bulky and therefore expensive to transport.
The cost of transporting a tonne of roadstone for 100 km is about the same as the cost of a tonne of
roadstone at the quarry gate.
Student Sheet 11
Unit 12: Which roadstone?
So ifroadstone costs £8 per tonne at the quarry100 km away, it will cost £16.
200 km away, it will cost £24.
5.3
U se the map to work out the cost per tonne of roadstone delivered from the nearest source area to:
a) London
b) your home town
. , areas where
wearing-course
roadstone may
be found.
o
kilometres
200
L . . . '- - ' _ - ' - - - - ' - - - - ' ,
Figure 5. Map showing areas of rock suitable for use as wearing-course roadstone.
(After Open University 'Earth's Physical Resources')
5.4
Find out where the stone used for the wearing-course of the roads in your district comes from. There
are two ways of doing this:
a) Try to identify a specimen ofthe stone, then study a geological map to discover where the nearest
outcrops occur;
b) Contact your local Highways Department, a local contractor, or possibly the geologist at your
nearest museum.
tb~
s·
~
Criteria for a good roadstone
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Grain
size (mm)
Minerals in the rock, with hardness of
each mineral
A
B
C
D
E
F
>2
feldspars (6), quartz (7), micas (2.5)
V
V
X
V
V
V
gabbro
>2
feldspar (6), augite (5.5)
V
V
X
V
V
V
basalt
< 0.5
as above
V
V
V
V
V
V
*
dolerite
V
V
V
V
V
v
*
poorly cemented sandstone
X
V
V
X
X
X
well cemented sandstone
X
V
V
V
V
V
shale
X
X
V
X
X
X
oolitic limestone (made of
little spheres of carbonate)
X
X
-
X
X
V
crystalline limestone
X
X
-
V
V
V
flint
X
V
V
V
V
X
schist
X
X
X
X
V
V
slate
X
X
V
V
V
V
V
V
V
V
V
V
*
greywacke
-_ ... __ .. _-
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Student Sheet 1
Unit 13: The geological time scale
1.
Introduction - Who studies the past?
In your studies of history, have you ever stopped to think how the subject is defined? Are people other
than historians interested in the past. If so, what length of time scale do they think of as 'normal'?
Figure 1 names some of the other areas of study which involve trying to understand the past. It also
shows that there is considerable overlap between the various studies. Be careful how you read this
diagram: it is plotted on logarithmic paper, which enables us to show recent events and very ancient
ones on the same graph. The bottom line represen ts 10,000 million years! Where would the life span
of your grandparents plot on this scale?
o
T
I
I
I
I
I
I
I
I
I
:
I
I
I Crab Nebula I
(1054 AD)
I
I
10
100
....,
1,000
r::
<l)
m
T
I
!
10,000
r
T
J Recent History
g
5 Yw,"go)
I Industrial Revolution
(18th Century)
HISTORIAN
1
Chaldean records
(2234 BC)
~ End of ice age
<l)
S.
-5
T
(10,000 years ago)
<l)
<l)
....
<8
100,000
ARCHAEOLOGIST
<l)
..0
....m
(1j
<l)
~
1,000,000
Early ancestors of Man
(2-1.5 my ago)
10 million
GEOLOGIST
100 million
ASTRONOMER
1
1,000 million -
Fo,motio" of tho Eruth (4600 my",,)
Origin of the Universe (10000 my ago)
10,000 million
=
main period of study
extension to the present, to allow comparison etc.
Figure 1. The range of interests of people who study the past.
Student Sheet 2
Unit 13: The geological time scale
If we accept that historians use written records in their
studies, then we must go back over 4000 years, since we have
written records this old. For example, the Chaldeans kept
written records as early as 2234 B.C.
The archaeologist is interested in a span oftime which overlaps
that of the historian and the geologist. The branch of archaeology called Industrial Archaeology overlaps history. The overlap
with geology is clear when we note, for example, that the cave
paintings at Altamira in Spain date from 13,000 years before the
present. At the same time, great ice sheets covered much of
northern Europe - a time which geologists have come to know as
the Ice Age. (ending about 10,000 years ago.) In Tanzania,
remains have been found of an early man-like creature in rocks
as old as 1,750,000 years. The fossils have been called Homo
habilis, or 'handyman', since the living creature was clearly
capable of making and using simple tools. At the other end ofthe
scale, geologists are interested in the earth's oldest rocks. The
oldest specimens so far discovered date from about 3,800 million
years ago. With the coming of the 'Space Age', astrogeologists
are discovering moon rocks as old as 4,600 million years.
Astronomers are aware that the Universe itselfis much older, and have evidence that itformed as long
ago as 10,000 million years. Strangely enough, they are also interested in quite recent events, such
as the explosion of a star in A.D. 1054, which led to the formation of the Crab Nebula.
2.
Some odd ideas
Human beings have always wondered about the age of the earth, but some of their ways of trying to
find out about it have been odd indeed! Before the 'scientific age' of geology began, two well known
attempts were made to find the age of the earth.
Today, these efforts seem laughable, but in their time they were taken seriously by many and it took
a long while before geologists felt that they could challenge the results. One ofthese was Archbishop
Ussher of Armagh in Ireland. In the 1640's he studied the information on the ages and generations
of the people mentioned in the early parts of the Bible and declared that the earth was created 4036
years before the birth of Christ.
At much the same time, John Lightfoot, a Hebrew scholar at
Cambridge University attempted a more accurate calculation.
He concluded that creation took place during the week 18th 24th. October 4004 BC and that Adam was created on 23rd October at 9.00 am, 45th meridian time! In commenting on this,
one writer has said, "Closer than this, as a cautious scholar, the
Vice-Chancellor of Cambridge University did not venture to
commit himself!" Remember, though, that at that time, just
about everybody believed that these calculations were correct.
Student Sheet 3
Unit 13: The geological time scale
3.
The geological column
The early geologists (working in the late 1700's and early 1800's) soon realised that these time scales
were far too short. However, there was no reliable method for
doing a lot better, so they concentrated instead on trying to work
out the sequence of geological events. This was largely done by
noting that certain groups of fossils only occurred in certain
beds. Beds above and below contained fossils which were
significantly different from the first ones. We know that this is
because of the evolution of the animals and plants concerned,
although the early geologists did not at first understand the
reason.
One group of rocks, however, had the old timers beaten! There
did not appear to be any fossils, no matter how hard they looked.
These rocks were known to be the oldest, since they lay below
the fossiliferous strata, but how old - nobody knew. All that the
geologists could do was to call this period of time the Precambrian, since it came before their lowest division offossiliferous
rocks, the Cambrian.
~Y"U'cUjJJo"""
Much of the column shown in Figure 2 was worked out and named before the end of the 19th Century
and is learned by heart by every geologist today. All the rocks on earth are now related to this time
scale, wherever possible.
The best known divisions of time represented on the column are known as Periods. (Geologists use
the word system when they are talking about the actual layers of rocks which were deposited during
each time Period). Each Period, or System, is named according to a feature near to the area where
it was first recognised, or after some characteristic of the groups of rocks found within it. Some ofthe
more obscure names have been explained for you.
3.1
Try to find out the meanings of the names of the other Periods. In doing so, you will discover
something about the rocks deposited during that Period, or else a part of Europe where the Period was
first recognised. (You may need to consult a teacher of Classics and an Atlas!)
There are some other names which appear in Figure 2. The Eras of geological time represent major
divisions. Each ofthem consists of several Periods. The Greek names given to them refer to the fossils
which are found in the rocks. 'Palaeozoic' means 'ancient life'; 'Mesozoic' means 'middle life' and
'Cainozoic' means 'new' life.
The term 'Phanerozoic' is used as a
lump title for all geological time
younger than the Precambrian. It
means 'evident life' and refers to
the fact that rocks from the Cambrian upwards may contain visible
fossils. Fossils in the Precambrian
rocks are frequently unfossiliferous. When they do occur, the fossils
are usually of microscopic proportions only.
