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Science Stage 5
Set 5: Lessons 25 to 30
Continents
on the move
Set 5: Plate tectonics
Number: 40714
Title: Continents on the move
This publication is copyright New South Wales Department of Education and Training (DET), however it may contain
material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Extracts from Science Syllabus Years 7-10 © Board of Studies, NSW 2003
Photograph of the Eiffel Tower © Ian McKee
Photograph of three boys © Rhonda Caddy
Photograph of man standing near tillite © Barbara Gurney
Photograph of Ferns © Julie Haeusler
Photograph of the Grand Canyon © Barbara Gurney
Photograph of a folded mountain range © Barbara Gurney
Outcomes pp vi-ix
Set 1 p 1
Set 1 p 2
Set 1 p 26
Set 1 p 31
Set 5 p 14
Set 5 p 15
COMMONWEALTH OF AUSTRALIA
Copyright Regulations 1969
WARNING
This material has been reproduced and communicated to you on behalf of
the
New South Wales Department of Education and Training
(Centre for Learning Innovation)
pursuant to Part VB of the Copyright Act 1968 (the Act).
The material in this communication may be subject to copyright under the
Act. Any further reproduction or communication of this material by you
may be the subject of copyright protection under the Act.
CLI Project Team acknowledgement:
Writer(s):
Reviewer(s):
Illustrator(s):
Narelle McSpadden and Rhonda Caddy
Jenny Glen, Richard Glen and Jane West
Barbara Gurney and Tim Hutchinson
All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in good faith.
Published by
Centre for Learning Innovation (CLI)
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_______________________________________________________________________________________________
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Copyright of this material is reserved to the Crown in the right of the State of New South Wales. Reproduction or
transmittal in whole, or in part, other than in accordance with provisions of the Copyright Act, is prohibited without the
written authority of the Centre for Learning Innovation (CLI).
© State of New South Wales, Department of Education and Training 2005.
i
Continents on the move
Here are the names of the lessons in this unit.
☞
Set 1
Where is the evidence?
Lesson 1
Believe it or not?
Lesson 2
Using evidence
Lesson 3
Evidence from rock
Lesson 4
Big rocks from little rocks
Lessons 5 and 6
Fossils
Set 2
The great continental drift debate
Lesson 7
Problems, problems!
Lesson 8
Making hypotheses
Lessons 9 and 10
Reading the rocks
Lessons 11 and 12
The continental jigsaw
Set 3
More clues from the past
Lesson 13
Glacier tracks
Lessons 14 and 15
The impossible ice age
Lesson 16
Poles apart
Lesson 17
Backwards and forwards
Optional Lesson 18
Magnetic stripes
Set 4
Seafloor spreading
Lesson 19
Lesson 20
Lesson 21
Lesson 22
Lesson 23
Lesson 24
Clues from the deep
Looking for patterns
Seafloor spreading
The search for more evidence
Making a new ocean
Gobble gobble, munch munch!
Plate tectonics
Lesson 25
Lessons 26 and 27
Lesson 28
Lesson 29
Lesson 30
From hypotheses to a theory
So what is plate tectonics?
Plate tectonics today
The moving plates
Plate tectonics in the future
Set 5
Continents on the move
Set 5
ii
Set 5: Plate tectonics
Contents
What will you learn in Set 5? .................................................................. iii
What do you need for Set 5? ................................................................... iv
Lesson 25
From hypotheses to a theory ................................ 1
Lessons 26 and 27
So what is plate tectonics?..................................... 7
Lesson 28
Plate tectonics today ............................................ 19
Lesson 29
The moving plates ................................................ 33
Lesson 30
Plate tectonics in the future ................................ 41
Suggested answers ................................................................................... 47
Continents on the move
Set 5
iii
What will you learn in Set 5?
At the end of this set, you should be able to:
•
explain the difference between a hypothesis and a theory
•
explain why plate tectonics is a theory
•
describe how an idea becomes accepted by the scientific community
as a theory
•
judge which hypothesis – continental drift, seafloor spreading or
subduction zones – is supported by statements of evidence
•
identify the structures at a subduction zone
•
map the positions of some volcanoes on a world map using coordinates
•
locate earthquakes and volcanoes on a diagram of a subduction zone
•
explain why earthquakes and volcanoes occur at plate boundaries
•
evaluate the usefulness of plate tectonics for explaining
earthquakes and volcanoes
•
explain how a mountain range may form
•
give examples of how the theory of plate tectonics is useful
•
identify factors which may be involved in causing tectonic plates to move
•
make a continental cartoon to show how the continents have changed
position in the last 210 million years
•
explain the continental cartoon to a friend
•
make and evaluate a model for the future location of continents
•
state the theory of plate tectonics
•
summarise the evidence for plate tectonics
•
interpret and complete diagrams and keys
•
match descriptions with diagrams and labels.
Continents on the move
Set 5
iv
What do you need for Set 5?
Here is a reminder of the items you need for Set 5. To save time,
it might be a good idea to get all these things ready before you start.
Items marked with a star, *, are optional.
Lessons 26 and 27
•
scissors
•
blue, red and green coloured pencils
•
glue
Lesson 28
•
coloured pencil
Lesson 29
•
scissors
•
coloured pencil
•
2 rubber bands
•
sheet of paper
•
computer with Internet access
Lesson 30
•
scissors
•
glue
•
ruler
•
sharp pencil
•
sticky tape
•
computer with Internet access
•
2 sheets of paper
Continents on the move
Set 5
aa
1
Lesson 25
From hypotheses
to a theory
With the discovery of ocean ridges and subduction zones,
it became obvious that ideas about the ocean floor
had to be revised.
Geologists had once thought that the ocean floor
was flat and unchanging. New information suggested
that seafloor was being made at ocean ridges and
destroyed at subduction zones. As the seafloor moved,
the continents were carried along with it.
an ocean ridge
where new rock is formed
a subduction zone
where rock is removed
a
the plate moves towards
the deep ocean trench
the plate moves away
from the ocean ridge
the continental crust moves along
with the oceanic crust
Geologists considered the three hypotheses they were using.
These hypotheses were:
• continental drift
• seafloor spreading
• the 'eating up' of crust at subduction zones.
