Transcript 1.2
Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 1.2 Why is our earth unstable? Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? What is the structure of the earth? Crust Mantle Let’s study these three layers. Core Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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? Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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) Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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. Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 ) Quit Part 1 1 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 2 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit Part 1 3 Opportunities and risks─Is it rational to live in hazard-prone areas? 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 Quit