What it shows
The Earth is made of layers: a thin crust, a thick mantle, a liquid outer core and a solid inner core. The cut-away shows their relative thickness.
The science
The crust is about 5 to 70 km thick, the mantle about 2,900 km, the liquid outer core about 2,200 km and the solid inner core about 1,200 km in radius. Pressure and temperature rise with depth, with the inner core near 5,000 degrees Celsius. It stays solid because of the extreme pressure. Scientists learnt this by studying how earthquake waves travel through the Earth.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A thermocol ball 12 cm wide, or two ball halves
- Clay in four colours
- A kitchen knife or thin wire (adult only)
- Poster paint
- Glue and a toothpick for labels
- A ruler
Safety
For this project: An adult must cut the thermocol. Wear a mask when cutting, because the dust can irritate the nose.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
An adult cuts a quarter wedge out of the thermocol ball so the layers can be seen.
Scoop out the centre to leave a small ball space for the inner core, about 2.5 cm across.
Fill this with a yellow clay ball as the inner core.
Wrap a layer of orange clay as the outer core.
Add a thick layer of red clay as the mantle, making it the biggest layer.
Paint the outside surface a thin layer of brown and green for the crust.
Label each layer with a toothpick flag and its thickness.
Compare the thickness of the crust to the skin of an apple.
What you should see
A cut-away ball showing four layers with the crust as thin as a skin and the mantle as the thickest layer.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which layer is thickest?
The mantle.
2Is the inner core solid or liquid?
Solid, due to extreme pressure.
3How do we know the Earth’s layers?
From earthquake waves.
4What is the crust?
The thin rocky outer layer where we live.
Take it further
Scale the layers to a 12 cm ball and calculate each thickness in centimetres.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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