Each hypothesis explained many observations.
Each hypothesis had been tested and supported by more observations.
Check your understanding of these hypotheses and
their supporting evidence by completing Mastery test 1
on the next page.
Continents on the move
Set 5
2
Mastery test 1
Supportive evidence
Decide which hypothesis is supported by each piece of evidence listed below.
Tick the appropriate column to indicate your answer.
Which hypothesis
does this observation support?
Observation
Continental
drift
Coal was found in Antarctica.
The seafloor gets older as you
move away from an ocean ridge.
Some continental outlines match up.
Lava erupts in rift valleys
along ocean ridges.
The seafloor on one side of a trench
is often a different age from the seafloor
on the other side of the trench.
Large areas of tillite are found in
many southern continents.
The seafloor is made of basalt.
Similar plant fossils are found
in Europe and North America.
The magnetic stripes on either side of
an ocean ridge are mirror images
of each other.
Please check your answers by referring to the answer pages.
Continents on the move
Set 5
Seafloor
spreading
Subduction
zones
3
What about plate tectonics?
In 1968, the idea of plate tectonics was put forward.
This idea linked all the evidence which had been
discovered up until that time.
At first, the idea of plate tectonics was treated like
any other new scientific idea. Scientists tested it
and examined the evidence very closely. New evidence
was used to refine the idea so that it became a better
and better explanation of all the observations.
(If evidence had been discovered that refuted the idea,
then the idea would have needed major changes or
would have been rejected. This didn’t happen.)
The evidence supporting the idea of plate tectonics
was very strong. And this new idea explained how
the hypotheses of continental drift, seafloor spreading
and subduction zones fitted together.
The evidence for each hypothesis added to
the evidence for the new idea of plate tectonics.
The new idea became known as the theory
of plate tectonics. Scientists agree that it is
an important idea which combines several hypotheses
that deal with the same topic.
A theory is a big idea that usually explains
how several hypotheses fit together.
Continents on the move
Set 5
4
A mandarine model of a theory!
You can use a mandarine model to picture how hypotheses
add together to support a theory.
Think of a mandarine. Each segment
is like a hypothesis. Scientists have
evidence to support each hypothesis
a theory
and accept that each one is a good
explanation of some evidence.
But if all the segments can be
fitted together, you have a mandarine.
It’s easier to understand the shape and
size of each segment when you see
how separate segments make
one piece of fruit.
separate
hypotheses
So, when several hypotheses fit together, there is a bigger idea –
a theory – that helps scientists understand more about
the hypotheses and the evidence on which they are based.
On the diagram to the right,
label the three hypotheses (segments)
that come together in the theory of
plate tectonics.
theory of
plate tectonics
There’s an answer in the answer pages.
Why do scientists accept the theory?
Not all scientists do! There are some scientists who disagree with
some of the inferences that have been made. They have suggested
other theories to explain how the hypotheses fit together.
However, most scientists think that the theory of plate tectonics
is a good explanation of current evidence. The theory can also
be used to make predictions, and these predictions agree with
new observations that have been made.
Will the theory ever change?
It may. New ways to collect evidence may lead to new discoveries.
The theory and the hypotheses on which it is built, may not be able
to explain this new evidence. Then the theory could be changed or
replaced with a new theory.
But scientists are rather confident that this idea is a good one.
They are not certain that it is true, but it is a very useful idea
that is supported by a great deal of evidence.
Continents on the move
Set 5
5
Send-in page
Name
Lesson 25:
Exercise 25
______________________________
From hypotheses to a theory
What is a theory?
1.
What is the difference between a theory and a hypothesis?
2.
Why is plate tectonics referred to as a theory?
3.
How does an idea, such as plate tectonics, become accepted
by scientists as a theory?
4.
What do scientists use to decide if a scientific theory
should be accepted and used?
Continents on the move
Set 5
6
Continents on the move
Set 5
7
Lessons 26 and 27
So what is
plate tectonics?
The theory of plate tectonics suggests that
the outermost layer of the Earth is divided into
a number of rigid pieces that move relative to each other.
These pieces are called tectonic plates. Tectonic is another
word that comes from Greek. The Greek word means
relating to building or construction or architecture.
The Earth’s surface is built out of these tectonic plates.
And the building of new rocks, mountains and valleys
occurs near the edges, or boundaries, of these plates.
The crust is divided into tectonic plates.
Some plates contain oceanic crust only
while others have oceanic and
continental crust.
Continents on the move
Set 5
8
The main tectonic plates are shown on the map below.
EURASIAN PLATE
NORTH
AMERICAN
PLATE
AFRICAN PLATE
PACIFIC PLATE
COCOS
PLATE
NAZCA
PLATE
INDIAN-AUSTRALIAN PLATE
ANTARCTIC PLATE
Look at the map. Point to the six largest plates
that contain continents.
Did you choose these plates?
The Indian-Australian, Antarctic, North American,
South American, Eurasian and African plates
all contain continents.
The other two major plates are the Pacific plate
and the Nazca plate. They do not include
any very large landmasses.
Now look at the positions of the boundaries (edges)
of the plates. What do you notice?
Did you see that most boundaries run either across oceans,
or lie in oceans near the edges of continents? For example,
there is a boundary across the middle of the Atlantic Ocean
but in the Pacific Ocean, the boundary runs around
the edges of North and South America and Asia.
This fits with the ideas of ocean ridges (where plates move apart)
and ocean trenches (where one plate goes under another)
that you learned in Set 4.
Continents on the move
Set 5
SOUTH
AMERICAN
PLATE
aa
9
You’ve seen what plates look like from the surface of the Earth.
What do they look like under the surface?
Here again is a cross-section through the Earth.
onic plate
ct
a te
os
a
c
he
re
0
cr
us
t
sti
0
in
0 5
3
e
10
nc
ta
6
is
D
ma
nt
le
m
a
n
lower
e
pla
upper m
a n t l litho
e
sp
d
tl
li
so
s
re
et
m
lo
ki
Key
00
to
n
29
aw
dr
ot
(n
co
re
continental crust
oceanic crust
00
64
e)
al
sc
rest of lithosphere
The tectonic plates are the top layers of the Earth.
