Earth Magnetic field & Paleomagnetism

(Geology Approach on the causes and mechanism of magnetic reversal)

# A magnetic field is a region of space where an object experiences a force by a magnetic source

# Earth magnetic field generates by circulation of liquid iron alloy in the outer core of the earth.

# Earth field is a magnetic dipole, it has two ends of opposite polarity. (north and south magnetic pole)

# Earth magnetic poles move constantly, so averaged over thousands of years, they roughly coincide with Earth’s Geographic poles

# At present however, the magnetic poles lie hundreds of kilometres away from the geographic poles, it tilts about 11 degrees relative to the earth’s Geographic poles (spin axis)

# Magnetic reversals may be the result of changes in circulation patterns in the outer core

# When the earth has reversed polarity, the south magnetic pole lies near the north geographic pole, and the north magnetic pole lies near the south geographic pole. (The Geographic pole does not reverse!)

# Thus, if you were to use a compass during periods of reversed magnetic field, the ‘north-seeking’ end of the needle would point to the south geographic pole. (again the geographic pole does not reverse when the magnetic field reversed)

Paleomagnetism

How does Geologist discover paleomagnetism?

•       Geologist study the magnetic orientation of ancient rock.

• One process happens when magma cools to form rock. As it start to cool and solidify into rock, tiny magnetite crystal begin to grow. The magnetite dipole align with Earth’s magnetic field. With more cooling, dipoles lock into this orientation (as permanent magnetisation)

• Geologist study the Marine Magnetic anomaly ( Sea floor spreading at the Mid oceanic ridge)
• Geologists applied the technique of isotopic dating to determine the ages of rock layers in which they obtained their paleomagnetic measurements, and thus determined when the magnetic field of the earth reversed
• Earth magnetic-reversal chronology shows that reversals do not occur regularly.
• There are four polarity “chrons” that shows normal and reversed polarity of earth magnetic fields. (Gilbert, Gauss, Matuyama and Brunhes)

[Diagram : magnetic chronology :]

Instant Physics! (Magnificent of the earth magnetic field):

• The solar wind interacts with earth magnetic field. Solar wind distorts into a huge teardrop pointing away from the sun to the earth.
• The magnetic field deflects most of the wind so that most of the particles in the wind do not reach earth surfaces.
• The magnetic field, Magnetosphere protect life on earth from dangerous radiation (cosmic rays).
• Some charges particles flow toward Earth’s magnetic poles and cause gases in the atmosphere to glow, forming colourful Aurora in polar skies.

Aurora at polar skies