Earth's Shield of Life: The Changing Magnetic Field

by Eric McLamb
In collaboration with, Dr. Weijia Kuang,
Geophysicist and Applied Mathematician,
NASA Goddard Space Flight Center

Earth’s magnetosphere is shaped by the magnetic field and deflects most harmful radiation away from and around the planet as seen here. Without it, earth would be toast! Read more about Earth’s Shield of Life… (Image: European Space Agency).

Earth’s magnetic field is the planet’s only defense against the sun’s formidable electromagnetic radiation. Without it, the sun would blast away Earth’s atmosphere and all life on the planet would perish.

The magnetic field is generated at Earth’s core which starts about 1,800 miles (2,897 km) beneath its surface with the molten outer core. The outer core – which is made mostly of iron with some nickel — is about 1,400 miles (2,253 km) thick and swirls around the solid inner core. The inner core is approximately 800 miles thick starting at about 3,200 miles (5,150 km) underneath Earth’s surface where the inner core ends.

Earth’s magnetic field is much like a bar magnet with the magentic field lines running from the south magentic pole to the north magentic pole. (Image: NASA Goddard Space Flight Center)

It is the swirling motion of the molten outer core – which produces electricity – around the solid iron inner core that generates Earth’s magnetic field. This field acts like a bar magnet where the magnetic energy flows from the magnet’s south pole to its north pole. It’s the flow of this energy from the planet’s magnetic South Pole to its magnetic North Pole that creates Earth’s magnetic field and subsequently its protective magnetic cocoon called the magnetosphere. Though Earth’s magnetic field is invisible, it can be felt by a compass needle on its surface which is why compasses will point towards the magnetic North Pole (the direction of the flow of magnetic energy).

Continuously Fluctuating Shape

arth’s magnetic field is generated at its core, but these individual field lines are not uniform as seen in the computer simulation above. Thus the magnetic field around the Earth is not uniform and changes as it is generated within the core. (Courtesy: Core and Crustal Magnetics Group in NASA GSFC)

It is the magnetosphere — which extends 45,000 miles into space – that protects Earth from the continuous bombardment of harmful solar electromagnetic radiation. Most solar electromagnetic radiation that hits the magnetosphere is deflected away from Earth around the magnetic field to continue on out into space. It’s the radiation that makes it through this field that creates the auroras as well as problems for human society’s technological infrastructure.

It is not a perfectly symmetrical shroud around the planet, but far from it as it fluctuates with the changes in the planet’s dynamo (electricity generating) core and strength of the individual magnetic field lines. This magnetic cocoon varies in shape and strengths due to fluctuations in the magnetic field generated from the earth’s iron core. Solar activity bends around this magnetic field in more of an oblong shape as it is deflected around Earth and continuing on out into space.

Constantly on the Move

The magnetic poles are constantly moving. Earth’s magnetic poles are located near but not exactly on the planet’s geographic North and South Poles. This is why a compass does not point directly to true north, but it will get you close. The magnetic poles are not connected by a straight geographic line through the Earth like the geographic poles but they are dipolar, meaning the electromagnetic charge flows from the magnetic South Pole to the magnetic North Pole around the earth. This is what forms Earth’s magnetic field.

The current distance between the south magnetic pole – which is located in Antarctica near Russia’s Vostok Station — and the geographic South Pole is approximately 1,776 miles (2,858 km). The magnetic North Pole is located near Canada’s Ellesmere Island and is about 500 miles (800 kilometers) from the geographic North Pole.

Impending Reversal of the Magnetic Field

Earth’s magnetic field lines as depicted before (left) and during a complete pole reversal. (Computer Image: NASA)

The magnetic poles are moving faster than at any time in human history,,, almost 40 miles a year… indicating a reversal may be near. The rapid shifting of the pole’s position has prompted some experts to speculate that the Earth’s entire magnetic field may be preparing to “flip,” which will cause all compasses invert and point south instead of north. It may sound radical, but in geological time, pole reversals are relatively common. Though they typically occur once every 400,000 years or so, it’s been 780,000 years since the last flip… and 10,000 years ago civilization did not exist!

It is the time when the poles completely reverse that Earth will be the most vulnerable to coronal mass ejections (CMEs) and other harmful solar and interstellar radiation that impacts the planet. Should a massive CME directly impact Earth during a period of reversal, the results would likely be severe to the human-dependent technological infrastructure around the world.

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This article is a companion to Earth’s Greatest Threat on Ecology Prime.

(Updated August 1, 2022)