S276 Geology

Are you ready for S276?

Contents

1 Introduction 1

2 Suggested prior study 2

3 Key concepts introduced in recommended prior courses and further

developed in S276 2

4 Concepts that are desirable, but NOT essential, for S276 3

5 Self-assessment test of key concepts 4

5.1 Further reading and revision for key concepts 7

6 Mathematical skills and concepts 8

7 Self-assessment test of mathematical skills and concepts 8

7.1 Further reading/revision for mathematics 10

8 Other skills 11

8.1 Further reading/revision for other skills 11

9 Answers to self-assessment questions 11

1 Introduction If you intend to study Geology (S276), enjoy the course fully and give yourself

the best possible chance of completing it successfully, you should make sure

beforehand that you have the necessary background knowledge and skills to give

you a sound platform from which to tackle this work. This is especially important

if you haven’t studied any of the recommended courses listed in Section 2.

Even if you have already successfully studied the suggested Open University

(OU) courses, please read through this document carefully and work through the

self-assessment tests: working through this material will remind you of the

knowledge, skills and concepts that it is assumed S276 students will bring with

them when they begin the course, and on which they will build.

If you have not studied with The Open University before or if after working

through this material you are still not sure whether S276 is the right course for

you, then we recommend you contact an advisor to discuss your plans.

In Sections 5, 7 and 8 of this document we have suggested sources of further

reading that should help you to fill any gaps, or revise areas of weakness, in your

knowledge and skills in readiness for studying this geology course.

Copyright © 2009 The Open University WEB 01412 2

1.1

2 Suggested prior study Geology (S276) is one of the core 30-point courses of the Geosciences

programme. If you have followed the suggested study route for this programme

you will already have completed:

� Exploring science (S104) or its predecessor Discovering science (S103).

Both these Level 1 courses give a broad and integrated view of the whole of science, including some core Earth sciences concepts that you will need to understand before you start S276.

If you are not following this route, perhaps because you already have some

science background but want to extend your knowledge of Earth sciences, then

you should check that you understand the Earth sciences concepts that are

introduced in S104 by working through Section 5 of this document. Even if you

have studied S104, this would be useful revision.

The following courses also give you some useful background information for

S276, but do not cover all the concepts that you need to know before you start

S276:

� Science starts here (S154) – this course introduces you to basic scientific

concepts and to the skills needed to study successfully with the OU.

� Science short courses – these give you an opportunity to try out an area of

study before you commit yourself to a longer course. Some that are

particularly relevant to Earth sciences are:

Fossils and the history of life (S193)

Maths for science (S151)

Volcanoes, earthquakes and tsunamis (S186)

� Introducing environment (Y161) – this is a suitable course for beginners with

little previous scientific knowledge, who may need to develop their general

study skills.

� Practising science (SXR103) – this course gives you practical experience and

is usually taken at the same time as, or following, Exploring science (S104).

3 Key concepts introduced in recommended prior courses and further developed in S276

� The rock cycle

(S104 Book 2: Chapter 10; Book 6: Chapters 4 and 6; SXR103 Study Book: Section 2.8)

� Igneous, metamorphic and sedimentary rocks: identification of these

three major groups, processes of formation and characteristics

(S104 Book 2: Chapter 5; Book 6: Chapters 4, 5 and 6; SXR103 Study Book)

� Weathering and erosion processes: chemical and physical

(S104 Book 1: Chapter 7; Book 2: Chapters 5 and 10; Book 6: Chapter 5)

� Tectonics: the concept of crustal movements, folding and faulting of the

crust

(S104 Book 2: Chapters 8, 9 and 10; Book 6: Chapters 4 and 6)

� Plate tectonics: processes at constructive, destructive and conservative

plate margins

(S104 Book 6: Chapter 4)

2

� Making simple observations of rock samples and interpreting these in

terms of geological processes

(S104 Book 2; SXR103 Study Book and Activity A)

� Geological time; the stratigraphic column and geological timescale

(S104 Book 6: Chapter 2)

