Science Lesson: Waves and Structure

Abstract
In this lesson students will analyze the structure of the Earth’s interior using the findings of two geologists and information from the past week’s lesson.

Purpose –Apply knowledge to determine the physical structure of the Earth.

Objectives
Students will be able to:
1. Create a model of the Earth that is consistent with scientific understanding of earthquake waves.

National Science Education Standard:
CONTENT STANDARD D – Earth and Space Science
THE ORIGIN AND EVOLUTION OF THE EARTH SYSTEM
• Interactions among the solid earth, the oceans, the atmosphere, and organisms have resulted in the ongoing evolution of the earth system. We can observe some changes such as earthquakes and volcanic eruptions on a human time scale, but many processes such as mountain building and plate movements take place over hundreds of millions of years.

Teacher Background
For the past century geologists have described the earth as having 4 layers, the crust, mantle, outer and inner cores. The nature, composition and interaction among these layers is more debatable. Andrija Mohorovicic, a Croatian scientist, established that there was a difference in the velocity that earthquake waves traveled in the mantle as compared to the crust. This difference marked a ‘discontinuity’ that informs us where the mantle and the crust meet. Measuring P and S waves, Mohorovicic also noted that they do not pass through the earth in a straight line. He established that the mantle is denser that the crust.

The German geologist, Beno Gutenberg, also used information about how waves traveled to establish the nature of the earth’s structure.
http://volcano.und.nodak.edu/vwdocs/vwlessons/lessons/Ch1CMB/Content1.html

Earth’s Structure
http://www.zephryus.demon.co.uk/geography/resources/earth/struc.html

Seismic Waves and the Earth’s Interior
http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html

Related and Resource Websites

Earth Science Archives
http://www.madsci.org/posts/archives/mar2001/985815079.Es.r.html

Activity

1. Tell students, “Let us suppose there is an earthquake strong enough so it is felt over the entire world. If the epicenter is in the United States, where would the waves arrive last? [China] Why? [It’s on the other side of the world?] What countries would feel the waves quickly? [Mexico and Canada, etc] Why? [Mexico and Canada are our neighbors]

2. Ask students to remind you how and through what media the P and S waves travel. What else can they tell you about waves? Ask students how we might find the epicenter of an earthquake.

3. Finally, tell students they have been set a challenge. They will be assuming the roles of two geologists, Andrija Mohorovicic and Beno Gutenberg who, separately, were able to use their knowledge along with some advanced math to decipher earthquake information to figure out how earthquake waves propagated and determined the structure of the earth. All their groups will be given is the Earth’s Interior Hand Out. It shows a model of the earth with 6 earthquake epicenters and the locations where resulting waves were felt. Students need to use only this data along with rulers and compasses to answer the question at the bottom of the sheet, “What does the inside of the Earth look like?”

4. Allow students time to work. As they do, circulate and question students to get a grasp of their thinking process and level of understanding. If needed, ask leading questions to get groups back on track.

5. When groups have finished, have them present their findings to the class.

6. Reveal the Earth’s interior to the students. Tell students their activity was somewhat simplified. Actually the P waves are deflected as they travel. This enabled the scientists to determine that the crust is a solid, the mantle is a semi-solid, the outer core is a liquid, and the inner core is a solid. Be sure to understand and use terms such as reflection, refraction, and propagation.

7. Finally, show students the overhead of the Earth’s Interior with curved lines and the computer simulation at Exploring Earth

Embedded Assessment

Can students create a model? Does it show a liquid layer that deflects the S waves?

Homework
Write a 2-3 sentence conclusion in your science notebook.

Embedded Assessment