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III) STRUCTURE 1 Look at the illustration of the different layers that make up the Earth. Complete the sentences below: a) The ___________________ is in the centre of the Earth. b) The ___________________ is the layer surrounding the ___________________. c) The layer above the ___________________ is the ___________________. d) The ___________________ covers the ___________________ . It is the outer layer of the Earth. 2 Look at the illustration on the left and complete the sentences: a) The crust is a thin layer between 5 and _____ km thick. b) The lower and the upper mantle cover the core and are about _____ km thick. c) The core is about _____ km thick. The earth is made up of 4 distinct layers: 1. The inner core is in the centre of the earth and is the hottest part of the earth. The inner core is solid. It is made up of iron and nickel with temperatures of up to 5500°C. 2. The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot here, with temperatures similar to the inner core. 3. The mantle is the widest section of the earth. The mantle is made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but nearer the core, the rock is soft. 4. The crust is the outer layer of the earth. It is a thin layer between 5-75 km thick. The crust is a solid rock layer. We live on this layer. 3 Read the text on the preceding page and write the words “soft” and “hard” into the correct circles. inner core outer core Lower mantle Upper mantle 4 Study this cross section of the Earth. 1) What layer does the black colour represent? 2) Is this layer the same size all around the Earth? Lithosphere The crust and the upper parts of the mantle are called the lithosphere. There are two types of lithosphere: Oceanic lithosphere carries water. Continental lithosphere carries land. Oceanic lithosphere is typically about 50-100 km thick. Continental lithosphere is about 150 km thick. What does the illustration on the left represent? Write the correct names next to the numbers. a. _________________ b. _________________ c. _________________ 5 Asthenosphere The asthenosphere is the region of the Earth between 100 and 200 km below the surface. It is the weak or "soft" zone in the upper mantle. It lies just below the lithosphere. Plate Tectonics The lithosphere is broken up into pieces. These pieces are called plates. Heat rising and falling inside the mantle creates currents. These currents move the plates. The movement of the plates, and the activity inside the earth, is called plate tectonics. Plate tectonics cause earthquakes and volcanoes. The point where two plates meet is called a plate boundary. Earthquakes and volcanoes usually occur either on or near plate boundaries. Now go to the following website: http://www.bbc.co.uk/schools/gcsebitesize/geography/index.shtml Click on “plate tectonics”. Now click on “Revise” (Plate Tectonics) Then click on plates and plate boundaries. Discuss a) the different movements of the plates b) the distribution of earthquakes and volcanoes 6