.05mm
L--..J
A microscopic fossil
A trilobite fossil
Student Sheet 4
Unit 13: The geological time scale
Era
PeriodlSystem
Epoch and meanings of names
Quaternary
Holocene-wholly recent
Pleistocene-almost recent
Tertiary
Pliocene-more recent
Miocene-Iess recent
Oligocene-little recent
Eocene-dawn of recent
Palaeocene-ancient recent
Cretaceous
*
Jurassic
*
Triassic
In Germany, where this period was first named in
1834, there is a clear three-fold division of rock types.
Permian
Named after the town of Perm in Russia, in 1841,
where fossil-bearing limestones occur.
Carboniferous
*
Devonian
*
Silurian
Ordovician
The 'Ordovices' and 'Silures' were ancient Celtic tribes
of the Welsh Borders, where rocks of these ages were
first mapped in the mid 1800s.
Cambrian
*
Cainozoic
(new life)
..=
:Q)
Q)
:
Mesozoic
(middle life)
>
Q)
.
11
~
e~
Q)
=
Palaeozoic
(old life)
Precambrian
'Before the Cambrian'
(N.B. You might be wondering why the top end ofthe column has names like 'Tertiary' and 'Quaternary' whilst lower down, the names relate to types of fossils. 'Tertiary' means Third and 'Quaternary'
means fourth. The reason is that in the early days, the Palaeozoic was known as the Primary and the
Mesozoic was called the Secondary. At some point, some of the names were changed, but not all, so the
outcome is somewhat of a compromise!)
Figure 2. The geological column, showing the origins of some of the names. (* = for you to find
out for yourselves)
Going the other way, geological time is broken down into smaller and smaller units, which are
only of interest to the specialist. We have, however, included some of the more recent Epochs,
since you are likely to read about them in books and might wonder where they fit in.
3.2
Write a mnemonic to help you to remember the Periods of geological time. This is a sentence
where each word in order begins with the first letter of the series of words you want to remember.
Your sentence might begin, 'Cows Often ... .'
Student Sheet 5
Unit 13: The geological time scale
4.
Geological time scales
In the 19th Century attempts were made to determine the age ofthe earth, using geological principles
alone. Although not very successful by today's standards, they did show that the planet was millions
of years old, not just thousands. More accurate estimates had to await the discovery of radioactivity.
Some minerals contain minute amounts of radioactive elements. These decay (break down) over a
period of time to produce new elements. The original radioactive elements are known as 'parent
elements' and the newly formed ones are called 'daughter elements'. The rates at which the various
radioactive elements decay can be measured in the laboratory. We can therefore, work out how old
a specimen is by measuring how much of the daughter element has been produced. This is compared
with the amount of the parent element which remains. This period is called radiometric dating.
One of the first geologists to use radiometric dating to build up a geological time scale was Professor
Arthur Holmes. He published his first paper on the subject in 1911 and continued refining his
techniques and revising his time scales until a few years before his death in 1965. Since then, further
work has been done and the most recent column to be generally accepted was published in 1985, by
the Geological Society of London.
Figure 3 shows a simplified version of the Geological Society's time scale. Please note that this time
scale will probably only remain valid for a few years. Scientists continue to review the techniques of
measurement. Also, geologists may find fresh geological evidence for the boundaries between the
various Periods. This evidence from the rocks themselves may result in the boundaries being moved
up or down the column by a few million years or so!
Era
Divisions of geological time
Period.
Epoch
Commencement date in
millions of years (My)
Quaternary
Pleistocene
Cainozoic
Tertiary
Pliocene
Miocene
Oligocene
Eocene
Palaeocene
Mesozoic
Cretaceous
Jurassic
Triassic
135
205
250
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
290
355
405
435
510
570
Palaeozoic
Precambrian
Formation of the Earth
1.6
5
24
37
58
65
about 4600
Figure 3. The geological time scale (adapted from Snelling, Geological Society of London, 1985)
Student Sheet 6
Unit 13: The geological time scale
In many ways, drawing a column like the one in Figure 3 is misleading. Your eye does not at first notice
the huge difference in time between the length of, say, the Precambrian and the Silurian. Itis much
better to draw it out to scale, where a certain length represents so many million years. Even so, the
job is difficult because of the enormous differences noted above. There are, therefore, several
techniques which can be used.
Your task now is to devise several different
types of geological time scale, using the
suggestions on Student Sheets 7 to 12.
If you have the time (humanly speaking
now!) you might be able to try all the ideas.
Ifnot, your teacher will ask you to deal with
one time scale and then to compare yours
with others. At home, you could try to think
out some ideas of your own.
Check with your teacher before you start
work, to see which time scale you are being
asked to do.
Student Sheet 7
Unit 13: The geological time scale
5.
D-I-Y time scales
5.1 Geological column of Phanerozoic time
This is the standard diagram found in most text books. It shows the last 570 million years, i.e. from
the Cambrian to the present day. It does not show the Precambrian.
You need:
1 A4 sheet of graph paper with 2mm squares
ruler (metric)
ball point pen and/or pencil
coloured pencils
Procedure:
Draw a vertical column to scale, using the dates given in Figure 3. The suggested scale is 1 cm to 25
million years (My). The total length ofthe column will then be 22.8 cm.
Draw a rectangle 22.8 cm high and 4 cm wide. This should be positioned in the centre ofthe graph
paper and 2 cm up from the bottom.
Mark off a scale from the top downwards with the values 0, 100,200 My etc., four centimetres apart.
Now mark to scale and label the 11 periods of geological time. For ease of working, count downwards
from the top, i.e. backwards in time. (Note that the duration of the Pleistocene - about 2 My - is, in
fact, the thickness of the top line.
On the left of the column, bracket the bottom six divisions (Cambrian to Permian) and label them
'Palaeozoic'. The next three Periods group together to form the 'Mesozoic' and the last two Periods
form the 'Cainozoic'
Colour and label the separate parts of the column.
Complete the work by adding to the bottom a short section to remind you that Precambrian time comes
before the Phanerozoic, as shown. Don't attempt to draw it to scale.
I Cambrian
[ Precambrian
Student Sheet 8
Unit 13: The geological time scale
5.2 Clock diagram. for total geological time
In this diagram, the whole of geological time from the formation of the Earth to the present is
represented by the face of a 12 hour clock.
You need:
1 sheet of A4 paper
calculator
pair of compasses
protractor
ruler
pen or pencil
Procedure:
Draw a circle of radius 5 cm. (make sure that the centre point can be found later).
Mark the circle at the top (12 o'clock position)
Using a protractor, mark the circle at 30° intervals.
Label these marks to show hours - 1, 2, 3 etc.
Draw a vertical line from the centre of the circle to the top and label it Formation of the earth 4600 My ago
Working anticlockwise from the present day, draw lines from the centre to represent;
The beginning of the Cambrian - 570 My ago
The earliest known life on Earth - 3300 My ago
The oldest known rocks on Earth - 3800 My ago
The calculations are done as follows:
The clock circle represents 4600 My
Thus, if 4600 My is shown by 360°,
570 My ago (beginning of Cambrian) is shown by
360 x 570
4600
Now, you calculate the other two angles by a similar method.
When you have finished the clock diagram, label your lines. Shade and label Phanerozoic time (i.e.
from Cambrian to present day)
Complete your work with a title and a statement of the scale.
Student Sheet 9
Unit 13: The geological time scale
5.3 Geological time line· multi-scale diagram
This time line uses different scales, depending on whether you are trying to show the vast length of
the time since the origin of the earth, or the great detail ofthe recent history of the last few centuries.
Work in small groups (e.g. 4 people), with each person working on a different time line. The lines you
will be copying are shown on the next sheet. The * shows where the next scale line begins.
