Introduction to Earth System

1
The Earths Magnetic Field
B (X, Y, Z) Or B (F, I, D ) OrB
(D, H, Z)
F intensity I inclination D declination H
Horizontal component
The seven elements of the (local) magnetic
fieldin the geographic coordinate system
I. Geomagnetic field Local Geomagnetic
Field Vector
2
The Earths Magnetic Field
From this Magnetic pole is the point where H0
D - 90 Magnetic Equator the point where D0
F intensity I inclination D declination H
Horizontal component
Where 3000nTltHlt6000nT erratic zone (compass work
badly) Where Hlt3000nT unusable zone (compass does
not work)
I. Geomagnetic field Local Geomagnetic
Field Vector
3
Tesla (T) Magnetic flux density Wb/m2 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.
TN/Am
V velocity m/s E electric field N/C V/m BN/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)
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 http//www.geophysik.uni-muenchen.de/obse
rvatory/geomagnetism
Big diurnal variation and annual variation what
can cause it?
7
Temporal (diurnal and secular) variations
other secular variation reversal
From Butler, Palaeomagnetism, 1992.
Magnetic storm
Slide I. Geomagnetic field Temporal
Variations
CompareX 3 nT/km 33 km/h gt 100 nT/hY
0.3 nT/km 33 km/h gt 10 nT/h,Thus, diurnal
changes matter !
8
other secular variation reversal
From Butler, Palaeomagnetism, 1992.
Slide I. Geomagnetic field Temporal
Variations
9
PaleoMagnetic FieldMagnetization 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.
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.
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???