1.2 Why is our e arth u nstable ?

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

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

6. 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. 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 1 1-13 This experiment simulates how the plates move. Please click above for footage

8. How do plates move? asthenosphere The plates float on the ______________. The heat in the asthenosphere creates powerful ___________ __________. They drag the plates to move in different directions. currents convection Plate Upper mantle (asthenosphere)

9. How do plates move? three The plate movements result in _______ different types of plate boundaries. Plateboundaries 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. Continental crust Crust Mantle Oceanic crust Core 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 Continental crust Oceanic crust 0 km 0 km 100–200 km 6–70 km Thick and light silica Rich in _________ and ____________ 350– 500 km Convection currents of magma aluminium

13. Crust Oceanic crust Under the oceans Oceanic crust 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 crust Mantle lies below the _______, as it is denser. It can be divided into three parts: Uppermost part of the mantle (solid/plastic/liquid) 0 km This layer and the crust are collectively called lithosphere 100– 200 km 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 corein 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