How Earth generates its Magnetic Field?

It was a sunny day 4,000 years ago when a Greek shepherd went out to the open fields in magnesia with the sheep. In the afternoon, he was exhausted and sat on a rock and started poking the pebble in a pool beside the rock. He started noticing that the pebbles are sticking to the iron hook of his crook. Out of curiosity, he wanted to take a look at the pebbles in the pool and tried to make a forward step and suddenly he felt something pulling his shoe to the rock below it. He decided to dig around the rock to find what is the mysterious force, which causes the nails of his shoe and hook to stick to the rock. So, he dug up and found there was nothing but the rock. That was the time when humanity first encountered the property of magnetism. The rock was a loadstone(magnetite) which is then named as magnet by the name of the shepherd Magnes. The second time, its new properties were discovered in China, when a piece of loadstone put on a bronze plate always directed in a particular direction. Later, it was found to be useful for navigation and it led to the exploration of the earth.

What is Magnetism?

Charge and magnetism are two manifestations of the same thing. Particles that are charged also possess magnetic property. It was first discovered in the oersted experiment when a compass placed near a current-carrying wire deflects from its natural position, which is pointing to geographic north and south. It was later found that magnetism is just electrostatic force when viewed in a different frame of reference by relativistic effect. Consider a current-carrying wire and a charge at rest relative to the wire. The wire is neutral as the number of protons and electrons is the same. We see no effect on the charge, but when the charge is moving in the direction of electrons, we see that the charge is deflected. It was considered that the current-carrying wire produces a magnetic field but, it is due to length contraction of changes in the wire which causes the charges in the wire to come closer relative to the charge outside and form a charge difference which by the electrostatic force causes it to deflect from its path. This is how electromagnets work. But for permanent magnets, it’s a different story. As we know, charged particles possess magnetic fields which makes them tiny magnets. Protons and electrons supposed to have a spin which determines their magnetic field direction, but protons are not considered due to their weak field compared to electrons. Electrons that revolve around the nucleus in specific orbitals, produce currents which indeed produce magnetic fields cancel out by the other electron in the same orbital, which produces opposite currents. The overall magnetic field is caused due to the individual unpaired electrons in the outer shell of an atom. As their orbitals are half-filled, electrons in them have the same spin, thus the same magnetic field direction. All these fields add up to give a magnetic orientation to the atom. It is not necessary that elements having half-filled orbitals should have magnetic properties. It depends on their crystal structures and the domains of the material.

How Earth generates its Magnetic Field?

Since the compass is invented, sailors used them to map the earth. Later they found out that compasses point towards the geographical north and south poles of the earth. If the earth is considered as a giant bar magnet then, its magnetic north pole is present at the geographical south pole of the earth. Later, it was discovered that Earth’s magnetic poles do not align with the axis and they are continuously changing their position. Natural magnets (loadstone) are formed such that, when they are in the liquid state, they align to the earth’s magnetic field of that time. Geological pieces of evidence of loadstone having different magnetic orientations show that the Earth’s magnetic field has flipped many times in the past. By this, the myth that the earth is a giant bar magnet is busted. So, the only other way to produce a magnetic field is with currents. To understand how the earth produces its magnetic field we have to know the interior of the earth. Earth’s interior is made up of crust at the top, the mantle in the middle, and the outer and inner core in the center. Crust and mantle are made up of silicate rocks, which are not electrically conductive. (Many people have a belief that mantle is a liquid but it is solid because even though having high temperatures, the pressure is so high that it only allows forming a solid.) The inner and outer core of the Earth contains heavy elements like Iron, Nickel, and their compounds. The outer core is liquid as the temperatures are too high but, the inner core is solid due to the high pressure. The inner core is made up of purely Iron and Nickel but the temperatures inside the earth are way above the curie temperatures of constituent elements (Cure temperature of a material is a tipping point of temperature from which they cannot behave as permanent magnets anymore) Researchers believe that the magnetic field is produced by a Dynamo Effect. It is a process of amplification of the existing magnetic field. Inside the core, as heat is radiated outward, the core grows inside out leaving the lighter elements like sulfur flow to the top. Due to the convection and the Coriolis effect by the earth’s rotation(To know more click https://www.youtube.com/watch?v=HIyBpi7B-dE ), helix patterns are made in the liquid core. These Helix patterns drag the magnetic field and create currents. As the helix patterns are in circles, the currents produced are circular. Circular currents produce magnetic fields which all add up to form a Geomagnetic Field. In this system, even if we take out all the magnetic field, it again attains it because even just with a small and weak field it can be amplified.

Why Earth’s magnetic field is important?

Ever thought that why mars don’t have life? While the obvious answer is that, its atmosphere is so thin to sustain life in it. Mars can maintain an atmosphere with its gravity, but due to the reason that it doesn’t have a magnetic field solar storms took away some part of the atmosphere every time they hit, which led to thinning of the atmosphere. Earth on the other side has a geomagnetic field stretched so wide into space that deflects the solar winds and preserves the atmosphere. Some particles are directed to the poles, where they collide with molecules in the atmosphere and form Aurora.