Other planets have magnetic fields
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 prevailed in the entire earth's core. We can then measure this on the surface as the “Earth's magnetic field”.
But 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.
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 then disappear back 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.
How is the earth structured?
In the beginning, young earth was a hot ball of molten matter. All components were initially well mixed, just as they were distributed when the earth was formed: Metals, rocks, trapped water and gases and much more - a big mess.
But in the course of time that changed: The heavier substances sank down to the center of the earth - especially metals. Rocks, on the other hand, were a little lighter and rose, the lightest to the surface of the earth. There they slowly cooled down and froze.
So the material of the earth separated into the three spherical layers that we know today. You can imagine the structure of the earth like a peach: on the outside a wafer-thin “shell” made of light, solid rock - the Earth crust. On average, it is only 35 kilometers thick.
Under the crust is the "pulp" - the almost 3000 kilometers thick Mantle made of heavy, viscous rock. And inside the earth lies that Earth core from the metals iron and nickel.
The core of the earth itself consists initially of an outer layer about 2200 kilometers thick, the outer core. It is over 5000 degrees Celsius there, which is why the metal has melted and is as fluid as mercury.
That is right inside inner core, slightly smaller than the moon. At over 6000 degrees Celsius, it is a little hotter than the outer core - but surprisingly solid. This is because with increasing depth, not only does the temperature increase, but also the pressure. The outer layers that weigh on the earth's core compress its material so unimaginably that it cannot liquefy.
What is happening inside the earth?
The lava lamp - cult from the 70s: thick bubbles rise slowly in a viscous liquid, sink back to the ground and bubble up again. A similar circular motion of hot, viscous rock also takes place directly under our feet in the interior of the earth. But what is the reason for this?
Regardless of whether it is a lava lamp, water in a saucepan or the earth's mantle, the reason is always the same: When a liquid is heated, warm bubbles rise to the top. This is because the tiny particles that make it up move back and forth more and more as the temperature increases. To do this, they need more space and no longer huddle together so closely. There are now fewer particles in the same volume than in the vicinity, so it is lighter and rises upwards. There this bubble cools down again and the particles take up less space. The volume piece becomes heavier than the surroundings, sinks again and the cycle starts all over again. When a liquid flows in a circle due to a temperature difference, it is also called convection.
In a lava lamp, the heat from the lamp sets the liquid in motion. In the interior of the earth, the hot, solid inner core of the earth is the source of heat. It heats the overlying liquid metal of the outer core of the earth. This rises up and transfers its heat to the earth's mantle, which gradually cools it down. Then it sinks back down, where it heats up again.
A second, similar cycle takes place in the earth's mantle: its heated rock moves upwards from the core towards the earth's crust, to which it in turn gives off heat. After it cools down, it flows down to the Earth's core, where the cycle begins again. Because the earth's mantle rock is very tough, the convection current only moves a few centimeters per year - a cycle lasts a long time.
Due to the rock currents in the earth's interior, great heat and pressure act on the thin earth crust. It cannot always keep up: Every now and then it tears open in individual places and hot rock escapes through volcanoes to the surface of the earth.
Why is the earth warm inside?
The liquid interior of the earth bubbles under our feet. Volcanic eruptions and geysers show the heat there - over 6000 degrees Celsius in the earth's core. But why is it so hot in the earth?
Much of the heat comes from Earth's childhood days when dust and rocks condensed into a planet. The word “condense” sounds a bit too harmless, however: In reality, you have to imagine how many large meteorite impacts - each impact a gigantic explosion that heated up the young planet and melted the material.
Since then it has become a little quieter and the earth is cooling down again. However, it does this extremely slowly, the heat in the interior of the earth can only very slowly escape into space. Hot magma flows in the tough earth mantle transport the heat upwards. There it remains enclosed under the rigid earth's crust as if under a lid. The crustal rock only slowly releases its heat into space.
In addition, heat is still being produced inside the earth. This is because the core of the earth contains a lot of radioactive substances such as uranium. Since our planet was formed, they have been disintegrating and giving off heat over a very long period of time. This “fuel” will last for billions of years.
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 that's not all: 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.
What is the Coriolis Force?
Airplanes flying from New York to Frankfurt have a lot of tailwind. The wind that drives them blows from west to east at a height of about 10 kilometers. Jetstream is the name of this strong air current that can reach speeds of up to 500 km / h. Their direction is the result of the so-called Coriolis force.
It is named after the French scientist Gaspard Gustave de Coriolis, who was the first to examine it mathematically in 1835. The cause of the Coriolis force is the rotation of the earth around its own axis: At the equator, the earth rotates at 1670 kilometers per hour to the east; in the direction of the poles, the speed continues to decrease. When air masses flow from the equator to the North Pole, they take the momentum to the east and then move faster than the earth's surface. Viewed from the surface of the earth, it looks as if they are diverted from their north course to the east - i.e. to the right. Conversely, air masses that flow from the pole to the equator are overtaken by the earth's surface, so on their southward course they are deflected to the west - also to the right.
On the way to the South Pole, the directions are reversed: Air masses on the way to the Pole are diverted from their south course to the east, i.e. to the left - just like the air masses on the north course towards the equator, which are diverted to the west. So the Coriolis force leads to a right deflection in the northern hemisphere and a left deflection in the southern hemisphere, the stronger the closer you get to the poles.
In this way, the Coriolis force influences the global wind system, the great air currents on earth. It therefore has a major influence on the weather: In our latitudes, for example, the air flows towards the North Pole and is therefore deflected to the east. With us, the wind mostly comes from the west, from the Atlantic, and therefore brings more humid air with moderate temperatures. The jet streams also owe their direction to the Coriolis force.
Even tropical cyclones several 100 kilometers in diameter are created with the help of the Coriolis force. Because through them, hot, humid air begins to rotate until it grows into a destructive vortex. The Coriolis force not only affects large air masses, it also deflects ocean currents. This explains why the warm Gulf Stream drifts to the right on its way north and heats large parts of Northern Europe.
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