Transcript Plate Tectonics

Plate Tectonics
1 of 26
© Boardworks Ltd 2003
Teacher’s notes and Flash files
Most slides contain notes to accompany the presentation.
This icon
indicates that the notes contain particularly
detailed instructions or extension activities.
To access these notes go to ‘Notes Page View’ (PowerPoint
97) or ‘Normal View’ (PowerPoint 2000/2002).
Notes Page View
Normal View
This icon
indicates that a Flash file has been
embedded into the PowerPoint slide. These files are
not editable.
2 of 26
© Boardworks Ltd 2003
How old is the Earth?
The Earth is…
2 million years old
100 million years old
4600 million years old
30 million years old
3 of 26
© Boardworks Ltd 2003
Mark the following events on your time line.
What do you notice?
India collides with Asia – 50 m
First flowers appear – 100 m
Man (homo sapiens) inhabits the Earth – 0.1 m
Formation of the Alps – 30 m
Dinosaur extinction – 65 m
You were born! – 0.00013 m
Industrial Revolution (UK) - 0.0001 m
(figures are in ‘millions of years ago’)
4 of 26
© Boardworks Ltd 2003
Cross section of the Earth
5 of 26
© Boardworks Ltd 2003
Continental drift
6 of 26
© Boardworks Ltd 2003
Evidence for plate tectonics
1. Study of fossils – similar fossils are found on different
continents. This is evidence that these regions were once
very close or joined together.
2. Pattern of rocks – similar pattern of rock layers on
different continents is evidence that the rocks were once
close together or joined.
3. Shape of continents fit together like a jigsaw.
Africa
South
America
7 of 26
© Boardworks Ltd 2003
Evidence for plate tectonics
4. Magnetic field pattern in iron containing rocks
The reversal of the Earth’s magnetic field is recorded in
the rocks that solidify at constructive margins. The
symmetry around the margin is evidence that the rocks are
moving apart.
constructive
margin
SN S S S
N N
N
N
S N
pattern same both sides
8 of 26
© Boardworks Ltd 2003
9 of 26
© Boardworks Ltd 2003
Why do the plates move?
Crust
Convention
Currents
Mantle
10 of 26
© Boardworks Ltd 2003
Eurasian
North
American
Pacific
African Plate
Nazca
South
American
Indo Australian
Plate
Antarctic
Plate Names
11 of 26
© Boardworks Ltd 2003
AfricanAPlate
Indo Australian
Plate B
Plate Boundaries
12 of 26
Can you name plates A and B?
© Boardworks Ltd 2003
Plate boundaries
13 of 26
© Boardworks Ltd 2003
Constructive
Plate
Boundary
At a constructive plate boundary, two
plates move apart. As the two plates
move apart, magma rises up to fill
the gap. This causes volcanoes at
this type of boundary. However, since
the magma can escape easily at the
surface the volcano does not erupt
with much force. Earthquakes are
also found at constructive
boundaries.
An example of a constructive
boundary is the Mid-Atlantic Ridge.
14 of 26
© Boardworks Ltd 2003
Constructive plate boundary
15 of 26
© Boardworks Ltd 2003
Mid-Atlantic ridge
Sea Floor Spreading!
Did you know that the
ocean floor in the
Atlantic is growing by
3cm per year?
Which of the following pairs of continents are moving
further away from each other?
1) Europe and Africa
2) Europe and North America
3) South America and North America
16 of 26
© Boardworks Ltd 2003
How fast do plates move?
The plates move at different rates.
The Nazca and Pacific plates are moving apart at a rate of
18cm per year while the Eurasian and North American
plates are moving apart at a rate of 3cm per year.
To the nearest metre, how far will the Nazca and Pacific
plates have moved over the next 200 years?
6 metres
17 of 26
36 metres
200 metres
928 metres
© Boardworks Ltd 2003
A destructive plate boundary is found
where a continental plate meets an
oceanic plate.
Destructive
Plate
Boundary
18 of 26
The oceanic plate descends under the
continental plate because it is denser.
As the plate descends it starts to melt
due to the friction caused by the
movement between the plates. This
melted plate is now hot, liquid rock
(magma). The magma rises through
the gaps in the continental plate. If it
reaches the surface, the liquid rock
forms a volcano.
© Boardworks Ltd 2003
19 of 26
© Boardworks Ltd 2003
Collision
Boundary
20 of 26
Collision boundaries occur when 2
plates of similar densities move
together (i.e. a continental plate and a
continental plate). This causes the
material between them to buckle and
rise up, forming fold mountains.
The Himalayas are an example of a
chain of fold mountains. They have
been formed by the African plate
colliding into the Eurasian plate.
© Boardworks Ltd 2003
21 of 26
© Boardworks Ltd 2003
Conservative plate boundaries
exist where two plates do not
directly collide but slide past
each other along a fault
(weakness).
Conservative
Boundary
No volcanoes are found along
these plate boundaries, but
earthquakes do occur.
An example of such a boundary
is the San Andreas Fault in
California.
22 of 26
© Boardworks Ltd 2003
23 of 26
© Boardworks Ltd 2003
Attach labels to the correct part of the diagram.
Outer core
Crust
Mantle
Inner core
24 of 26
© Boardworks Ltd 2003
Name this plate boundary
A
G
B
E
C
F
D
Match the labels to the letters
Earthquakes occur due to friction
The oceanic crust sinks under
the less dense continental crust
Oceanic plate
Continental crust
25 of 26
Explosive volcanoes
The oceanic crust
melts and rises
Mantle
© Boardworks Ltd 2003
Constructive plate boundaries
MID OCEAN
RIDGE
B
A
Ocean
Mantle
Where would you find older rocks – at A or at B?
26 of 26
© Boardworks Ltd 2003