Chemistry C3

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Tectonic Plates:

Tectonic plates are directly beneath the crust and float on the molten layer of magma in the mantle. Convection currents in the mantle are caused by the heat from the Earth's core. The heat causes the magma to rise in the form of convection currents. The currents then force the tectonic plates to move in certain directions. When they are moved apart, the magma rises to the surface and when it is cooling, the iron inside is magnetised with the magnetic field of the Earth. Every 1/2 million years, the Earth's axis flip so the magnetic fields swap. Therefore, when new rock forms, they are magnetically aligned in a different direction. This is why the iron in the rocks are facing different directions because they were formed at different times. his proves the idea of sea-floor spreading because the floor is naturally expanding when the new rock is formed.

Salt mining:

There are 3 ways of obtaining salt.

Salt Mining - This is when rock salt underground is drilled, blast or dug into. It is then brought up to the surface using machinery. This salt is usually quite big and is often used in grit salt to stop ice from forming.

Solution mining - This is when water is deposited into the salt deposit. This dissolves the water to make a solution called brine. Pressure forces the brine to come up to the surface through a piper and then it is stored in a refining plant where all the impurities are filtered out. It is then boiled to make it evaporate and only leave the salt behind.

Both types of mining leave scars on the landscape as well as having a massive impact on the environment. Sometimes land can collapse into the holes (subsidence). The risk of subsidence can be reduced by supporting the mines to ensure that they are stable enough. Also they can be filled in with rocks when they are no longer being used. Additionally, mining uses a lot of energy (especially machinery used to pull substance and salt to the surface). This comes from burning fossil fuels, which causes pollution.

Salt from the sea - This can only be done in hot countries. The water flows into shollow pools and collects there. As a result of the heat, it


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