� Relative dating and the difference between relative and absolute ages

(S104 Book 6: Chapter 2)

� Familiarity with chemical symbols and formulae

(S154 Chapter 6; S104 Book 4)

� Using graphs, maps and diagrams to show information or illustrate ideas

and processes

(S104 Book 2: Chapter 3; S154 Chapters 2, 3, 4 and 7; SXR103 Study Book)

� Recognising areas of different rocks on a geological map, using the key

(S104 Book 6: Chapter 7)

4 Concepts that are desirable, but NOT essential, for S276

There are a number of concepts that you may have come across before, especially if

you have studied Exploring science (S104). If you are familiar with any of the

following you will find it helpful, but you will be able to study the course without

any prior knowledge of these concepts as they are explained in the course materials.

From S104 Book 2

� the nature of earthquakes and volcanic eruptions

� the structure of the Earth’s interior.

From S104 Book 5

� the broad course of biological evolution

� the binomial system of naming species and the way in which species can be

classified.

From S104 Book 6

� development of different magmas through partial melting and fractional

crystallisation, and in relation to their tectonic setting

� magma crystallisation: processes, temperature/depth relationships and order

of mineral crystallisation

� distribution of silicate minerals in crustal rocks

� radiometric dating

� subdivision of igneous rocks according to their grain size and their mineral

and chemical compositions

� the effects of tensional and compression forces on rocks

� the main sedimentary processes operating at the Earth’s surface, i.e. the

action of physical and chemical weathering, and the conditions that result in

erosion, transportation and deposition of sedimentary material

� indications of the environment of formation of sedimentary rocks from grain-

size distribution, sedimentary structures and mineral composition

3

� subdivision of sedimentary rocks according to grain size

� fossils: identification of common groups, and fundamental differences in

body plans

� key events in the history of life, e.g. mass extinctions and evolutionary

radiations

� the use of fossils and relationships between bodies of rock (i.e. strata, igneous

intrusions) and geological structures in establishing a relative geological timescale.

5 Self-assessment test of key concepts Try to answer the following self-assessment questions (the answers are given in

Section 9 of this document). This will help you to judge your level of knowledge

of some of the key concepts listed above. We’ve included a score sheet in the

answers section where you can note down your own assessment of how well you

demonstrated your understanding.

Question 1

What is the rock cycle? Describe the essential processes that link the different

stages in the cycle.

Question 2

Which of these terms could you use to describe rock texture?

crystalline light sharp coarse grained

dark rough fragmental scratchy

aligned thick banded heavy

dense jagged smooth random orientation

Question 3

How are igneous rocks formed? Describe their texture and explain the

significance of grain size.

Question 4

How are sedimentary rocks formed? Describe their texture and name a few

common examples.

Question 5

How are metamorphic rocks formed? Describe their texture.

Question 6

What are subduction zones? Describe the kinds of geological activity that are

associated with these zones.

4

5

Question 7

What is the stratigraphic column?

Question 8

Name the three Eras of geological time following the Precambrian.

Question 9

What is meant by weathering and what part does this play in the rock cycle? What

are the essential differences between chemical and physical weathering

processes?

Question 10

Figures 1 and 2 show two geological cross-sections.

(a) Which of these geological cross-sections shows an example of a fault

produced by compression? What type of tectonic force produced the fault in

the other cross-section?

(b) What type of fault is shown in Figure 1 and what type of fault is shown in

Figure 2? In each case, state whether the rock section is shortened or

lengthened.

limestone

sandstone

mudstone

conglomerate

Key

Figure 1 Geological cross-section for use with Question 10.

limestone

sandstone

mudstone

conglomerate

Key

Figure 2 Geological cross-section for use with Question 10.

Question 11

Does the energy of a transporting medium (such as wind or water) need to be high

or low to transport relatively large grains of sediment?

Question 12

A specimen of rock is made up of mud and silt with occasional whole fossil shells

of organisms that lived on the seabed. Explain what you can deduce about the

energy of the environment where this rock formed.

