1. The Earth’s Magnetic Field
B = (X, Y, Z)
Or B = (F, I, D ) Or B = (D, H, Z)
F: intensity
I: inclination
D: declination
H: Horizontal component
The seven elements of the (local) magnetic field in the geographic coordinate system
I. Geomagnetic field – Local Geomagnetic Field Vector

2. The Earth’s Magnetic Field
From this:
Magnetic pole is the point where
H=0 D= +- 90
Magnetic Equator the point where
D=0
F: intensity
I: inclination
D: declination
H: Horizontal component
Where 3000nT<H<6000nT erratic zone (compass work badly)
Where H<3000nT unusable zone (compass does not work)
I. Geomagnetic field – Local Geomagnetic Field Vector

3. Tesla (T) Magnetic flux density = Wb/m^2
Weber (Wb) The weber may be defined in terms of Faraday's law, which relates a changing magnetic flux through a loop to the electric field around the loop. A change in flux of one weber per second will induce an tension of one volt.
T=N/Am
V velocity m/s
E electric field N/C V/m
B=N/Am
BiotSavart Law

4. The numerical interpolation of the data is called
Geomagnetic models. Every 5 yr a new model is released by
The international community now we have the IGRF 2005
From Press, 1992.
90% of spatial field distribution can be explained by a simple dipolar field
I. Geomagnetic field – Geocentric inclined dipole

5. Geomagnetic inclination (IGRF)
The magnetic poles can be independent and do not need to be at the antipodes
I. Geomagnetic field – Worldwide Variation of I

6. The dipolar field is called the MAIN FIELD
It changing slowly (this is why we update the model
Every 5 yr by IAGA)
The external field can change quickly.
How does the field change:
Big diurnal variation and annual variation what can cause it?

7. other secular variation: reversal
Temporal (diurnal and secular) variations
10 nT / hour
other secular variation: reversal
From Butler, Palaeomagnetism, 1992.
Magnetic storm
Slide I. Geomagnetic field – Temporal Variations
Compare: X = 3 nT/km * 33 km/h => 100 nT/h Y = 0.3 nT/km * 33 km/h => 10 nT/h, Thus, diurnal changes matter !

8. other secular variation: reversal
From Butler, Palaeomagnetism, 1992.
Slide I. Geomagnetic field – Temporal Variations

9. PaleoMagnetic Field: Magnetization of Rocks
DRM
Detrital
Remanent
Magnetization
TRM
Thermal
Remanent
Magnetization

10. Secondary Magnetization

11. Dating the Magnetic Reversal

12. PaleoPole position If we measure I we can compute
The original Latitude, from this
If we know the position of the
Sample we compute the
Position of the paleopole.
Note if the plate move we have an
Apparent Polar Wander

13. APW
Apparent Polar Wander

14. Where the magnetic field came from?
Dipole inside the Earth
can not have reversal
b-c) Uniformly magnetic mantle
Or core, mantle of silicate
too hot
d) Current in the core
Most likely

15. Where the magnetic field came from?
Self Sustaining dynamo

16. Where the magnetic field came from?
From Fowler, 2004

17. based on the size and electrical conductivity of the Earth's core, the field, if it were not continually being generated, would decay away in only about 20,000 years since the temperature of the core is too high to sustain permanent magnetism.
The convection in the fluid outer core is thought to be driven by both thermal and compositional buoyancy sources at the inner core boundary that are produced as the Earth slowly cools and iron in the iron-rich fluid alloy solidifies onto the inner core giving off latent heat and the light constituent of the alloy. These buoyancy forces cause fluid to rise and the Coriolis forces, due to the Earth's rotation, cause the fluid flows to be helical. Presumably this fluid motion twists and shears magnetic field, generating new magnetic field to replace that which diffuses away.

18. Since the mechanism of generation of the magnetic field is influenced by the rotation the dipole is mainly oriented along the rotation axis and people use the magnetic pole as past proxy for the rotation axis

19. External Field
MAGNETOSPHERE
IONOSPHERE
Meloni, 1993

20. Interaction with Solar Wind
Meloni, 1993

21. Ocean Spreading
Looking for subs the British and Americans developed a map of
Magnetic anomalies of the sea floor, in 1961 Harry Hess explained
It using seafloor spreading theory.

22. A tape recorder “An essay of GeoPoetry”

23. A tape recorder “An essay of GeoPoetry”

24. Dating the Magnetic Reversal

25. Continental Drift
In 1912 Wegener suggested that the current position of the continents has evolved and that the continents were once fit together in a supercontinent called PANGAEA.

26. Evidences for Continental Drift
The shape of the continent seems to fit together.

27. Evidences for Continental Drift
The shape of the continent seems to fit together.
Matching Geological Units

28. Evidences for Continental Drift
The shape of the continent seems to fit together.
Matching Geological Units
Distribution of Fossils

29. Evidences for Continental Drift
The shape of the continent seems to fit together.
Matching Geological Units
Distribution of Fossils
Distribution of Climatic Belts

30. Evidences for Continental Drift
The shape of the continent seems to fit together.
Matching Geological Units
Distribution of Fossils
Distribution of Climatic Belts
Location of past glacial regions.

31. Evidences for Continental Drift
The shape of the continent seems to fit together.
Matching Geological Units
Distribution of Fossils
Distribution of Climatic Belts
Location of past glacial regions.
BIG PROBLEM!!!!
HOW CAN THE WEAK CONTINENTS MOVE TROUGH THE
STRONG OCEANS?? WHERE THE FORCES TO MOVE
THE CONTINENTS COME FROM???