A team of scientists led by Simon Anzellini made a new discovery. During some experiments, they established new qualities of the solid part of the earth's core
Scientists have found that the iron core of the earth is heated to 6 thousand degrees Celsius, and this information is a thousand degrees higher than previously thought. And this fact now allows us to understand the nature of the magnetic field of our planet.
Simon Ancellin, a member of the French Commissariat for Atomic Energy in Grenoble, and his colleagues were able to calculate the temperature of the Earth's iron core by observing the behavior of iron under ultra-high pressure.
A group of scientists used their own method to determine the properties of iron. A piece of iron was placed inside a diamond anvil and compressed under a pressure of 2.2 million atmospheres, and then heated by a laser beam to 4.5 thousand degrees Celsius.
The experiment was carried out to obtain data that will help scientists determine the temperature of the solid part of the earth's core, in which the pressure reaches 3.3 million atmospheres. To the surprise of scientists, the temperature in the core reached 6-6.5 thousand degrees Celsius, which exceeds earlier ideas by a thousand degrees. As scientists say, the new discovery fits well into the general understanding of scientists about the nature and structure of the planet. And it allows us to explain the cause of the Earth’s magnetic field.
Source of the Earth's magnetic field
The history of the study of the issue of terrestrial magnetism begins in 1600, when the work of William Gilbert, the court physician of the English Queen Elizabeth I, was published, and it was called “On the Magnet, Magnetic Bodies and the Great Magnet - the Earth.” The essence of the work is that the scientist comes to the conclusion that the Earth is a large dipole magnet.
Until the 17th century, this work was the main work on geomagnetism. From the 17th to the 20th centuries, many studies and observations began to take place, which led scientists to new conclusions and properties. At this time, the work of such scientists as Halley Halley, Alexander von Humboldt, Joseph Gay-Lussac, James Maxwell, Carl Gauss is celebrated.
The formation of the theory of electromagnetism by Maxwell in the 70s of the 19th century is quite significant. From his equations it turns out that the magnetic field is formed by electric current. Consequently, this leads to the equivalence of closed elementary currents and magnetic dipoles, the moment of which is also called the magnetic moment of the current. When added, these quantities form, say, the magnetic field of a cylindrical magnet, which is approximately equal to the field of a solenoid of the same length and the same cross-section.
But at the moment, there was no clear idea of where the Earth's magnetic field comes from. Modern scientific works on the nature of geomagnetism indicate the following: “Now, turning to the “big magnet,” the matter at first glance is not so difficult: to find in the middle of the planet current systems of the required configuration and forces that form a field on the Earth’s surface, the structure of which we have studied well. When we head into the Earth, then, having passed the crust, the upper mantle and the lower mantle, we will reach a huge liquid core, the existence of which was determined in the mid-20th century by Harold Jeffreys of the University of Cambridge. The actual liquid state of a large part of the core provides the conclusion of the mechanism for generating the geomagnetic field. The point is that the permanent magnetic field of the Earth is formed by electric currents that appear during the movement of a conducting fluid in the core. Another theory on this issue has not yet been invented.
When we go further and try to understand the essence of the processes of generating the Earth’s geomagnetic field, then it’s time to use the dynamo mechanism for this purpose. In short, we will assume that the formation of a magnetic field in the outer liquid core of the Earth is carried out in the same way as in a self-excited dynamo, where a coil of wires rotates in an external magnetic field. Consequently, due to electromagnetic induction, an electric current arises in the coil and forms its own magnetic field. It increases the external magnetic field, and the current in the coil also increases.
Naturally, the liquid core of the planet is not a dynamo. But when thermal convection appears in a liquid conductor, a certain system of flows of electrically conductive liquid is formed, which is consonant with the movement of the conductor. It would not be a gross violation of nature to assume the existence of certain seed magnetic fields in the nucleus. Consequently, if a liquid conductor, during its relative motion, crosses the lines of force of these fields, then an electric current is formed in it, creating a magnetic field, which increases the external seed field, and this, in turn, increases the electric current and so on, like the song about the pope and his dog, who carelessly ate a piece of meat. The process will continue until a stationary magnetic field is established, when various dynamic processes balance each other."
The earth's magnetic field is the energy of the future
Those who are interested in the history of science and technology certainly know about Tesla's electric car. As historiographical reports state, this car moved thanks to an electric motor, and it drew energy from the space around it. Developers of space systems have long been trying to find its practical application.
Russian scientist Candidate of Physical and Mathematical Sciences Evgeny Timofeev, an employee of RSC Energia, has been working on this problem for many years. He has already managed to create a prototype of such a generator that would generate energy from the Earth's magnetic field. The generator works like this: when the device is set in motion, a sensitive voltmeter registers the occurrence of electromotive force in the circuit. The inventor clarifies that the method of operation of the device is based on the intersection of the Earth's magnetic field with a solenoid, some part of the winding of which is protected by a magnetic shield.
As the scientist states, in terms of practical use of the energy of sunlight, humanity is already much further ahead than the use of the Earth's magnetic field. In some aspects we are at the same level Tesla was at 75 years ago.
The question has always arisen, how does a compass work? And today we will talk about such a thing as the EARTH'S MAGNETIC FIELD. And since, unfortunately, the editor is limited in time, and we want to give something interesting, we will tell you about “terrestrial magnetism” using several different sources.
