The Origin

It was first suggested by Gilbert that the Earth rotated because it was magnetic. Blackett who won the Nobel Prize for his work on cosmic rays, considered the opposite possibility, i.e, he suggested that there existed a universal phenomena that any rotating object was intrinsically magnetised. In those days, this theory did not seem such a wild idea. For instance, the electrons. But connecting the earth, Blackett guessed wrong.

Some even suggested that, the magnetic field was due to the presence of magnetic materials in the core of the earth. This theory was later discarded because at such high temperatures, the materials can't retain their magnetism. 

DYNAMO THEORY

The earth's inner core is solid. Outer core is liquid. At such high temperatures, the outher core exists in its ionic form. These ions are in constant motion. This constitutes a current which is associated with a magnetic field. Any electrical conductor moving relative to a magnetic field constitutes a dynamo. The earth's core is a dynamo too....The magnetic field produced generates more current in a self exciting manner. Such self exciting dynamos have been created in the labs too...they do show ocassional flipping.....But none of them can characteristically demonstrate the earth's dynamo.

Now any dynamo would require energy. Where does earth's dynamo get the energy from? Possible theories suggest that the energy for the dynamo is obtained by thermal convection arising from the heat released from the radioactive elements or due to latent heat of fusion due to the gradual soldification of the outer core....

A new theory suggests that, the liquid outer core of the earth at high temperature has plenty of ions in it. The earth's solid core rotates west to east  relative to the mantle. Relative to the solid core, the liquid core rotates east to west. Using Lenz's law, an east to west electric current mus also be induced in the innerpart of the liquid core. By Fleming's right hand rule, a south magnetic pole will be induced at the earth's geographic north pole. Today, the solid core rotates faster than the mantle because its volume is stretched in the N-S axis. But over longer times, its shape changes.It is oscillating between stretched in the N-S axis to stretching in the equitorial axis. When stretched in the equatorial axis, the solid core rotates slower than the mantle, This reverses the direction of the flow of teh liquid core and the induced current. This in turn results in the reversals or 'flipping' of the earth's magnetic field

The earth'z magnetic field

The earth's magnetic field is similar to having a bar magnet placed at the centre of the earth inclined at a small angle to the axis of rotation.

It has a dipole moment of 8*10^22 J/T and the direction of the dipole moment makes an angle of 11.5 degrees with the earth’s axis of rotation. The magnetic field lines emerge from the southern hemisphere at Antarctica and re-enter in the northern hemisphere. So the geographic north pole is actually the magnetic south pole.

The direction of the magnetic field at nay point n the earth is specified in terms of three terms:

1)      the field declination angle

2)      the field inclination angle.

3)      the horizontal component of the earth’s magnetic field

The magnetic declination at any point on the earth is the angle between the geographic meridian and the magnetic meridian. Isogonic lines are the lines where the angle of declination has the same value. The lines where the declination is zero are called agonic lines.

Determination: when we place a compass in the horizontal plane, its needle points to the geomagnetic North Pole. The angle between the needle and the geographic North Pole is the magnetic declination.

Magnetic inclination is the angle that the geomagnetic field is tilted with respect to the surface of the earth.
A magnetometer is a scientific instrument used to measure the strength and/or the magnetic field. Magnetism varies from place to place and differences in  Earth's magnetic field can be caused by the differing nature of rocks and the interaction between charged particles from the  and the sun magnetosphere of a planet. Magnetometers are often a frequent component instrument on spacecraft that explore planets.To know more about them…..http://en.wikipedia.org/wiki/Magnetometer

 

 

The mechanism

The earth's magnetic field has baffled many scientists with its occasional twists and turns....But, the magnetoshphere which is a consequence of this phenomenal property has been holding on to the earth for more than 3.5 billion years. To understand the mechanism of the magnetoshphere....it is very essential to understand the mechanism of the earth's magnetic field....

Not a fairy tale

Call it God's gift or what!!!!!!!!! The magnetosphere is doin' more than juz enough.....It protects the earth from the terribly deadly solar wind and at the same time puts on an awesome spectacle of the aurora borealis for nature lovers and curious onlookers....