You need:
ruler
calculator
pen or pencil
Copy the first scale line you have been asked to work on. Work from the nearest 'round number' near
the left hand end ofthe line. Write the following sentence underneath, adding the missing words and
figures:
''The line from .... to the present day is .... cm long. Therefore, the scale ofthe line is, 1 cm represents
.... millions of years" (or years, for lines 5 to 8)
Mark and label a key point on the line using the information below:
Scale line 1 Scale line 2 Scale line 3 Scale line 4 Scale line 5 Scale line 6 Scale line 7 Scale line 8 -
'Earliest known life appeared 3300 My ago'.
'Coal-forming conditions 300 My ago'.
'End of the Cretaceous Period and extinction ofthe dinosaurs, 65 My ago'.
'Start of Pleistocene Ice Age 1.6 My ago'.
'Neanderthal Man lived 100,000 years ago'.
'Cave paintings in northern Spain 13,000 years ago'.
'End ofIce Age in Britain 10,000 years ago'.
'The Norman Conquest of England 1066'.
'The 'Little Ice Age' (extending from 15th to 19th Centuries)'.
add to this last scale line, the year and brief details of family events, e.g. year of
Grandma's birth; your birth year; the year you started secondary school etc.
Repeat all the steps above for any other scale lines you have been asked to complete.
When everybody in your group has finished, compare your results with theirs.
Student Sheet 10
Unit 13: The geological time scale
Scale line 1
{Formation of Earth
,
*
I I
4500 My ago
Scale line 2
Start of Cambrian Period
Present
r-~L-----------------------------------------r------~
600 My ago
*
Scale line 3
Middle of Cretaceous Period
t
Present
••
100 My ago
*
Scale line 4
Present
I I
5 My ago
*
Scale line 5
Present
*
250,000 years ago
Scale line 6
Present
20,000 years ago
*
Scale line 7
Birth of Christ
Present
t
nearly 2000 years ago
*
Scale line 8
Present
1900 AD
Present
Student Sheet 11
Unit 13: The geological time scale
5.4 Multi-strip linear scale model
If you are working in separate groups, don't show Data Sheets 1 and 2 to those doing 5.3 - it shows
the answers!
Your job is to construct a cardboard model of the geological time scale, using Data Sheets 1 and 2.
You need:
Data Sheets 1 and 2
scissors
glue
First, look at the time strip carefully. What do you notice about the scale to which each strip has been
drawn? This has been done in order to plot the enormous span oftime represented by the record of
the rocks and yet also to be able to plot detailed events ofthe last few years. In other words, the scale
changes as we approach the present day.
To construct the model:
a) glue a copy of Data Sheets 1 and 2 onto card, unless your teacher has been able to print it directly
onto card for you.
b) cut out the strips and trim off any surplus card (shown by stripes)
c) glue the strips together where shown and stand the model on the bench. The stippled parts are
where the scale changes and the model protrudes towards you.
d) add some dates of significance for you or your family to the strip for the most recent years. You
might think of birth years, or the year you started school etc.
Student Sheet 12
Unit 13: The geological time scale
5.5 A cosmic calendar
Another way of trying to represent geological time in a simple way, is to liken it to the months and
days of the year, as on a calendar.
You need:
Data Sheet 3 or an old calendar from home.
coloured pencils or felt tipped pens.
Pick out from the table below the dates in the geological record which you consider to be the most
important and invent a system of colour codes to highlight them on the calendar. Preferably use an
old calendar from home, but failing that, use a copy of Data Sheet 3. Provide a key to show what
your colours mean. For the 'last hours of December 31 st,' you will need to use a copy of the enlarged
bar at the bottom of the page.
Given that September 14th represents the origin of the earth (4600 million years ago) try to calculate
how long ago the 'Big Bang' must have been. (Note that this isjust one theory for the ultimate origin
of the whole cosmos and that other scientists hold different views.)
A Cosmic Calendar
January-November
January 1
May 1
September 9
September 14
September 15
October 9
November 12
November 15
Big Bang
Origin of the Milky Way galaxy
Origin of the solar system
Formation of Earth
Origin oflife on Earth
Date of oldest fossils
Oldest fossil plants
First cells with nuclei
December
Monday 1
Tuesday 16
Wednesday 17
Thursday 18
Friday 19
Saturday 20
Sunday 21
Monday 22
Tuesday 23
Wednesday 24
Friday 26
Saturday 27
Sunday 28
Significant oxygen atmosphere
begins to develop on Earth
First worms
Precambrian Period ends; Palaeozoic
Era and Cambrian Period begin;
invertebrates flourish
First oceanic plankton
Ordovician period; first fish, first
vertebrates
Silurian Period; plants begin colonization ofland
Devonian Period begins, first insects;
animals begin colonization ofland
First amphibians; first winged
insects
Carboniferous Period; first reptiles.
Permian period begins; first dinosaurs
Triassic period; first mammals
Jurassic period; first birds
Cretaceous Period; first flowers;
dinosaurs extinct
Monday 29
Tuesday 30
Wednesday 31
Mesozoic Era ends; Cenozoic Era and
Tertiary Period begin; first primates
Early evolution of frontal lobes in the
brains of primates; first hominids,
giant mammals flourish
End of the Pliocene Period
December 31
10.30 pm
11.00 pm
11.46 pm
11.56 pm
11.59 pm
11.59:20 pm
11.59:51 pm
11.59:53 pm
11.59:55 pm
11.59:56 pm
11.59:58 pm
11.59:59 pm
Now the
first second
of New
Year's Day.
First humans
Widespread use of stone tools
Domestication of fire by Peking man
Beginning of most recent glacial
period
Extensive cave painting in Europe
Invention of agriculture
Invention of alphabet
Bronze and metallurgy, invention of
the compass
Birth of Buddha
Roman Empire; birth of Christ
Crusades
Renaissance in Europe; voyages of
discovery from Europe and from
Ming Dynasty China; emergence of
the experimental method in science
Widespread developments of science
and technology, first steps in a
spacecraft; planetary exploration and
the search for extraterrestial intelligence.
Student Sheet 13
Unit 13: The geological time scale
6.1 Time's up!
When you have completed your scale or scales, add some of the important events of geological time
to the scale by careful labelling. Select the events you want to add from the sheet called "A Cosmic
Calendar' (Student Sheet 12).
6.2
Study a geological map to find out the ages of rocks in your local area (Le. within 30 km). Add these
to your scale by using a phrase like ... "Triassic rocks are found nearby in the lakeside area ... "
The geology of Britain is very varied, so you might find that rocks of several ages are found locally.
6.3
Now look at all the different scales produced by the class. Write down which one you think best shows
how geological time works. Can you think of any better way of showing it? Write down your ideas.
Look for more ideas in your local library.
€....
~"""-
0+
I
rn
a
~
'd
S
-.
~
~
~
~
Present
Earliest life appeared
3300 My ago
Col
00
0..
~
'':
...,
....Cl)
~
"SnS
~
'"Cl)
Cl)
;:l..c
~
~
g.
~
Start of Cambrian Period
570 My ago
Present?
Coal forming conditions
300 My ago
a
b., ....Cl)
Cl)
;:l..c
~
- bO...,
0
Ord
1\
Dev
Si!
Carb
Perm Tri
Jur
"""-
=
Tert
~
If'
C'Il
End of Cretaceous and extinction of dinosaurs
65 My ago
~ 1 Middle of Cretaceous Period
-
~
-.j<
.~
100 My ago
~ I§~
tlCl) Cl)
;:l..c
be.s
I ~ 5 Million years ago
1
re~
'"'"
.9Cl)
o
Start ofPleistocene
Ice Age 1.6 My ago
.,
~
10
0..
., ~
E
g;J!
bb.s
I~~~
P::;
a
~
~
""".
=
.....
t-t-
/
Neanderthal man
100,000 years ago
Cro-Magnon man
40,000 years ago
~
••
<0
c:>.
...,
~ ~
.,
01:
t:I
Cl)
~1!
J:
'tiC.3
~
(D
~
(D
1'\
20,000 years
ago
r
0~
0
~
Cave paintings
at Altamira
13,000 years ago
End ofIce Age
10,000 years ago
t-
...,
c:>.
