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The Earth is made up of different layers:

1. The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C.
2. The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel.
3. The mantle is the thickest section of the Earth at approximately 2,900 km. The mantle is made up of semi-molten rock called magma.

The theory of plate tectonics

The crust is the outer layer of the Earth. It is a thin layer between 0 - 60 km thick. The crust is the solid rock layer upon which we live. It is either continental or oceanic.

The Earth's crust is broken into tectonic plates. It was once believed that convection currents in the mantle caused the plates to move. However, it is now recognised to be more complicated than this. Mechanisms called slab pull and ridge push are believed to move the tectonic plates. Ridge push is where the new crust formed at divergent plate margins is less dense than the surrounding crust and so it rises to form oceanic ridges. The older seafloor either side of the ridge slides away and this moves the seafloor apart – moving the tectonic plates.

Therefore, instead of tectonic plates moving because of the convection currents, evidence suggests it is the plates that drive the convection. Slab pull occurs where older, denser tectonic plates sink into the mantle at subduction zones. As these older sections of plates sink, newer and less dense sections of plate are pulled along behind. Sinking in one place leads to plates moving apart in other places.

The movement of the plates and the activity inside the Earth, is called the theory of plate tectonics.