1. Earth’s Interior Let’s get to the heart of the Earth By the Lunar and Planetary Institute For use in teacher workshops

2. Image credit: NASA

3. Compositional Crust Mantle Core Physical / Mechanical Lithosphere Asthenosphere Mesosphere Image credit: USGS

4. What We Know - Crust Two types of crust: Two types of crust: Continental Continental 30% of crust 30% of crust 40 Km thick 40 Km thick Oldest is 3.8 billion years (90% solar system age; missing ~700 m.y.) Oldest is 3.8 billion years (90% solar system age; missing ~700 m.y.) Oceanic crust Oceanic crust 5-10 Km thick 5-10 Km thick 200 Ma oldest; 100 Ma average 200 Ma oldest; 100 Ma average Image credit: USGS

5. What We Know - Mantle Density – between crust and core Density – between crust and core 3.3 - 5.5 g/cm 3 3.3 - 5.5 g/cm 3 Samples from volcanic eruptions, basalt composition; lab experiments Samples from volcanic eruptions, basalt composition; lab experiments Image credit: John Lahr, USGS Open-File Report 99-132

6. What We Infer – Core No direct samples No direct samples Probably heavy stuff Probably heavy stuff Liquid outer (molten iron), solid inner (iron, nickel) Liquid outer (molten iron), solid inner (iron, nickel) Image credit: John Lahr, USGS Open-File Report 99-132

7. What We Infer – Core Total density of Earth is ~5,500 km/g 3 Total density of Earth is ~5,500 km/g 3 Avg. surface density is ~3,000 km/g 3 Avg. surface density is ~3,000 km/g 3 Core must be very dense! Core must be very dense! Why iron? Meteorites! Why iron? Meteorites!

8. Earth’s Interior How do we infer the properties of the core? How do we infer the properties of the core?

9. Seismic Waves Earthquakes generate three types of waves – P, S, & surface waves We will just concern ourselves with P & S waves Image credit: USGS

10. Wave Types Transverse (S) Waves – particles move perpendicular to direction of disturbance; rock is moved (sheared) Transverse (S) Waves – particles move perpendicular to direction of disturbance; rock is moved (sheared) Image credit: USGS

11. Wave Types Longitudinal (P) Waves – push-pull waves; particles move parallel to direction of disturbance; rock changes volume (compressed & dilated) Longitudinal (P) Waves – push-pull waves; particles move parallel to direction of disturbance; rock changes volume (compressed & dilated) Image credit: USGS

12. Earthquake Waves P-waves (longitudinal) travel through liquids & solids P-waves (longitudinal) travel through liquids & solids S-waves (transverse) do NOT travel through liquids; solids only S-waves (transverse) do NOT travel through liquids; solids only

13. Earthquake Waves Hint at Internal Layering P-waves (longitudinal) are able to travel through liquids (outer core) S-waves (transverse) are NOT able to travel through liquids (outer core) Image credit: LPI

14. Websites Earthquake data Earthquake data http://www.iris.edu/hq/ TERC’s Exploring Earth FANTASTIC interactive lessons for students about Earth, visualizations, and more. In particular, explore how we have modeled Earth’s internal structure using seismic waves http://www.classzone.com/books/earth_science/terc/content/investigation s/es0402/es0402page04.cfm?chapter_no=investigation TERC’s Exploring Earth http://www.classzone.com/books/earth_science/terc/content/investigation s/es0402/es0402page04.cfm?chapter_no=investigation