Our planet has a magnetic field, which can be observed, for example, using a compass. It is mainly formed in a very hot molten core of the planet and, probably, there was most of the time the Earth existed. The field is a dipole, i.e., it has one north and one south magnetic pole. In them, the compass needle will point straight down or up, respectively. It looks like a fridge magnet field. However, the Earth's geomagnetic field undergoes many small changes, which makes the analogy untenable. In any case, we can say that at present there are two poles observed on the surface of the planet: one in the northern hemisphere and one in the southern.
An inversion of the geomagnetic field is a process in which the south magnetic pole turns into the north, and that, in turn, becomes the south. It is interesting to note that a magnetic field can sometimes undergo excursions rather than a U-turn. In this case, it undergoes a large decrease in its total strength, that is, the force that moves the compass needle. During the tour, the field does not change its direction, but is restored with the same polarity, that is, the north remains north and south to south.
How often does the Earth’s pole change occur?
According to the geological record, the magnetic field of our planet reversed polarity many times. This can be seen from the patterns found in volcanic rocks, especially those recovered from the ocean floor. Over the past 10 million years, an average of 4 or 5 turns per million years have occurred. At other moments in the history of our planet, for example, during the Cretaceous period, there were longer periods of change of the poles of the Earth. They cannot be predicted, and they are not regular. Therefore, we can only talk about the average inversion interval.
Is the Earth's magnetic field unfolding now? How to check it?
Measurements of the geomagnetic characteristics of our planet have been carried out more or less continuously since 1840. Some dimensions are even dated to the 16th century, for example, in Greenwich (London). If you look at the trends in the magnetic field over this period, you can see its decrease. Projecting data forward in time gives a zero dipole moment in about 1500-1600 years. This is one of the reasons why some believe that the field may be in the early stages of inversion. From studies of the magnetization of minerals in ancient clay pots, it is known that in ancient Rome it was twice as strong as it is now.
Nevertheless, the current field strength is not particularly low in terms of the range of its values over the past 50,000 years, and almost 800,000 years have passed since the last pole change of the Earth. In addition, taking into account what was said earlier about the excursion, and knowing about the properties of mathematical models, it is far from clear whether it is possible to extrapolate observational data for 1500 years.
How fast is the inversion of the poles?
There is no complete record of the history of at least one U-turn, therefore all the statements that can be made are mainly based on mathematical models and partly on limited evidence obtained from rocks that have retained the imprint of an ancient magnetic field since their formation. For example, the calculations suggest that a complete change of the Earth’s poles can take from one to several thousand years. It is fast by geological standards, but slowly on the scale of human life.
What happens during a U-turn? What do we see on the surface of the earth?
As mentioned above, we have limited data from geological measurements on the patterns of field changes during inversion. Based on models designed on supercomputers, one would expect a much more complex structure on the surface of the planet, in which there is more than one south and one north magnetic pole. The Earth is awaiting their “wandering” from their current position towards and through the equator. The total field strength at any point on the planet can be no more than one tenth of its value at present.
Danger to navigation
Without a magnetic shield, modern technology will be more at risk of exposure to solar storms. The most vulnerable are satellites. They are not designed to withstand solar storms in the absence of a magnetic field. So if the GPS satellites stop working, then all the planes will land on the ground.
Of course, airplanes have compasses as a backup, but they certainly will not be accurate during the magnetic pole shift. Thus, even the very possibility of failure of GPS satellites will be enough to land planes - otherwise they may lose navigation during the flight.
Ships will face the same problems.
Ozone layer
It is expected that during the inversion of the Earth’s magnetic field, the ozone layer will completely disappear (and reappear after this). Large solar storms during a U-turn can cause ozone depletion. The number of skin cancer diseases will increase 3 times. The impact on all living things is difficult to predict, but can also have disastrous consequences.
