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Transcript
RAGING PLANET Based on a poster created by Ivo Grigorov, a postgraduate student at Southampton Oceanography Centre,with the help of Sofie Almond and Emma Jung, pupils of St Anne's School, Southampton. Earth is a dynamic planet which is constantly changing. The outer shell is made up of thin, rigid plates that move relative to each other. The discovery of these plates lead to the theory of plate tectonics, which was formulated during the early 1960s. Scientists have successfully used Scientists use plate tectonics to explain many geological events such as earthquakes and volcanic eruptions as well as mountain building and the formation of the oceans and continents. If we could slice through the earth to look at its structure, this is what we'd see: mantle plate convection currents 2900km inner core outer core 5100km Inner core Outer core Mantle Crust The present-day boundaries of the plates that make up the Earth's surface are shown as jagged yellow lines on this map. Notice that the outlines of west Africa and South America look as though they once fitted together, like pieces of a jigsaw. TYPES OF PLATE MARGIN Conservative margins Conservative margins are commonly defined by shallow earthquakes. Most are found on the ocean floor, but they can also occur on land. The San Andreas fault zone (left), slices through two thirds of the length of California. The fault is about 1300km long, and in places tens of kilometres wide. The Pacific and North American plates have been grinding horizontally past each other for 10 million years, at an average rate of about 5cm per year. Photo: USGS h nc Tr e Continental crust Lithosphere Lithosphere Asthenosphere Mid-ocean spreading ridge Lithosphere Rising, diverging mantle convection currents Asthenosphere Continental crust Lithosphere Asthenosphere Continental crust Oceanic crust Subducting plate Hig pla h tea u Collision zones When two continents collide, neither is subducted because the continental rocks are relatively light. Instead, the crust tends to be pushed upward or sideways. The collision of India into Asia 50 million years ago resulted in the Himalayan mountain range. The Himalayas, towering as nearly 9,000m above sea level, form the highest continental mountains in the world, and the neighbouring Tibetan Plateau, at an elevation of about 4,600m, is higher than most peaks in the Alps. ar Oceanic crust ra ng e Constructive margins As hot magma rises due to convective processes, the crust is cracked and pushed apart by the cooling magma. As a result an underwater mountain range forms. These submerged mountain ranges are called the mid-ocean ridges and total nearly 60,000km in length. Major features of the mid-ocean ridges are underwater volcanoes and hydrothermal vents which are extremely hot water eruptions rich in dissolved minerals. c nd la Is M ou nt ai n Destructive margins If we could pull a plug and drain the Pacific Ocean, we would see a number of long, narrow curving trenches thousands of kilometres long cutting into the ocean floor. Trenches are the deepest parts of the ocean floor and are created by subduction. The Marianas Trench is nearly 11,000m deep. It plunges deeper into the Earth's interior than Mount Everest, the world's tallest mountain, rises above sea level. Continental crust Lithosphere VOLCANIC ACTIVITY AND EARTHQUAKES Subduction processes also result in volcanic activity. Earthquakes and rapid uplift of mountain ranges are common in such regions, for example the Andes. The deepest part of the subducting plate breaks into smaller pieces. These become locked in place for long periods of time before suddenly moving to generate large earthquakes, often accompanied by uplift of the land by as much as a few metres. Photo: USGS PLATE TECTONICS THROUGH TIME N PA 200 million years ago G AE A LAU RAS IA 135 million years ago GO ND WA NA No rth Am South America eric a Asia Europe 35 million years ago Africa India Eurasian Plate Australia Antarctica American Plate Pacific Plate African Plate Indo-Australian Plate Pacific Plate Present day Antarctic Plate Plate tectonics will continue long into the furture. The diagram to the left shows what might happen to the African and South American plates over the next 50 million years. The position of the Earth's plates has changed through time. Compare their positions in the cartoons to the left and you will see that it is a very slow process!
