Earth Layers

The different chemicals making up the layers of the Earth are not evenly distributed. Specific groups of chemicals are believed to be found at the Earth's surface and at different depths below its surface. Thus, the Earth has layers with different chemical compositions.

In this project, you will study and make models of the layers of the Earth as classified by their chemical composition and phase composition. You will calculate the radius or thickness of the Earth's layers as a percentage of the Earth's radius and design a pie chart to show these percentages. You will examine the relation of depth to temperature of the Earth's layers and prepare a table and a graph representing this relation.

Getting Started

Purpose: To make a model of the Earth's three layers based on chemical composition.

Materials

• drawing compass
• metric ruler
• 6-inch (15-cm) square of cardboard
• three lemon-size pieces of modeling clay: one yellow, one red, and one blue
• 12-inch (30-cm) piece of string

Procedure

1. Use the compass to draw a 6.B-cm-diameter circle in the center of the cardboard.
2. Draw a second circle around the first one with a diameter of 12.6 cm. The circumference of this circle will be 2.9 cm from the circumference of the inner circle.
3. Fill the inner circle with yellow clay and the outer circle with red clay.
4. Use the blue clay to make an outline as thin as possible around the circle of red clay (see Figure 10.1).

Results

A circular model with three colored layers is formed. The yellow inner layer has a diameter of 6.8 cm, the red layer is 2.9 cm thick, and the blue layer is very thin.

Why?

The three layers of clay represent the three layers of the Earth according to their chemical composition. Chemical composition refers to the elements and compounds that are present. The yellow inner layer of clay represents the Earth's core (the innermost layer of the Earth). The core is believed to be made mostly of two metals, iron and nickel. With a scale of 1 cm = 1,000 km (625 miles), a diameter of 6.8 cm represents 6,800 km (4,259 miles), which is the average diameter of the Earth's core. The core's thickness is equal to its radius, which is one-half its diameter, or 3,400 km (2,125 miles).

Surrounding the core is the mantle. This layer has a thickness of about 2,900 km (1,812 miles), thus the red clay representing this layer is 2.9 cm thick. The most common chemicals found in this layer are silicates, which are made of the elements silicon and oxygen combined with another element. The silicates in this layer are mostly combined with the elements iron and magnesium.

The outer layer of the Earth is called the crust. This is the layer you live on. Like the mantle, the crust contains large quantities of silicates. The elements combined with the silicates in the crust are largely aluminum, iron, and magnesium. This thin outer layer varies from about 5 to 50 km (3 to 30 miles) in thickness.

Try New Approaches

As a result of pressure and temperature, chemicals can be in a solid, liquid, or gas state. These forms of matter are called phases. On the surface, the Earth is solid, but deep inside the Earth, temperatures are great enough to melt all solid material. While the temperature can melt the solid, in much of the Earth's interior, high pressures do not allow the matter to melt. The balance between temperature and pressure in the Earth's interior varies. Thus, depending on this balance, layers of the Earth can be solid, liquid, or in between. The Earth can be divided into five layers, based on their phase composition (the phase of matter that is present). These five layers are the lithosphere (solid crust and uppermost part of the mantle), the asthenosphere (semiliquid layer of the mantle below the lithosphere), the mesosphere (solid remaining layer of the mantle below the asthenosphere), the outer core (liquid layer below the mesosphere), and the inner core (solid center of the Earth). Repeat the experiment making a model showing these five layers. With a pencil point, draw the boundaries of each layer in the clay. Use toothpicks and round labels to number the layers. Prepare a stand-up legend to identify the names that each number represents. Science Fair Hint: Make labels and a legend for the model in the original experiment. Display the models and legends from both experiments.

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