1. Paleomagnetisch Laboratorium Fort Hoofddijk

2. Magnetic noise Fort Hoofddijk compared to other Uithof building night Fort Hoofddijk Uithof building

3. Magnetism: a bit of history

4. Petrus Peregrinus (1269) Epistola de Magnete Discovered dipole properties of lodestone: first scientific treatise ever written !

5. Pierre de Maricourt AKA Petrus Peregrinus (pilgrim) 1269 AD: Siege of Lucera (Apulia) by armies of Charles d’Anjou Epistola de Magnete Castle of Lucera

6. What is a Magnet ? The Earth …. N S

7. De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure Gilbert (1600) The Earth is a Big Magnet... First known physical property of the Earth (Newton discovered gravity in 1672) William Gilbert (1600):

8. Carl Friedrich Gauss (1838): Mathematical description of the Earth’s magnetic field The Earth is a big magnet

9. Gauss (1838): mathematical description of the geomagnetic field

10. Records (ship logs) used for historical observations of the field Navigation (charts)

11. Jackson, Jonkers & Walker, 2000 Historical Observations: Navigation

12. Jackson, Jonkers & Walker, 2000

13. Earth Magnetic Field: Inclination

14. Plate Tectonics

15. Plate Tectonics: Fossils

16. ~305 Ma

17. Plate Tectonics: Rock types and Mountain belts

18. Plate Tectonics: Apparent Polar Wander Paths 6 7 3 2 4 5 7 6 5 4 3 2 1 d 1

19. North America and Eurasia: Atlantic Ocean as today North America rotated to make a single APWP, so a single pole Apparent Polar Wander Path (APWP)

20. Polarity reversals a dipole reversing at irregular times

21. Bernard Brunhes (1906): field reversals Motonori Matuyama (1926): Reversely magnetized rocks Some more history...

22. Sediments (DSDP) & biostratigraphy Lavas & K/Ar dating GPTS: Geomagnetic Polarity Time Scale Alexey Khramov (1962): Magnetostratigraphy

23. Some more history... Harry Hess (1960): Ocean floor spreading Vine and Matthews (1963): Magnetic anomalies Lawrence Morley (1963): Magnetic anomalies

26. Geomagnetic time scales

27. The Earth is a BIG magnet and protects us … a magnetic shield

29. External Fields: Solar Variation 1‰ of the internal field

30. Magnetic Storms Beautiful auroras ….

31. Magnetic Storms … but also damage (powerplants)

32. Magnetic Storms Magnetic storms have impact: - on satellites & planes - on global telecommunication - on pipelines Natural gas pipeline (Finland) I > 10 Ampere

33. Magnetic Storms: the biggest August 28 th – September 2 nd 1859 - Coronal Mass Ejection - Auroras seen in Hawaii, Cuba, Italy - Field reduced by 1600 nT (~4% of present-day field) March 13 th – 1989 - Coronal Mass Ejection - Auroras seen in Texas - Quebec: in 90 seconds 6 million people were without electricity Ice cores show evidence that events of similar intensity recur at an average rate of approximately once per 500 years. ‘Solar SuperStorm’

34. Origin and significance of the geomagnetic field

35. Let’s start simplest: ‘A Bar Magnet’ at the Centre of the Earth Also called a dipole …. Origin of the Field

36. Poles Geographic vs. Magnetic vs. Geomagnetic Butler, 1992

37. Origin of the Field

38. Secular Variation Averaged over time: Geomagnetic Pole coincides with Rotation Axis Geocentric Axial Dipole hypothesis (GAD)

39. Paleomagnetism 19 th century: Natural remanent magnetization (NRM) directions from ancient rocks like a tape recording... ‘rock music’ of the Earth

40.  D ~65°  I ~20° ~3000 yr Archeomagnetic Observations

41. Secular variation of the field Borssele, in 1615

42. Secular variation: declination

43. Magnetic & geomagnetic poles Northern Hemisphere

44. Magnetic & geomagnetic poles Southern Hemisphere

45. NRC 19-01-2013

46. Is the field decaying ? Consequences for the external magnetic field: ‘Space Weather’

47. Is the Field Decaying ?

48. Next Class: Fysics of magnetism Background reading for Wednesday! Essentials chapter 1