So:
The Earth's magnetic field has long remained a mystery, because there are no stone magnets, right? But once you discover that there is a colossal amount of iron inside the Earth, everything seems to fall into place. Iron does not form a “permanent” magnet like those attached to plastic piglets and bear cubs, which we, without knowing why, buy to attach to the refrigerator. The bowels of the earth are more like a dynamo. By the way, this is called a geomagnetic dynamo. As we already mentioned, the iron in the Earth's core is mostly in a molten state, with the exception of a solid, dense "ball" at the very center. The liquid part still continues to heat up. Previously, this phenomenon was explained by the fact that radioactive elements, being denser than everything else in the chemical composition of the planet, sank into the very center, being locked there, and the heat is provided by the radioactive energy emitted by them. Modern theory offers a completely different explanation: the liquid part of the core heats up, as the solid part cools down. Molten iron in contact with the solid core itself gradually solidifies, and heat is released. That heat has to go somewhere, it can't just disappear like a breath of warm air - there are thousands of miles of solid rock all around. Heat is transferred to the molten core layer, heating it.
You may be surprised by the fact that the part that comes into contact with the solid core can cool and solidify and, at the same time, heat up during this solidification process. The explanation is simple: hot molten iron rises as it heats up. Remember the hot air balloon. When you heat air, it rises. This happens because when air is heated, it expands, becomes less dense, and less dense substances float above denser ones. The balloon holds air in a huge silk bag, often brightly colored and emblazoned with the logos of banks or real estate agencies, and rises with the air. Hot iron is not painted with anything, but rises in the same way as hot air, moving away from the solid core. It slowly floats up, cooling, and then, when it gets too cold, or rather relatively cold, begins to sink into the depths again. As a result, the earth's core is in continuous motion, heating up inside and cooling outside. It cannot rise all at once, that is, some areas of the core float, while others sink again. This type of circulating heat transfer is called convection.
According to physicists, if certain three conditions are met, moving liquids can create a magnetic field. First, the liquid must conduct electric current, and iron does this very well. Secondly, at least a small magnetic field must initially be present, and there is good reason to believe that our Earth, then still very young, had a certain amount of personal magnetism. Thirdly, something must rotate this fluid, distorting the original magnetic field, and for the Earth such rotation occurs due to the Coriolis force, similar to the centrifugal force, but acting weaker and resulting from the rotation of the Earth around its axis. Roughly speaking, rotation distorts the initially weak magnetic field, twisting it like spaghetti on a fork. The magnetism then rises to the top, caught by the floating masses of the iron core. As a result of all this rotation, the magnetic field becomes much stronger.
Yes, in a sense, you can say that the Earth behaves as if it has a huge magnet inside it, but in reality everything is much more complicated. To make the picture a little more specific, let us recall that there are at least seven other factors that determine the presence of a magnetic field on the Earth. Thus, some components of the earth's crust can be permanent magnets. Like a compass needle pointing north, they gradually lined up with the stronger geomagnetic dynamo, further strengthening it. In the upper layers of the atmosphere there is a layer of charged ionized gas. Before satellites were invented, the ionosphere played a critical role in radio communications: radio waves bounced off charged gas rather than escaping into space. The ionosphere is in motion, and moving electricity creates a magnetic field. At an altitude of about 15,000 miles (24,000 km) flows a ring current—a layer of low-density ionized particles that forms a huge torus. This slightly weakens the strength of the Earth's magnetic field.
The next two factors are the so-called magnetopause and magnetic tail, which arose under the influence of the solar wind on the Earth’s magnetosphere. The solar wind is a constant stream of particles emitted by the hyperactive Sun. The magnetopause is the head wave of the Earth’s magnetic field, moving against the solar wind, and the magnetic tail is the trace of this wave from the opposite side of the planet, where the Earth’s own magnetic field “leaks” outward, moreover, being destroyed under the influence of the solar wind. In addition, the solar wind causes a kind of thrust along the Earth's orbit, creating an additional distortion of the magnetic field lines, known as the field-aligned current in the magnetosphere. And finally, there are auroral flows. The Northern Lights, or aurora borealis, are delightful, mysterious sheets of pale light shimmering in the northern polar sky. A similar performance, aurora australis, can be observed near the South Pole. Auroras are created by two bands of electrical current flowing from the magnetopause into the magnetic tail. This, in turn, creates new magnetic fields and two electric currents - western and eastern.
So, you say, the Earth is just a big magnet? Well, yes, and the ocean is a bowl of water.
Magnetic materials found in ancient rocks indicate that from time to time the Earth's magnetic field changes its polarity, the north magnetic pole becomes the south and vice versa. This happens approximately once every half a million years, although a strict pattern has not been observed. No one knows exactly why this happens, but mathematical models show that the Earth's magnetic field can be oriented equally likely in both directions, with neither direction being stable. Any position sooner or later loses stability and passes the baton to the opposite one. Transitions occur quickly, over about 5 thousand years, while the periods between them are a hundred times longer.
Most planets have magnetic fields, and this fact is even more difficult to explain than the earth’s field. We still have a lot to learn about planetary magnetism.
Alfred Wegener
One of the most impressive properties of our planet was discovered in 1912, but was not taken into account until the 60s. The most convincing evidence in its favor was precisely the change of magnetic poles. The point is that the earth's continents do not stand still, but slowly drift along the surface of the planet. According to a German scientist Alfred Wegener, who was the first to publish his theory, the current separate continents used to be one supercontinent, which he called Pangea(i.e. "The whole earth"). It existed about 300 million years ago.
