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THE EARTH´S STRUCTURE Page 67 and Page 74 • The Geosphere: Crust, Mantle and Core • The dynamics of the geosphere: Convection currents • The lithosphere: • Submerged relief: Continental platform: Continental shelf: Talud continental Abyssal plain: Llanura abisal Oceanic ridge: Dorsal oceánica Oceanic trench: Fosa oceánica the Earth’s spheres The geosphere • Of all the Earth’s spheres, the geosphere occupies the greatest volume. It is almost perfectly sphere-shaped. • It is divided into a number of layers: Crust: This is the thinnest layer of the geosphere. The hydrosphere, the biosphere and the atmosphere are located on this layer. Mantle: The thickest layer, the mantle is made of malleable rocks and some molten materials. Core: This is the innermost and hottest layer of the geosphere. It consists of the outer core, which is molten, and the inner core, which is solid. Go back to the start menu The dynamics of the geosphere The dynamics of the geosphere • The Earth’s internal heat, called geothermal energy, increases with depth, driving the inner dynamics of the geosphere. • The movements of the rocks in the mantle are convection currents. 2 1 The intense heat of the deep mantle makes the rocks less dense, causing them to rise towards the surface. As the rocks move towards the surface, they cool down and their density increases, causing them to sink back to the deeper zones, where they heat up and consequently rise again. The lithosphere and lithospheric plates What is the lithosphere? • The lithosphere is formed by the Earth’s crust and the upper part of the mantle (made up of hard rocks). • Its thickness varies, from 70 km under the oceans up to 200 km in the continents. • There are two types of lithosphere: the continental lithosphere and the oceanic lithosphere. Oceanic lithosphere Continental lithosphere Crust Lithosphere Hard mantle Submerged relief Continental platforms • Continental platforms are extensions of continents submerged in the ocean. • They are usually quite flat but get deeper the further into the sea they are. • The platform ends in a steep slope called the continental shelf. Continental platform Continental shelf Go back to the start menu Submerged relief Abyssal plains • These are large plains located at great depths (normally at depths of more than 3,000 metres). They make up the largest part of the ocean floor. • Submerged mountains and volcanoes can be found here. They are sometimes so high that they form islands. Volcanic island Abyssal plain Go back to the start menu Submerged relief Ridges • These are large underwater mountain ranges that are thousands of kilometres long. They cut through the abyssal plains. They can be so high that they emerge from the water and create islands, as is the case of Iceland. • Ridges have a fissure down their middle, called a rift. Rift Ridge Go back to the start menu Submerged relief Trenches • These are very deep, narrow, long depressions. • The largest trenches are more than 10 kilometres deep and hundreds of kilometres long. Trench The lithosphere and lithospheric plates Lithospheric plates • The lithosphere is not one continuous surface: it is divided into a number of pieces, called lithospheric plates, or tectonic plates. • Plate boundaries can be easily identified because they coincide with notable features of the lithosphere like oceanic ridges, oceanic trenches and large mountain ranges. North American plate Eurasian plate Philippine plate Juan de Fuca plate Arabian plate Cocos plate Pacific plate Nazca plate Scotia plate South American plate Pacific plate African plate Indo-Australian plate Antarctic plate Do you remember the following features of the lithosphere? • Oceanic ridge: …………… oceánica • Oceanic trench: …………… oceánica