Does the magnetic field have an edge

Moving geomagnetic field

The earth's magnetic field behaves in a similar way to that of an ordinary bar magnet. But there are also crucial differences. The earth's magnetic field is not rigid, but dynamic. Its magnetic poles are constantly in motion. Currently, the magnetic south pole is close to the geographic north pole. At around 40 kilometers a year, it migrates to the northwest. The magnetic north pole in Antarctica is also shifting, away from the geographic south pole.

So the magnetic poles are on the move. But not only that: in the course of history, the polarity of the earth's magnetic field has reversed completely several times. This has happened every 250,000 years on average. The last polarity reversal was about 780,000 years ago. So is another polarity reversal "overdue"? For some years now, experts have been measuring that the earth's magnetic field is becoming weaker. They see this observation as a sign that the Earth's magnetic field is actually slowly reversing: At some point the magnetic south pole will be in Antarctica, the magnetic north pole in the Arctic. Scientists suspect that it will take another 2,000 years for a complete polarity reversal.

The proof that the polarity of the earth's magnetic field has reversed several times is immortalized in the rock. This is particularly evident on the mid-ocean ridges, i.e. at the points where the ocean floor grows: here, glowing-hot rock slurry, which also contains iron, is constantly escaping. As long as this rock pulp is liquid, its iron components align with the current geomagnetic field. When the rock cools down and solidifies, this orientation remains “frozen” in it for a long time. Because it is known how much the ocean floors are growing, the magnetic alignment of this rock can be used to roughly calculate when and how often the polarity of the earth's magnetic field has already reversed.


On an Arctic expedition, polar explorer James Clark Ross discovered the magnetic south pole. His measuring instruments had shown him the way. The magnetic pole is on mainland Canada, about 2,300 kilometers from the geographic North Pole.

In May 1829 the British polar explorer John Ross and his nephew James Clark Ross set off on an expedition to the Arctic. The goal of the two researchers was the Northwest Passage. It is a sea route north of the American continent, which leads through the middle of the icy Arctic Ocean. When the two researchers reached a peninsula with their sailing ships, they discovered: They had reached the northernmost point of the American continent. Because of the huge ice masses and because of technical problems with the ships, they were stuck there. While exploring the mainland, James Clark Ross realized they were near the South Magnetic Pole. With the help of local Inuit, he set off on sledges and reached the Magnetic South Pole on June 1, 1831. The geographic North Pole was about 2,300 kilometers away from them. This makes the Briton James Clark Ross the first European to stay at the magnetic south pole.

When and how the expedition with the research duo Ross will return to Europe is currently not known due to ongoing technical problems.

The Boothia Peninsula

Boothia is the name of the peninsula that polar explorer John Ross discovered in the north of mainland Canada. He named it after his friend, the gin maker Felix Booth. This wealthy English businessman had largely paid for the polar expedition.

The Boothia peninsula is barren: tundra and bare frost debris and rock form the landscape. This is where the Inuit are at home, an ethnic group that is also native to Greenland. They live mainly from hunting seals, whales or polar bears and from fishing. Their means of transportation are kayaks and dog-drawn sleds. Only with the support of these natives was James Clark Ross able to reach the magnetic south pole.

Magnet earth

We don't notice it, but the compass needle clearly shows us that the earth is a giant magnet. It has two magnetic poles, a north pole and a south pole. And like all magnets, the earth is surrounded by a magnetic field: the earth's magnetic field.

In the area of ​​its magnetic field, a magnet exerts force on other magnets, for example on a compass needle. The effect of a magnet can also be made visible through fine iron filings: They are arranged around the magnet and point in the direction of its two poles. A line-like pattern is created that shows the magnetic forces. The lines of this magnetic field are the so-called field lines.

The earth's magnetic field also has such field lines. They emerge from the earth near the south pole, run outside the earth to the north pole and disappear there again into the earth. So they are arranged as if a giant bar magnet were pulling itself through the middle of the earth.

The south pole of this imaginary bar magnet points roughly to the geographic north pole, its north pole to the geographic south pole. What sounds confusing at first has a simple explanation: the north and south poles attract each other. That is why the north pole of the compass needle points to the magnetic south pole of the earth, the south pole on the needle points to the magnetic north pole.

