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Plate Tectonics
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How old is the Earth?
The Earth is…
2 million years old
100 million years old
4600 million years old
30 million years old
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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’)
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Cross section of the Earth
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Continental drift
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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
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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
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Why do the plates move?
Crust
Convention
Currents
Mantle
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Eurasian
North
American
Pacific
African Plate
Nazca
South
American
Indo Australian
Plate
Antarctic
Plate Names
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AfricanAPlate
Indo Australian
Plate B
Plate Boundaries
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Can you name plates A and B?
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Plate boundaries
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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.
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Constructive plate boundary
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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
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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
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36 metres
200 metres
928 metres
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A destructive plate boundary is found
where a continental plate meets an
oceanic plate.
Destructive
Plate
Boundary
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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.
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Collision
Boundary
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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.
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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.
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Attach labels to the correct part of the diagram.
Outer core
Crust
Mantle
Inner core
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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
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Explosive volcanoes
The oceanic crust
melts and rises
Mantle
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Constructive plate boundaries
MID OCEAN
RIDGE
B
A
Ocean
Mantle
Where would you find older rocks – at A or at B?
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