Question 13

Figure 3 shows an exposure of sedimentary rocks. Assuming that they have not

been overturned, which of the two rock units is the younger – the upper or lower

rock unit? Explain your answer.

Figure 3 Students examining an exposure of sedimentary rocks. For use with

Question 13.

Question 14

Figure 4 shows an exposure of rocks on a seashore. The dark-coloured

sedimentary strata have been intruded by a lighter-coloured igneous rock. Which

is older, the sedimentary rock or the igneous rock? Explain your answer.

Figure 4 An exposure of rocks on a seashore. For use with Question 14.

6

Question 15

What type of dating is being used in Questions 13 and 14? What type of dating

could you use to get a more accurate age for the igneous rock in Question 14?

Briefly describe the principle underlying this second method of dating.

Question 16

Complete the following table of common chemical elements and their chemical

symbols.

Element

Al

Symbol

C

sodium

Si

calcium

oxygen

sulfur

Fe

magnesium

5.1 Further reading and revision for key concepts

7

Open University courses

� Exploring science (S104):

Book 2: Earth and Space

Book 6: Exploring Earth’s History

� Science short courses:

Volcanoes, earthquakes and tsunamis (S186)

Fossils and the history of life (S193)

Natural History Museum publications (available from their online bookshop)

� Van Rose, S. and Mercer, I. (1999) Volcanoes (2nd edn), The Natural History

Museum, ISBN 0 565 09138 7.

� Edwards, K. and Rosen, B. (2004) From the Beginning (revised reprint), The

Natural History Museum, ISBN 0 565 09142 5.

Earthwise publications (available from the British Geological Survey online

bookshop

� Van Rose, S. (1997) Earthquakes – our trembling planet, ISBN 0852722877.

� Rigby, R. (1997) Fossils: the story of life, British Geological Survey,

ISBN 0852722842.

Teach yourself books (available from Hodder Education)

� Rothery, D. (2008) Teach Yourself Geology (3rd edn), Hodder Education,

ISBN 0 340 958790.

� Rothery, D. (2007) Teach Yourself Volcanoes, Earthquakes and Tsunamis,

Hodder Education, ISBN 0 340 94241X.

Other books

Edmonds, E. (1983) The Geological Map: an anatomy of the landscape, HMSO,

ISBN 0118807218.

Edwards, D. and King, C. (1999) Geoscience: understanding geological

processes (2nd edn), Hodder Education, ISBN 0 340 688432.

6 Mathematical skills and concepts If you are to study S276 effectively you should possess simple mathematical

skills and understand some mathematical concepts. You should be able to:

� carry out calculations using addition, subtraction, division and

multiplication

� use a scientific calculator

� manipulate large and small numbers using powers of ten (S154 Chapter 2

and Chapter 9; S104 Book 2: Chapter 13)

� use scientific notation

(S104 Book 1: Chapter 3)

� carry out simple unit conversions (e.g. mm to m, m to km)

� manipulate equations to make an unknown term the subject

� plot graphs choosing appropriate scales and axes; interpret graphs correctly.

Plot a graph and draw a best-fit line, and use it to interpret the data.

Understand the concepts of interpolation and extrapolation.

� express quantities as ratios, fractions or percentages and to the correct

number of significant figures

� calculate areas or volumes using given formulae, e.g. the volume of a

4 sphere, V = π 2

r where r is the radius of the sphere, and use the units 3

correctly.

7 Self-assessment test of mathematical skills and concepts

Try to answer the following questions to check your understanding of the

mathematics needed to study S276.

Question 17

8

Use your calculator to evaluate the following:

(a) 6998 – 993

(b) (8 + 6) × (5–2)

a (c) X = × 100% , where a = 15 and b = 81. Find X and express its value to

b

three significant figures.

Question 18

Calculate the volumes of the following rectangular blocks to two significant figures:

(a) 2.0 m 3× 8.0 cm × 9.0 mm (give the answer in cm ).

(b) 87 cm × 9.0 cm × 8.0 m (give the answer in m3).