Surely Wegener was not the first to think of this. His idea was, at least in part, influenced by the striking similarity between the coastlines of Africa and South America. This is especially noticeable on the map. Naturally, Wegener relied on other data. He was not a geologist, but a meteorologist, a specialist in ancient climates, and he was surprised that in regions with a cold climate rocks were found that clearly arose in regions with a warm one, and vice versa. For example, in the Sahara you can still find the remains of ancient glaciers, which are 420 million years old, and in Antarctica you can find fossilized ferns. In those days, anyone would have told him that the climate had simply changed. However, Wegener was convinced that the climate remained almost the same, with the exception of the Ice Age, and that the continents themselves changed, that is, moved. He assumed that they separated as a result of convection in the Earth's mantle, but he was not sure.
This idea was considered crazy, especially since it was not proposed by a geologist, and besides, Wegener ignored all the facts that did not fit into his theory. And the fact that the similarity between Africa and South America is not so ideal, and that continental drift could not be explained. Convection clearly has nothing to do with it, since it is too weak. Great A'Tuin(suspects that A'Tuin is a girl) may carry the whole world on his back, but he is just a fiction, and in the real world, it seems, such forces are simply unthinkable.
We did not use the word “unthinkable” by chance. Many brilliant and respected scientists often repeat the same mistake. They confuse the expression “I don’t understand how this can be” with “It’s completely impossible.” One of these, ashamed as it may be to admit, one of us two, was a mathematician, and an excellent one at that, but when his calculations showed that the earth’s mantle cannot move continents, it did not even occur to him that the theories on which the calculations were based were wrong. His name was Sir Harold Jeffreys, and his problem was that he clearly lacked a flight of fancy, because not only the outlines of the continents on both sides of the Atlantic coincided. From the point of view of geology and paleontology, everything also converged. Take, for example, the fossilized remains of a beast named mesosaur, who lived 270 million years ago in both South America and Africa. It is unlikely that the mesosaur swam across the Atlantic Ocean; rather, it simply lived on Pangea, having managed to settle across both continents when they were not yet separated.
However, in the 60s of the twentieth century, Wegener’s idea was recognized, and his theory of “continental drift” was established in science. At a meeting of leading geologists, a young man named Edward Ballard, who closely resembled Ponder Toups, and two of his colleagues demonstrated the capabilities of a then new device called a computer. They tasked the machine to find the best match not only between Africa and South America, but also North America and Europe, taking into account possible but small changes. Instead of taking the current contours of the coastline, which was not a very bright idea to begin with, allowing opponents of the drift theory to argue that the continents did not coincide, the young scientists used a contour corresponding to a depth of 3,200 feet (1,000 m) below sea level, since, according to in their opinion, it was less subject to erosion. The contours fit well and the geology was so great. And although people at the conference still did not come to a consensus, the theory of continental drift finally received some recognition.
Today we have much more evidence and a clear understanding of the drift mechanism. In the central part of the Atlantic Ocean, halfway between South America and Africa, one of the mid-ocean ridges stretches from south to north (these, by the way, exist in all other oceans). Volcanic materials rise from the depths along the entire ridge and then spread along its slopes. And this has been happening for 200 million years. You can even send a submarine and just watch the process. Of course, a lifetime would not be enough to notice this, but America is moving away from Africa at a rate of 3/4 inch (2 cm) per year. Our nails grow at approximately the same speed, however, modern equipment is capable of recording these changes.
The clearest evidence of continental drift comes from the Earth's magnetic field: rocks on both sides of the ridges have a curious pattern of magnetic stripes that change polarity from north to south and back again, with the pattern on both slopes being symmetrical. This means that the strips froze in the magnetic field as they cooled. When the earth's dynamo changed its polarity from time to time, the rocks of the ridge became magnetized in its field. Then, after the magnetized rocks were separated, identical patterns appeared on opposite sides of the ridge.
The surface of the Earth is not a solid sphere. Both the continents and the ocean floor float on huge, particularly hard plates that can move apart when magma seeps between them. (And most often this happens due to convection in the mantle. Jeffreys simply did not know everything about the movement of the mantle that we know.) There are about a dozen plates, ranging in width from six hundred (1000 km) to six thousand (10,000 km) miles, and they turn around all the time. Where their boundaries touch, rub and slide, earthquakes and volcanic eruptions constantly occur. Especially in the Pacific Fire Belt, which stretches along the entire perimeter of the Pacific Ocean and includes the west coast of Chile, Central America, the United States and beyond the Japanese islands and New Zealand. They are all on the edge of one giant slab. Where the plates collide, mountains arise: one plate ends up under the other and lifts it, crushing and crushing its edge. India is not a part of the Asian continent at all, it simply crashed into it, creating the highest mountains in the world - the Himalayas. It accelerated so much that it still continues its movement, and the Himalayas are growing.
(c) Discworld Science, Terry Pratchett, Jack Cohen, Ian Stewart(In general, read this book; you won’t find a better guide in an entertaining form (but before that, familiarize yourself, in principle, with Pratchett’s “Discworld” series in bibliographical NOT IN ANY POPULAR order)).
Video of the Magnetic Field from Roscosmos:
How does a compass work?