01:
t:I
~ ~
Cl)
5l
J:
Cl)
::l..c:
"60.3
re.
~
~
""".
t-t-
=
rn
(D
Little Ice Age
Norman Conquest
1066 AD
co
c:>.
01:
...,
~ ~
Cl)
Cl)
::l..c:
'tiiJ.3
~
t:I
5l
J:
I
1900 AD
1::
5lCl)
...
Po.
~
~
~
(D
Data Sheet 3
Unit 13: The geological time scale
Jan
Feb
Mar
Apr
May
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
Jun
Jul
Aug
Sep
Oct
Nov
Dec
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
11
11
11
11
11
11
11
11
11
11
11
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
12
13
14
15
16
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
10.00
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
10.30
11.00
11.30
11.46 midnight
I
A Cosmic Calendar
Student Sheet 1
Unit 14: ''Who's for a hot tight squeeze in inner
space?<'Or, ''How do temperature and pressure change as you go down into the Earth?)
1.
''Inner Space"
It is common knowledge that materials ofgreat value in everyday life come from the layered rocks that
lie beneath your feet. These include: oil and natural gas (collectively known as hydrocarbons), water,
sand, gravel, salt, clay and sometimes even metal deposits like copper and lead.
, , ,
r COAL
7--
LrE,TiJNG-
MU) 1'v1A-T£PJALS
-r-RoM
TH£ Ro[kS BELoW D5/1
Raw materials like these are the basis of the economies of all nations, Each year they contribute about
£40 billion of the U.K.'s total economy of £330 billion - rather more than your yearly pocket money!
Total income of
the U.K. (i.e. its
Gross National
Product) or GNP
Materials
From rocks
=£40,000,000,000
£330,000,000,000
Student Sheet 2
I
,
Unit 14: 'Who's for a hot tight squeeze in inner
space?'
1.1 What percentage of our GNP comes from the rocks each year?
The purpose ofthis Unit is to help you work out what kind of space and what conditions there
are underground. Can there really be enough space down there for all these things? Can oil
and gas form, migrate and become concentrated? How will geologists know where to start
looking for oil and gas, so that they may be extracted and used for the benefit of society?
What is it like down there in inner space?
So, how do water, oil and gas fit in? And how do they manage to move around?
It turns out that:
*
there are mostly layered sedimentary rocks in the upper part of the 'crust'.
*
temperature varies (but in what way? Could things cook or freeze at depth?)
*
there is an awful lot of rock above (but what kind offorces operate and how big are they?)
*
there is little space to move
*
it is not easy to squeeze from place to place (but how fast can things like oil, gas and water
move through the rocks?)
Before we tackle some of these problems, try these three exercises:
1.2
From your own general knowledge, discuss with your teacher the most likely answers to the
questions in the list above, and write them down.
1.3
Use the specimens or photographs provided to help you become familiar with some natural raw
materials.
As you study the specimens, fill in the details on a copy of Data Sheet 1. Try to match the letter
on each item to the name in the table.
Suggest uses for each item and tick ifit is found within, say, 50km of your school.
Try to guess its relative importance to this country's economy and show your answer as "1" for
the most important and so on down the list. Your teacher will give you the actual values later.
Student Sheet 3 :
Unit 14: ''Who's for a hot tight squeeze in inner
space?'
In this Unit, we are only considering economic materials that occur in layered rocks. The next
diagram, (Figure 1) shows how some of these layered rocks are formed. Some ofthem take millions
of years to form completely.
1.4
Study the diagram and try to write the words from the list below it in the most appropriate
spaces provided. Do this from your own general knowledge and make good use of the process
of elimination! Then check your answer with your teacher .
•
Figure 1. The origin of layered sedimentary rocks.
List of words for use in Figure 1
weathering and erosion
transport
deposit of sand
deposit of mud
deposit of oily source rock
deposit of peat
warm lagoon with salt evaporites
river delta
consolidated sandstone
consolidated mudstone
layer of sedimentary rock (stratum)
layer of coal
basin of deposition
Student Sheet 4
I
Unit 14: 'Who's for a hot tight squeeze in inner
space?'
2.
What problems do we face in Inner Space?
We have already suggested that the conditions of temperature and pressure are very different at
depth in the earth from those at the surface. To find out about these conditions directly is extremely
difficult and expensive. The deepest mine in the world is only 3.5km deep. The longest borehole
extends for about 13km. The crust ofthe earth alone is up to 50km thick and the radius ofthe whole
earth is 6350km! We are, therefore, only scratching the surface.
However, the measurements we can make near the surface are very useful. We can also imitate some
of the conditions in less extreme ways in the laboratory.
Working in pairs or groups (and discussing with your parents or friends at home, but not other groups
in the class), decide in outline how the topics listed below could be investigated. Write down your
suggestions.
Heat and pressure
2.1
a) How does temperature vary in
the layered rocks under the
earth'surface in the U.K.?
b) Suggest how these temperatures
might be measured.
c) How do they compare with the
variations on the surface?
((
2.2
a) What different forces apply
pressure to rocks underground?
b) How great do you think they are?
c) How would you measure them?
Your ideas might lead to methods you could try in the school laboratory, or in the grounds, using
familiar equipment. Some of you might think of methods which could be used by large companies or
Government bodies, such as the British Geological Survey.
Discuss the following in outline and write down your conclusions:
2.3
How much space is there for oil, gas, water and other minerals in layered rocks underground?
2.4
How fast can gas, oil and water squeeze through rocks underground?
You may be given the opportunity to work out how these might be measured and to carry out your own
experiments.
Student Sheet 5
Unit 14: ''Who's for a hot tight squeeze in inner
space?'
How does temperature vary underground?
We shall now concentrate on the variation of temperature below the earth's surface. If any of your
ideas for investigations on temperature could be done at school, see if you can design and set up a
suitable experiment.
In fact, temperature measurements have been carried out in various parts of the country. Calculations have also been made to suggest what happens at those depths which boreholes cannot reach.
The result is a series of figures which represent the geothermaI gradient below each place. This
means the rate at which temperature changes with depth below ground. There are some surprisingly
large differences across the country, as you can discover for yourself from the following exercises:2.5
Copy and complete Table 1, for a series of different geothermal gradients. Assume an initial
surface temperature of +10 °C at all places. This has been shown in the table already and the
first column has been started for you.
Geothermal gradient, ie. rise of temperature with depth COC per Km)
Depth
Km
0
Welsh Borders
Cheshire
East Anglia
West
Yorkshire
Lake District
North Pennines
Devon &
Cornwall
Central
Dartmoor
15°ClKm
20°ClKm
25°ClKm
30°ClKm
35°ClKm
40°ClKm
10
10
10
10
10
10
1 - - - -1 - - - - - - - -
1
25
2
40
3
55
4
70
--_.
T
e
m
p
e
5
> ra
6
r
7
e
s
t
u
8
9
I
10
J
Table 1. A table showing how temperature can change with depth.
2.6
Design and plot a graph of depth (in km) on one axis and temperature on the other, using data
from your copy of Table 1. Mark on the graph the geothermal gradients for each region ofthe
country. Label these.
If your main conclusion has been that temperatures get much higher as you go down in the earth's
crust, you might wonder if this geothermalheat could be put to good use. We shall consider two very
important outcomes:
Student Sheet 6
I
Unit 14: 'Who's for a hot tight squeeze in inner
space?'
Geothermal heat and the oil and gas industry
Oil and natural gas are derived from microscopic
organisms, whose remains lie buried in the rocks.
Rocks which contain an abundance of these tiny
plants or animals are known as "source rocks", but
the oil or gas will not be produced unless the rocks
are heated for a long time. In other words, the
source rocks need to mature (i.e. to "cook" properly) before the organisms can be converted into
useful hydrocarbons like oil or gas. If the heating
is too little, oil or gas will not be produced: if it is
too much, all the oil will be altered to gas or may be
lost altogether.
