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Structure of the Earth

Godfrey Nowlan, GSC
Beverly Ross, Rundle College Junior High School


The Earth is actually a ball of rock that weighs 6.6 sextillion (6.6 x 1021) tons. The outer layer cooled more rapidly and a crust formed. Gravity caused the heavier elements to settle toward the middle where they remain. There are three main zones within our planet: Earth's Core
  • Crust - consists of solid rock and a very thin layer (centimetres to metres) of soil. The crust is approximately 8 km thick under the ocean and 32 km thick where there are continents.
  • Mantle - this zone is 2896 km thick and consists of semi-solid rock. The temperature is around 871°C at the outer part where it meets the crust, but it gets progressively hotter downward. The mantle is in constant motion due to convection currents.
  • Core - this can be divided into an outer core and an inner core. The outer core is 2252 km thick and consists of melted iron and nickel at a temperature of 2200°C. The inner core is 1287 km to the centre of the Earth. It is made of solid iron/nickel at a temperature of 5000 to 7000°C.



  • Hard boiled egg OR Apple
  • Knife
  • Overhead of cut-away Earth


  • Explain to the students that the Earth is very much like an egg or an apple. The shell is thin and can be cracked easily. They can go ahead and do this, but tell them not to peel the shell off yet. Explain that the cracks are similar to plate boundaries, faults and mountain belts within the Earth's crust.
  • Have groups of students carefully cut an egg in half. With a marker, they can make a dot about the size of a pea in the centre of the yolk. This represents the solid inner core of the Earth. The rest of the yolk is the outer core. The white is the semi-solid mantle, and the shell is the crust. The relative proportion in size between shell, white and yolk is a fairly accurate representation of the Earth's layers.

The same activity can be done with an apple but it is not as representative. However, the room ends up smelling a lot better!


    Last Modified: 2004-12-10