ESCI A.S2.O1.A3 Inferring Layer Composition

• Trace the lines of scientific evidence (e.g., seismic studies, composition of meteorites, and samples of the crust and mantle) that led to the inference that Earth's core, mantle, and crust are separated based on composition. 
• Trace the lines of scientific evidence that led to the inference that Earth's lithosphere, asthenosphere, mesosphere, outer core, and inner core are separated based on physical properties.

What is Ultrasound?
Ultrasound or ultrasonography is a medical imaging technique that uses high-frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales, and dolphins, as well as SONAR used by submarines (Links to an external site.). In ultrasound, the following events happen:

1. The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe.
2. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue, and bone).
3. Some of the sound waves get reflected (Links to an external site.) back to the probe, while some travel on further until they reach another boundary and get reflected.
4. The reflected waves are picked up by the probe and relayed to the machine.
5. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second).
6. The machine displays the distances and intensities of the echoes on the screen, forming a two-dimensional image.

Now...what does that have to do with Earth's insides?

Scientists use a method that is very similar to ultrasound in order to determine the location, state of matter, density, and thicknesses of Earth's interior layers. The main difference is that instead of using sound waves (we could never produce sound powerful enough to penetrate through the planet) scientists use data from seismic waves! Watch this video to see how.

ESCI A.S2.O1.A3 Earth's Interior VID  Links to an external site.

Meteorites (From CK-12 Links to an external site.) 

Scientists study meteorites to learn about Earth’s interior. Meteorites formed in the early solar system. These objects represent early solar system materials (Figure below Links to an external site.). Some meteorites are made of iron and nickel. They are thought to be very similar to Earth's core Links to an external site.. An iron meteorite is the closest thing to a sample of the core that scientists can hold in their hands!

Density

Earth’s overall density is higher than the density of crustal rocks Links to an external site., so the core must be made of something dense, like metal.

Magnetic Field

Since Earth has a magnetic field, there must be metal within the planet. Iron and nickel are both magnetic.

Summary

• Different types of seismic waves behave differently in different materials. Their behavior can tell scientists about the material they travel through.
• Earth must contain metal. It's density and the fact that it has a magnetic field require it.
• Meteorites formed early in the solar system. They indicate something about Earth's interior.

Your assignment: answer the following questions. Make sure to number them in the submission box.

1. What types of waves do earthquakes produce?
2. What are the fastest body waves?
3. What is the shadow zone?
4. What do S-waves do?
5. List and explain the two types of surface waves.
6. How do scientists know that Earth's interior contains metal?
7. What do meteorites tell us about Earth's interior?
8. How do scientists use seismic waves to learn about Earth's interior?
9. Compare and contrast an ultrasound showing a baby before its birth and the methods used by scientists to determine the structure of Earth's interior.