Question 19

In the answer to Question 18, scientific notation is mentioned as being a better

and less-ambiguous way of expressing numbers. Check your understanding of

this form of notation by completing the following table.

Number Number in scientific notation

3.2 × 103

143

7 × 10–3

10

Question 20

Scientists use SI unit prefixes as an alternative way of representing multiplying

factors, for example ‘kilo’ as in kilogram (kg) or kilometre (km) means ×1000 or

×103, i.e. 1 kilogram = 1000 grams (103 gm) and 1 kilometre = 1000 metres (103 m).

What multiplying factors do the SI unit prefixes in the following table represent?

Show these factors in ordinary and scientific notation. What are their symbols?

Prefix Multiplying factor Symbol

giga

Ordinary notation Scientific notation

mega

milli

micro

nano

Question 21

Express the volume of the planet Mars (which is 1.64 × 1011 km3) in scientific

notation in m3 .

Question 22

9

When you need to use an equation to find an unknown quantity it is useful to be

able to manipulate the equation to make the unknown term the subject.

m (a) Rearrange the equation ρ = so that you could calculate the mass (m) of a

V

rock if you knew the volume (V) and the density (ρ).

(b) Rearrange v =

µ s

so that µ is the subject. ρ

Question 23

When you carry out a calculation you also need to be able to give the answer with

the correct units.

m In the equation 3ρ = , if the volume (V) is given in m and the mass (m) is given

V

in kg, what are the units of density (ρ)?

Question 24

This question deals with some of the conventions and skills associated with using

graphs.

(a) If the scale on the vertical axis (y-axis) is temperature in degrees Celsius, how

would you write this?

(b) How would you calculate the gradient of a straight-line graph?

(c) Figure 5 shows the travel time of a seismic wave from its origin to a point on

the Earth’s surface, plotted against distance from the earthquake’s epicentre.

(i) Which of these quantities is the independent variable?

(ii) How long does it take for the seismic wave to travel 150 km?

(iii) Why does the line of the graph not go exactly through all three points?

trav

el ti

me

afte

r ea

rthq

uake

occ

urre

d/s

40

30

20

10

0 100 200distance from epicentre/km

Figure 5 Travel time of a seismic wave. For use with Question 24.

7.1 Further reading/revision for mathematics

10

Open University courses Science starts here (S154) and Exploring science (S104)

should have given you all the grounding that you need to begin S276, but if you

have not planned to include these courses in your degree profile, or you would

like to brush up your maths skills, you might want to take the Science short

course Maths for science (S151), especially if you have some time to spare before

starting Geology (S276). (Alternatively, you might prefer to study one of the

other science short courses.)

8 Other skills Basic study skills

You should be able to:

� organise your time for study, remembering that a 30 point course involves

around 300 hours of study

� pace your study, in particular making sure that you have done the relevant

work in time to attempt assignments and submit them in good time for the

cut-off date

� read effectively, understanding concepts that are explained to you,

summarising what you have read, extracting information from tables and

diagrams, and extracting relevant information and data from scientific texts

and accounts.

Writing skills

You should be able to:

� write clear, concise and coherently structured answers with appropriate

diagrams

� describe, contrast and compare information and discuss and interpret

information on a given topic.

Elementary practical geology

It is desirable for you to have had some practice of observing and describing

simple geological hand specimens and to be aware of how geological information

is presented in maps and cross-sections.

8.1 Further reading/revision for other skills

Northedge, A., Thomas, J., Lane, A. and Peasgood, A (1997) The Sciences Good

Study Guide, Open University Worldwide, ISBN 0749234113.

9 Answers to self-assessment questions A ‘score sheet’ is included at the end of this section so that you can record how

well you did. This should help you to decide if you are ready for Geology (S276).

Question 1

The rock cycle is the process by which rocks are continuously formed and

destroyed.

Rocks exposed at the Earth’s surface are subjected to the processes of weathering

and erosion. The particles formed are transported and deposited as sediments,

which may be compacted and subjected to high temperatures and pressures so that

metamorphic rocks are formed. Ultimately, partial melting of deeply buried rocks

may occur and the resulting magma may then erupt at the surface or be intruded

into the crust.