As with your efforts in the kitchen, the time it takes depends on how high the temperature is. Ifthe
geothermal gradient is high, it takes a relatively short time, e.g. tens of millions of years. If the
geothermal gradient is low, it will take much longer.
Geologists talk of an "oil window", i.e. a range of "cooking temperatures" for source rocks between
which oil will form. It lies between 70 QC and 170 QC. Above this temperature only gas is formed.
2.7
Mark on your graph of geothermal gradients the limits of the "oil window" - the region between
70 QC and 170 QC, where oily hydrocarbon source rocks mature. Mark "gas window" for the
region of higher temperatures where only gas is released by the source rocks.
2.8
Write the section heading above and then copy the following sentences into your book. Fill in
the blanks.
''The oil window would be reached at ___km on a geothermal gradient of20 QC per km;
on 25 vC per km;
km on 30 QC per km.
km
Ifmost oily hydrocarbons are "cooked", i.e. mature between 70 QC and 170 QC, on a normal geothermal
gradient of 30 QC per km they would lie at depths between
km and
km. Suitable
rocks could be "cooking" at these depths under my feet now.
Geothennal heat and public heating systems
Most of your family's fuel bill goes to pay for
heating water. But there is an ample source
of hot water beneath your feet (but many
kilometres down!)
Student Sheet 7
i
Unit 14: 'Who's for a hot tight squeeze in inner
space?'
In some parts of the country this hot water is now being piped up to the surface and used to heat
buildings. To be of any use it must be at a temperature of at least 40°C. To find out how far you would
have to drill down for "free" hot water, mark the 40°C line on your graph.
2.9
Write the heading ofthis section and then copy the following sentences into your book and fill
in the blanks;
"Water hot enough to run a town's central heating scheme (>40 CC) would be found beyond a depth
of
km on a 20°C per km gradient;
km on a 25°C per km gradient;
km
km on a 35°C per km gradient. The water would be found
on a 30°C per km gradient and
below
km under a town like Crewe or N antwich in Cheshire and below
km
under Devon and Cornwall.
3.
Experimental Investigations:
A)
What forces, of what type, operate underground?
In Section 2 you were asked to think of ways in which changes in temperature and pressure within
the earth might be measured. We shall now concentrate on pressure. Our experimental work will
deal mostly with sandstones, which make up about 20% of all layered rocks.
Sandstones consist mostly of worn grains of solid matter (largely of quartz) surrounded by a liquid
mineral substance - water. The pressures in rocks like sandstone at depth are due to the weight-force
of both the solid and the liquid mineral matter.
We shall investigate the pressure due to the burial of the solid mineral matter first. This is called
lithostatic pressure (Lithos, in Greek, means rock).
What pressures are due to the solid mineral matter in the rocks underground? How great are they?
(Pressure is force per unit area, measured in newtons per square metre: N / m 2)
3.1
If you were able to suggest an experiment to
imitate underground pressures (in Section
2.2), discuss it with your teacher and try it
out, ifthere is time and ifit seems feasible.
If not, go on to this class experiment.
Use the cubic blocks of sandstone rock and
the top-pan balance to design an experiment
to see if an increase in the thickness of the
"rock-pile" increases the pressure at differen t depths. Remember that pressure is force
per unit area, measured in newtons per
square metre.
'/ 7f rL Seems Feo..Sl6le III "
Student Sheet 8
!
I
Unit 14: 'Who's for a hot tight squeeze in inner
space?'
3.2
Make a table of your results. Design and plot a graph of them and call it Graph A.
3.3
Calculate, or use the figures provided by your teacher, to read off what rock pressures per
square metre would exist at depths ofl, 2, 3, 4, 5, 6, 7,8,9 and 1 Okm, if the whole rock sequence
was made of sandstone. Write down these results.
3.4
Work out and write down the rate of increase of pressure per square metre with depth.
3.5
What do we call the force(s) which act(s) to increase the pressure in this way?
As we have seen above, pressure exerted by the grains of the sandstone is only part ofthe story. We
must not forget the water in the pore spaces of the rock.
B)
What pressures are there due to water underground? How great are they?
(Pressure due to water is called hydrostatic pressure.)
3.6
Pressure due to a column of still water that is not moving underground. Use a
normall000ml plastic measuring cylinder, with the measuring beakers, to design an experiment to show how water pressure varies with depth. Discuss your ideas with your teacher
before you carry out your experiment and take care not to flood the laboratory! Make a table
of your results and plot a graph. Call it Graph B.
For the sake of comparison with the sandstone blocks, convert some of your hydrostatic pressures into
newtons per square metre. (The area of a circle is 1t r2)
3.7
Pressure due to a column of water that is moving underground. Design a similar
experiment to that in 3.6, to show how water pressure varies with depth, when the water is
moving. You may use the specially adapted measuring cylinders for this. Make a table of your
results and plot a graph. Call it Graph C.
3.8
Write a paragraph about what would happen underground if water was confined and still (as
in the normal cylinder) and what would happen ifit was allowed to move (as in the adapted
cylinder).
c) How do lithostatic and hydrostatic pressures operate together in oil, gas and
water prospects?
A lot of people believe that oil, natural gas and water occur in great underground lakes, waiting to
be tapped. THEY ARE USUALLY WRONG! These fluids actually occur within the pore spaces of the
rock, as in a sponge.
The next experiment is designed to imitate this more realistic situation. You will find out how rock
pressures (lithostatic) and water pressures (hydrostatic) affect underground water, oil and gas
prospects.
3.9
Fill the specially adapted 1000ml measuring cylinder with small pebbles, weighing the whole
apparatus after every 50ml offill. Keep a table of results and plot a Graph (D) ofthe increase
of lithostatic pressure with depth.
3.10 Take your cylinder full of small pebbles and fill it with water, keeping a constant head of water
by pouring it in at the top of the cylinder to keep a constant level about 1 cm below the rim. (See
Figure 2)
Student Sheet 9
I
I
Unit 14: 'Who's for a hot tight squeeze in inner
space?'
lem
water
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pebbles
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,
.,,(
,/
,/
/
lab. timer
,-
,-
/
...J---~~~~
---IJ..----
beakers
-
/
~
I
Figure 2. Experiment to investigate how water pressure changes at depth within a sediment.
Using beakers, measure the amount of water issuing from each of the three holes in turn over
a standard time period, e.g. 60 seconds. Keep a table of results and plot them on Graph E.
3.11 To test the effects of different sized particles, fill two adapted cylinders with a) granules (24mm in size), b) medium sand CO.25-0.50mm in size), weighing the apparatus at 50ml
intervals as you go. In each case keep a table of your results and plot them on Graph D.
What results are you likely to get if you fill each of these cylinders with water in the same way as
before and measure the amount of water issuing from each of the holes in 60 seconds? Mark your
predictions as lines on graph paper. Then do the experiment, keeping tables of results. Plot the
results on Graph E.
4.
Inner Space Review
4.1
What conclusions can you derive from these experiments concerning rock and water pressures
underground in "inner space"?
4.2
Write up your experiments, explaining the problem and the way in which these experiments
helped you to come to some conclusions about rock and water pressures underground and how
water can move in "inner space".
4.3
Discuss and predict how these factors might affect the origin, movement and accumulation of
water, oil, gas and mineral solutions underground.
4.4
Next time you read about a new oil well coming "on stream", see if you can find out:
a) How deep is the well?
b) Of what age are the oil-bearing rocks?
c) How much oil is being drawn from the wen each day?
~
g
s-:l.
e.
Letter on
specimen
or photo.
Tick if
found
locally
Suggested uses
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economic
material
Order of
importance
to economy
of Britain
"-your ideas-"
r.n
Actual value to economy
of Britain 1986 in £millions
Your idea
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your teacher}
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Student Sheet 1
Unit 15: Rock Power! - Geothermal energy resources
1. Why Geothermal Energy?
In the last twenty years much has been talked about the so-called "Energy Problem". Oil and gas
resources are running out, coal is expensive to mine and has pollution problems and there are doubts
about the safety of nuclear power and the disposal of nuclear waste.
