Download The Earth`s Structure - Geog

The Earth’s Structure And
Tectonic Processes
IB SL
Cross section of the Earth
Breakdown
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Crust
Thin, outer-layer of the earth.
It is as thin as the skin of an apple is to its
flesh.
Mantle
Composed mainly of silicate rocks, which
contain a lot of magnesium and iron.
It extends to a depth of 2900km.
Temperatures can reach 5000 degrees
Celsius, which generate convection
currents.
Core
Contains iron and nickel.
Situated approximately 6371km below the
surface.
Temperature is around 5500 degrees
Celsius.
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
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
N S N SN S N SN
S
N S N S N S NS N
Pattern same both sides
S
Crust
Convention
Currents
Mantle
Plate Tectonic Theory
• The location of continents today of far removed from
what it was millions of years ago, when it is believed
that all continents were joined to one land mass.
Alfred Wegener put forward a theory regards their
movement in 1912 with his theory of Continental
Drift. His theory was based on observations such as:
• Biological: Coal is found in UK but needs warm, wet,
humid conditions to form.
• Observational: The shapes of countries appear to 'fit'
one another, for example, S. America and Africa.
Plate Movements
• In the 1940's-1960's the theory was revised
and Plate Tectonic theory emerged.
• It is based on the premise that the lithosphere
(crust and rigid upper mantle) is divided into
plates, which are moved by convection
currents coming from the earth's core.
2 Types Of Crust
Young (under 200 million years), thin,
Oceanic Crust dense and heavy, will sink. Always
(Sima)
being created and destroyed. For
example, Basalt.
Old, light, thick (up to 150km under
Continental
mountains) permanent, does not sink.
Crust (Sial)
For example, Granite.
Plate Margins
• Movement of plates is in one of 3 ways:
• Towards each other: Convergent (destructive or
collision).
• Away from each other: Divergent.
• Alongside each other: Transform or transcurrent.
• There is a further subdivision for Convergent plates,
which is dependent on the properties of the plates
moving towards each other (oceanic / continental
crust).
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.
Constructive Plate Boundary
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
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
36 metres
200 metres
928 metres
Convergent Plate Boundaries (Together)
• The two types of margins that occur here are
Destructive Margins or collision Zones...
Oceanic crust moves towards continental
crust. Oceanic crust sinks, and slowly
Destructive
destroyed. Results in deep ocean trenches,
margins
island arcs and fold mountains. Can be
referred to as subduction zones.
Collision
Zones
Two continental crusts meet, neither sinks,
fold mountains result. For example, the Alps.
Divergent Plate Boundaries (Away)
• Also known as a Constructive margin.
• Plates move away from each other, for
example, N. American and Eurasian plates,
cresting mid-ocean ridges such as the Mid
Atlantic Ridge.
• New material appears at the ocean ridge.
Transcurrent Boundaries (Side-By-Side)
• Here plates simply move alongside each other,
land is neither created nor destroyed.
• Plates rub against each other causing friction
resulting in earthquakes only at these
boundaries.
Examples
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Destructive Plate Margins
Peru - Chile Trench as oceanic crust is subducted.
Earthquakes, due to the heat created as the
Nazca plate is destroyed.
Fold Mountains such as the Andes.
Volcanoes if heat from the subduction zone has
the opportunity to reach the surface, for
example, Cotopaxi.
Island arcs and volcanic islands, for example,
Japan.
Examples
Collision Zones
• Indian Plate and Eurasian Plate created the
Himalayas.
Constructive Margins
• North American plate moving away from the
Eurasian plate resulting in the mid Atlantic ridge.
Transform Faults
• Earthquakes such as those linked with the San
Andreas Fault.
Hot Spots
• There are examples where volcanic activity is
not linked to plate margins as in the case of
the Hawaiian Islands.
• This is believed to be due to the presence of
'hot spots' - places of localised heat under the
earth's crust that then find their way to the
surface.
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
Explosive volcanoes
The oceanic crust
melts and rises
Mantle
Constructive plate boundaries
MID OCEAN
RIDGE
B
A
Ocean
Mantle
Where would you find older rocks – at A? or at B?
Activity 1
Using Essential AS Geography P31, answer the
following…
1. What are the 3 major relief features
associated with constructive margins?
2. Create a diagram to show/describe the
processes operating at constructive margins.
3. What is “Palaeomagnatism” and how does it
explain the idea of sea floor spreading?
Activity 2
Using Essential AS Geography P33-35, answer
the following…
1. What is a destructive margin?
2. How are Earthquakes, Volcanoes, Ocean
Trenches, and Island Arcs associated with
these boundaries?
3. Describe the formation of the Himalayas and
explain why there are few earthquakes and
no volcanoes there.