Earth’s crust: thinner than you think

Learning objectives:

• that the Earth's crust is a tiny fraction of the Earth’s radius

Timing: 20 minutes (less if the extension calculation activity is not done)

Use a postage stamp stuck on the surface of a football (or similar size balloon) to demonstrate how thin the Earth’s crust is

The average thickness of the crust is 35 km below continents, 6 km below oceans (plus 5 km of sea water). The maximum thickness of the crust is about 90 km, below the Himalayas. The average crustal thickness is around 15 km.

Extension activity

Learning objectives:

• problem solving
• numerical skills
• the use of effective models to aid understanding of an idea

Pupils use the fact that the radius of the Earth averages about 6400 km and the crust 15 km to work out the thickness of a postage stamp. Alternatively, they may use a micrometer to measure the thickness of the postage stamp and devise a method for measuring the radius of a football to check whether this analogy is valid. Pupils could discuss the use of models such as this in science education as an aid to learning and understanding.