Many people see the future in a group of resources known as the "Alternative Energy Resources".
Included among these is GeothennalEnergy. This means energy obtained from heat coming out of
the earth.
1.1 What other "Alternative Energy Resources" are shown on the cartoon below (Figure 1). What others
do you know that we were not able to fit on to the cartoon?
Figure 1. Alternative Energy Sources.
Student Sheet 2
Unit 15: Rock Power! - Geothermal energy resources
Geothermal energy is almost an odd-man-out among energy resources. It is, with nuclear energy, the
only one that does not look to the Sun as the ultimate source ofthe energy. Sources such as wind, tides
and waves are all driven by energy originating from outside the earth. Even the fossil fuels such as oil
and coal are really stores of past solar energy. Geothermal and nuclear are both energy sources directly
from within the Earth. The source ofgeothermal energy is in fact partly from nuc1earreactions occurring
within the earth, and partly from the original heat of the Earth when it first condensed from a hot
gaseous cloud.
As you go down into the earth it gets hotter, as for example for miners working in a deep mine. This
increase in temperature is called the geothermal gradient
*
1.2 We can show the geothermal gradient on graph paper. A grid for this is provided in Figure 2.
tcmp/'
1~
/oc
21
3i
dcpty
/
Km
Figure 2. Graph for drawing geothermal gradients.
Because we are dealing with temperature increase as we go down into the earth, we will draw the
graph "upside-down". Use your own graph paper.
a) Use the y-axis (vertical line) of the graph to represent the depth into the earth starting at Okm.
This should be drawn from the top of the grid and the depths written down the paper. Show
depths down to 5km.
b) The x-axis (horizontal line) represents the temperature and should be drawn at the top of the
paper from 0 to 300°C (to keep it simple we will assume that ground temperatures at the surface
are 10°C).
c)
Draw a line on your graph paper to represent a geothermal gradient of30 °C per kilometre. This
is an average figure for the U.K.
d) What is the temperature at 5km depth?
e) At what depth will a temperature of 1 00 °C be reached?
We will use this graph again later in this study.
The heat you have just been studying in your graph-work has been recognised as a potential source of
energy for a long time. There are three ways that it can be exploited, in three different environments.
We wi11look at each in turn.
*
You will find a list of these terms and their meanings at the end of the L'nit.
Student Sheet 3
Unit 15: Rock Power! - Geothermal energy resources
2. Geothermal Energy from Volcanic Heat
You may have heard of hot water bubbling out
of the ground as thermal springs, or shooting
into the air as geysers. The most famous geyser
is probably "Old Faithful" in Yellowstone
National Park in America. It erupts about once
every hour in ajet that pours more than 45,000
litres ofhot water and steam up to 60m into the
air.
There are many geysers in Yellowstone and
many hundreds in active areas in Iceland and
New Zealand. Some are bigger than "Old
Faithful" but none are so regular in their eruption.
2.1 The cartoon shows a picture of a geyser.
They are important tourist attractions in
some places, though the public are not
encouraged to go too near.
Why not?
Geysers themselves do not make good
sources of direct energy.
Can you suggest why not?
Geothermal power stations do tap the
source of the geysers' heat by drilling deep
into the earth in the same area.
Thermal springs and geysers result from hydrothermal convection CUITents within the crust. This is
the circulation whereby cold water from the surface travels deep into the Earth's crust, is heated, and
rises to the surface again.
2.2 We
can demonstrate a simple hydrothermal convection current in the
laboratory. (Figure 3)
Potassium
permanganate
I - - - - - - - - - l crystals
a) Gently warm a beaker of water on
a tripod above a Bunsen burner.
" -0-
b) Carefully drop a few crystals of potassium permanganate into the
water and observe their movement. (Alternatively, you could
use naturally buoyant plastic
balls).
c)
Describe the pattern of the movement.
Figure 3. Experiment to demonstrate convection currents in water.
'\Vater
Student Sheet 4
Unit 15: Rock Power! - Geothermal energy resources
What you have just seen is a convection current. This is the one source of geothermal energy that has
been widely developed. Countries exploiting this resource include Iceland, Italy, New Zealand, Mexico,
Philippines, Japan and U.S.A. (in California).
2.3 Figure 4 shows the operation of the Wairakei Power Station In New Zealand. Use the information
in the diagram to explain in your own words how it works.
,,,.----..
The borehole produces high pressure
steam and water. The steam is
-~
- ~_ ~C~~)
={
~
~;l~!e!~~:: ;;:s:ua::~;,n:ted. ~.
~ :.~ ~C.,~;.·.~~"",,,
'-.. .-
,
,~;.' ~
,'- / . -~ '-'~
'\ ~
__ ~ j
-.....--'-'"-_...
. therefore, filled with clouds of steam. ~ Well head of boreholes. . :~_. ,c-:.:-".;,'"
'/-.
\,
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,',
hI'
) ~
';'"
.
' ; \~ p
••..:... ~ / . ,
~
'~- - , 3' ,', There are over 60 bore 0 es.,"
,.?.~'-;:= "'"':...
. •• '., { \
.':~
:;'.:. _ ?:' '.:., going to a depth of 600m. .~ S~am ~ll;;ting ':
vaporises and the whole area is,
,, 0:1:
~:
~;-
.
,
,
..1
,-{
Figure 4. The Wairakei geothermal power station, New Zealand.
,pipes feeding to the
main pipeline. '
Student Sheet 5
Unit 15: Rock Power! - Geothermal energy resources
The heat in these hydrothermal regions comes to the surface as hot springs or steam vents. Cold water,
from rainfall, seeps down cracks or faults, is heated by the warm rock and returns to the surface through
a different set of cracks. The steam can then be used to generate electricity. In large towns it is piped
into buildings for central heating.
2.4 We can build our own imitation hydrothermal convection system in the laboratory.
Collect the apparatus as
shown in Figure 5.
Thermometer
-----~
-+---- "Head" of cold water
Hot Water-----.
Thermometer
--~
Measuring _ _ _I
cylinder
-?i----
Block
Figure 5. Apparatus to study hydrothermal convection currents.
a) Heat the sand and gravel mixture in a metal dish in an oven set at about 100°C for about an
hour. This represents the hot "rock".
b) Set up the apparatus as shown in Figure 5. Do not add the water yet.
c) Record the temperature of the "rock" at the start of the experiment.
d) Record the temperature of the tap water at the start ofthe experiment.
e) Add the water slowly into the glass tube so that there is always a head of water in the tube.
f)
Record the temperature of the water in the measuring cylinder every 25cm, throwing the water
away after each measurement. At the same time record the "rock" temperature.
Record your results on a table similar to the one set out below.
Volume of water
in measuring cylinder
Temperature of water
in measuring cylinder
Temperature of "rock"
in density can
(emS)
(OC)
(OC)
0
25
50
75
100
etc.
water temp. at start - ?
"rock" temp. at start - ?
When you have completed the experiment, use the table to dra w a graph ofthe results. Plot temperature
against volume of water and draw two coloured lines to show the water temperature and the "rock"
temperature.
Student Sheet 6
Unit 15: Rock Power! - Geothermal energy resources
Now try to answer the questions below:
a) Is there a difference in temperature between the water and the "rock"? If so, why?
b) Does the difference remain the same throughout the experiment? Can you explain this pattern?
c) What would happen to the temperatures of the "rock" and the water if the water passed through the
apparatus more quickly?
d) How would you need to change the apparatus to allow water to pass through more quickly?
e) Think carefully about your answers so far. In view of what you have said, do you think geothermal
energy supplies will last for ever? Would we describe it as an infinite energy source?
f)
Look again at your answer to question c). Does your answer help to explain why there is a limit
to the size of power stations that can be set up on a hydrothermal energy field?
g) One problem with our experiment is that we stopped heating the "rock" before putting it into the
density can. Can you suggest a simple way in which you could continue to heat the "rock" while the
experiment was running?
