Cross Section of the Earth: Egg Modeling
The interior of the Earth is composed of three primary layers: the crust, the mantle, and the core. The outermost layer is the crust. This thin layer, composing only 1 percent of Earth's mass, is made of hard, solid rock. Beneath the crust is the mantle, a layer of solid and molten rock. The mantle is about two-thirds of the mass of Earth. The center of the Earth beneath the mantle is called the core. The core, almost one-third of the mass of the Earth, is divided into a liquid outer region and a solid inner region. Scientists speculate that the core is made primarily of iron and nickel. In this activity you will use a boiled egg to model a cross section of Earth.
Boiled egg (in its shell); Plastic knife; Small cup of water; Pushpin; Paper plate
- Look at the boiled egg and imagine that it represents the Earth. Look at the shell surrounding the egg. What part of the Earth do you think this represents?
- Dip the blade of the plastic knife in water and carefully cut the egg in half lengthwise. Do not peel the egg; cut through the shell as well.
- Examine the inside of one half of the egg. Set the other half aside for the extension activity.
- Use the pushpin to make a small indention in the center of the yolk in the interior of the egg.
- What does the shell of the egg represent? What does the egg white represent? What is represented by the majority of the egg yolk? What does the pinprick inside the yolk represent?
- How is the egg model similar to the real Earth? Which elements in this model are wrong?
- The eggshell represents the Earth's crust, the egg white is the mantle, the yolk represents the core, and the pinprick inside the yolk represents the inner core.
- Answers will vary and could include the fact that the egg and the Earth have similar layers, but the egg and the Earth are not exactly the same shape.
Gently crack the external shell of the unused egg half so that it has several broken segments. What do you think this now represents? Note that these segments can push against one another. What does that represent?