They are made of the top part of the mantle and the
crust.
Look at the layer of crust in the diagram. Remember, there are
two types of crust – continental crust and oceanic crust.
1.
Which is thicker, continental crust or oceanic crust? ___________
2.
Which type of crust is more likely
to be cut by a plate boundary? ______________________________
3.
Use three different colours to shade the continental crust,
oceanic crust and the top part of the mantle on the cross-section.
Shade the key beside the cross-section too.
Please turn to the answer pages to check your solution.
Continents on the move
Set 5
10
What happens at plate boundaries?
You know that tectonic plates are moving.
So what happens at the edges of plates
where they touch?
There are three different things that can happen.
Description of plate boundary
Surface feature you could observe
Some plates are moving apart.
The edges of the plates are
stretched and become thinner.
The plate edges can become
so stretched that they crack.
Then molten material rises
to the surface and
new rock forms.
Plate boundaries like this are
called divergent boundaries.
Other plates are moving
together. The edges of the
plates are squashed and the
crust becomes thicker.
Mountains may be made or
a deep ocean trench forms.
Plate boundaries like this
are called convergent
boundaries.
Other plates are sliding
sideways along each other.
Plate boundaries like this are
called lateral boundaries.
Continents on the move
Set 5
a
a
11
The three diagrams at the bottom of this page
are structural features that you could observe at
an divergent boundary, a convergent boundary
and a lateral boundary. Which one is which?
Cut around the three diagrams.
Then match each with one of the descriptions
on page 10.
The three labels below match the descriptions and diagrams.
You should recognise the ocean ridge and subduction zone.
The other diagram is a fault.
Cut out the labels and match them with the descriptions and diagrams.
Check your matches in the answer pages, then glue the diagrams
and labels into place beside the descriptions on page 10.
Fault
Ocean ridge
Subduction zone
a
Continents on the move
Set 5
12
Continents on the move
Set 5
13
Identifying different boundaries
The map below shows the three types of plate boundaries.
Arrows indicate the directions that the tectonic plates
are moving at the boundaries.
▲
▲
▲
COCOS
PLATE
▲ ▲
▲
▲
PACIFIC PLATE
▲
▲ ▲
▲
▲
▲
▲
NAZCA
PLATE
SOUTH
AMERICAN
PLATE
▲
▲ ▲
▲
▲
▲ ▲ ▲
▲ ▲
▲
INDIAN-AUSTRALIAN PLATE
ANTARCTIC PLATE
Key
▲ ▲ ▲
▲
▲
1.
Look on the map for plates that are moving apart.
Use a blue pencil to trace along all these plate boundaries.
Also colour blue the matching symbol in the key.
Beside the symbol, write ‘ocean ridges at divergent boundaries’.
2.
Look for plates that are moving together.
Trace along these plate boundaries in red.
Complete the key with red shading and the words,
‘subduction zones at convergent boundaries’.
3.
Now identify the plates that are sliding past each other.
Trace these plate boundaries using green.
Shade the symbol in the key and write, ‘faults at lateral boundaries’.
4.
Which direction is each tectonic plate moving?
It will move away from an ocean ridge towards a subduction zone.
It will slide along another plate at a lateral boundary.
Predict the direction for each large plate.
Draw a large arrow across each plate to show the direction it moves.
Please compare your solution with the one in the answer pages.
Continents on the move
Set 5
▲▲
▲ ▲ ▲
▲
PHILIPPINE PLATE
▲
▲ ▲
▲ ▲
CARIBBEAN
PLATE
▲
▲
▲
▲
▲ ▲
▲
NORTH
AMERICAN
PLATE
▲ ▲ ▲ ▲
▲ ▲ ▲
▲ ▲
▲
▲
▲
▲
▲
▲
▲
▲
▲ ▲ ▲ ▲ ▲ ▲ ▲
▲ ▲ ▲ ▲
▲ ▲ ▲ ▲ ▲
AFRICAN PLATE
▲
▲
▲
▲
▲ ▲
EURASIAN PLATE
▲
▲
▲ ▲
14
Another look at plate boundaries
You would probably find it easy to explain what
happens at an ocean ridge on an divergent boundary.
You learned about these stretching boundaries in Set 4.
But what happens at convergent boundaries
where tectonic plates collide?
What happens when a continental plate collides with an oceanic plate?
What happens when denser oceanic crust collides
with less dense continental crust? The oceanic crust
tends to sink and slides underneath the continental crust.
A deep ocean trench forms where the oceanic crust
goes under the continental crust.
© Barbara Buining
What is this trench like? The longest, deepest valley on Earth
is the Grand Canyon in USA. It really is amazing –
it’s enough to take your breath away.
An ocean trench could be almost ten times longer and
ten times deeper than the Grand Canyon.
Ocean trenches are staggeringly huge things!
The edge of the continental plate may also be compressed and
changed as the oceanic plate grinds into it as it slides underneath.
This may produce different kinds of rocks and folded rock layers.
Continents on the move
Set 5
15
What happens when two continental plates collide?
Two continental plates will both tend to float.
When they collide, one does not sink under the other.
What happens instead?
As the continents press together, the continental crust
crumples up and blocks up the subduction zone.
The crumpled edges of the continents form
a large mountain range.
© Barbara Buining
The mountains are called fold mountains because
they buckle and bend as the rock is compressed.
A folded mountain range forms when two continents meet at a subduction zone
What happens when two oceanic plates collide?
What would you predict?
There is a suggestion in the answer pages.
Are you ready to test your understanding
of the theory of plate tectonics?
Attempt Mastery test 2 now!
Continents on the move
Set 5
16
Mastery test 2
The theory of plate tectonics
1.
Here is a map showing the main tectonic plates.
Using a coloured pencil, shade the Indian-Australian Plate.
This plate is moving north.
2.
From memory, can you name six other tectonic plates? Try!
(Hint: If you need help, turn back to the map on page 13.
There are more than six tectonic plates to choose from!)
_________________________
_____________________
_________________________
_____________________
_____________________
_____________________
Continents on the move
Set 5
aa
17
This map shows ocean ridges and subduction zones.