Who hasn't seen a compass? A small thing that looks like a clock with one hand. You twist it and turn it, but the arrow stubbornly turns in one direction. The compass needle is a magnet that rotates freely on the needle. The principle of operation of a magnetic compass is based on the attraction and repulsion of two magnets. Opposite poles of magnets attract, like poles repel. Our planet is also such a magnet. Its strength is small, it is not enough to manifest itself on a heavy magnet. However, a light compass needle, balanced on a needle, also rotates under the influence of a small magnetic field.
sports compass
So that the compass needle does not dangle, but clearly shows the direction regardless of shaking, it must be quite strongly magnetized. In sports compasses, the bulb with the arrow is filled with liquid. Non-aggressive for plastic and metal parts, does not freeze at winter temperatures. The air bubble left in the flask serves as a level indicator to orient the compass in the horizontal plane.
The lead in the study of the Earth's magnetic field belongs to the English scientist William Gilbert. In his book “On the Magnet, Magnetic Bodies and the Great Magnet - the Earth,” published in 1600, he presented the Earth in the form of a giant permanent magnet, the axis of which does not coincide with the axis of rotation of the Earth. The angle between the axis of rotation and the magnetic axis is called magnetic declination.
As a result of this discrepancy, it is not entirely true to say that the compass needle always points north. It points to a point located at a distance of 2100 km from the north pole, on Somerset Island (its coordinates are 75 °, 6 N, 101 ° W - data for 1965). The Earth's magnetic poles are slowly drifting. In addition to such an error in the direction of the arrow (we will call it systematic), we must also not forget about other reasons for the compass not working correctly:
- Metal objects or magnets located near the compass deflect its needle
- Electronic devices that are sources of electromagnetic fields
- Mineral deposits – metal ores
- Magnetic storms that occur during years of strong solar activity distort the Earth's magnetic field.
Now, try answering these questions for the smart ones:
In the meantime, I’ll give you some interesting facts about the Earth’s magnetic field.
It turns out that it weakens by about 0.5% every 10 years. According to various estimates, it will disappear in 1-2 thousand years. It is assumed that at this moment a polarity reversal between the magnet and the Earth will occur. After which the field will begin to increase again, but the north and south magnetic poles will change places. It is believed that this has happened to our planet a huge number of times.
It turns out that migratory birds also navigate “by compass,” or more precisely, the Earth’s magnetic field serves as a guide for them. Recently, scientists have learned that birds have a small magnetic “compass” in the eye area - a tiny tissue field in which magnetite crystals are located, which have the ability to magnetize in a magnetic field.
You can make a simple compass yourself. To do this, leave the sewing needle next to the magnet for several days. After this, the needle will be magnetized. After moistening it with fat or oil, carefully lower the needle onto the surface of the water poured into the cup. The fat will not let it sink, and the needle will turn from north to south (or vice versa:).
Are you impressed? Now you can check your answers to the questions:
- Where do you think the compass needle will point if you are between the north geographic pole and the north magnetic pole?
- The northern end of the arrow will point... to the south, and the southern end - to the north! - Where does the arrow point when the compass is near the magnetic pole?
- it turns out that an arrow suspended on a thread in the area of the magnetic pole tends to turn around... downwards, along the magnetic lines of the Earth! - If, guided by a compass, you walk strictly to the northeast for a very long time, then where will you end up?
– you will come to the north magnetic pole! Try to trace your path on the globe, it turns out to be a very interesting route.
and this is what the sea compass on Columbus's ship might have looked like
We hope you enjoyed this material. If yes, then we will make more of these different ones!
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According to modern ideas, it was formed approximately 4.5 billion years ago, and from that moment our planet has been surrounded by a magnetic field. Everything on Earth, including people, animals and plants, is affected by it.
The magnetic field extends to an altitude of about 100,000 km (Fig. 1). It deflects or captures solar wind particles that are harmful to all living organisms. These charged particles form the Earth's radiation belt, and the entire region of near-Earth space in which they are located is called magnetosphere(Fig. 2). On the side of the Earth illuminated by the Sun, the magnetosphere is limited by a spherical surface with a radius of approximately 10-15 Earth radii, and on the opposite side it is extended like a comet's tail over a distance of up to several thousand Earth radii, forming a geomagnetic tail. The magnetosphere is separated from the interplanetary field by a transition region.
Earth's magnetic poles
The axis of the earth's magnet is inclined relative to the earth's rotation axis by 12°. It is located approximately 400 km away from the center of the Earth. The points at which this axis intersects the surface of the planet are magnetic poles. The Earth's magnetic poles do not coincide with the true geographic poles. Currently, the coordinates of the magnetic poles are as follows: north - 77° north latitude. and 102°W; southern - (65° S and 139° E).
Rice. 1. The structure of the Earth’s magnetic field
Rice. 2. Structure of the magnetosphere
Lines of force running from one magnetic pole to another are called magnetic meridians. An angle is formed between the magnetic and geographic meridians, called magnetic declination. Every place on Earth has its own declination angle. In the Moscow area the declination angle is 7° to the east, and in Yakutsk it is about 17° to the west. This means that the northern end of the compass needle in Moscow deviates by T to the right of the geographic meridian passing through Moscow, and in Yakutsk - by 17° to the left of the corresponding meridian.