The earth's magnetic field is not only used for orientation on this planet. Together with the atmosphere, it also protects us from dangers from space. One of these threats is a stream of charged particles that the sun is constantly ejecting in all directions. This so-called solar wind is deflected by the earth's magnetic field. Like a capsule, the earth's magnetic field redirects the charged particles so that they fly past the earth and can no longer be dangerous for us.

Why is the earth magnetic at all?

The fact that the earth has a magnetic field is very practical: Among other things, it protects us from charged particles from space (the “solar wind”) and was - at least from GPS - an important aid when navigating the sea and in unknown terrain. But why is the earth magnetic at all?

Explaining this in detail is not that easy - scientists are still researching the details to this day. One thing is clear: the earth's magnetic field is created in the earth's core. It consists mainly of the metals iron and nickel and has a temperature of over 5000 degrees Celsius. The metals in the outer core of the earth have melted and are therefore liquid, and further inside the pressure is so high that the inner core of the earth is solid.

The solid inner core acts like a hotplate: it heats the liquid above, the heated liquid rises and finally meets a slightly cooler layer. There it passes on its warmth and cools itself down a bit in the process. As a result, it sinks back down. This cycle is called "convection flow".

In the outer core of the earth there are currents made of iron - a conductive material. You can almost imagine it like a wire that moves. And we know from a wire that moves in a magnetic field that a voltage is generated (“induced”) in it. This voltage in turn causes electrical current to flow and this again generates a magnetic field.

While the iron masses move in the earth's core, the earth also rotates on its own axis. This has the effect that these liquid flows are additionally twisted. With the right combination of flow movement and earth rotation, this can result in the generated magnetic field being oriented in such a way that it supports and strengthens the original magnetic field. And this amplified magnetic field induces a stronger voltage, which allows a stronger electric current to flow, which further amplifies the magnetic field. In this way, the magnetic field can ultimately keep itself stable.

So at the beginning there must have been a small magnetic field by chance. Driven by the rotation of the earth and geothermal energy, this mechanism has led to this mechanism becoming increasingly stronger. So strong that little by little a magnetic field with a uniform direction has established itself in the entire earth's core. We can then measure this on the surface as the “Earth's magnetic field”.

However, it can also happen that the flow conditions in the core change a little. Then this mechanism, in which the magnetic field is self-sustaining, no longer works so well. As a result, the earth's magnetic field can become weaker overall - and it is even possible that suddenly in one part of the earth's core the opposite direction gains the upper hand and this gradually asserts itself throughout the whole of the earth's core. In the end, the earth's magnetic field has completely reversed: the North Pole became the South Pole and vice versa. Scientists have found that such a “pole reversal” has taken place many times in the past, on average about every 250,000 years.

The ocean floor

The surface of the ocean glistens in a dark blue. It is hard to believe that the sea floor is sometimes many kilometers deeper and that a spectacular underwater landscape is hidden there below. Because the sea floor is not as smooth as the bottom of a swimming pool: On the sea floor there are high mountains, deep trenches and lava-spewing volcanoes as well as extensive plains.

The water in the oceans is not the same depth everywhere. The shallow shelf seas lie around the continents. Here the seabed slopes gently down from the coastline until it reaches a depth of around 200 meters below sea level. The bottom of the shelf seas consists of continental crust. Therefore it actually belongs to the mainland, even if it is washed over by sea water.

Only many kilometers away from the coast, on average after 74 kilometers, does the flat shelf area end with the shelf edge. From this edge it goes down steeply like a slide to a depth of about four kilometers. This steep slope forms the transition to the deep sea, into which no light can penetrate. That's why no plants grow down there. Only a few animal species were able to adapt to this habitat, despite the hostile conditions.

In the midst of the oceans rise mountains, the mid-ocean ridges. These underwater mountains stretch across the world's oceans over long distances. In some places they protrude as islands above sea level. Iceland, for example, lies directly on the mid-Atlantic ridge, the longest mountain range in the world.

