Earth's Magnetic Field: Definition & Characteristics

Instructor: Michael Blosser

Michael has a Masters in Physics and a Masters in International Development. He has over 5 years of teaching experience, teaching Physics, Math, and English classes.

This lesson will discuss Earth's magnetic field, why our planet has one, what causes it, and how Earth's magnetic field is essential for the survival of human beings.

An Unknown Field that Is Essential for Life on Earth

You can't see it or feel its presence, and unless you are using a compass you probably won't even notice that it is there. What I am talking about is Earth's magnetic field. Although inconspicuous, Earth's magnetic field is vital for the survival of human beings on this planet. But what is Earth's magnetic field? And how and why did it get here?

Earth's Magnetic Field

The magnetic field surrounding Earth
Earths Magnetic Field

Earth's magnetic field is a magnetic field that emanates from Earth's core and encircles the Earth. It can be looked at as sort of a force field that encompasses the Earth and protects our planet from solar radiation. Without a magnetic field, cosmic rays and radiation would enter our planet, and a form of solar radiation from the sun called the solar wind would strip away Earth's atmosphere, destroying most forms of life on our planet. The famous 'Northern Lights' are caused by the deflection of deadly cosmic rays by the Earth's magnetic field. This 'force field' or magnetosphere that encircles our planet extends several thousands of kilometers into space around Earth.

We can imagine the Earth as one big geomagnet, with a north pole and a south pole. The north pole and south pole are relatively near the top and bottom of the planet, which is why at times we reference the Arctic region as the North Pole and the area near Antarctica as the South Pole. Magnetic field lines extend from both these poles into space to create this magnetosphere around Earth (see photo). Another interesting fact about Earth's magnetic field is that it is tilted at an angle of 10 degrees from the Earth's axis.

Why Does the Earth Have a Magnetic Field?

We have learned that the Earth has a magnetic field that encircles it and acts as a sort of force field that protects us from cosmic radiation and the solar wind. But why does the Earth have a magnetic field? What causes it?

Earth's core is composed of various metals, mostly iron and nickel but also other heavy metals such as gold, platinum and uranium. So is Earth's magnetic field the result of the metals in its core? While most metals have magnetic properties, we have also learned in our studies on magnetism that at extremely high temperatures, such as is the case of the Earth's core, metals lose their magnetic properties. So what causes the Earth's magnetic fields then?

The Earth's magnetic field is the result of what is called the dynamo effect. The dynamo effect is when a rotating electric current creates a magnetic field. The flowing molten metal in Earth's core generates an electric current. And since the Earth is rotating, this creates a magnetic field. Therefore, no flowing metal or no rotation, then no magnetic field. This is believed to be what happened to Mars. Mars, being a rocky planet, has a metal core like Earth, and like Earth it rotates on its axis. However, Mars doesn't have flowing molten metal that would create an electric current. Therefore, scientists believe that Mars, without a magnetic field to protect it from the solar wind, lost most of its atmosphere due to the solar wind ripping it away.

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