1.2 Why is our earth unstable? · earth. It can be subdivided into two layers: Outer core Inner...

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Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas?

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1.2 Why is our earth

unstable?



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Our earth can be divided into _______ layers. three

From the surface to the centre, they are:

Crust

_______

_______

_______

Mantle

Core

What is the structure of the earth?



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They are arranged

according to their

_________. density

In general, layers with

( lighter / heavier ),

( less dense /

denser ) minerals lie

on the top.

In what

ways are

the three

layers

arranged?

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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Crust

Mantle

Core

Let’s study these

three layers.




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What are plates? These pieces are called

plates. Forces are constantly generated

from within the earth.

They break the solid lithosphere

into pieces.

Which plate does

Hong Kong rest on?



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( Regular / Irregular ) in shape

Variable in thickness from 100 to 200 kilometres

Great differences in sizes, varying from a few hundred to thousands of kilometres across

Lying and floating on the asthenosphere and moving slowly in different directions at a rate of a few centimetres per year

What are plates? Plates have the following characteristics: Some of the plates carry both oceanic crust and continental crust

Eurasian Plate

Indo-Australian Plate

Pacific Plate

, while some of them only carry oceanic crust



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How do plates move?

Please click above for footage

This experiment

simulates how

the plates move.

Convection

currents occur in

the water when it

is heated. They

drag the wood

pieces at the

surface.

The wood pieces

sometimes knock

against each other

and sometimes

flow apart. The

higher the heat,

the faster the

movement.

1-2-4e.mpg



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How do plates move? The plates float on the ______________.

asthenosphere

The heat in the asthenosphere creates powerful

___________ __________. They drag the plates to

move in different directions. currents convection

Plate

Upper mantle

(asthenosphere)



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How do plates move? The plate movements result in _______ different types of plate boundaries.

three

Destructive

plate

boundaries

Constructive

plate boundaries

Conservative

plate

boundaries

Plate boundaries

The theory that describes how convection currents in the

mantle cause plate movement is known as __________

__________. plate

tectonics



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If the plates move in the

directions shown throughout

the history, imagine how the

continents were distributed

in the distant past.

How do plates move?



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Core

Mantle Crust

Continental

crust

Oceanic

crust

Crust

Crust is made up of two types.

Continental crust

Making up the continents and the continental shelves, which are gently sloping plains bordering the continents

Thick and light

Rich in _________ and ____________

silica aluminium

Continental crust

0 km

6–70

km

0 km

100–

200

km

350–

500 km Convection currents of magma

Oceanic crust



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Crust Oceanic crust

Oceanic crust

0 km

6–70

km

0 km

100–

200 km

350–

500 km Convection currents of magma

Under the oceans

Thinner, denser

and heavier than

continental crust

Rich in silica and

____________ magnesium



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Mantle

Mantle lies below the _______, as it is denser.

It can be divided into three parts:

0 km

100–

200 km

350–500

km

Asthenosphere

Lower mantle

Uppermost part of the

mantle

( solid / plastic / liquid )



Magma flows in convection

Under high pressure

crust

This layer and the crust are

collectively called lithosphere



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Core

The core is the ( hottest / coldest ) and the ( densest / least dense ) part of the earth.

It can be subdivided into two layers:

Outer core

Inner core



Why is the outer

core in liquid form

but the inner core

in solid form?

The intense heat causes the

materials of the outer core to melt

The inner core is under

the greatest pressure.

The materials are kept in

solid form

Core

Mantle



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1 Constructive plate boundaries

Please click above for animation

When convection currents diverge or move apart:

Plates _____ _____

from each other split

________ wells up

and fills the gap

between the plates

Magma

New crust is formed

when solidified

away

1-2-1e.mpg



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2 Destructive plate boundaries


When convection currents converge:

Plates move

( towards each other

/ apart )

When plates collide,

the denser one _____,

or subducts into the

asthenosphere

sinks

The sinking part of

the plate melts into

magma

1-2-2e.mpg



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Plates

converge

diverge

slide past each other


The plate materials are ( either / neither ) created ( or / nor ) destroyed.

3 Conservative plate boundaries

1-2-3e.mpg

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1.2 Why is our earth unstable? · earth. It can be subdivided into two layers: Outer core Inner...

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