Life exists on our Earth, which is due to many factors, among them the magnetic field is the one. Our Earth is a big magnet and has a magnetic field which is essential for survival of life on it. Do you know from where the Earth gets its magnetic property? As we know that the core of Earth is mainly consists of molten iron, electrical currents flowing in the slowly moving molten iron generate the magnetic field of Earth, called "dynamo effect".
Earth's field is also known as geomagnetic field. The presence of a magnetic field acts like a protective shield around the Earth, which saves life on Earth from harmful cosmic rays coming from the outer space and the charge particles and radiations coming from the Sun. The Earth's magnetic field extends millions of kilometers into the space but have very small magnetic field strength.
Earth's magnetic field resembles with the field of a bar magnet and is shown in figure 8.18, where from the Sun side the field is pushed a little inside due to continuous striking solar winds consists of radiations and charged particles. The opposite side of the Earth to the Sun, the field is extended several millions of kilometers.
Aurora (the dancing lights in the sky) at the northern and southern poles of Earth forms due to the magnetic field pattern of Earth. As shown here the charged particles coming from the Sun hit the Earth at poles due to polar cusps of Earth's magnetic field. When these particles enter the atmosphere they ionize the atoms of air (gases) and hence produce light of different colors depending the nature of gas.
If we look at the map of our Earth we see the poles on it, the north-pole is shown at Arctic and the south-pole is at Antarctic. But these poles on map are the geographical poles of the Earth not magnetic poles of Earth. Our Earth spins about its geographical axis (The line joining the geographical poles of the Earth). The magnetic poles of Earth are inclined at an angle of 11.3° to the geographical poles as shown in figure 8.20. Hence the compass needle does not point towards the north-pole shown on maps instead it points 11.3º away towards the magnetic pole.
Magnetism plays a vital role in the survival of life on Earth. It also plays a main role in the behavior of many species living on the planet. Like human's heart and brain produce some magnetic fields for their working, without these fields these organs are of no use. These magnetic fields produced by brain and heart are also used for diagnostic techniques.
In ancient times people use to send messages through pigeons. How they locate their destination to deliver the messages? Iron crystals are found in the beaks of pigeons. These crystals give the bird a nose for north. Pigeons can sense Earth's magnetic field. With the help of this magnetic navigation pigeons locate their destinations. Similarly some other migrating birds have cryptochrome-4 molecule in their eyes, which is sensitive to the magnetism.
Draw by yourself the geographical and magnetic poles of Earth. Also draw magnetic field lines and explain why these lines are different from the field lines of a bar magnet. Similarly some other species use magnetic fields of Earth for different purposes. Migratory animals, birds, sea turtles and whales use the magnetic field of Earth to navigate. They use to migrate in spring and autumn or some in winter and summer using the polarity of north and south.