Wednesday, December 16, 2009



It is quite interesting to know the changes in polarity of the earth’s magnetic field.  Suppose the earth’s magnetic field suddenly shifted means what will happen?  The entire radio communication of the world will get jammed, the birds and animals migration will not happen. Interesting, Is not it?  Let us see more about the earth’s magnetic field.

Around 7,80,000 years ago the earth’s magnetic field was reversed exactly 180 degrees.  For the last few decades scientists and geo physicists have known that earth’s magnetic field has shifted several times in the past.  But the exact timing and causes of these magnetic shifts are still not clear to the scientists.

Firstly we have to recollect some basics of the earths crust. The earth behaves like a giant magnet and its magnetic poles are not strictly aligned with rotational axis of the earth they are inclined about 11 degree and hence the magnetic poles are away form the geographical poles.

 The magnetic effect is caused by the electric current produced by the moving molten matter in the earth’s core.  This is like a dynamo hence the scientists call this theory as Dynamo theory.

Since the changes occurred a long ago it is very tough to know the shifts in the earth’s magnetic field, but it is unfolded by the rocks that makes up the earth’s crust.  When the rocks were formed the prevailing directions of the magnetic fields are frozen inside them. They are magnetized for a long time.

When the igneous rocks formed by the volcanic eruptions, the magnetic materials   present in the molten magma behaved as a magnetic compass needles and they deposited according to the earth’s magnetic field.  For finding this residual magnetism the scientists uses magnetometers and maps the fluctuations in the magnetic field.

In 1960 the French scientist Bernard Brunches determined the present magnetic epoch was happened 780000 years ago and hence it was named after his name.  What he did is, He discovered a series of lava flows with reversal polarity.  After finding them he record the ages of the events happened, by judging the age of the rocks series and makes it possible to date with greater certainty.  This is the only way of dating the rock series.

This procedure has revealed so many hidden secrets.  The rock series of normal and reverse polarity makes a zebra striped symmetry.  This shows the Ocean floor is spreading which is a proof to the Continental drift theory. When the shifting of magnetic field happens, the magnetic poles prefer certain routes such as north south route through America.

At present the magnetic field is weakening noticeably which is the system for a new shifting of earth’s magnetic field is going to happen.

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