▲
▲
▲ ▲ ▲
▲
▲ ▲
▲ ▲
▲ ▲
▲
▲
▲ ▲
▲
▲
▲
▲ ▲ ▲ ▲
▲
▲
NORTH
AMERICA
▲
AFRICA
▲
▲
▲
INDIA
▲
▲
▲ ▲
▲
▲ ▲ ▲
▲ ▲
▲
▲
▲ ▲ ▲ ▲ ▲ ▲ ▲
▲ ▲ ▲ ▲
▲ ▲ ▲ ▲ ▲
▲
▲
▲
▲
▲ ▲
▲
▲
▲
ASIA
EUROPE
▲ ▲
▲
3.
▲
▲ ▲
▲
▲
▲
▲
▲
▲
▲ ▲ ▲
▲ ▲
▲
AUSTRALIA
SOUTH
AMERICA
ANTARCTICA
Key
▲ ▲ ▲
▲
▲
subduction zones
ocean ridges
other structures
(a) Name two continents that are moving away from each other.
(Hint: Look for two continents which have an ocean ridge between them.)
_______________________
_____________________
(b) Name two continents that are moving towards each other.
(Hint: Look for two continents which have a subduction zone between them.)
_______________________
4.
_____________________
Here is a diagram representing some plate boundary interactions.
a
(a) Draw a square around the part of the diagram showing
an divergent boundary, where new crust is being made.
(b) Draw a circle around the part of the diagram showing
a convergent boundary, where crust is being subducted.
Continents on the move
Set 5
18
5.
Today, India is part of the Asian continent but this has not always been so.
60 million years ago, India was an island.
An ocean existed between India and Asia.
▲ ▲ ▲ ▲
▲ ▲
▲
▲ ▲
▲ ▲
▲ ▲ ▲
▲
▲
ASIA
▲
▲
▲ ▲
▲
▲
▲ ▲ ▲ ▲ ▲ ▲
▲ ▲ ▲ ▲ ▲ ▲
AFRICA
▲
▲
INDIA
Today, the ocean has disappeared. Instead of an ocean,
there is a folded mountain range called the Himalayas.
(a) How have the Himalayas formed?
(b) Draw a diagram to show what you have explained.
Now compare your answers with the solutions in the answer pages.
Continents on the move
Set 5
19
Lesson 28
Plate tectonics today
When was the most recent earthquake?
Where is a volcano erupting, today?
You will regularly hear reports on the news about
earthquakes and volcanoes because they affect people
and the environment. These geological changes are
happening all the time, somewhere in the world.
If you have Internet access, do a search using keywords
such as volcano, earthquake, tsunami.
If the theory of plate tectonics is a useful one,
it must be able to explain changes in the Earth’s past
as well as changes in the present and future.
Can the theory of plate tectonics explain earthquakes
and volcanoes that are happening now?
Looking for a link
When scientists were studying deep ocean trenches,
they found that earthquakes and volcanic eruptions
were frequent in areas near these trenches.
They also measured earthquakes near rift valleys
and in areas with large faults. These are all places
that scientists thought were near the edges of
tectonic plate boundaries.
So what causes earthquakes and volcanoes?
And why do they occur near tectonic plate boundaries?
Continents on the move
Set 5
20
Earthquakes
Although you cannot feel it, the tectonic plate below
you is moving now. If you are in the middle of a plate
you won’t feel any of this movement because the plate
moves slowly – only a few centimetres each year.
But it is different at some plate boundaries!
Where plates touch, there are forces as the plates slide
under or into or past each other. These forces
produce movements that you may feel.
Earthquakes are an example of a movement that
you could feel. The ground can shake from side to side
or up and down. If an earthquake occurs under water,
movements of the seafloor may produce large waves
called tsunamis, or less correctly tidal waves.
Scientists make careful studies of earthquakes
throughout the world. Their results are quite interesting.
The diagram below shows the position of
some earthquakes that took place near the Java Trench.
The Java Trench is north of Australia, between Australia
and Indonesia.
volcanic islands
in Indonesia
Java
Trench
NORTH
SOUTH
0
Depth below the surface (km)
100
200
300
400
500
600
• •
700
•
Timor
Sea
••
•
••
•
•••
•
•••
•
••
••
•
•
•
•
••
Earthquakes
Continents on the move
Set 5
aa
21
1.
Use a pencil to draw a line through the places
on page 20 where earthquakes occur.
2.
Describe the pattern of the earthquakes.
3.
What happens to the depth of the earthquakes
as you move further away from the trench?
There are answers in the answer pages.
How did scientists explain what they observed?
From the theory of plate tectonics, scientists said
that trenches were in subduction zones
where one plate moved under another plate.
volcanic islands
in Indonesia
Java
Trench
Timor Sea
NORTH
0
••
•
••
•
•••
•
•••
•
earthquakes
••
seem to occur
subduction
along a line
of the plate
•• •
•
•
•
••
•
•
oceanic crust
of the Eurasian Plate
oceanic crust of the
Indian-Australian Plate moving this way
a
Depth below the surface (km)
100
SOUTH
200
300
400
500
600
700
seafloor rocks melt as
the plate goes deeper
•
Earthquakes
Scientists inferred that the earthquakes were happening
where the two plates touched.
Continents on the move
Set 5
upper part of the mantle
22
Does this explanation account for all the earthquake areas
of the world?
Here is a map showing the areas where major earthquakes
have occurred in the last 50 years.
Earthquake belt
Compare this with the map on page 17.
(Look carefully! The maps are different views of the world.)
1.
Do earthquakes tend to occur at subduction zones?
Yes or no?
2.
__________________
What other geological structure seems to be associated
with earthquakes?
If you’d like to check your answers, turn to the answer pages.
Continents on the move
Set 5
23
Scientists decided that earthquakes could be explained
using the theory of plate tectonics.
They said that earthquakes occur when tectonic plates
are moving in different directions. This is why most
of the world’s earthquakes are found along the edges
of tectonic plates.
Earthquakes near a subduction zone are caused
when one tectonic plate is forced under another plate.
Earthquakes near ocean ridges are caused as the crust
stretches and cracks. Earthquakes a occur as plates slide
past each other.
What about volcanoes?
Do they fit into the theory of plate tectonics?