A freely suspended magnetic needle is located horizontally only on the line of the magnetic equator, which does not coincide with the geographical one. If you move north of the magnetic equator, the northern end of the needle will gradually descend. The angle formed by a magnetic needle and a horizontal plane is called magnetic inclination. At the North and South magnetic poles, the magnetic inclination is greatest. It is equal to 90°. At the North Magnetic Pole, a freely suspended magnetic needle will be installed vertically with its northern end down, and at the South Magnetic Pole its southern end will go down. Thus, the magnetic needle shows the direction of the magnetic field lines above the earth's surface.
Over time, the position of the magnetic poles relative to the earth's surface changes.
The magnetic pole was discovered by explorer James C. Ross in 1831, hundreds of kilometers from its current location. On average, it moves 15 km in one year. In recent years, the speed of movement of the magnetic poles has increased sharply. For example, the North Magnetic Pole is currently moving at a speed of about 40 km per year.
The reversal of the Earth's magnetic poles is called magnetic field inversion.
Throughout the geological history of our planet, the Earth's magnetic field has changed its polarity more than 100 times.
The magnetic field is characterized by intensity. In some places on Earth, magnetic field lines deviate from the normal field, forming anomalies. For example, in the area of the Kursk Magnetic Anomaly (KMA), the field strength is four times higher than normal.
There are daily variations in the Earth's magnetic field. The reason for these changes in the Earth's magnetic field is electric currents flowing in the atmosphere at high altitudes. They are caused by solar radiation. Under the influence of the solar wind, the Earth's magnetic field is distorted and acquires a “trail” in the direction from the Sun, which extends for hundreds of thousands of kilometers. The main cause of the solar wind, as we already know, is the enormous ejections of matter from the solar corona. As they move towards the Earth, they turn into magnetic clouds and lead to strong, sometimes extreme disturbances on the Earth. Particularly strong disturbances of the Earth's magnetic field - magnetic storms. Some magnetic storms begin suddenly and almost simultaneously across the entire Earth, while others develop gradually. They can last for several hours or even days. Magnetic storms often occur 1-2 days after a solar flare due to the Earth passing through a stream of particles ejected by the Sun. Based on the delay time, the speed of such a corpuscular flow is estimated at several million km/h.
During strong magnetic storms, the normal operation of the telegraph, telephone and radio is disrupted.
Magnetic storms are often observed at latitude 66-67° (in the aurora zone) and occur simultaneously with auroras.
The structure of the Earth's magnetic field varies depending on the latitude of the area. The permeability of the magnetic field increases towards the poles. Over the polar regions, the magnetic field lines are more or less perpendicular to the earth's surface and have a funnel-shaped configuration. Through them, part of the solar wind from the dayside penetrates into the magnetosphere and then into the upper atmosphere. During magnetic storms, particles from the tail of the magnetosphere rush here, reaching the boundaries of the upper atmosphere in the high latitudes of the Northern and Southern Hemispheres. It is these charged particles that cause the auroras here.
So, magnetic storms and daily changes in the magnetic field are explained, as we have already found out, by solar radiation. But what is the main reason that creates the permanent magnetism of the Earth? Theoretically, it was possible to prove that 99% of the Earth’s magnetic field is caused by sources hidden inside the planet. The main magnetic field is caused by sources located in the depths of the Earth. They can be roughly divided into two groups. The main part of them is associated with processes in the earth's core, where, due to continuous and regular movements of electrically conductive matter, a system of electric currents is created. The other is due to the fact that the rocks of the earth’s crust, when magnetized by the main electric field (the field of the core), create their own magnetic field, which is summed with the magnetic field of the core.
In addition to the magnetic field, there are other fields around the Earth: a) gravitational; b) electric; c) thermal.
Gravitational field The earth is called the gravity field. It is directed along a plumb line perpendicular to the surface of the geoid. If the Earth had the shape of an ellipsoid of revolution and masses were evenly distributed in it, then it would have a normal gravitational field. The difference between the intensity of the real gravitational field and the theoretical one is a gravity anomaly. Different material composition and density of rocks cause these anomalies. But other reasons are also possible. They can be explained by the following process - the equilibrium of the solid and relatively light earth's crust on the heavier upper mantle, where the pressure of the overlying layers is equalized. These currents cause tectonic deformations, the movement of lithospheric plates and thereby create the macrorelief of the Earth. Gravity holds the atmosphere, hydrosphere, people, animals on Earth. Gravity must be taken into account when studying processes in the geographic envelope. The term " geotropism" are the growth movements of plant organs, which, under the influence of the force of gravity, always ensure the vertical direction of growth of the primary root perpendicular to the surface of the Earth. Gravity biology uses plants as experimental subjects.
If gravity is not taken into account, it is impossible to calculate the initial data for launching rockets and spacecraft, to carry out gravimetric exploration of ore deposits, and, finally, the further development of astronomy, physics and other sciences is impossible.
In 1905, Einstein named the cause of terrestrial magnetism one of the five main mysteries of contemporary physics.
Also in 1905, the French geophysicist Bernard Brunhes carried out measurements of the magnetism of Pleistocene lava deposits in the southern department of Cantal. The magnetization vector of these rocks was almost 180 degrees with the vector of the planetary magnetic field (his compatriot P. David obtained similar results even a year earlier). Brunhes came to the conclusion that three quarters of a million years ago, during the outpouring of lava, the direction of the geomagnetic field lines was opposite to the modern one. This is how the effect of inversion (reversal of polarity) of the Earth's magnetic field was discovered. In the second half of the 1920s, Brunhes's conclusions were confirmed by P. L. Mercanton and Monotori Matuyama, but these ideas received recognition only by the middle of the century.
