chemistry C1 (6)

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  • Created by: haidee
  • Created on: 28-04-12 11:45

The structure of the Earth

  • The earth was formed when a molten mass of material cooled down over a period of millions of years
  • The earth is nearly spherical with a layered structure
  • The atmosphere is a layer of gases (about 100km thick) above the crust, consisting mainly of nitrogen and oxygen
  • The earth’s crust varies in thickness from 5km under the oceans to 70km under the continents
  • The mantle is under the crust
  • This layer is much thicker, nearly 3000km thick
  • The mantle behaves like a solid, but it can flow in parts very slowly
  • The earth’s core is in the centre, and is about half the radius of the earth
  • It is made of a mixture of two magnetic metals nickel and iron
  • The outer core is a liquid while the inner core is a solid
  • It is important to remember that the earth’s crust, the atmosphere and the oceans are the only source of minerals and other resources that humans need
  • The outer part of the earth is called the lithosphere, which includes the crust and the upper part of the mantle
  • It is cracked into a number of huge pieces called tectonic plates
  • The plates are moving at a speed of a few centimetres each year
  • Natural radioactive processes in the earth’s core produce a lot of heat- this results in convection currents in the mantle, which makes the tectonic plates move very slowly
  • The currents are caused by heat released inside the earth from `the natural breakdown (decay) of radioactive atoms
  • As rock in the mantle gets hotter it becomes less dense and rises
  • It is pushed to the side by more rock where it cools the cooling means that it becomes more dense and sinks back down
  • It is the sideways movement of the rock that moves the plate above it
  • As plates move past, over , under or apart from each other magma from the mantle can escape resulting in a volcano
  • Friction between the moving plates can make them move in sudden jerks, producing earthquakes

Earthquakes and volcanoes

  • It is difficult for sciences to predict exactly when earthquakes and volcanic eruptions are likely to occur
  • Scientists know where earthquakes are likely and many buildings in danger zones are built with special foundations to help them withstand earthquakes
  • The warning signs before an earthquake:
  • - increased seismic activity -small socks that may not be detected by people but are detected by scientific instruments
  • - water levels in wells fall
  • - some animals act strangely
  • Volcanic eruptions are much easier to predict than earthquakes because we know where volcanoes are and the signs are more definite
  • Warning signs before a volcanic eruption:
  • - increasing temperature of the volcano due to magma moving underground
  • - rising ground level due to the build-up of magma
  • - more sulphur dioxide (SO2) gas given out
  • When these warnings signs appear, people can be moved to safety
  • However, scientists cannot reliably predict major earthquakes or volcanic eruptions exactly
  • It

Comments

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zahra abbas

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Rohan

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fariii

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