Volcanoes
What happens at a volcano? Molten material
rises to the Earth’s surface. The molten material, called
magma, rises through cracks in the solid, brittle upper
mantle.
When the magma reaches the surface it is called lava.
The lava often sprays into the air with bursts of gas
and steam. There must be large forces within
the structure of the Earth to produce such
explosive eruptions!
If you have Internet access, you could find out
more about volcanoes and volcanic eruptions by accessing
links from the following website:
www.cli.nsw.edu.au/kto12
Go to Science, the Stage 5 Junior Science, then click on
the links in Continents on the move.
Volcanic eruptions are often accompanied by earthquakes.
For example, did you notice the volcanic islands
on the diagrams showing positions of earthquakes?
Look back at page 20.
Volcanoes and earthquakes tend to occur together.
Continents on the move
Set 5
24
On the world map below, mark and label the positions of the volcanoes listed.
These volcanoes are all able to erupt, or active. The first one is marked for you.
Grid position (X,Y) Volcano
(3,8)
(14.5,6.5)
(21,10)
(4,10)
(19,13)
(20.5,7.5)
Grid position (X,Y) Volcano
Apo, Philippines
Chimborazo, Ecuador
Etna, Italy
Asama, Japan
Hekla, Iceland
Cameroon, Cameroon
(8.5,8.5)
(12.5,9)
(2,6.5)
(11.5,11)
(6,5.5)
(9,13)
Mauno Loa, Hawaii
Paricutin, Mexico
Semeru, Indonesia
St Helens, USA
Tabwémasana, Vanuatu
Wrangell, Alaska
19
18
17
16
15
14
13
12
11
10
9
Apo
8
7
6
5
4
3
2
Earthquake
belt
Earthquake
Earthquakebelt
belt
Earthquake
belt
1
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
There are hints and a completed map in the answer pages.
Now compare the shading on the map for earthquake areas
with the locations of these volcanoes.
What do you notice?
Continents on the move
Set 5
aa
25
How do scientists explain volcanoes?
Scientists thought about what would happen
in the mantle at a subduction zone where
rock, water and sediment on the seafloor
are being pulled down into the Earth.
Remember, it is hot inside the Earth. It’s hot enough
for parts of the Earth’s core and mantle to melt!
So as the seafloor moves into the mantle,
it will become hotter and hotter.
The water will form steam;
the rocks will begin to melt.
This liquid mixture, or magma, will escape to
the surface through any cracks, or fractures,
producing volcanoes.
volcanic islands
trench
0
Molten rock rises
to the surface
through fractures
a
Depth below the surface (km)
100
sea
200
300
400
500
600
700
The solid part of the
upper mantle melts
readily as the crust
grates against
rocks
subduction
of the plate
upper mantle
Seafloor rocks melt as
the plate goes deeper
Subduction zones at ocean trenches produce
lines of island volcanoes, such as the volcanoes of
Indonesia and Japan.
Continents on the move
Set 5
26
aa
Subduction zones close to continents produce mountain ranges,
such as the Andes Mountains in South America.
volcanic mountains
continental
crust
0
sea
Molten rock rises
to the surface
through fractures
aa
Depth below the surface (km)
100
trench
200
300
400
500
600
700
The solid part of the upper mantle
melts readily as the crust
grates against rock
subduction
of the plate
upper mantle
Seafloor rocks melt as
the plate goes deeper
Does this account for all the world’s volcanoes?
What about volcanoes such as the ones in Hawaii?
Some volcanoes are not near plate boundaries.
Geologists call these volcanoes ‘hot spots’.
They suggest that the upper part of the mantle under
places such as Hawaii is particularly hot. Magma rises
through a crack, or vent to build a volcano out of the
seafloor.
As the tectonic plate moves over the ‘hot spot’,
a chain of volcanoes forms. The volcanoes are in a line,
showing the direction that the plate is moving
over the ‘hot spot’.
a volcanic island
develops at a ‘hot spot’
a volcano is not active when
it moves off a ‘hot spot’
magma rises through vents from
deep within the upper part of the mantle
Continents on the move
Set 5
aa
27
Send-in page
Lesson 28:
Name
______________________________
Plate tectonics today
Exercise 28.1
Use what you have read to answer the following questions.
1.
The following diagram shows the seafloor near a trench.
ocean
a
(a) Using a coloured pencil, shade in the area
where you would expect to find earthquakes.
(b) Label the following features:
• oceanic crust
• trench
• mantle.
(c) Use arrows to show the direction that oceanic crust is moving.
(d) Volcanic islands often form in the ocean near a trench.
Draw two volcanic islands on the diagram.
(e) Write a paragraph explaining why earthquakes and
volcanoes occur at plate boundaries.
Continents on the move
Set 5
28
2.
The Andes Mountains run for 7 200 kilometres
down the western side of the South American continent.
The mountains rise straight out of the Pacific Ocean
and contain folded rocks and many volcanoes.
Explain how this mountain range may have formed.
You can use sentences, a labelled diagram or both!
You may find the map on page 13 helpful.
3.
Do you think that the theory of plate tectonics can explain
earthquakes and volcanoes that happen today? Why or why not?
Continents on the move
Set 5
29
Why is plate tectonics important today?
Did you think that plate tectonics is an interesting
theory, but so what? There are many reasons
why the theory is important to people today.
To increase understanding
The theory of plate tectonics has enabled scientists
to explain many features which they have observed
on the Earth’s surface.
Plate tectonic explains:
•
why most earthquakes and volcanoes are found
in narrow strips on the Earth’s surface
•
why the seafloor is so much younger
than the continents
•
how large mountain ranges such as the Himalayas
and Andes have been formed.
Plate tectonics is a very important theory because it shows
that events such as mountain building, seafloor spreading
and the movement of continents are part of the same
large-scale process.
To protect property and people
A knowledge of plate movement has also given
scientists a much better understanding of why
volcanic eruptions and earthquakes occur. They are
using this knowledge to help predict the sites of
future earthquakes and when volcanoes may erupt.
This may mean that property damage and loss of life
can be prevented.
Continents on the move
Set 5
30
To obtain useful substances
Plate tectonics can also give scientists an idea of where
to look for such things as oil and mineral deposits.
