The Earth's structure and plate movement

The Earth has four main layers - the inner core, the outer core, the mantle and the crust.

• The inner core is 5,500°C - extremely hot. It is a very dense solid made from iron and nickel.
• The outer core is 2,000 km thick and is a liquid.
• The mantle is semi-molten and about 3,000 km thick.
• The crust is the rocky outer layer. It is thin compared to the other sections, approximately 5 to 70 km thick. If the Earth was scaled down to the size of an apple, the crust would be about the thickness of the apple skin. The crust is made up of pieces called plates. There are two types of crust: oceanic and continental crust. The oceanic crust is found under the sea and is thinner and more dense than the continental crust.

Plate movement

It was once believed that heat from the Earth's core caused convection currents in the mantle and that these currents slowly moved the crust around.

It is now thought that plate movement is driven by a mechanism called slab pull. Slab pull occurs where older, denser tectonic plates sink into the mantle. 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 spreading apart in other places.

Earthquakes and volcanoes are primarily found at plate boundaries. The plates are like giant rafts that slowly move around. At the boundaries between plates, molten magma is able to force its way to the surface and escape as lava.