11

Weathering and erosion of surface rocks will eventually expose buried sediments,

intrusive igneous rocks and metamorphic rocks at the surface, where they will be

subjected to weathering and erosion.

Question 2

12

Rock texture is the fabric of the rock. The terms that can be used to describe rock

texture are highlighted:

crystalline light sharp coarse grained

dark rough fragmental scratchy

aligned thick banded heavy

dense jagged smooth random orientation

The other terms do not describe texture: ‘dark’ and ‘light’ refer to colour; ‘dense’,

‘thick’ or ‘heavy’ are linked to the mass or size of a rock specimen; ‘rough’,

‘jagged’, ‘smooth’, ‘sharp’ and ‘scratchy’ are words you could use to describe the

feel of a rock specimen – but note this is not what is meant by its texture!

Only the words crystalline, course grained, fragmental, aligned, banded and

random orientation describe the rock texture.

Question 3

Igneous rocks are formed by the cooling and crystallisation of magma. They are

usually characterised by an interlocking crystalline texture in which the crystals

are randomly arranged. Intrusive igneous rocks are usually coarser grained than

extrusive igneous rocks. The main reason for this is that molten magma cools and

crystallises more slowly at depth, giving crystals time to grow, since it is

insulated by surrounding rock. When molten magma is erupted as lava, it cools

and crystallises more rapidly because of contact with air or water; this means that

crystals have less time to grow and cannot reach a large size.

Question 4

Sedimentary rocks are formed when sediments that have been deposited at the

Earth’s surface undergo processes such as burial, compaction and cementation (or

lithification). Sedimentary rocks usually (but not always) have a fragmental

texture, with individual grains cemented together. Common examples of

sedimentary rocks are sandstone, mudstone and limestone.

Question 5

Metamorphic rocks can be derived from sedimentary or igneous rocks, or from

pre-existing metamorphic rocks. They are rocks that have had their texture and/or

mineralogy changed by the action of heat and/or pressure, whilst their chemical

composition stayed the same and the rocks remained in a solid state. They have

an interlocking crystalline texture and often display some form of mineral

alignment or banding.

Question 6

A subduction zone is a linear region along which oceanic lithosphere is conveyed

down into the mantle at a destructive (convergent) plate margin. The zone is

associated with earthquakes (shallow to deep focus) and also with volcanic

activity at an island arc or Andes-type mountain belt.

Question 7

The stratigraphic column is a diagrammatic representation of geological time

units that results from stacking them vertically, with the oldest at the base

overlain by successively younger units.

Question 8

From oldest to youngest, the three geological Eras after the Precambrian are:

Palaeozoic, Mesozoic and Cenozoic.

Question 9

Weathering describes the action by wind, rain and frost that slowly breaks down

rocks at the Earth’s surface, producing grains of sediment and ions in solution.

Physical (or mechanical) weathering describes the physical action of wind, rain,

ice and extremes in temperature that breaks rocks into small fragments. Chemical

weathering processes are caused by the action of chemical elements dissolved in

water and present in the atmosphere, and also the chemical action of plant roots,

microbes and other living organisms in the soil. These processes act on the rock

fragments produced by physical weathering processes.

Question 10

(a) The fault in Figure 1 has been produced by compression and that in Figure 2

by tension.

(b) Figure 1 shows a reverse fault and the overall effect is to shorten the section

of rock. The normal, extensional fault in Figure 2 has lengthened the section

of rock.

Question 11

The transporting medium must have a relatively high energy to transport large

grains.

Question 12

Because the sediment is fine grained, it has been deposited in a low-energy

environment. This is supported by the fact that fossil shells have stayed whole: in

a higher-energy environment they would usually have been broken into

fragments.

Question 13

According to the principle of superposition, the older beds will be those that are

lower down.

Question 14

The sedimentary rocks must already have been in place for the igneous rock to be

intruded into them, so the sedimentary rocks are older.