For example, the Andes Mountains, on the edge of the
South American Plate, are a rich resource of gold, silver,
lead, mercury, platinum, sulfur and copper.
Geologists have discovered that many ore deposits
are found along plate boundaries. Petroleum deposits
are often found where ocean ridges have started and
metal deposits are formed along ocean ridges.
Geologists today are trying to find old plate boundaries
as these are good places to search for minerals and oil.
Continents on the move
Set 5
31
Send-in page
Name
______________________________
Lesson 28:
Plate tectonics today (continued)
Exercise 28.2
New developments
The theory of plate tectonics has caused many geologists to
completely change their ideas. It has also helped geologists
to gain a better understanding of changes on the Earth’s surface.
Describe two ways in which the theory of plate tectonics
is helping scientists to solve problems facing people today.
•
_____________________________________________________________________
•
_____________________________________________________________________
Continents on the move
Set 5
32
Continents on the move
Set 5
a
33
Lesson 29
The moving plates
Have you thought about why tectonic plates move?
This is the same kind of problem that Wegener had
at the beginning of the twentieth century.
Why do tectonic plates move?
Scientists agree that the continents move on tectonic plates
but they have not yet found a good explanation of
why the plates move.
One explanation was suggested by a Scottish geologist,
Arthur Holmes, in 1928. He hypothesised that currents
in the mantle pull the crust across the surface of the Earth.
The currents are called convection currents because
he said that they were caused by hot material in the mantle
rising upwards and cold material sinking downwards.
crustal plates are moved by convection cells in the upper mantle
a
crust
Each ‘circle’ of arrows
represents one
convection cell
hot material rises
upper mantle
cold material sinks
Scientists think that Holmes had the right idea
even though his hypothesis came 40 years before
the theory of plate tectonics!
Continents on the move
Set 5
34
However, scientists think that tectonic plates themselves
are involved in the process too. They are not just pushed by
convection currents. At ocean ridges, the plates are hot and
magma pushes up between the plates forcing them apart.
At trenches, an oceanic plate is cold and dense.
Gravity pulls the plate edge down into the mantle,
dragging the rest of the plate after it.
This explanation of plate movement takes account of:
•
ridges
•
trenches
•
convection currents
•
gravity.
But scientists are still not satisfied with the explanation.
A good theory will also explain:
•
what made the plates start to move
in the first place
•
why the original supercontinent broke up
into the continental pieces of today.
Scientists will continue to look for evidence,
to make inferences and to suggest and test hypotheses.
Perhaps you could be the scientist who works out
how these hypotheses fit together into a theory of
tectonic plate movements!
Continents on the move
Set 5
35
Send-in page
Name
Lesson 29:
Exercise 29
1.
2.
______________________________
The moving plates
Looking for a theory
Draw lines to match the features listed below with their
possible involvement in the movement of tectonic plates.
Features
Involvement in tectonic movements
convection currents
magma rises between plates,
pushing them apart
gravity
cool, dense plates slide into
the mantle
ridges
hot material in the mantle rises and
cool material sinks, pulling the plates
across the Earth’s surface
trenches
the weight of dense rock pulls
the plate edge towards the centre
of the Earth
Scientists are looking for one big idea that will explain
all the features in Question 1 and also explain how and why
tectonic plates first began to move.
(a) When the idea is found, it will be called a theory.
Why will it be a theory, not a hypothesis?
(b) Imagine that you come up with that one big idea!
What would have to happen before scientists
accepted your idea as a theory?
Continents on the move
Set 5
36
Continents on the move
Set 5
37
Where have the plates moved?
Using information from seafloor and continental rocks,
scientists have been able to deduce movements
of the continents over the last 450 million years.
450 million years ago
most of the continents
were separated.
Over the next 250 million years
they moved together …
… and then separated to form
the familiar arrangement
of today.
Now for some fun!
In the next activity, you’ll make a ‘continental cartoon’
so that you can watch the way the continents moved
as they were carried along by tectonic plates
over the last 210 million years.
Continents on the move
Set 5
38
Watching the continents move
When you watch movies, you are really looking at
a series of individual pictures.
Each picture is slightly different from the one before.
When the pictures are flashed up so that one quickly
follows another, the object in the picture seems to move.
In movie film, the movie camera takes fifteen separate
photographs for every second of action!
Cartoons are made in the same way.
Thousands of separate drawings are prepared to make
the cartoon characters look like they are moving.
Computer programs make this cartooning process easier.
In the next activity, you are going to make your own cartoon
to show the movement of the continents.
The drawings have already been done so all you have to do
is put them together!
Your continental cartoon condenses 210 million years
into just a few seconds!
Making a continental cartoon
Read through the instructions carefully.
You will need:
•
scissors
•
a coloured pencil
•
2 rubber bands.
What to do:
1.
Remove pages 55 to 62 from the back of this booklet.
Continents on the move
Set 5
39
2.
Using a coloured pencil,
quickly shade in the land
on each of the small world maps.
This makes your cartoon clearer.
3.
Carefully cut out the
large rectangles on each of
the four pages.
110
20
Cut only along the thick
dark lines. Do not cut out
the small world maps!
50
70
4.
A small number has been printed at the top left corner
of each small world map. This number tells you
how many million years ago the continents were in this position.
For example, this map shows the position of the continents
130 million years ago.
130
Continents on the move
Set 5
40
5.
Stack the rectangles in order so that the highest number (210)
is at the top. Remember that there are two copies of each rectangle.
Also note that there are no diagrams for 10 million or 30 million years ago.
6.
Wrap the rubber bands very tightly around the left hand side of the stack.
rubber bands
7.
Your cartoon is now ready for viewing!
Hold the stack in your left hand and flick it using your right thumb.
You should see the continents slowly move apart to their present positions!
8.
Show your continental cartoon to a friend or family member.
Explain what it shows.
Did your friend understand your explanation?
Yes or no?
_____________
Do you think that you explained clearly
how and why the continents move?
Yes or no?
_____________
How could you improve your explanation?
Please send your continental cartoon to your teacher with your send-in pages.
You might like to attach a short report about how your friend understood
and enjoyed the cartoon!
