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Earth's Layers
The Earth's rocky outer layer, or crust, is between 3 and 40 miles thick. The mantle is the layer directly beneath the crust. Approximately 1,800 miles thick, the mantle is the thickest of the Earth's layers. The mantle consists of solid rock but heat and pressure make it malleable enough to move like a thick liquid. The next layer down is called the outer core. The outer core consists of molten rock approximately 1,400 miles thick. The inner core consists of a sphere of solid metal approximately roughly 807 miles around.
Types of Clay
Many different types of clay are available for building a model of the Earth's interior. Baker's clay, for example is made from flour, salt and water. Baker's clay can be colored with food coloring and hardened in the oven. Homemade modeling clay made from salt, cornstarch and water can be air-dried and painted. Non-hardening clays contain oil that keeps them soft. Non-hardening clays can be purchased at any store that carries art supplies or made from flour, water, salt and vegetable oil. Homemade non-hardening modeling clay can be colored with food coloring.
Amounts of Clay
Each of the Earth's layers takes up a different percentage of the Earth's volume. For example, the mantle takes up approximately 82 percent of the Earth's volume so the clay representing the mantle will take up about 82 percent of the model. If the model is 10.5 ounces, about 8.6 ounces of clay would represent the mantle. The Earth's inner core represents about 0.7 percent of the planet's volume. The piece of clay representing the inner core would be less than an ounce.
Building the Model
Make a model of Earth from three balls of clay. A ball about 0.47 inches around represents the inner core. The outer core is represented by a ball 1.18 inches around. The mantle is represented by a ball 2.36 inches around. The crust represents about 1.6 percent of the Earth's volume. At this scale, a piece of clay can't be pressed thinly enough to accurately represent the planet's crust. If the model is built out of clay that hardens, the crust can be painted onto the mantle. If non-hardening clay is used, several pieces of clay flattened as thinly as possible can represent the crust. After the spheres are formed, they are wrapped around each other one at a time until a single sphere is formed. The sphere is then cut in half revealing the layers.