1. Understanding Earth Fifth Edition Chapter 14: EXPLORING EARTH’S INTERIOR Copyright © 2007 by W. H. Freeman and Company Grotzinger Jordan Press Siever

2. Compressional wave ConductionConvection Core-mantle boundary Depositional remanent magnetism DipoleGeotherm Lower mantle Low-velocity zone Mohorovičić discontinuity (MOHO) Paleomagnetism Phase change Principle of isostasy Seismic tomography Shadow zone Shear wave Thermo-remanent magnetization Concepts we will use in this class In bold are the ones I consider most important

3. Lecture Outline 1. Exploring the interior with seismic waves 2. Layering and composition of the interior 3. Earth’s internal heat and temperature 4. 3-Dimensional structure of the mantle 5. Earth’s magnetic field

4. Chapter 14 Exploring Earth’s Interior

5. Background facts about Earth’s Interior The center of the Earth is about 6400 km below us … the deepest well is 10 km. The center of the Earth is about 6400 km below us … the deepest well is 10 km. Heat inside the Earth drives the core’s geodynamo and the mantle’s convection. Heat inside the Earth drives the core’s geodynamo and the mantle’s convection. Earth’s interior is explored by using information from seismic waves and their passage through the body of the Earth. Earth’s interior is explored by using information from seismic waves and their passage through the body of the Earth.

6. 1. Exploring the interior with seismic waves ● Basic types of waves ● compressional (P waves) ● shear (S waves) ●Reflection and refraction ● Reflection and refraction

7. 1. Exploring the interior with seismic waves ● Paths of seismic waves ● wave bending (refraction) ● shadow zones (P and S) ●reflection at internal boundaries ● reflection at internal boundaries

8. P-wavepaths

9. S-wavepaths

10. P- and S-wavepaths from an earthquake

11. P-, S-, and surface wave paths: from focus to seismograph

12. P-, S-, and surface waves recorded on a seismograph

13. 2. Layering and composition of the interior (a.k.a. Seismology model of Earth’s layers ) ● crust and lithosphere ● asthenosphere ● mantle with internal phase change at 400 km change at 400 km

14. 2. Layering and composition of the interior ● Seismology model of Earth’s layers (continued) (continued) ● core-mantle boundary ● core (inner and outer core)

15. Earth’slayering revealed by seismology

16. Earth’smantlestructure beneath an old ocean basin:S-wave velocity to depth of 900 km

17. 3. Earth’s internal heat and temperature ● Heat flow through Earth’s interior ● conduction (lithosphere) ● convection (mantle and core)

18. Topography of mid-ocean ridges in the Atlantic and Pacific oceans

19. 3. Earth’s internal heat and temperature ● Temperatures in the Earth ● geothermal gradient ● normally 20 to 30º C / km ● 1300-1400º C at base of lithosphere lithosphere ● 3000-6000º C + in core

20. An estimate of the geotherm: temperature increases with depth in the Earth

21. 4. 3-Dimensional structure of the mantle ● Seismic tomography ● Earth’s gravity field ● The geoid

22. Mantle structure

27. The geoid: shape of planet Earth

28. 5. Earth’s magnetic field and the dynamo ● Earth’s dipole field ● complexity of the magnetic field field ● non-dipole field component component ● secular variations in the field field ● magnetic reversals

29. Change in the location of the Northmagnetic pole from 1600 to 2000

30. Earth’s magnetic field and the geodynamo

32. Earth’smagneticfield and the geodynamo

33. Earth’smagneticfieldlines

34. Earth’smagneticfieldreversals: Step 1

35. Earth’smagneticfieldreversals: Step 2

36. Earth’smagneticfieldreversals: Step 3

37. Earth’smagneticfieldreversals: Step 4

38. 5. Earth’s magnetic field and the dynamo ● Paleomagnetism ● records of magnetization ● thermo-remanent ● depositional remanent ● magnetic stratigraphy ● magnetic stratigraphy

39. Thermoremanent

40. Depositional remanent

42. Magnetic stratigraphy

43. 5. Earth’s magnetic field and the dynamo ● Magnetic field and the biosphere ● magnetic orientation ● magnetic frame of reference ● field offers protection from the solar wind the solar wind