Physics

1
Physics Chemistry of the EarthMagnetism

• Jesse Fisher Lawrence

2
Magnets Magnetic Fields

• A magnet is an object with certain materials that
  continuously create a magnetic field. Every
  magnet has at lease two poles (centers of maximal
  magnetic flux). Earth is largely a dipole (di
  means 2).
• North Pole the pole that the magnetic particles
  leave the magnet through.
• South Pole the pole that the magnetic particles
  enter the magnet through.

• Magnetism is a result of quantum spin.
• Protons, neutrons, electrons are made up of
  quarks with up down spin.
• Only atoms with partially filled electron shells
  have a net magnetic moment.
• Only materials with atoms that are aligned can
  have a net magnetic moment.
• Atoms tend to align with an external magnetic
  field.

3
Earths Core

• The Earths core is composed mostly of Iron.
• Iron is highly magnetic.
• The Earths magnetic field orients our compasses.

4
Changes in Magnetic Field

• Over time the Earths magnetic field changes.
• Dipole direction
• Polar drift
• 10s of years to 100s years.
• Reversals
• Average 5,000 years
• Irregular 104-108 years
• Intensity
• Field strength changes with time
• Field strength changes with location
• Over 105 years the average the magnetic North
  Pole is aligned with the axis of spin (True
  North).

5
World Vertical Component Map
6
Declination Inclination
North

• True North North pole as defined by the spin
  axis.
• Magnetic North The direction of magnetic flux.
• Magnetic Declination (D) The horizontal angular
  difference between true and magnetic north.
• Magnetic Inclination (I) The angular difference
  between the horizontal and the flow of magnetic
  flux.

D
East
F
I
Z
7
Declination Inclination
North

• Magnetic Declination
• Magnetic Inclination
• Magnetic Intensity

X
H
D
East
Y
F
I
Z
8
Declination Inclination

• Magnetic Intensity

• Pole Strength P0 and P1
• Magnetic Permeability ?
• Distance/radius r

9
Declination Over Time
10
Magnetic North over Time
11
World Declination Map
12
World Intensity Map
13
Intensity Variation with Time
14
Core Dynamo

• The core was formed through differentiation very
  early in the history of Earth.
• Earth cools, driving heat toward the surface
  through convection.
• Some iron froze as the center cooled.
• High pressure keeps Fe solid at 4000 K.
• The core has grown over the past 1-4 billion
  years.
• The magnetic field is formed in the outer core.

15
Core Dynamo

• Core convection is different inside outside the
  tangent cylinder.
• Tangent Cylinder the North-South cylinder
  bisecting the inner core.
• Outside the rotation of the Earth causes
  convection to organize into columnar flow.
• Flow is predominantly East-West.
• Northern hemisphere moves north
• Southern hemisphere moves south.
• Inside vortices with more radial flow

16
Sun-Earth Interaction
Solar Wind
Magnetosphere
Sun
17
Sun-Earth Interaction
18
Aurora Borealis
19
Magnetic Field Lines
Courtesy of G. Glatzmaier
20
Magnetic Reversals in Oceanic Crust
21
Magnetic Reversals in Oceanic Crust
22
Magnetic Ages Dating
23
Magnetic Dating