We now know that the geomagnetic field has existed for at least 3.5 billion years, and during this time the magnetic poles have swapped places thousands of times (Brunhes and Matuyama studied the most recent reversal, which now bears their names). Sometimes the geomagnetic field maintains its orientation for tens of millions of years, and sometimes for no more than five hundred centuries. The inversion process itself usually takes several thousand years, and upon completion, the field strength, as a rule, does not return to its previous value, but changes by several percent.
The mechanism of geomagnetic inversion is not entirely clear to this day, and even a hundred years ago it did not allow for a reasonable explanation at all. Therefore, the discoveries of Brunhes and David only reinforced Einstein’s assessment - indeed, terrestrial magnetism was extremely mysterious and incomprehensible. But by that time it had been studied for over three hundred years, and in the 19th century it was studied by such stars of European science as the great traveler Alexander von Humboldt, the brilliant mathematician Carl Friedrich Gauss and the brilliant experimental physicist Wilhelm Weber. So Einstein truly looked at the root.
How many magnetic poles do you think our planet has? Almost everyone will say that two are in the Arctic and Antarctic. In fact, the answer depends on the definition of the concept of pole. Geographic poles are considered to be the points of intersection of the earth's axis with the surface of the planet. Since the Earth rotates as a rigid body, there are only two such points and nothing else can be thought of. But with magnetic poles the situation is much more complicated. For example, a pole can be considered a small area (ideally, again a point) where the magnetic lines of force are perpendicular to the earth's surface. However, any magnetometer records not only the planetary magnetic field, but also the fields of local rocks, ionospheric electric currents, solar wind particles and other additional sources of magnetism (and their average share is not so small, on the order of several percent). The more accurate the device, the better it does this - and therefore makes it increasingly difficult to isolate the true geomagnetic field (it is called the main one), the source of which is located in the depths of the earth. Therefore, pole coordinates determined by direct measurement are not stable even over a short period of time.
You can act differently and establish the position of the pole on the basis of certain models of terrestrial magnetism. To a first approximation, our planet can be considered a geocentric magnetic dipole, the axis of which passes through its center. Currently, the angle between it and the earth's axis is 10 degrees (several decades ago it was more than 11 degrees). With more accurate modeling, it turns out that the dipole axis is shifted relative to the center of the Earth towards the northwestern part of the Pacific Ocean by about 540 km (this is an eccentric dipole). There are other definitions.
But that's not all. The Earth's magnetic field actually does not have dipole symmetry and therefore has multiple poles, and in huge numbers. If we consider the Earth to be a magnetic quadrupole, a quadrupole, we will have to introduce two more poles - in Malaysia and in the southern part of the Atlantic Ocean. The octupole model specifies the eight poles, etc. The modern most advanced models of terrestrial magnetism operate with as many as 168 poles. It is worth noting that during the inversion, only the dipole component of the geomagnetic field temporarily disappears, while the others change much less.
Poles in reverse
Many people know that the generally accepted names of the poles are exactly the opposite. In the Arctic there is a pole to which the northern end of the magnetic needle points - therefore, it should be considered southern (like poles repel, opposite poles attract!). Likewise, the magnetic north pole is based at high latitudes in the Southern Hemisphere. However, traditionally we name the poles according to geography. Physicists have long agreed that lines of force come out of the north pole of any magnet and enter the south. It follows that the lines of earth's magnetism leave the south geomagnetic pole and are drawn towards the north. This is the convention, and you shouldn’t violate it (it’s time to remember Panikovsky’s sad experience!).
The magnetic pole, no matter how you define it, does not stand still. The North Pole of the geocentric dipole had coordinates of 79.5 N and 71.6 W in 2000, and 80.0 N and 72.0 W in 2010. The true North Pole (the one revealed by physical measurements) has shifted since 2000 from 81.0 N and 109.7 W to 85.2 N and 127.1 W. For almost the entire twentieth century it did no more than 10 km per year, but after 1980 it suddenly began to move much faster. In the early 1990s, its speed exceeded 15 km per year and continues to grow.
As Lawrence Newitt, the former head of the geomagnetic laboratory of the Canadian Geological Research Service, told Popular Mechanics, the true pole is now migrating to the northwest, moving 50 km annually. If the vector of its movement does not change for several decades, then by the middle of the 21st century it will end up in Siberia. According to a reconstruction carried out several years ago by the same Newitt, in the 17th and 18th centuries the north magnetic pole mainly shifted to the southeast and only turned to the northwest around 1860. The true south magnetic pole has been moving in the same direction for the last 300 years, and its average annual displacement does not exceed 10–15 km.
Where does the Earth's magnetic field even come from? One possible explanation is simply glaring. The Earth has an inner solid iron-nickel core, the radius of which is 1220 km. Since these metals are ferromagnetic, why not assume that the inner core has static magnetization, which ensures the existence of the geomagnetic field? The multipolarity of terrestrial magnetism can be attributed to the asymmetry of the distribution of magnetic domains inside the core. Polar migration and geomagnetic field reversals are more difficult to explain, but we can probably try.
