Thursday, August 19, 2021

Earth’s magnetic pole reversal, Detailed explanation

The magnetic field of Earth acts like a protective shield around the planet which repels, traps and protects it from charged particles from the Sun and cosmic radiation originating from outer space. But the magnetic poles of Earth do not remain at the same location of Earth rather they change their position and even flip sides!

This field reversal is a very random process and it occurs in a highly irregular pattern.
 According to scientists and researchers, over the last 150-170 million years, the magnetic poles of Earth has reversed its location/direction about 300 times and the last field reversal occurred about 780,000 years ago. Presently Earth appears to be in a period of gradual magnetic field decline and if this process continues, then this weakening of the geomagnetic field could lead to a reversal during the next few thousand years

Geomagnetic field reversals have occurred during all geologic periods however, between 123 million and 83 million years ago, no reversals occurred for 40 million years and many evidence suggests that the rate of geomagnetic field reversals peaked during mass extinctions.[Read – How Voyager reached so far?]

The field reversals might occur along with reversals of convective currents in the core, which is responsible for generating the magnetic field by the dynamo effect. For the case of Earth’s dynamo, very slight rotation rate differences between the solid inner core and the mantle generate the geomagnetic field and the liquid outer core acts as an electrical conductor.

Causes of Earth's magnetic pole reversal
There are many reasons behind the reversal of geomagnetic field such as the reversals in the convective currents in the fluid outer core could be due to the fluctuations in the level of turbulence in the core caused by heat loss at the core-mantle boundary and the growth of the solid inner core, which provides the gravitational energy to power the earth’s dynamo.

Another cause for the reversal of geomagnetic field is due to the changes in core pressure brought on by tectonic events, glaciation, and large meteorite impacts which could cause fluctuations in the core’s turbulence and hence causing the reversal of the geomagnetic field.

How reversal of geomagnetic field takes place?
After a period of thousands to millions of year of stability, a sudden drop in the magnetic field intensity of nearly 20 percent of normal intensity occurs in about 2000 years, which is followed by a delay of about 20,000 years before the actual reversal begins.

The magnetic field then abruptly collapses, reverses, and then slowly builds back to its normal strength. This entire process takes about 10,000 years to complete. After 1,000 years, the field finally regains its full magnetic intensity.

Relation between Earth's magnetic pole reversal and impacts on Earth
According to researchers and scientists, the geomagnetic field has reversed 11 times during the last 4 million years and about half of these magnetic reversals appear to be associated with large impacts. Many scientists have tried to find a correlation between geomagnetic reversal and events taking place on Earth’s surface and a comparison of many geomagnetic reversals with known fluctuations in the climate shows a striking agreement.

Surprisingly last two magnetic reversals correspond to the impacts of large asteroids or comet nuclei and the magnetic reversals occurring 2, 1.9 and 0.7 million years ago also coincides with extreme cold period on Earth. The most striking example of a meteorite impact causing geomagnetic reversal is the 15-mile-wide Ries crater in southern Germany, which dates to about 14.8 million years ago. 

Relation between Earth's magnetic pole reversal and surface temperature of earth
Variations in the magnetic field intensity over the past millions of years show a close agreement with variations in surface temperature of Earth. During geomagnetic field reversal, when Earth lets down its magnetic shield, Earth’s climate cools down, but how? Let us see.

When the magnetic field of Earth weakens, more cosmic rays can penetrate to the lower atmosphere of Earth and warm it, causing a thermal imbalance that affect the climate. Furthermore, when the strength of geomagnetic field is low, the atmosphere is exposed to the solar wind and high-intensity cosmic radiation.

This increased bombardment of air molecules influences the composition of the upper atmosphere of Earth by making more nitrogen oxides, which could block out sunlight and changes the climate. The climate changes resulting from comet strikes could also cause geomagnetic reversal. The comet strikes produce debris and smoke from widespread fires, which cause darkening of the atmosphere and creating cold climatic conditions.

One of the main effect of the drop in temperatures would be increase glaciation of land areas near the Poles and as a result, the accumulation of ice would suddenly drop sea levels. This shift in Earth’s mass due to the accumulation of ice in the polar regions could be sufficient to change its rotation. The change in rotation speed would then disrupt convection currents in the liquid outer core that produces the magnetic field, hence causing it to reverse polarity.

Note that not every comet shower would result in a geomagnetic reversal specially during warm periods when they probably would not cool Earth sufficiently to cause glaciation. 

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