1. The Earth’s Magnetic Field

3. Source: NASA http://www.nasm.si.edu/research/ceps/etp/earth/img/dipole_earth.gif

4. Source: NASA http://www.nasm.si.edu/research/ceps/etp/earth/img/magneto.gif

5. spher. harmonic analyses

9. magnetic reversals, secular variation

11. Earth’s Magnetic Field Mostly a dipole field (modern and paleomagnetic evidence) Can change direction (polarity) Secular variation (small-scale changes in direction and magnitude)

12. Magnetic Units: Magnetic field – Tesla field mostly described in micro-Tesla or gamma (γ) 1γ = 10 -9 T

13. http://geophysics.ou.edu/solid_earth/notes/mag_earth/earth.htm

16. Mathematical description: Spherical harmonic analyses

18. Short-term changes: Careful measurements since 1600 Navigational purposes

19. http://gsc.nrcan.gc.ca/geomag/nmp/early_nmp_e.php

22. Paleomagnetism – history of the earth’s magnetic field Earth is dipole field –Relationship between Inclination and latitude tan I = 2 tan λ

25. Identification of magnetic minerals in rocks Rocks are assemblages of diamagnetic, paramagnetic, and ferrimagnetic minerals. Concentration of ferrimagnetic minerals is usually very small (< 1 %) Microphotograph of a thin section of norite dolomite limestone sandstone shale Sedimentary rocks Volcanic rocks granite gabbro basalt 1 10 -1 10 -2 10 -3 10 -4 10 -5 Magnetic susceptibility, κ (SI units) Median values and ranges of the magnetic susceptibility in common rock types Modified from Lowrie, 1997

31. Magnetic Polarity

32. Duration of a Polarity Chron

36. Generation of the Magnetic Field No big fat bar magnet Dynamic processes inside the outer core

37. Early (Simplistic) Model

46. Ultimate driver of magnetic field ?

47. Magnetic Field of Other Planets Mercury – yes, but weak Venus – no, or very weak Mars – no clear evidence for field, but might have had field in the past Jupiter – yes, very strong (20,000 times earth) Saturn – yes 500 times earth Uranus – yes, strong tilt with respect to rotational axis

48. Source: NASA http://photojournal.jpl.nasa.gov/jpeg/PIA02008.jpg