However, nothing comes of this. All ferromagnets remain ferromagnetic (that is, they retain spontaneous magnetization) only below a certain temperature - the Curie point. For iron it is 768°C (for nickel it is much lower), and the temperature of the Earth's inner core significantly exceeds 5000 degrees. Therefore, we have to part with the hypothesis of static geomagnetism. However, it is possible that there are cooled planets with ferromagnetic cores in space.
Let's consider another possibility. Our planet also has a liquid outer core approximately 2,300 km thick. It consists of a melt of iron and nickel with an admixture of lighter elements (sulfur, carbon, oxygen and, possibly, radioactive potassium - no one knows for sure). The temperature of the lower part of the outer core almost coincides with the temperature of the inner core, and in the upper zone at the boundary with the mantle it drops to 4400°C. Therefore, it is quite natural to assume that due to the rotation of the Earth, circular currents are formed there, which may be the cause of the emergence of terrestrial magnetism.
Convective dynamo
“To explain the appearance of the poloidal field, it is necessary to take into account the vertical flows of matter in the nucleus. They are formed due to convection: heated iron-nickel melt floats up from the lower part of the core towards the mantle. These jets are twisted by the Coriolis force like the air currents of cyclones. In the Northern Hemisphere, updrafts rotate clockwise, while in the Southern Hemisphere they rotate counterclockwise, explains University of California professor Gary Glatzmeier. - When approaching the mantle, the core material cools down and begins to move back inward. The magnetic fields of the ascending and descending flows cancel each other, and therefore the field is not established vertically. But in the upper part of the convection jet, where it forms a loop and moves horizontally for a short time, the situation is different. In the Northern Hemisphere, the field lines, which faced west before convective ascent, rotate clockwise by 90 degrees and are oriented north. In the Southern Hemisphere, they turn counterclockwise from the east and also head north. As a result, a magnetic field is generated in both hemispheres, pointing from south to north. Although this is by no means the only possible explanation for the emergence of the poloidal field, it is considered the most likely.”
This is precisely the scheme that geophysicists discussed 80 years ago. They believed that the flows of the conducting fluid of the outer core, due to their kinetic energy, generate electric currents covering the earth's axis. These currents generate a magnetic field of predominantly dipole type, the field lines of which on the Earth's surface are elongated along the meridians (such a field is called poloidal). This mechanism evokes an association with the operation of a dynamo, hence its name.
The described scheme is beautiful and visual, but, unfortunately, wrong. It is based on the assumption that the movement of matter in the outer core is symmetrical relative to the earth's axis. However, in 1933, the English mathematician Thomas Cowling proved the theorem according to which no axisymmetric flows are capable of ensuring the existence of a long-term geomagnetic field. Even if it appears, its age will be short-lived, tens of thousands of times less than the age of our planet. We need a more complex model.
“We don’t know exactly when Earth’s magnetism arose, but it could have happened soon after the formation of the mantle and outer core,” says David Stevenson, one of the leading experts on planetary magnetism, a professor at the California Institute of Technology. - To turn on the geodynamo, an external seed field is required, and not necessarily a powerful one. This role, for example, could be taken on by the magnetic field of the Sun or the field of currents generated in the core due to the thermoelectric effect. Ultimately, this is not too important; there were enough sources of magnetism. In the presence of such a field and the circular motion of flows of conducting fluid, the launch of an intraplanetary dynamo became simply inevitable.”
Magnetic protection
Earth's magnetism is monitored using an extensive network of geomagnetic observatories, the creation of which began in the 1830s.
For the same purposes, shipborne, aviation and space instruments are used (for example, scalar and vector magnetometers of the Danish Ørsted satellite, operating since 1999).
Geomagnetic field strengths range from approximately 20,000 nanoteslas off the coast of Brazil to 65,000 nanoteslas near the south magnetic pole. Since 1800, its dipole component has decreased by almost 13% (and since the mid-16th century by 20%), while its quadrupole component has increased slightly. Paleomagnetic studies show that for several thousand years before the beginning of our era, the intensity of the geomagnetic field persistently climbed up, and then began to decrease. Nevertheless, the current planetary dipole moment is significantly higher than its average value over the past hundred and fifty million years (in 2010, the results of paleomagnetic measurements were published indicating that 3.5 billion years ago the Earth’s magnetic field was half as weak as it is now). This means that the entire history of human societies from the emergence of the first states to our time fell on a local maximum of the earth’s magnetic field. It is interesting to think about whether this has affected the progress of civilization. This assumption ceases to seem fantastic if we consider that the magnetic field protects the biosphere from cosmic radiation.
And here is one more circumstance that is worth noting. In our planet’s youth and even adolescence, all the matter in its core was in the liquid phase. The solid inner core formed relatively recently, perhaps only a billion years ago. When this happened, the convection currents became more orderly, which led to more stable operation of the geodynamo. Because of this, the geomagnetic field has gained in magnitude and stability. It can be assumed that this circumstance had a beneficial effect on the evolution of living organisms. In particular, the strengthening of geomagnetism improved the protection of the biosphere from cosmic radiation and thereby facilitated the exit of life from the ocean to land.
Here is the generally accepted explanation for such a launch. For simplicity, let the seed field be almost parallel to the Earth's rotation axis (in fact, it is sufficient if it has a non-zero component in this direction, which is almost inevitable). The speed of rotation of the material of the outer core decreases as the depth decreases, and due to its high electrical conductivity, the magnetic field lines move with it - as physicists say, the field is “frozen” into the medium. Therefore, the force lines of the seed field will bend, going forward at greater depths and falling behind at shallower ones. Eventually they will stretch and deform so much that they will give rise to a toroidal field, circular magnetic loops that span the Earth's axis and point in opposite directions in the northern and southern hemispheres. This mechanism is called the w-effect.
