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1.2
Why is our earth
unstable?
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What is the structure of the earth?
Our earth can be divided
into _______
three layers.
From the surface
to the centre, they
are:
_______
Crust
Mantle
_______
_______
Core
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What is the structure of the earth?
In what
ways are
the three
layers
arranged?
They are arranged
according to their
density
_________.
In general, layers with
( lighter / heavier ),
( less dense /
denser ) minerals lie
on the top.
Density of minerals:
Magnesium: 1,738 kg/m3
Silica (silicon): 2,330 kg/m3
Aluminium: 2,700 kg/m3
Iron: 7,874 kg/m3
Nickel: 8,908 kg/m3
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What is the structure of the earth?
Crust
Mantle
Let’s study these
three layers.
Core
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What are plates?
These
are lithosphere
called
They
Forces
break
arepieces
constantly
the solid
generated
plates.
from into
within
pieces.
the earth.
Which plate does
Hong Kong rest on?
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What are plates?
Plates have the following characteristics:
Some
of the
plates carry
oceanic crust and continental
( Regular
/ Irregular
) in both
shape
crust, while some of them only carry oceanic crust
Variable in thickness from 100 to 200 kilometres
Eurasian Plate
Pacific Plate
Great differences in sizes, varying from a few hundred to
thousands of kilometres
acrossPlate
Indo-Australian
Lying and floating on the asthenosphere and moving slowly in
different directions at a rate of a few centimetres per year
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How do plates move?
Footage
01_e_movie_01.mpg
Simulation experiment on how plates are
driven (Old, but have to modify)
NSS Part 1 1-13
TheConvection
wood pieces
currents occur
in
sometimes
knock
the water
when
it
against
each
other
This
experiment
is heated.
They
and
sometimes
simulates
how
dragapart.
the wood
flow
The
the
plates
pieces
atmove.
the
higher
the
heat,
thesurface.
faster the
movement.
Please click above for footage
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How do plates move?
The plates float on the ______________.
asthenosphere
The heat in the asthenosphere creates powerful
___________
currents They drag the plates to
convection __________.
move in different directions.
Plate
Upper mantle
(asthenosphere)
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How do plates move?
The plate movements result in _______
three different types of
plate boundaries.
Plate boundaries
Constructive
plate boundaries
Destructive
plate
boundaries
Conservative
plate
boundaries
The theory that describes how convection currents in the
mantle cause plate movement is known as __________
plate
__________.
tectonics
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How do plates move?
If the plates move in the
directions shown throughout
the history, imagine how the
continents were distributed
in the distant past.
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Crust
Continental
crust
Crust is made up
of two types.
Making up the
Continental crust
Oceanic
crust
Continental
continents and the
crust
0 km
continental
0 km
100–
shelves, which are 6–70
200
Crust
km
km
gently sloping
Mantle
plains bordering
Oceanic
Core
the continents
crust
Thick and light
Rich in _________
silica
and ____________
aluminium
Convection currents of magma
350–
500 km
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Crust
Oceanic crust
Under the oceans
Oceanic crust
0 km
0 km
100–
200 km
6–70
km
Thinner, denser
and heavier than
continental crust
Rich in silica and
magnesium
____________
Convection currents of magma
350–
500 km
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Mantle
Mantle lies below the _______,
crust as it is denser.
It can be divided into three parts:
0 km
100–
200 km
Uppermost part of the
mantle
( solid / plastic / liquid )
This layer and the crust are
collectively called lithosphere
Asthenosphere
( solid / plastic / liquid )
Magma flows in convection
350–500
km
Lower mantle
( solid / plastic / liquid )
Under high pressure
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Core
Why is the outer
The
coreinisliquid
the ( form
hottest /
core
coldest ) and the ( densest /
butdense
the inner
least
) partcore
of the
earth.in solid form?
It can be subdivided into two
layers:
The intense heat causes the
materials of the outer core to melt
Mantle
Outer core
( solid / plastic / liquid )
Core
The inner core is under
the greatest pressure.
The materials are kept in
solid form
Inner core
( solid / plastic / liquid )
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Constructive plate boundaries
When convection currents
diverge or move apart:
Plates _____
split _____
away
from each other
Magma wells up
________
and fills the gap
between the plates
Please click above for animation
New crust is formed
when solidified
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Destructive plate boundaries
 
When convection
currents converge:
Plates move
( towards each other
/ apart )
When plates collide,
the denser one _____,
sinks
or subducts into the
asthenosphere
Please click above for animation
The sinking part of
the plate melts into
magma
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Conservative plate boundaries

Plates
 converge
 diverge
 slide past each
other
The plate materials
are ( either / neither )
created ( or / nor )
destroyed.
Please click above for animation
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