1. 1.2 Why is our earth unstable?

2. What is the structure of the earth?
Our earth can be divided into _______ layers.
three
_______
Crust
From the surface to the centre, they are:
Mantle
Core

3. 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

4. Let’s study these three layers.
What is the structure of the earth?
Crust
Let’s study these three layers.
Mantle
Core

5. What are plates? Which plate does Hong Kong rest on?
They break the solid lithosphere into pieces.
Forces are constantly generated from within the earth.
What are plates?
These pieces are called plates.
Which plate does Hong Kong rest on?

6. Indo-Australian Plate
What are plates?
Plates have the following characteristics:
Some of the plates carry both oceanic crust and continental crust
( Regular / Irregular ) in shape
, 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 across
Indo-Australian Plate
Lying and floating on the asthenosphere and moving slowly in different directions at a rate of a few centimetres per year

7. This experiment simulates how the plates move.
How do 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.
Footage
01_e_movie_01.mpg
Simulation experiment on how plates are driven (Old, but have to modify)
NSS Part
This experiment simulates how the plates move.
Please click above for footage

8. 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.
convection
currents
Plate
Upper mantle
(asthenosphere)

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

10. 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.

12. Crust Continental crust Crust is made up of two types.
Making up the continents and the continental shelves, which are gently sloping plains bordering the continents
Core
Mantle
Crust
Continental crust
Oceanic crust
Continental crust
Oceanic crust
0 km
0 km
100–200 km
6–70 km
Thick and light
Rich in _________ and ____________
silica
350– 500 km
aluminium
Convection currents of magma

13. Crust Oceanic crust Under the oceans
0 km
Thinner, denser and heavier than continental crust
0 km
100– 200 km
6–70 km
Rich in silica and ____________
magnesium
350– 500 km
Convection currents of magma

14. Mantle Mantle lies below the _______, as it is denser. crust
It can be divided into three parts:
Uppermost part of the mantle
( solid / plastic / liquid )
0 km
100– 200 km
This layer and the crust are collectively called lithosphere
Asthenosphere
Upper mantle
( solid / plastic / liquid )
Magma flows in convection
350–500 km
Lower mantle
( solid / plastic / liquid )
Under high pressure

15. Core
Why is the outer core in liquid form but the inner core in solid form?
The core is the ( hottest / coldest ) and the ( densest / least dense ) part of the earth.
It can be subdivided into two layers:
Crust
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 )

16. 1 Constructive plate boundaries
When convection currents diverge or move apart:
 
Plates _____ _____ from each other
split
away
________ wells up and fills the gap between the plates
Magma
New crust is formed when solidified
Please click above for animation

17. 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
Please click above for animation

18. 3 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