You probably thought of putting a Bunsen burner beneath the density can. Could such a thing happen
in nature?
Geologists have indeed found that some areas are much hotter than others. This is not because of the
sun's heat, but is because extra heat is being produced within the earth. The two main reasons are:
(i) there are huge convection cells deep in the earth (below the crust), rather like your first experiment,
(ii) great friction takes place between different sections of the outer layers ofthe earth. This produces
heat, rather like rubbing your hands together quickly.
The sections of the earth's outer layers just mentioned are known as plates. Figure 6 shows the most
important ones and the thick lines show where they meet. The countries where hydrothermal
convection heat has been used for energy have been plotted on the map.
Eurasian Plate
Pacific
Plate
Figure 6. Map showing plate boundaries and location of states with geothermal power stations.
Student Sheet 7
Unit 15: Rock Power! - Geothermal energy resources
2.5 a) Is there any connection between the countries and the plate boundaries?
b) The United Kingdom cannot exploit hydrothermal convection heat. Can you suggest why not?
The fact that heat is being added from below means that hydrothermal convective sources may last for
a long time. It will, however, depend on the degree of volcanic activity in the area and the rate at which
the heat is extracted. Other geothermal sources we shall study will not last as long. Britain is located
within a "plate", not on the edge. This means there is no opportunity in this country to use hydrothermal
convective sources. However, the second source of geothermal energy is showing promise at the
moment.
3. Geothermal Energy from Sedimentary Basins
We have already learned that the geothermal gradient is, on average, 30°C per km. Therefore, if we
can discover water bearing rocks (aquifers) at a few kilometres depth, then we may be able to use the
heat within them. Alternatively, if the rock allows the water to pass easily through it (it is very
permeable) then water can be pumped through it and heat obtained in this way.
The waters of the Roman Baths, in Bath, are heated through this natural process. Figure 7 explains
how this works.
Key (the rock layers are
in order of age)
tXt2~ Triassic mudstones
fault
F1
Coal measures
E23
Carboniferous limestone ..
f:.·. ·.· ::.1
Devonian sandstone ..
~
Silurian
1000
2000
.--" flow of water
o
2km
3000
metres
¥
hot spring
(* = rocks which are permeable aquifers. This means that they are water-bearing and will let the water pass
through the rock.)
Figure 7. How the hot spring at Bath works.
3.1 Use Figure 7 to describe in your own words why the spring at the Roman Baths is hot. (It flows at
a constant temperature of 46.5 QC)
3.2 Look back at your experiment to demonstrate the extraction of geothermal energy from the
sediment in the density can. How well does your experiment demonstrate the situation in Bath?
It may interest you to know that the water flowing from the spring at Bath is thought to have fallen on
the Mendip Hills 10,000 years ago. Clearly it has taken a long time for it to flow through the "natural
apparatus" of the area!
Student Sheet 8
Unit 15: Rock Power! - Geothermal energy resources
It is this heat in deep sedimentary basins that geologists are seeking to use. Fortunately, this type of
geothermal energy is not restricted to plate boundaries, but can be found anywhere that suitable
aquifers occur deep in the Earth.
Such a geothermal energy supply has been exp loited near Paris for many years. Now attempts are being
made to use a similar source in Britain and especially in Southampton. Let us look more closely at what
is going on in this city on the south coast of Britain.
Southampton is situated in the heart of a geological feature called the Hampshire Basin. The geological
map and section (Figures 8 and 9) show that the rocks are folded into a bowl shape beneath
Southampton. The diagrams also show geologists' names for rocks of particular ages. For example, in
this area the Permo-Triassic rocks are the oldest and the Tertiary rocks are the youngest. The PermoTriassic beds are about 220 million years (m.y.) old and are known to contain a number of very permeable
sandstones that would make suitable aquifers.
o
Tertiary
o
Cretaceous
lZ2d Jurassic
[J
N
--- --
~--
--
--
--
PermoTriassic
x
r
Figure 8. Sketch map of the geology of the Hampshire Basin.
Depth /
/Km
x
Southampton
& Marchwood
y
Isle ofWight
o
0.5
1.0
l.5
2.0
2.5
3.0
Figure 9. Geological cross section of the Hampshire Basin.
possible
__ upper
aquifer
Student Sheet 9
Unit 15: Rock Power! - Geothermal energy resources
3.3 Figure 9 shows the possible aquifer in the Permo-Triassic rocks. Measure its depth below
Marchwood, near Southampton.
3.4 Now look back at the graph of geothermal gradients you drew earlier in 1.2. You plotted an average
geothermal gradient of30 °C per km below Southampton. Read off the temperature of the water
that might be found in the Permo-Triassic aquifer for the depth you have measured in 3.3.
The Central Electricity Generating Board (CEGB) did a similar calculation to yours. This led them to
drill an experimental borehole at their research laboratories at March wood in 1979/80. Marchwood was
also the location of an oil-fired power station and the CEGB were hoping to use the hot water to cut down
some of their costs of oil.
Unfortunately, the Permo-Triassic aquifer was reached at only 1.7km. This is much less than you
measured, isn't it?
3.5 What temperature could have been expected from this aquifer at only 1.7km? Use your graph to
obtain the answer.
All was not lost, however! In fact engineers were surprised to find that they obtained water at 70 °C.
This was much hotter than had been expected.
3.6 The geothermal gradient below Marchwood is clearly higher than averge. Draw a line on your graph
to represent this geothermal gradient and label it "Hampshire Basin". Calculate its value in °C per
km.
Now that hot rocks had been found beneath Southampton, geologists and engineers had to carry out
further investigations.
3.7 Look back at your experiments with the density can.
Look at the answers you gave to some of the follow-up questions.
In view of what you said then, what questions did the geologists and engineers have to ask to be able
to assess the potential ofthe hot rock as a source of energy?
Notice that the questions they would ask are not the same as simply asking what the temperature
IS.
What controls the amount of heat that could be supplied?
It is these factors that need to be investigated.
As well as the geological and engineering questions, the economic questions needed to be answered. The
existence of hot water in sedimentary basins is well known. But three points severely limit its use.
a) It is not usually hot enough to allow electricity generation on its own.
b) The water could be used for central heating in an area known as district heating, but then there
is the cost of carrying the water over any distance. If the user is too far from the borehole the cost
of keeping the water hot will be too expensive.
c) The cost of a borehole is expensive, and not all boreholes will be successful in finding hot water and
in sufficient quantities. You have already seen how the Marchwood borehole yielded water at a
shallower depth than had been predicted and, therefore, at a lower temperature.
You can see that the economics of geothermal energy from sedimentary basins may mean that it is not
possible to use it. The CEGB decided they could not economically use the hot water at Marchwood.
The Department of Energy (DoE) drilled a second borehole nearby in the centre of Southampton to
examine the possibility of a district heating scheme. This obtained water at 74 oC, which is now being
Student Sheet 10
Unit 15: Rock Power! - Geothermal energy resources
pumped out ofthe ground. The heat is extracted, and then the water is emptied into the nearby tidal
River Test.
Southampton City Council has linked with a French company to develop the scheme which is explained
in the newspaper article on Data Sheet 1.
3.9 Read the article and answer the questions on it below. It will also allow you to check your answer
to Task 3.7.
a)
b)
c)
d)
e)
Who is paying for the project?
Who is using the heat from the project?
How much is it expected to save on heating bills?
How long is it thought that the heat source will last?
Is the scheme expected to make a large profit?
It is worth noting that the newspaper article mentions that the borehole cost £2.75 million to drill and
was paid for by the Department of Energy as part oftheir investigation into geothermal energy. Ifthis
Department had not paid for the borehole, the project would not have been economic.
4.
For the moment then, this type of geothermal energy scheme, for economic and geological reasons has
only a limited future. Other boreholes have been drilled elsewhere in the country but their future is
uncertain. However, the third type of geothermal energy source may solve some of these problems in
the long term.