Deep trenches also crisscross the oceans. Most of them are in the Pacific. One of them is the Mariana Trench, the deepest trench in the world. It reaches down to 11,034 meters below sea level. Only two people have ever been down there: the oceanographer Jacques Piccard and his companion Don Walsh on their record dive in 1960.

Where plates diverge

A long, deep crack gapes in the earth and is getting wider and wider. Huge forces are tearing the earth's surface to pieces: the East African Rift runs along this break through the continent. Africa began to break up here 20 million years ago. Hot magma from the interior of the earth pushed upwards and tore the earth's crust apart. Since then, the pieces of crust have drifted apart, by about an inch every year. The fact that the earth is very active here can also be seen from the many volcanoes that rise along the rift. Should seawater ever penetrate, the East African Rift will become an ocean. Something similar happened in the Red Sea. The African and Asian continental plates have been separating there for 25 million years. The resulting crack was flooded by sea water.

There where continental Crust breaks apart, one arises Rift valley. Where against it oceanic When pieces of crust move away from each other, mountains grow on the sea floor: the Mid-ocean ridges. They consist of magma that seeps up from the Earth's mantle through the oceanic crust. New sheet material is formed here. It presses itself, so to speak, between two oceanic plates and solidifies to form basalt rock that piles up further and further.

In some places the mid-ocean ridges protrude as islands above sea level. Iceland, for example, and the still young Icelandic island of Surtsey are nothing more than parts of the Mid-Atlantic Ridge. The oceanic crust is constantly growing here due to the replenishment of solidified rock. It not only grows in height, but also to the sides. The two oceanic plates are pushed outwards. Because they spread apart in the process, one also speaks of one Divergence zone.

In this way, new seabed is created and the ocean is slowly getting wider - but only a few centimeters a year. But modern satellites can measure the continents with millimeter precision. From the movement one can calculate that the Atlantic has been 25 meters wider since Columbus' crossing in 1492.

But because the earth as a whole is not getting any bigger, the increase in the seabed has to be compensated for elsewhere. This happens where the oceanic crust is submerged under the continental crust: While the Atlantic continues to grow, the Pacific slowly sinks under the plate margins of America and East Asia.

Polar regions - Arctic and Antarctic

The largest ice sheets on earth are around the North Pole and the South Pole. Because of their special location, the polar regions receive very little sunlight and solar heat, and the summers are particularly short there. That is why it is always extremely cold there - temperatures of down to minus 70 degrees Celsius prevail all year round. The cold caused huge ice masses to form in the polar regions.

The ice of the Arctic around the North Pole covers a large part of the Arctic Ocean in winter. It then extends over an area of ​​several million square kilometers. For the most part, it is a layer of ice that floats on the sea. In addition, the Arctic ice covers the northern areas of Europe, Asia and North America.

On the other hand is the South Pole on a continent that Antarctic. Antarctica is the coldest place on earth. Their landmass is almost completely buried under an armor of ice and snow that is up to 4 kilometers thick. Almost three quarters of the fresh water on earth is stored in this ice.

People, animals and plants have adapted to life in the "eternal ice". Polar bears or reindeer, for example, protect themselves against the cold with a layer of fat and thick fur. The Antarctic is inhabited by only a few people, the Arctic is a little more populated. The most famous inhabitants of the Arctic are the Inuit in North America and Greenland, there are also the Lapps in northern Scandinavia and indigenous peoples in northern Siberia. They used to live there as nomads and get around with dog sleds. Today they use snowmobiles and many of them live in cities.

Hardly anything grows in the ice deserts around the poles because of the extreme cold. The ground between the polar regions and the cold-temperate zone is permanently frozen to a great depth. After the Latin word “permanere” for “to last”, this subsurface is also called permafrost. It only thaws a little a few months a year. Then particularly hardened plants such as mosses, lichens or dwarf shrubs can grow on it. This region around the polar regions is also called subpolar tundra.

The polar regions are the coldest areas on earth. It is precisely here that the earth is heating up: For several years now, researchers have been observing that the ice masses of the Arctic and Antarctic are melting. The consequences of this warming cannot yet be precisely estimated. But it is already clear that many habitats are threatened by the melting of the poles.