If you have access to the Internet, you might like to access more
information about the break-up of the super continent Go to the:
www.cli.nsw.edu.au/kto12. Go to Science, the Stage 5
Junior Science, then click on the links in Continents on
the move to find links to some websites of interest.
Continents on the move
Set 5
41
Lesson 30
Plate tectonics in the future
Imagine that you are studying science,
20 million years in the future!
Your teacher sends you a map of the world.
How will this map be different from the world maps
that you see today?
According to the theory of plate tectonics,
continents move as the tectonic plates change shape.
But how quickly do plates move?
How fast do tectonic plates move?
Most plates on the Earth’s surface are moving at about
2 to 3 cm per year. This is about the same rate as
your fingernails grow.
This does not seem very fast. However,
when you consider the long period of time involved,
the continents have moved quite large distances.
Consider the Indian-Australian Plate.
Remember, it is moving north.
How far has Australia moved?
•
In the last 10 years, Australia has moved about 25 cm.
•
Since the arrival of the First Fleet in 1788,
Australia has moved five metres further to the
north.
•
Since the arrival of the first Aborigines,
Australia has moved ten kilometres closer to
Indonesia.
Continents on the move
Set 5
42
Altogether, Australia has moved 3 000 km northwards
since it first separated from Antarctica about 50 million years ago.
Do all tectonic plates move at the same speed?
Well, no! Some plates move faster than others.
Australia is on one of the fastest-moving plates.
Plates move faster if they have large subduction zones.
A long ocean ridge also makes plates move quickly.
Look at the map below. Which other plates
do you think would be moving quickly?
▲
▲
▲
▲ ▲
▲
▲ ▲
▲
▲
PACIFIC PLATE
▲
▲
▲
▲
▲
▲
NAZCA
PLATE
SOUTH
AMERICAN
PLATE
▲
▲ ▲
▲
▲
▲ ▲ ▲
INDIAN-AUSTRALIAN PLATE
▲ ▲
▲ ▲
▲ ▲
▲
COCOS
PLATE
▲▲
▲ ▲ ▲
PHILIPPINE PLATE
▲ ▲
▲
▲
CARIBBEAN
PLATE
▲
▲ ▲ ▲
▲ ▲
▲
NORTH
AMERICAN
PLATE
▲ ▲ ▲ ▲
▲
▲
▲
▲
▲
▲
▲
▲
▲ ▲ ▲ ▲ ▲ ▲ ▲
▲ ▲ ▲ ▲
▲ ▲ ▲ ▲ ▲
AFRICAN PLATE
▲
▲
▲
▲
▲ ▲
▲ ▲
▲
▲
EURASIAN PLATE
▲
ANTARCTIC PLATE
Key
▲ ▲ ▲
▲
▲
subduction zones
at compressional
boundaries
faults at lateral
boundaries
ocean ridges at
extensional boundaries
direction that tectonic plates are moving
The fastest-moving plates are
_________________________________
There’s an answer in the answer pages.
Continents on the move
Set 5
43
So what have you learned?
Tick the statements below that are true for you.
You have learned about:
❒
❒
❒
❒
❒
❒
❒
❒
❒
how scientific ideas are developed
how scientific ideas are tested and compared
how models can be used to explain ideas and to make predictions
how rocks form and how they are used by scientists
how fossils form and how they are used by scientists
the hypothesis of continental drift and other hypotheses
that have led to the theory of plate tectonics
the theory of plate tectonics and the evidence that supports it
some reasons why tectonic plates may move
why earthquakes, volcanoes and mountains occur at plate boundaries.
You have learned to:
❒
❒
❒
❒
❒
❒
❒
make observations and inferences from a variety of sources
find patterns in observations and inferences
predict outcomes and suggest explanations for observations
and inferences
use evidence to make judgements about inferences,
hypotheses and theories
use scientific processes to solve problems
make and evaluate models
use rocks to infer the environment in an area
when the rocks were formed.
Well done!
Continents on the move
Set 5
44
Continents on the move
Set 5
45
Send-in page
Lesson 30:
Name
______________________________
Plate tectonics in the future
Exercise 30.1
Do you like a challenge? Here is an exercise in which you can show
how well you have understood the theory of plate tectonics and
the evidence that supports it, and how well you can communicate
your ideas in writing.
In your own words, summarise the evidence for the theory of plate tectonics.
You may use points or decide to write your answer in sentences.
Whichever form you choose, your answer should be clear and easy to read.
Your answer should refer to evidence from both the continents and
the seafloor. You will need to refer back through Sets 2 to 5
to complete your answer.
Suggested length: up to 112 pages. You can prepare and present your answer
on your own paper if you’d like.
State the theory of plate tectonics.
Continents on the move
Set 5
46
Summarise the evidence for the theory of plate tectonics.
Continents on the move
Set 5
47
Suggested answers
Lesson 25
Page 2
From hypotheses to a theory
Mastery test 1 – Supportive evidence
Ticks indicate which hypothesis is supported by each piece of evidence.
Which hypothesis
does this observation support?
Observation
Continental
drift
Seafloor
spreading
✔
Coal was found in Antarctica.
The seafloor gets older as you
move away from an ocean ridge.
✔
✔
Some continental outlines match up.
Lava erupts in rift valleys
along ocean ridges.
✔
The seafloor on one side of a trench
is often a different age from the seafloor
on the other side of the trench.
✔
Large areas of tillite are found in
many southern continents.
✔
✔
The seafloor is made of basalt.
Similar plant fossils are found
in Europe and North America.
✔
The magnetic stripes on either side of
an ocean ridge are mirror images
of each other.
Continents on the move
Subduction
zones
✔
Set 5
48
aa
Lesson 25 continued
Page 4
A mandarine model of a theory!
Here is a completed diagram.
theory of
plate tectonics
continental drift
hypothesis
seafloor spreading
hypothesis
Lessons
26 and 27
Page 9
subduction zone
hypothesis
So what is plate tectonics?
