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

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

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

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

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

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: http://www.geophysik.uni-muenchen.de/observatory/geomagnetism Big diurnal variation and annual variation what can cause it?

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 !

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

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

Secondary Magnetization

Dating the Magnetic Reversal

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

APW Apparent Polar Wander

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

Where the magnetic field came from? Self Sustaining dynamo

Where the magnetic field came from? From Fowler, 2004

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. http://www.es.ucsc.edu/~glatz/geodynamo.html 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.

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

External Field MAGNETOSPHERE IONOSPHERE Meloni, 1993

Interaction with Solar Wind Meloni, 1993

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.

A tape recorder “An essay of GeoPoetry”

A tape recorder “An essay of GeoPoetry”

Dating the Magnetic Reversal

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.

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

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

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

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

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.

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???