Imagine a Scotch egg......
1. The outer shell of the Earth is called the CRUST (breadcrumbs)
2. The next layer is called the MANTLE (sausagemeat)
3. The next layer is the liquid OUTER CORE (egg white)
4. The middle bit is called the solid INNER CORE (egg yolk)
2. The next layer is called the MANTLE (sausagemeat)
3. The next layer is the liquid OUTER CORE (egg white)
4. The middle bit is called the solid INNER CORE (egg yolk)
The deepest anyone has drilled into the earth is around 12 kilometres, we've only scratched the surface. How do we know what's going on deep underground?
There are lots of clues:
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.
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).
Iron and Nickel are both dense and magnetic.
Scientists can follow the path of seismic waves from earthquakes as they travel through the Earth. The inner core of the Earth appears to be solid whilst the outer core is liquid (s waves do not travel through liquids). The mantle is mainly solid as it is under extreme pressure (see below). 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.
The Earth is sphere (as is the scotch egg!) with a diameter of about 12,700Kilometres. 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 crust is very thin (average 20Km). This does not sound very thin but if you were to imagine the Earth as a football, the crust would be about ½millimetre 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. It's made of solid rock and behaves like an extremely viscous liquid - (This is the tricky bit... the mantle is a solid which flows????) The convection of heat from the centre of the Earth is what ultimately drives the movement of the tectonic place and cause mountains to rise.
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 the bit in the middle!. It is made of solid iron and nickel. Temperatures in the core are thought to be in the region of 5000-6000°c and it's solid due to the massive pressure.
