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# Fiery Interior: How Can You Make a Model of the Earth's Interior?

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Author: Janice VanCleave

### PROBLEM

How can you make a model of the earth's interior?

### Materials

• 2 sheets of white poster board, each 22 × 28 inches (55 cm × 70 cm)
• Yardstick (meterstick)
• Scissors
• Red crayon

### Procedure

1. On one sheet of the poster board, draw a thermometer and the pie-shaped sections of the earth's interior layers, using the measurements shown in the diagram.
2. Cut out the 22-inch × 4-inch (55-cm × 10-cm) section that is above the thermometer bulb from the poster board.
3. From the second sheet of poster board, cut two strips: one 14 inches × 28 inches (35 cm × 70 cm), and the second 8 inches x 28 inches (20 cm × 70cm).
4. Color one whole side of the narrower strip red.
5. Cut a 100inch (25-cm) slit 4 inches (10 cm) from the short edge of the wider strip. The slit should be centered horizontally.
6. Tape this strip behind the cut-out section of the thermometer.
7. Insert the narrow paper strip into the slit so that the red side shows through the cut-out section of the thermometer.
8. Tape the poster to a door.
9. Slowly pull the red strip down, and observe its height at each layer of the earth's interior.

### Results

Moving the red-colored strip up and down makes the temperature on the thermometer appear to increase and decrease. The temperature goes up as you near the core of the earth, and goes down as you move toward the outer layers.

### Why?

The earth can be divided into three main sections: the crust (the outermost and coolest layer), the mantle (the second layer; hotter than the crust), and the core (the innermost and hottest layer). As the depth toward the center of the earth increases, so does the temperature. Scientists know that the earth's interior is hot because they find hot materials escaping through the surface from below. The temperature of the crust increases by about 86° Fahrenheit (30° C) for every 0.6 miles (1 km) beneath the surface. The cause of the heat is still being investigated, but three possibilities are original heat, radioactive decay (a breaking apart of the nucleus of an atom), and friction (a force that acts against motion) between great masses of rock. The original heat is the remainder of some of the heat trapped inside the earth when the earth was formed. Because radioactive decay and friction produce heat, there is an ongoing heating of the earth's interior.

### LET'S EXPLORE

The layers of the earth vary in size and temperature. Use an earth science text to determine the thickness of each layer and the temperature at the top and bottom of each layer. Add this information to the model of the earth. Science Fair Hint: Display the model as part of your project.

### SHOW TIME!

1. Scientists gain information about the earth's interior by studying its outer layer, the crust. Miners have discovered that high temperatures and great pressures prevent them from drilling at depths greater than about 5 miles (8 km). The molten rock that boils out of volcanoes (openings in the earth's crust from which molten rock pours) gives evidence of the makeup and temperature of the inner mantle layer. Gather these and other examples of how we know about the interior of the earth, and construct a graph with temperature on the vertical scale (bottom to top) and depth on the horizontal scale (left to right).
2. The core of the earth has two layers: the inner core and the outer core. Find out more about the core and the other layers of the earth's interior. Make a clay model of the earth, using four different-colored layers of clay to represent the different layers of the earth. Cut away a quarter section to reveal the layers. Include at least one volcano by making a small lump in the crust and showing the movement of magma from the earth's interior to the surface. Display the model along with a key to indicate which color of clay represents each layer of the earth.

### CHECK IT OUT!

Most of the earth is not visible from the surface. Use an earth science text to discover how seismic waves are used as probes to study the unseen parts of the earth's interior. To learn more about how seismic waves are used to discover information about the earth's structure, see Janice Vaneleaves Earthquakes (New York: Wiley, 1993), by Janice VanCleave.