Learning outcomes

• The Earth consists of a core, mantle and crust.

• The core is in the centre, surrounded by the mantle with the crust on the outside.

1. Discuss with the children what they know about the Earth and what it is made of.

Planet Earth was formed about 4.6 billion (4,600 million) years ago - as far as we know - from materials thrown out from the original explosion of the Universe - the Big Bang.

We live on the crust of the Earth which is relatively thin (only 6 -70 km thick) like the skin of an orange. Underneath the crust of the Earth is the Mantle - a layer of rock about 3,000 km thick. In places the mantle is so hot the rock has melted to form a thick, treacle-like substance called magma.

Underneath the mantle is the outer core - made of metal so hot that it is liquid. As the Earth rotates, this layer moves around very slowly producing the Earth’s magnetic field.

At the centre of the Earth is the core. It is solid and made from nickel and iron. It is extremely hot - about 5000 degrees C.                 (background image)

One of the best ways to teach the children about our planet is as follows :-

1. Use plasticine to show the children what the Earth is like inside.
2. Start with a 2 cm diameter ball of plasticine. Explain that this represents the core of the Earth and describe it.
3. Wrap a thick layer of plasticine - about 3 cm thick- of another colour around the first and explain that this is the outer core and is liquid.
4. Wrap a third colour around - about 1cm thick - and explain that this is the mantle and is thick and porridge-like.
5. Now place pieces of blue and green plasticine on the surface and explain that the crust of the Earth is made up of large plates which are very slowly moving.
6. The plasticine model could now have a segment cut out with a very sharp knife and the layers labelled and put on the display table. The model should look like the diagram below.
7. The children could complete worksheet D3 (G) by labelling the parts of the Earth.

The children could investigate how the outer core of the Earth moves by half-filling a dish with water. Now make a disc from a margarine tub lid or thick card and use waterproof colours to make a design on it. Float the disc on the water then turn the dish slowly. Watch what happens to the floating disc. Investigate whether the disc turns at the same speed as the dish - slower or faster? What happens if you change the speed of the dish turning? (if the dish cannot be turned easily try placing it on a metal tray or turn a plate upside-down and put the dish on top - watch it does not fall off!)

(The water in the dish does not rotate at the same speed as the dish. Water at the edges will be dragged by the dish and so will rotate but water further in slips on the outer water and so does not turn as fast)

Extension

Would you get the same effect with a thicker liquid? - try half set jelly then set jelly.

This is similar to the way the layers of the Earth move at different speeds - the crust and mantle rotate but the inner core of thick viscous liquid moves more slowly.