chemistry C1 (6)

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…