The Earth is sphere with a diameter of about 12,700 kilometres. As we go deeper and deeper into the earth the temperature and pressure rises. The core temperature is believed to be an incredible 5000-6000°C. The deepest anyone has drilled into the earth is around 12 kilometres, so we've only scratched the surface. How then do we know what's going on deep underground? We have to deduce the structure deep inside from evidence

The overall density of the Earth is much higher than the density of the rocks we find in the crust. This tells us that the inside must be made of something much denser than rock.

 

 

The crust is very thin (average 20 km). This does not sound very thin but if you were to imagine the Earth as a netball, the crust would be about ½ millimetre thick. The thinnest parts are under the oceans (OCEANIC CRUST) and go to a depth of roughly 10 kilometres. The thickest parts are the continents (CONTINENTAL CRUST) which extend down to 35 kilometres on average. The continental crust in the Himalayas is some 75 kilometres deep.

The mantle is the layer beneath the crust which extends about half way to the centre (make sure any sketch diagrams you do show this!!). It's made of rock that behaves like an extremely viscous liquid. The convection currents of the heat energy from centre of the Earth are what drive the movement of the tectonic plates.

The outer core is the layer beneath the mantle. It is made of liquid iron and nickel. Complex convection currents give rise to a dynamo effect which is responsible for the Earth's magnetic field.

The inner core is made of solid iron and nickel. Iron and Nickel are both dense and magnetic. Temperatures in the core are thought to be in the region of 5000-6000°C and it is solid due to the massive pressure it is under.

The outer shell of the Earth is called the CRUST (breadcrumbs)
The next layer is called the MANTLE (sausagemeat)
The next layer is the liquid OUTER CORE (egg white)
The middle bit is called the solid INNER CORE (egg yolk)

More to think about...

Meteorites (created at the same time as the Earth, 4.6 billion years ago) have been analysed. The commonest type is called a chondrite and they contain iron, silicon, magnesium and oxygen (Others contain iron and nickel). A meteorite has roughly the same density as the whole earth. A meteorite minus its iron has a density roughly the same as Mantle rock (e.g. the mineral called olivine).

Scientists can follow the path of seismic waves from earthquakes as they travel through the Earth. They use this information to deduce facts about the structure of the Earth.

They deduce that the inner core of the Earth is solid whilst the outer core is liquid (because S waves do not travel through liquids). The mantle is mainly solid as it is under extreme pressure. We know that the mantle rocks are under extreme pressure, diamond is made from carbon deposits and is created in rocks that come from depths of 150-300 kilometres that have been squeezed under massive pressures.

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