Plate Tectonics - Newcastle School for Boys

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Plate Tectonics
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What is continental drift?
In 1912, a German scientist called Alfred Wegener
proposed that South America and Africa were once joined
together and had subsequently moved apart.
He believed that all the continents were once joined
together as one big land mass called Pangaea and this
was intact until about 200 million years ago.
The idea that continents are slowly shifting their positions
is called continental drift.
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Evidence for continental drift
Study of fossils
Similar fossils are found on different continents.
This is evidence that these regions were once very
close or joined together.
Pattern of rocks
Similar pattern of rock layers on different continents is
evidence that the rocks were once close together or joined.
Shapes of continents
Some continents fit together like a jigsaw.
Africa
South
America
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Continental drift
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What is plate tectonics?
Wegener knew the continents had drifted but he couldn't
explain how they drifted.
It wasn't until the 1960's that geologists used ocean
surveys to explain continental drift with the theory of
Plate Tectonics.
What is Plate Tectonics?
The Earth's surface is made up of a number of large plates (like
pieces of a jigsaw puzzle) that are in constant, slow motion.
The ocean floors are continually moving, spreading from the centre
and sinking at the edges.
At the edges of these plates (plate boundaries) earthquakes and
volcanoes occur.
Convection currents in the mantle move the plates. The source of
heat driving the convection currents is radioactive decay which is
happening deep in the Earth.
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Why do the plates move?
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Plate names
North
American
Eurasian
Pacific
Pacific
African
Nazca
South
American
Indo-Australian
Plate
Antarctic
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Plate names
Can you name plates A and B?
A
African Plate
B
Indo-Australian Plate
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Plate names
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Learning objectives
How old is the Earth?
What is the Earth made from?
What is Plate Tectonics?
What happens at the different types of
plate boundary?
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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. 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?
Tectonic 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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Learning objectives
How old is the Earth?
What is the Earth made from?
What is Plate Tectonics?
What happens at the different types of plate
boundary?
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Cross section of the Earth
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Cross section of the Earth
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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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Destructive plate boundary
A destructive plate boundary is found where a
continental plate meets an oceanic plate.
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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Destructive plate boundary
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Collision plate boundary
Collision boundaries occur when two 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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Collision plate boundary
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Conservative plate boundary
Conservative plate boundaries exist where two plates do
not directly collide but slide past each other along a fault
(weakness).
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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Conservative plate boundary
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Destructive plate boundary
Match the labels to the letters.
F
E
A
B
D
1.oceanic plate
2. The oceanic crust sinks under
the less dense continental crust.
4. continental crust
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C
5. explosive volcanoes
3. The oceanic crust
melts and rises.
6. mantle
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Plate definitions
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