According to Professor Stevenson, it is very important to understand that the toroidal field of the outer core arose due to the poloidal seed field and, in turn, gave rise to a new poloidal field observed at the earth's surface: “Both types of planetary geodynamo fields are interconnected and cannot exist without each other.” .
15 years ago, Gary Glatzmeier, together with Paul Roberts, published a very beautiful computer model of the geomagnetic field: “In principle, to explain geomagnetism, there has long been an adequate mathematical apparatus - the equations of magnetic hydrodynamics plus equations describing the force of gravity and heat flows inside the earth's core. Models based on these equations are very complex in their original form, but they can be simplified and adapted for computer calculations. That's exactly what Roberts and I did. A run on a supercomputer made it possible to construct a self-consistent description of the long-term evolution of the speed, temperature and pressure of matter flows in the outer core and the associated evolution of magnetic fields. We also found out that if we play the simulation over time intervals of the order of tens and hundreds of thousands of years, then geomagnetic field inversions inevitably occur. So in this respect, our model does a good job of conveying the planet's magnetic history. However, there is a difficulty that has not yet been resolved. The parameters of the material of the outer core, which are included in such models, are still too far from real conditions. For example, we had to accept that its viscosity is very high, otherwise the resources of the most powerful supercomputers would not be enough. In fact, this is not the case; there is every reason to believe that it almost coincides with the viscosity of water. Our current models are powerless to take into account turbulence, which undoubtedly occurs. But computers are gaining strength every year, and in ten years there will be much more realistic simulations.”
“The operation of a geodynamo is inevitably associated with chaotic changes in the flow of iron-nickel melt, which result in fluctuations in magnetic fields,” adds Professor Stevenson. - Inversions of terrestrial magnetism are simply the strongest possible fluctuations. Since they are stochastic in nature, they can hardly be predicted in advance - at least we don’t know how to do so.”
Such a phenomenon as magnetism has been known to mankind for a very long time. It got its name from the city of Magnetia, which is located in Asia Minor. It was there that a huge amount of iron ore was discovered. We can find the very first mentions of unique ones in the works of Titus Lucretius Cara, who wrote about this in the poem “On the Nature of Things”, approximately in the 1st century BC.
Since ancient times, people have found use for the unique properties of iron ore. One of the most common devices whose action was based on the attraction of metals was the compass. Now it is very difficult to imagine various industries that would not use simple magnets and electromagnets.
The Earth's magnetic field is the area around the planet that protects it from the harmful effects of radioactive radiation. Scientists still debate the origin of this field to this day. But most of them believe that it arose due to the Center of our planet having a liquid external and solid internal component. During rotation, the liquid part of the core moves, charged electrical particles move and a so-called magnetic field is formed.
The Earth's magnetic field is also called the magnetosphere. The concept of “magnetism” is a comprehensive and global property of nature. At the moment, it is impossible to create a completely complete theory of solar and terrestrial gravity, but science is already trying to understand many things and it manages to give quite convincing explanations of various aspects of this complex phenomenon.
Recently, scientists and ordinary citizens have been greatly concerned about the fact that the Earth's magnetic field is gradually weakening its influence. It has been scientifically proven that over the past 170 years the magnetic field has been steadily weakening. This makes you think, since it is a certain kind of shield that protects the Earth and wildlife from the terrible radiation effects of the sun's rays. resists the flow of all such particles that fly towards the poles. All these flows linger in the upper layer of the atmosphere at the poles, forming a wonderful phenomenon - the northern lights.
If the Earth’s magnetic field suddenly disappears or weakens significantly, then everything on the planet will be under the direct influence of cosmic and solar radiation. In turn, this will lead to radiation diseases and damage to all living organisms. The consequence of such a disaster will be terrible mutations or complete death. To our great relief, such a development is unlikely.
Paleomagnetologists were able to provide fairly reliable data that the magnetic field is constantly oscillating, and the period of such oscillations varies. They also compiled an approximate curve of field fluctuations and found that at the moment the field is in a descending position and will continue to decline for another couple of thousand years. Then it will begin to intensify again within 4 thousand years. The last maximum value of the magnetic field attraction occurred at the beginning of the current era. The reasons for such instability have been put forward in a variety of ways, but there is no specific theory on this matter.
It has long been known that many magnetic fields have a negative effect on living organisms. For example, experiments carried out on animals have shown that an external magnetic field can delay development, slow down cell growth and even change the composition of the blood. That is why they lead to a deterioration in the health of weather-dependent people.
For humans, a safe magnetic field of the Earth is a field with a strength value of no more than 700 oersteds. It is worth noting that we are not talking about the Earth’s magnetic field itself, but about the electromagnetic fields that are formed during the operation of any radio and electrical device.
The physical side of the process of the influence of the Earth’s magnetic field on humans is still not entirely clear. But we managed to find out that it affects plants: germination and further growth of seeds directly depend on their initial orientation in relation to the magnetic field. Moreover, its change can either accelerate or slow down the development of the plant. It is possible that someday this property will be used in agriculture.
Earth is the force of its gravity. It varies in some places, but the average is 0.5 oersted. In some places (in the so-called tension increases to 2E.
