We hope you have heard of the fact that the planet we live on, is itself a giant magnet, and if you haven’t, that’s what this post is all about. Before getting into this, let’s get you some basic ideas on the magnetic field which you would need to know in order to understand this behavior exhibited by some planets like our earth.
Magnetic field
Magnets, as we know, exhibit a unique property that is the result of one of the most fundamental forces in our nature, Electromagnetic force. A Magnet has two poles: North & South. When two magnets with their north poles (Like poles) facing one another are brought close to each other, it’ll end up repelling one another. If the same is done with the unlike poles(South-North), they would attract each other.
These magnetic fields are created with the movement of electron(s) when they are allowed to flow freely. Consider an electron flowing along a circular path, this would result in a current flowing in the same plane but in a direction opposite to the direction of electrons (Conventional electric current). By Fleming’s rule, the electric field, magnetic field, and the force all act in a direction mutually perpendicular to each other. This movement of electron produces a magnetic field perpendicular to the plane containing electric current forming magnetic loops. This is not just the case with electrons but also with ions.
You can check this by piercing a wire through a paper with some iron filings (iron powder) spread uniformly. If you pass the current through the wire then you will find the iron fillings lining themselves up with the magnetic field. This is a clear indication of the magnetic field present along with the current.
Layered planet
Our earth is comprised of several layers. Each layer’s temperature increases as we move deeper towards the center of the planet. The outermost surface (possibly the coolest part) which we live on is known as the crust (0-100 km), mainly comprised of silica and is a perfect solid in nature. Below this is the mantle (100-2900 km) which is somewhat solid with a highly ductile nature and as a result, it experiences what is known as solid-state convection. In this, the hotter portion of the mantle which is near the core of the planet moves up towards the crust and the cooler portion drifts down towards the core. After a while, the part that was drifted down absorbs heat and moves up thus continuing a 500 million years cycle of going up and down. This part is mainly composed of aluminum, magnesium, and silica.
Then comes the core (2900-6370 km) which is divided into 2 regions: the outer core and the inner core. The inner core has considerable iron content and is a dense solid as it experiences greater pressure due to the mass it encompasses. The temperature at this part is almost equal to the surface temperature of the sun (6100°C) while the outer layer is at a temperature close to 4400°C. The outer layer is liquid in nature as the pressure experienced by it is less when compared to the inner core. The outer layer comprises iron, nickel, and some lightweight substances like Sulphur.
Magnetic Earth
The outer core experiences convection similar to the one we saw in the mantle but at a rate faster than that, as it is a liquid. Here the cycle takes place between the mantle and the inner core. On the other hand, the inner core region increases i.e the volume of the solid region increases due to the inner-outer core boundary cooling down over time and thus the boundary keeps growing like an inflating balloon.
During the densification process, iron is trapped into the solid core being a part of its expansion but the lightweight sodium forms plumes that emerge outward due to the convection current. These emerging flumes are composed of ions that raise upwards in a spiral path. This can be imagined as a current flowing in a spiral due to the presence of ions. As we described in the above image, they will be engulfed by a magnetic field around the spiral, perpendicular to the direction of flow of current.
These ionic loops when repeated at several parts will produce magnetic fields in different directions. All these currents and magnetic fields produced combine together to give a resultant magnetic field which makes our earth look like a single bar magnet(Dipole) with localized north and south poles.
The Shield
This magnetic field around the earth extends up to an altitude of 65000 km and does the job of protecting the earth from charged particles that hits the earth from various parts of the solar system. This field is an important reason why life sustains on this planet as they trap enough cosmic rays and also divert the solar storms that occur now and then. This is also the reason why you could see auroras (polar lights) near the poles. But these fields are observed to be weakening and at times they would even change the earth’s north and south poles with the whole world drowning in chaos.
The disappearance of this field would result in:
- High energy particles enter the atmosphere thus ripping it out as the gases will become unstable with their contact.
- With the disappearance of the atmosphere, the atmospheric pressure would drop thus vaporizing all the water molecules present in the planet which makes our condition like mars.
- It is believed that today’s mars had an atmosphere that was destroyed due to the lack of a magnetic field.
- Interaction of these particles with any biological matter will result in ripping off their molecules like DNA, resulting in mutation or a possible extinction.
- This would create an electronic failure all around the globe as our equipment will not be able to handle these particles without proper shielding. We have already faced a powerful solar storm in 1989, hitting Canada which led to blackout all over the country.
A Changing magnetic field is a threat not only to the present day civilization but also for all the other life forms residing on the earth. Maybe our future tech will be able to prevent such disaster from happening but currently we are not anywhere close to such a breakthrough. Till then, with the raging cosmic radiation and the sun in front of us, the hope for life on this planet rests on this field.
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