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# Earth's Core

## There is an inner and an outer core made of dense metal; it is known from seismic waves and density calculations.

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Practice Earth's Core

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Earth Polygraph 2
Teacher Contributed

## Earth’s Polygraph

Seismographs

### Student Exploration

#### Have you ever caught a friend lying to you about what they were doing and wanted them to take a lie detector test?

Just as a polygraph captures your friend’s nervous twitches, a seismograph captures the Earth’s tremors.

How can seismographs give us insight into the Earth’s secrets? What is the Earth not telling us?

### Extension Investigation

1. Seismograph readings share secrets of the Earth’s interior with scientists. How so? Take a look: http://aspire.cosmic-ray.org/labs/seismic/seismic.swf
1. How can scientists determine the number of layers of the Earth’s interior? List the evidence that they have collected.
2. How can scientists determine the state of matter (solid, liquid, gas) of each layer? List the evidence that they have collected.
3. How can they determine the temperature and density of each layer? List the evidence.
2. Use the Mighty Wave Maker (http://aspire.cosmic-ray.org/labs/seismic/index.htm) to simulate a P-wave, an S-wave, and a surface wave.
1. What happens when you change the density of the material that the wave is traveling through? What would this look like as a seismic wave is travelling through the Earth?
2. What happens when you change the stress direction? Connect each wave type with the appropriate stress direction. Which waves do you expect to cause the most destruction on the surface of the Earth? Why?

### Resources Cited

Astrophysics Science Project Integrating Research and Education (ASPIRE).

### Connections to other CK-12 Subject Areas

#### Earth Science

• Locating Earthquake Epicenters
• Measuring Earthquake Magnitude

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