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KS4 Physics Earth’s Structure 1 of 20 32 © Boardworks Ltd 2005 2004 Contents Earth’s Structure Earth and earthquakes Seismic waves More about plate boundaries Continental drift Summary activities 1 2 of 20 32 © Boardworks Ltd 2005 2004 Structure of the Earth crust mantle inner core outer core 1 3 of 20 32 © Boardworks Ltd 2005 2004 Tectonic plates The Earth’s crust is made of sections called tectonic plates. Where two plates meet is called a plate boundary. Convection currents in the mantle plates move these tectonic plates, which can move towards each other, move away from each other and or move past each other. 1 4 of 20 32 © Boardworks Ltd 2005 2004 Plate boundaries 1 – sliding plates Two plates can slide past each other, but this doesn’t always happen smoothly. The large friction forces involved mean that strain builds up and the plates move suddenly when the strain gets too much. plate A plate B This sudden movement of plates is called an earthquake and it can be very destructive. 1 5 of 20 32 © Boardworks Ltd 2005 2004 Plate boundaries 1 – conservative boundary 1 6 of 20 32 © Boardworks Ltd 2005 2004 Why do earthquakes happen? 1 7 of 20 32 © Boardworks Ltd 2005 2004 Features of an earthquake 1 8 of 20 32 © Boardworks Ltd 2005 2004 Cross-section of the Earth – labels Which part of this cross-section of the Earth should each label point to? crust outer core mantle inner core 1 9 of 20 32 © Boardworks Ltd 2005 2004 Effect of an earthquake An earthquake has occurred in the area shown in this picture. If the plates moved in the directions indicated by the arrows, what would the location would look like after the earthquake? plate A 1 10ofof20 32 plate B © Boardworks Ltd 2005 2004 Contents Earth’s Structure Earth and earthquakes Seismic waves More about plate boundaries Continental drift Summary activities 1 11ofof20 32 © Boardworks Ltd 2005 2004 Plate boundaries 2 – colliding plates What happens at a plate boundary where an oceanic plate and a continental plate collide? The thinner, more dense oceanic plate is driven down into the mantle. This is known as subduction. thicker, less dense continental plate convection current thinner, more dense oceanic plate convection current melted oceanic plate 1 12ofof20 32 © Boardworks Ltd 2005 2004 Plate boundaries 2 – destructive boundary 1 13ofof20 32 © Boardworks Ltd 2005 2004 Plate boundaries 3 – plates moving apart What happens at a plate boundary when oceanic plates move apart due to convection currents in the Earth’s mantle? oceanic plate Magma moves up to the convection surface, cools current and forms new oceanic plate. 1 14ofof20 32 oceanic plate convection current This is known as sea-floor spreading. © Boardworks Ltd 2005 2004 Plate boundaries 3 – constructive boundary 1 15ofof20 32 © Boardworks Ltd 2005 2004 Words about plate boundaries subduction sea-floor spreading friction 1 16ofof20 32 The force that causes earthquakes. When an oceanic plate is pushed down into the mantle as it collides with a continental plate. When two oceanic plates move apart to create new crust. © Boardworks Ltd 2005 2004 Contents Earth’s Structure Earth and earthquakes Seismic waves More about plate boundaries Continental drift Summary activities 1 17ofof20 32 © Boardworks Ltd 2005 2004 What is continental drift theory? It is thought that all the continents were once joined together in a huge supercontinent called Pangaea. Over millions of years the continents drifted apart because the tectonic plates they were on moved apart due to convection currents in the Earth’s mantle. 1 18ofof20 32 © Boardworks Ltd 2005 2004 Continental drift theory animation 1 19ofof20 32 © Boardworks Ltd 2005 2004 Evidence for continental drift theory There are a number of pieces of evidence to support the theory of continental drift: 1. The shapes of the continents fit like a jigsaw. 2. The rock strata on separated continents are identical. continent A continent B 3. The fossil records on separated continents are identical. 1 20ofof20 32 © Boardworks Ltd 2005 2004 Contents Earth’s Structure Earth and earthquakes Seismic waves More about plate boundaries Continental drift Summary activities 1 21ofof20 32 © Boardworks Ltd 2005 2004 Glossary (1) continental drift – The theory that millions of years ago all the continents formed a huge supercontinent and have been slowly drifting apart ever since. core – The central region of the Earth below the mantle. The outer part is liquid and the inner part is solid. crust – The thin, rocky, outer layer of the Earth. earthquake – A sudden movement of the Earth’s crust, which causes vibrations that travel through the Earth. mantle – The layer of the Earth, between the crust and the core, which is mostly solid rock that can flow very slowly. P waves – These are the fastest type of seismic waves. They are longitudinal waves and can travel through solids and liquids. 1 22ofof20 32 © Boardworks Ltd 2005 2004 Glossary (2) plate boundary – An area where two tectonic plates meet. S waves – These are the slowest type of seismic waves. They are transverse waves and can only travel through solids. sea-floor spreading – This occurs under oceans where plates move apart and magma rises to the surface and cools to form new crust. seismic waves – Vibrations that travel through the Earth as a result of an earthquake. subduction – This occurs where plates move together and one of the plates is driven down into the mantle. tectonic plates – Large sections of the Earth’s crust and upper mantle that move slowly over the surface of the Earth. 1 23ofof20 32 © Boardworks Ltd 2005 2004 Anagrams 1 24ofof20 32 © Boardworks Ltd 2005 2004 Multiple-choice quiz 1 25ofof20 32 © Boardworks Ltd 2005 2004