13

Question 15

The type of dating used in Questions 13 and 14 is known as relative dating

because it considers the relative ages of the rocks concerned rather than their

actual dates of formation.

The type of dating that could be used to get a more ACCURATE date for the

igneous rock in Question 14 is known as absolute dating and uses radiometric

dates calculated from a knowledge of radioactive decay half-lives and the ratio of

measured abundances of radioactive isotopes to their decay products.

Question 16

This is the complete table:

Element

Al

Symbol

aluminium

C carbon

Na sodium

Si silicon

Ca calcium

O

S

oxygen

sulfur

Fe iron

Mg magnesium

Your score

How do you think you did? It pays to be honest with yourself! Remember that the

questions were testing concepts and knowledge that you should already have

before starting S276 if you are to enjoy the course and have a good chance of

completing it successfully.

Question I answered this well I need to revise this I didn’t do well on this

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

14

Question 17

15

(a) 6005

(b) 42

since 8 + 6 = 14, 5 – 2 = 3 and 14 × 3 = 42.

(c) X = 18.5%

15 since X = ×100% = 0.1852 ×100%

81

= 18.52% = 18.5% (to three significant figures).

Question 18

(a) 1400 cm3

since (200 cm × 8.0 cm × 0.90 cm) = 1440 cm3, which is 1400 cm3 to two

significant figures.

Note: this is an ambiguous way of writing this quantity because it doesn’t

indicate whether or not the final zeros are significant. It is better to write it in

scientific notation as 1.4 103 cm3× .

(b) 0.63 m3

since (0.87 m × 0.09 m × 8.0 m) = 0.6264 m3 which is 0.63 m3 when rounded up to two significant figures.

Note: the zero before the decimal point is not regarded as a significant figure. This could alternatively be written in scientific notation as 6.3 3

× 10–1 m .

Question 19

Number Number in scientific notation

3200 3.2 × 103

143 1.43 × 102

0.007 7 × 10–3

10 1 × 101

Question 20

Prefix Multiplying factor Symbol

Ordinary notation Scientific notation

giga 109 1000 000 000 G

mega 106 1000 000 M

milli 10–3 0.001 m

micro 10–6 0.000 001 µ

nano 10–9 0.000 000 001 n

Question 21

1 km = 103 m, so 1 km3 = (103)3 m3 = 109 m3.

Volume of Mars = 1.64 1011 3

× km

= 1.64 3× 1011 × 109 m

= 1.64 3× 1020 m .

Question 22

(a) The first step is to multiply both sides by V. This gives

mV V ρ =

V

Cancelling V on the right-hand side gives

ρV = m

(b) The equation can be written as µ

= v s

ρ

Start by squaring both sides, which gives:

µ 2

= v

s

ρ

Now multiply both sides by ρ to give µ = v 2 s ρ.

Question 23

You can carry out a calculation with units in exactly the same way as with

numbers and this can often be a useful check that you’ve used the right equation,

or rearranged it correctly.

m Start by substituting the units into the equation ρ = .

V

kgThis gives ρ = which is conventionally written as kg m–3 .

m 2

So the units of density are kg m–3 .

Question 24

16

(a) Conventionally this is written as temperature/°C

(b) The gradient of a straight-line graph is calculated by dividing the ‘rise’ by the

‘run’:

y 2 − y1

x2 − x1

Where y relates to the y-axis and x relates to the x-axis.

(c) (i) Distance from the epicentre is the independent variable.

(ii) 28.5 s

(iii) The line is the straight line that best fits all of the data plotted. The points

plotted show that although the wave has travelled at a fairly constant

speed (hence an almost straight-line graph), at certain times the seismic

wave has travelled slightly faster or slightly slower than the mean, i.e. at

25 seconds it has travelled slightly further than expected and at

35 seconds it has travelled slightly less far than expected.

Your score

How do you think you did? Again, remember that it pays to be honest with

yourself and if you want more advice you should contact an advisor at your

Regional Centre.

Question I answered this well I need to revise this I didn’t do well on this

17

18

19

20

21

22

23

24

17