bearspace.baylor/Vince_Cronin/www/EarthInterior/

1. How does Vince Cronin teach about the basic internal structure of Earth in an introductory physical geology course? http://bearspace.baylor.edu/Vince_Cronin/www/EarthInterior/

2. Earlier we learned... • Earth accreted from stuff in the solar nebula ~4.55 billion years ago

3. Earlier we learned... • Earth accreted from stuff in the solar nebula ~4.55 billion years ago • Early on, Earth was entirely molten: a big drop of liquid

4. Earlier we learned... • Earth accreted from stuff in the solar nebula ~4.55 billion years ago • Early on, Earth was entirely molten: a big drop of liquid • Earth is ~6,371 km in radius and has midriff bulge

5. Earlier we learned... • Earth accreted from stuff in the solar nebula ~4.55 billion years ago • Early on, Earth was entirely molten: a big drop of liquid • Earth is ~6,371 km in radius and has midriff bulge • Earth has a density of ~5.53 times that of liquid water

6. How do we gain direct knowledge of a physical phenomenon?

7. We see something.

8. We see something. (That is, we detect and process electromagnetic radiation in the visible spectrum of ~380 to 775 nanometers.)

9. We hear something.

10. We hear something. (That is, we detect and process variations in pressure with a frequency of between ~20 and 20,000 cycles per second.)

11. We smell something.

12. We smell something. (That is, we detect and process trace amounts of airborne chemical compounds, using chemical receptors in our head.)

13. We feel something.

14. We feel something. (That is, we detect and process information about stresses imposed upon our skin or other stress/pressure sensitive organs.)

15. Can we really trust information that we do not directly sense?

16. How far is it to the center of the Earth?

17. How deep is the deepest mine on Earth?

18. How deep is the deepest well on Earth?

19. If the radius of Earth is represented by a strip of paper that is 5 meters long, how long would the deepest well be at that same scale?

20. 5 meters is to 6,371,000 meters as _____ meters is to 12,261 meters.

21. How do we know what it’s like in the middle of the Earth? After all, we can’t get there from here.

22. Recess Time! (Only Dr. Cronin gets to play)

23. Hoan Bridge in Milwaukee, Wisconsin

25. ~13 seconds direct wave reflected wave average crustal P-wave velocity ~6-7 km/sec Seismograph from Hohn Bridge demolition, Milwaukee, December 2000.

26. Croatian seismologist Andrija Mohorovičić discovered the base of the crust in 1909. In his honor, this fundamental boundary is called the Mohorovičić discontinuity. Because most of us are linguistic wimps, we call it the Moho (rhymes with Ho Ho).

27. If Earth was the same density everywhere, seismic waves would spread out from an earthquake focus (star) in spherical wavefronts (pink curves).

28. The propagation of seismic waves can be represented as rays (red arrows). If Earth was the same density everywhere, the rays would be straight lines.

29. This model for Earth’s interior generates specific predictions about how long it should take for energy from an earthquake to reach specific points on Earth’s surface.

30. Homework Results: Do the observed data support an Earth interior that is the same density throughout? yes - no - maybe so

31. These travel-time predictions have been proven to be wrong. The hypothesis that Earth is the same density throughout has been falsified/ disproven.

35. When energy (sound, light) moves from a material through which it travels with one speed into a material through which it travels at another speed, its path will change by reflecting or refracting (bending).

36. Nerdy Fun Alert: Learn about Snell’s Law on the web, starting with http://www.haverford.edu/physics/songs/snell.htm When energy (sound, light) moves from a material through which it travels with one speed into a material through which it travels at another speed, its path will change by reflecting or refracting (bending).

37. A model of Earth with a simple increase in density (but no change in composition) with depth would result in curved rays propagating from an earthquake focus.

38. This model for Earth’s interior generates specific predictions about how long it should take for energy from an earthquake to reach specific points on Earth’s surface.

39. These travel-time predictions have been proven to be wrong. The hypothesis that Earth is the same composition but increases in density with depth has been falsified/disproven.

40. What do the reproducible observations (i.e., the data) tell us about the inside of Earth?

42. P-wave front emerging from earthquake focus

43. P-wave front emerging from earthquake focus

44. P-wave front emerging from earthquake focus

45. P-wave ray paths radiating perpendicular to wave front. P-wave front emerging from earthquake focus