1.2 Why is our e arth u nstable ?

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

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1.21.2 Why is our Why is our eeartharth u unstablenstable??


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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?

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?

Which plate does Hong Kong rest on?


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( Regular / Irregular ) in shapeVariable in thickness from 100 to 200 kilometres

Great differences in sizes, varying from a few hundred to thousands of kilometres acrossLying 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?Footage

01_e_movie_01.mpg

Simulation experiment on how plates are driven (Old, but have to modify)

NSS Part 1 1-13

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.


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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.

currentsconvection

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 __________ __________.

platetectonics


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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.

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

MantleCrust

Continental crust

Oceanic crust

CrustCrust 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 ____________

silicaaluminium

Continental crust

0 km

6–70 km

0 km

100–200 k

m

350– 500 kmConvection currents of magma

Oceanic crust


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CrustOceanic crust

Oceanic crust

0 km

6–70 km

0 km

100– 200 km

350– 500 kmConvection currents of magma

Under the oceans

Thinner, denser and heavier than continental crust

Rich in silica and ____________magnesium


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MantleMantle 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

Up

per m

antle

crust

This layer and the crust are collectively called lithosphere


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CoreThe 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?

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

Crust


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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 betwee

n the plates

Magma

New crust is formed when solidified

away


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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 a

sthenosphere

sinks

The sinking part of the plate melts into

magma


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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 Why is our e arth u nstable ?

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