Licchavi Lyceum


Licchavi Lyceum

Fundamentals of Geomagnetism

How magnetic field protects life on Earth?

The magnetic field deflects most of the charged particles (towards Poles) emanating from the Sun in the form of solar winds.

If there were no magnetic field, the particles of the solar wind would strip away the ozone layer, which protects the Earth from harmful ultraviolet rays.

One of the reasons that there is no atmosphere at Mars is that its magnetic field is turned off which led to the loss of carbon dioxide due to scavenging of ions by the solar wind.

How it is formed?

The Earth’s magnetic field is believed to be caused by electric currents in the liquid outer core, which is composed of highly conductive molten iron. The dynamic magma acts like a dynamo and produce magnetic field. American scholar William Gilbert is credited with the study of geomorphology.

Reversal of the fields

Based on data from ancient and new rocks, it has been observed that Earth’s north and south magnetic fields have reversed polarity many times. This is because the polarity of the Earth’s magnetic field is recorded in igneous rocks.

The switching from north to south (an individual reversal event) seems to take around a couple thousand years to complete; once the reversal takes place, periods of stability seem to average about 200,000 years.

It is believed that geomagnetic field is slowing weakening, so Earth might be heading for a long-overdue magnetic reversal.

Intensity gradient of the Geomagnetic Field

The intensity of the geomagnetic field is greatest near the poles and weaker near the Equator. A map of intensity contours of the geomagnetic field is called an isodynamic chart. Isodynamic chart for the Earth’s magnetic field shows that minimum intensity of the magnetic field is over South America while maximum is over northern Canada, Siberia, and the coast of Antarctica south of Australia.

Magnetic Dip (Vertical Component)

Magnetic dip or magnetic inclination is the angle made with the horizontal by the compass needle of a vertically held compass.

Magnetic dip, dip angle, or magnetic inclination is the angle made with the horizontal by the Earth’s magnetic field lines. This angle varies at different points on the Earth’s surface. Positive values of inclination indicate that the magnetic field of the Earth is pointing downward, into the Earth, at the point of measurement, and negative values indicate that it is pointing upward.

Magnetic Declination (Horizontal Component)

The angle in horizontal plane between the Magnetic north axis and Geometric north axis. By convention the declination is positive when Magnetic north is east of Geometric north and vice versa.

Isoclinic lines

Contour lines along which the dip measured at the Earth’s surface is equal are referred to as isoclinic lines.

Magnetic equator

The locus of the points having zero dip is called the magnetic equator or aclinic line.


Directly above the magnetic equator, at altitudes of around 110 km in the atmosphere, a system of electric currents exists that flows from west to east along the magnetic equator. It is known as Equatorial Electrojet.


The study of record of direction and intensity of magnetic field locked in rocks in different geological time period is called Palaeomagnetism.

Frederick Vine and Drummond Matthews

Their work looked at the patterns of magnetic stripes on the ocean floor. If Hess was right, they hypothesized, the symmetrical pattern of stripes was no accident, but indicated that the Earth’s magnetic field switches direction over time, from its current (normal) direction to the opposite (reversed) direction.

When material from the mantle rises up through mid ocean ridges and cools, it preserves a record of the polarity of the Earth’s magnetic field. This is because magnetite in the basalts is strongly magnetic, and aligns with the field when it cools.

Vine and Matthews noticed there was a symmetrical pattern of magnetic stripes on either side of the mid ocean ridges. In addition when the basalts of the sea floor were dated, they were found to be the same age at similar distances away from the ridge on each side. This suggested that the ocean floor was created at the mid ocean ridges, and then was split in half by later activity and pushed sideways.