Here is the completed diagram.
ct
a te
onic plate
a
upper m
a n t l litho
sp
e
lid
0
in
0 35
e
10
nc
ta
6
is
D
ma
nt
le
a
m
Key
00
to
n
29
aw
dr
ot
(n
co
re
continental crust
oceanic crust
00
64
e)
al
sc
2.
re
n
lower
s
re
et
m
lo
ki
1.
he
cr
us
t
tic
e
0
s
pla
tl
so
rest of lithosphere
Which is thicker, continental crust or oceanic crust? continental crust
Which type of crust is more likely
to be cut by a plate boundary? oceanic crust
Continents on the move
Set 5
a
49
Lessons 26 and 27 continued
Page 10
What happens at plate boundaries?
Here are the three different types of plate boundaries.
Type of plate boundary
Divergent boundaries
Surface feature you could observe
Ocean ridge
aa
Convergent boundaries
Lateral boundaries
Subduction zone
Fault
Continents on the move
Set 5
50
Lessons 26 and 27 continued
Page 13
Identifying different boundaries
Here is the completed map showing the three types of plate boundaries
and the directions that plates are moving.
▲
▲
▲ ▲
▲ ▲ ▲
▲
COCOS
PLATE
▲ ▲
▲
▲
PACIFIC PLATE
▲
▲
▲
NAZCA
PLATE
SOUTH
AMERICAN
PLATE
▲
▲
▲
▲
▲ ▲ ▲
INDIAN-AUSTRALIAN PLATE
▲ ▲
▲ ▲
▲
▲ ▲
▲ ▲
▲
PHILIPPINE PLATE
▲
▲
▲
CARIBBEAN
PLATE
▲
▲ ▲
▲
▲▲
▲
NORTH
AMERICAN
PLATE
▲ ▲ ▲ ▲
▲ ▲ ▲
▲ ▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲ ▲ ▲ ▲ ▲ ▲ ▲
▲ ▲ ▲ ▲
▲ ▲ ▲ ▲ ▲
AFRICAN PLATE
▲
▲
▲
▲
▲ ▲
EURASIAN PLATE
▲
▲
▲ ▲
ANTARCTIC PLATE
Key
▲ ▲ ▲
▲
▲
subduction zones
at convergent
boundaries
faults at lateral
boundaries
ocean ridges at
divergent boundaries
direction that tectonic plates are moving
Page 15
What happens when two oceanic plates collide?
What would you predict?
You might expect that two oceanic plates would crush into each other
and make underwater mountains, just like the continental plates do.
This is a logical answer because the densities of the two oceanic plates
are similar so you wouldn’t expect one to sink under the other.
But guess what? The logical answer isn’t the right answer!
When two oceanic plates meet, one subducts under the other.
Geologists don’t know why.
Nor can they predict which plate will subduct … yet.
Continents on the move
Set 5
51
Lessons 26 and 27 continued
Pages
16 and 17
Mastery test 2 – The theory of plate tectonics
1.
The shaded plate is the Indian-Australian Plate.
2.
Some other tectonic plates are:
African Plate
North American Plate
Eurasian Plate
Caribbean Plate
Philippine Plate
Cocos Plate
Pacific Plate
South American Plate
Antarctic Plate.
Nazca Plate
You could have chosen any six of these answers, or named other plates.
3.
(a) Name two continents that are moving away from each other.
All the answers below are correct.
Africa and Antarctica
Europe and North America
Australia and Antarctica
South America and Africa
Africa and India
Africa and Australia
(b) Name two continents that are moving towards each other.
You could give any of these answers.
Africa and Europe
Europe and India
Australia and Asia
Asia and India
(probably Asia and North America)
Continents on the move
Set 5
52
aa
Lessons 26 and 27 continued
Page 17
4.
Here is a diagram representing some plate boundary interactions.
convergent boundary
divergent boundary
aa
Page 18
5.
Today, India is part of the Asian continent but this has not always been so.
60 million years ago, India was an island. An ocean existed between
India and Asia.
Today, the ocean has disappeared. Instead of an ocean,
there is a folded mountain range called the Himalayas.
(a) How have the Himalayas formed?
The Himalayas have formed where two continental plates have collided
at a subduction zone. As the continental plates are compressed together,
the rocks have been squashed and folded into a mountain range.
(b) Draw a diagram to show what you have explained.
Here is an example of a suitable diagram.
Himalayas
oceanic crust
Lesson 28
Page 21
ocean
continental crust
Plate tectonics today
Earthquakes
2.
3.
Describe the pattern of the earthquakes.
The earthquakes lie along a line.
What happens to the depth of the earthquakes
as you move further away from the trench?
The earthquakes become deeper in the asthenosphere
as you move away from the trench.
Continents on the move
Set 5
53
Lesson 28 continued
Page 22
Page 24
How did scientists explain what they observed?
1.
Do earthquakes tend to occur at subduction zones? yes
2.
What other geological structure seems to be associated
with earthquakes?
Ocean ridges are also associated with earthquakes.
Volcanoes
The grid positions are coordinates. They are two numbers separated by a comma.
The first number tells you the position across the X axis (horizontal axis).
The second number is the position up the Y axis (vertical axis).
Go across the X axis for the first number, then go up to the position
opposite the second number on the Y axis. Mark the point with a cross.
Write the name of the volcano beside the cross.
Here is the completed map.
19
18
17
16
15
14
Wrangell
Wrangell
13
Hekla
Hekla
12
St Helens
Helens
St
11
Etna
Etna
Asama
Asama
10
9
Mauno Loa
Apo
8
7
Paricutin
Paricutin
Cameroon
Chimborazo
Semeru
6
Tabwémasana
5
4
3
2
Earthquake
belt
Earthquake
Earthquakebelt
belt
Earthquake
belt
1
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Did you notice that most volcanoes are located in the earthquake belt?
Continents on the move
Set 5
54
Lesson 30
Page 42
Plate tectonics in the future
Do all tectonic plates move at the same speed?
The fastest-moving plates are the Indian-Australian, Pacific and Nazca Plates.
These plates have long convergent boundaries (subduction zones) and
long divergent boundaries (ocean ridges).
Continents on the move
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55
Continents on the move
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56
Continents on the move
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57
Continents on the move
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58
Continents on the move
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59
Continents on the move
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60
Continents on the move
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61
Continents on the move
Set 5
62
Continents on the move
Set 5