Almost everyone has heard of the northern lights. People now book their vacations to Iceland and Norway in the winter to be able to see them. There are also the lesser-known southern lights. Both phenomena are known as the Aurora Borealis and Aurora Australis. But have you ever wondered how they are created?
You see the Earth has a magnetic field — created because our internally active planet has a dynamo spinning away deep below its surface. To understand this magnetic field we have to start with what the Earth is made of. Its innermost layer is the solid iron core (the outer edge of which is about 5,150 kilometers below the surface).
Then comes the outer core — this is a fluid layer made of iron and nickel lying above the solid inner core, at about 2,890 kilometers below the planet’s surface. On top of the outer core is the mantle, which is composed of silicate rocks, rich in iron and magnesium. It is primarily solid but behaves as a viscous fluid over geological time. So, we have the solid inner core, the fluid outer core, the mantle and then the crust. Convection of the mantle generated by the Earth’s rotation allows the tectonic plates of the final layer — the crust — to move and crash into each other, and that’s how we get earthquakes and volcanoes.
The magnetic field on the other hand is created by the motion of convection currents of the fluid outer-core and this magnetic field extends outward like spaghetti. Its extent is known as the magnetosphere, reaching tens of thousands of kilometers into space. Just as we have the geographic north and south poles, the magnetic field gives us the magnetic poles, which although usually located near the geographic poles, are not the same. They are at an angle of around 11 degrees from them.
Let’s go over the different poles that the Earth has. We have the geographic poles, defined by the spot where all the human made longitudinal lines meet and which are also the points where the axis on which the earth rotates meets its surface. Then we have the magnetic poles generated by the magnetic field of the Earth. The Magnetic North Pole is the location where the planet’s magnetic field points vertically downwards. If a compass were used in the Magnetic North Pole, it will point downwards toward the center of the Earth. This will be the opposite at the Magnetic South Pole.
Our magnetic field is extremely useful to us; it protects us from harmful solar winds, which blast us with the Sun’s radiation and solar particles. The field also helps in navigation, and it may have even played a crucial role in the evolution of life.
Now, let’s talk about how the the auroras — or northern and southern lights — come about. When solar winds reach the Earth they hit the magnetic field and the charged particles in both the solar winds and the magnetosphere are disturbed. This results in that the particles becoming ionized, emitting light of varying colors. Red and green are oxygen, and blue is nitrogen — yellow and pink are a mix of these. There is also of course infrared and UV auroras but we cannot see them with the naked eye.
Now while these are magnificent sights, the main thing that the magnetic field does is protect us from harmful solar radiation by deflecting solar wind particles. Life would not exist on this planet if we did not have the magnetosphere. The planet Mars has no magnetosphere because its outer core stopped moving; as a result it lost all of its atmosphere and became uninhabitable. But here is the fascinating bit: The Earth’s magnetic poles move around.
The exact position of the Magnetic North Pole was calculated for the first time in 1831. By 1904, it had moved 50 km (31 mi). In 2001, the Geological Survey of Canada calculated its average position to be 81.3 degrees North by 110.8 degrees West.
Recently, it has been determined that the magnetic north pole has been moving East at an unusually fast pace, heading from the Canadian Arctic toward Siberia at a speed of 55 km (34 miles) per year, although it has slowed recently to 40 km (25 miles) per year. This unusually fast pace led to an earlier than expected update to the World Magnetic Model (which is our mathematical foundation system for navigation). Usually, the model is updated every 5 years with the last one updated in 2015 but due to the new position, it had to be updated in February 2019 instead of 2020, so that our communications and navigation systems can be up to date.
Why is the Magnetic North Pole moving? The answer is that it has always moved, primarily due to the pull and push of the magnetic field. It’s just that this time it moved a little faster than expected. The reason for this is not really known. It could be because the jet of the outer-core is becoming stronger. Or as Phil Livermore from the University of Leeds highlighted at the American Geophysical Union meeting in 2018, it’s a result of a “tug of war” between the two patches of magnetic field; one under Canada and one under Siberia. Historically, the Canadian arm was stronger but now it seems the Siberian arm is taking over.
As mentioned before, the poles have always moved. In fact, there have been times in the Earth’s geological history that they have flipped completely. We know this through rock analysis, which tells us that in the last 20 million years or so, the poles have flipped several times. In 2019, a tree was discovered in New Zealand, which also contains the record of the magnetic field reversal. This tree — called Agathis australis — (kauri in the Maori language), was found in New Zealand’s North Island. Carbon dating revealed that it lived around 41,000 to 42,500 years ago. And it shows that the magnetic field almost reversed at this point, though it did not do a complete flip.
The trend for complete reversal is every 200,000 to 300,000 years, with the last full reversal taking place around 780,000 years ago. So, we are due for one but this process is unpredictable, so no one can tell for sure. The range can be 100,000 years to 50 million years. However, the magnetic north pole has become weak recently, so you never know.
What will happen if the field does a full reversal? Past polar flips have been slow, taking place over thousands of years so nothing dramatic is expected. What will happen is that slowly but surely, the compass needle will move to align with wherever the North Pole is. A greater impact is likely to happen on animals and birds that use the magnetic field to navigate. They will get confused but there has been life on this planet for almost 3 billion years and like before, they will eventually figure it out.
Our main issue will arise if the field continues to get weaker. This is likely to bring in harmful radiation from the Sun, which obviously is a cause for concern. And it has been becoming weaker for about a century or so. In the Southern Hemisphere, we have a weak spot known as the South Atlantic Anomaly that causes problems for low-orbiting satellites. However, we don’t need to panic, because even if it continues to become weaker, it won’t entirely disappear for billions of years. Historically the field has weakened and then become stronger again — a phenomenon known as ‘excursions’.
Another thing that will happen is that the auroras will be visible at lower latitudes because a weaker field would mean solar particles would penetrate more into the Earth’s atmosphere. Of course, with more weakness, there would be more technical problems for our satellites. Overall though, a weak field would not be catastrophic for life on Earth and a complete north south pole reversal would not matter at all. But when it does happen, I think it will be epic!