Heat flow in
milliwatts per m 2
N
Hot Dry Rocks
over 90
We saw in 2.5 that Great
Britain does not lie on the
edge of a "plate". This
means that there is less
heat rising to the surface
than in New Zealand at
Wairakei Power Station.
Even so, some parts of our
country do have a higher
heat flow than others. The
differences are shown in
Figure 10. The units for
heat flow are milliwatts per
square metre, but don't let
this worry you! Although
the values are much lower
than at plate margins, the
possibility of making use of
the heat is worth looking
into.
Figure 10. Variations in heat flow in the United Kingdom.
80-89
70-79
CO-69
50-59
40-49
,lOO Km,
Student Sheet 11
Unit 15: Rock Power! - Geothermal energy resources
4.1 Use Figure 10 to say which areas in the United Kingdom have the highest heat flow and are,
therefore, possible sites for geothermal energy extraction.
4.2 Use an atlas to discover the type of rock that underlies most of South-West Britain.
Suggest what may be the cause of the above-average heat flow in this area.
4.3 The geothermal gradient in one part of South-West Britain has been measured at 50 cClkm. Return
to the graph you have been using for plotting geothermal gradients, and plot this figure for SouthWest Britain, and label it.
4.4 A borehole was sunk into the granite in West Cornwall. Using the geothermal gradient of 50 cCI
km calculate the temperature which the rock should be at a depth of 2km.
Rocks such as granite, found in the South-West, have an above-average geothermal gradient because
of the high proportion of radioactive minerals within them. These generate heat in the rock. Another
granite mass underlies an area of high gradient in the Northern Pennines. Such masses could be a
source of heat far greater than sedimentary basins, but unfortunately granites are much less permeable
than the aquifers in the Hampshire Basin.
4.5 From what we have learned so far about the way we obtain geothermal energy, explain why this lack
of permeability is a problem.
5. Geothermal Energy in the Future
Scientists at Camborne School of
Mines, Cornwall and at Los Alamos
in U.S.A. have been trying to solve
this problem of obtaining heat from
hot dry rocks. The method is to drill
into the granite to a depth where the
rock is hot enough. At this point a
controlled explosion is caused at the
bottom of the borehole to try to form
cracks within the granite.
5.1 The rest of the process is illustrated in Figure 11. Use this
diagram to explain how the heat
might be obtained from the
rocks.
Power Station
under pressure
t
Flow of cold
~water 75kg S-l
Area of rocks shattered
by explosives
------6K:rn
Figure 11. How energy might be extracted from hot dry rocks.
Student Sheet 12
Unit 15: Rock Power! - Geothermal energy resources
The size ofthe granite heat source means that it may be possible to drill many boreholes and therefore
extract large quantities of heat.
Modern drilling technology means that from one central point a large number of offset boreholes can be
drilled. Sufficient heat may, therefore, be extracted to make it economic to build geothermal power
stations similar to those in areas such as Italy, Iceland and New Zealand, as we discussed in the first
section of this study.
This is all in the future, and at the moment is only at the research stage. Present results are promising
although we are still a long way from replacing fossil fuels or nuclear power as a source of our energy
supplies.
The worldwide growth of the use ofgeothermal energy shows an interestingpattem as the table below
shows.
Year
Approx. installed capacity of
electricity generation in the world
Megawatts (MW)
1969
1979
1983
1985
1992 (projected)
750
1,700
2,300
4,700
7,700
5.2 Plot this information on a graph and comment on the results.
We have looked in this study at different types of geothermal energy. We have seen how each works and
have considered the present and future possibilities.
5.3 You should now be in a position to complete the table below which will summarise what you have
learned. (Make your own copy of it first)
5.4 How do you see the future of geothermal energy? Do you see it replacing traditional fuel sources?
Type of source
1. Hydrothermal
Convective
Sources
2. Sedimentary
Basins
3. Hot Dry Rocks
Origin of heat
Where is it used
at present? (place)
Where may it be
used in the
future? (place)
What is/will it
be used for?
(heat, power?)
Student Sheet 13
Unit 15: Rock Power! - Geothermal energy resources
Glossary of terms used in this unit
Aquifer
A water-bearing rock.
Cretaceous
A period of geological time extending from 135 to 65 million years ago.
District Heating
A system by which a whole area is supplied with heat and hot water from a
central source. Each user is independently charged in the same way as already
happens with gas and electricity.
Earth's Heat Flow
The rate at which heat is being lost from the surface of the earth. It is normally
measured as a unit of energy per unit area. e.g. milliwatts per square metre
(mW/m 2 ). On average it is about 60mW/m2 in this country.
Geotherma1 Gradient
The rate at which temperature increases with depth into the earth. In this
country it is an average of 30°C per km.
Granite
A type of rock formed from the solidification of molten rock (magma) beneath
the earth's surface. It is usually found in large masses many km across.
Hydrothermal
A term used by geologists when they talk about water that has been heated by
the earth's interior heat.
Permeability
The ability of a rock to allow water to pass through it either through pores or
cracks in the rock.
Permo-Triassic
A period of geological time extending from 280 to 195 million years ago.
Plate
The earth's outer layer (the Crust and Upper Mantle) is divided into a number
of separate plates. These are rigid units that move independently of each other,
driven by large convection currents deep in the earth.
Tertiary
A period of geological time extending from 65 to 2 million years ago.
Data Sheet 1
Unit 15: Rock Power! - Geothermal energy resources
HOT ROCKS DEAL SIGNED
Water will heat three big buildings
HOT ROCKS water, 5,500 feet beneath Southampton,
will soon be gushing to the surface heating three big
buildings in the city centre.
Britain's alternative energy experts are now looking to
Southampton to see if the country's first geothermal district heating scheme will work.
Council and Southampton Geothermal Heating Company
(SGHC) signing building and operating deals.
But the risky venture will not cost the city ratepayers a
penny, stressed assistant director of finance at the council,
Mr. David PitL
Instead the council will:
•
•
•
•
•
Lease the borehole site to SGHC.
Provide a site for the heat station.
Give consent for pipe laying.
Help with information and advice.
Be the first customer.
By JUSTIN JONES
The other customers for the natural heating scheme are the
Institute of Higher Education and Tyrrell and Green department store.
"By switching to the geothermal heating we reckon the
council will save £10,000 offits present £100,000 bill run
on gas", said Mr. Pitt.
He estimates that SGHC, which was set up by Utilicom,
the British branch of the French geothermal specialists
IDEX, needs only to win one more contract the size of the
civic centre to break even on their £1 1/ 2 million project.
And it would take nine buildings the size of the civic centre
capacity.
to hit maximum
And if the project makes money the council will have a
share in the profits, said Mr. Pitt.
"In the winter when the heating demand goes up the hot
water heating will have to be boosted by traditional gas
heating," said Mr. Pitt
Scheme would not lie down
TODAY'S signing ceremony marks
the final fruition of a project which
ran on the rocks and looked like
being dead and buried at least three
times since the idea first sprang up in
1980.
"In 1983 the Department of Energy
drilled the borehole at a cost of
£23/ 4 million," said Mr. Pitt.
"When they found the water at 740
centigrade they suddenly changed
their minds deciding the money for
developing the scheme would be
better spent on other things.
will work," said Mr. Pitt.
"They were about to pour tons of
concrete down the borehole when
the council stepped in to stop the
waste and approached geothermal
experts in France to save the project."
"The question is for how long. Estimates range from 15 to 20 years until
the supply dries up."
The EEC have backed the scheme
with a £304,000 grant and promise
to give £226,000 for heating station
equipment.
It could even be longer if more hot
rock water beds are found beneath
the city. The well head is in the car
park of Toys R Us.
Water is pumped up and the heat is
exchanged with fresh clean water
which flows through the pipes.
"There is no doubt that the project
Details of the Southampton Geothermal Energy Scheme (Southern Evening Echo, 3.7.87.)