EARTH'S RELIEF. English

UNIT: THE EARTH AND THE EARTH’S RELIEF: 1.- PARTS OF THE EARTH: Most of our planet is formed by the GEOSPHERE, that is a great rounded mass of rock, with a diameter of 13,000 km. It has got three layers: crust, mantle and core. It is covered by the HYDROSPHERE, that is the water from the oceans, seas, lakes, rivers, underground water, and ice in the mountains and in the poles. And finally, wrapping everything is the ATMOSPHERE, the gas layer composed by air and water steam. 2.- THE GEOSPHERE: It is formed by rocks. A rock is a natural material, hard and dense formed by chemical substances called minerals. Some rocks are formed only by one mineral (calcite), and others are formed by several minerals (granite: quartz, feldspar and mica). There are rocks that make up the continents and the bottom of the oceans in the crust, but they also form the mantle and core with some specific characteristics: they are very hot (about 5,000 ºC), they are very dense, and sometimes they are melted (magma) 3.- TECTONIC PLATES: The LITHOSPHERE is made up of the crust and the upper mantle. It’s formed by plates like tiles on the floor (Tectonic plates). These plates are 100km thick, and they can move very slowly from to another by forces in the mantle, because the mantle is formed by melted rocks. They can move only a few cm a year, but they touch, push or separate from each other, and the result of these movements is called: ‘CONTINENTAL DRIFT’. This theory says that millions of years ago all continents were joined as one called Pangea. Later this continent broke into two continents: Laurasia and Gondwana, separated by the Tethys Ocean. After that, North America separated from Europe, and South America from Africa. India and Australia moved to their actual places. These movements are still happening in the present, so in some millions years the Earth will be different than the one we know today.

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