Earth's Magnetic Pole Change: Implications for Power Systems
In one study, massive solar storms were identified as the likely cause of polar inversion. In another, the cause of this event will be global warming, and it can be caused by increased activity of the Sun. During a reversal, there will be no protection of the magnetic field, and if a solar storm occurs, the situation will worsen even more. Life on our planet will not be affected as a whole, and societies that are not technology dependent will also be in perfect order. But the Earth of the future will suffer terribly if a reversal occurs quickly. Electric networks will stop functioning (a large solar storm can disable them, and the inversion will affect much more). In the absence of electricity, there will be no water supply and sewage, gas stations will stop working, food supplies will stop. The performance of emergency services will be in question, and they will not be able to influence anything. Millions will die, and billions will face great difficulties. Only those who have stocked up food and water in advance will be able to cope with the situation.
Cosmic radiation hazard
Our geomagnetic field is responsible for blocking approximately 50% of cosmic rays. Therefore, in its absence, the level of cosmic radiation will double. Despite the fact that this will lead to an increase in mutations, it will not have fatal consequences. On the other hand, one of the possible causes of the pole shift is an increase in solar activity. This can lead to an increase in the number of charged particles reaching our planet. In this case, the Earth of the future will be in great danger.
Will life survive on our planet?
Natural disasters, cataclysms are unlikely. A geomagnetic field is located in a region of space called the magnetosphere, formed by the action of the solar wind. The magnetosphere does not deflect all the high-energy particles that the sun emits with the solar wind and other sources in the galaxy. Sometimes our star is especially active, for example, when there are many spots on it, and it can send clouds of particles in the direction of the Earth. During such solar flares and coronal mass ejections, astronauts in Earth orbit may need additional protection to avoid higher doses of radiation. Therefore, we know that the magnetic field of our planet provides only partial, but not complete protection against cosmic radiation. In addition, high-energy particles can even be accelerated in the magnetosphere.
On the surface of the Earth, the atmosphere acts as an additional protective layer that stops everything except the most active solar and galactic radiation. In the absence of a magnetic field, the atmosphere will still absorb most of the radiation. The air shell protects us as effectively as a concrete layer 4 m thick.
Without consequences
Human beings and their ancestors lived on Earth for several million years, during which many inversions occurred, and there is no obvious correlation between them and the development of mankind. In the same way, the time of turns does not coincide with the periods of extinction of species, as evidenced by the geological history.
Some animals, such as pigeons and whales, use a geomagnetic field for navigation. Assuming a reversal takes several thousand years, that is, many generations of each species last, then these animals can adapt well to a changing magnetic environment or develop other navigation methods.
More technical description
The source of the magnetic field is the Earth's iron-rich liquid outer core. It makes complex movements resulting from convection of heat deep inside the core and the rotation of the planet. The fluid movement is continuous and never stops, even during a U-turn. It can stop only after the exhaustion of the energy source. Heat is generated in part due to the conversion of a liquid core into a solid core located in the center of the earth. This process has been ongoing continuously for billions of years. In the upper part of the core, which is located 3000 km below the surface level under the rocky mantle, the fluid can move in the horizontal direction at a speed of tens of kilometers per year. Its movement across existing lines of force produces electric currents, and they, in turn, generate a magnetic field. This process is called advection. In order to balance the growth of the field, and thereby stabilize the so-called. "Geodynamo", diffusion is necessary, in which there is a "leak" of the field from the core and its destruction. Ultimately, the fluid flow creates a complex picture of the magnetic field on the Earth's surface with a complex change in time.
Computer calculations
Modeling geodynamo on supercomputers has demonstrated the complex nature of the field and its behavior over time. The calculations also showed an inversion of polarity when the Earth’s poles change. In such simulations, the strength of the main dipole weakens to 10% of the normal value (but not to zero), and the existing poles can travel around the globe together with other temporary north and south poles.
The solid iron inner core of our planet in these models plays an important role in controlling the reversal process. Because of its solid state, it cannot generate a magnetic field by advection, but any field that is formed in the liquid of the outer core can diffuse or propagate into the inner one. Advection in the outer core seems to regularly try to invert. But until the field locked in the inner core diffuses at first, a real change in the Earth’s magnetic poles will not occur. Essentially, the inner core resists the diffusion of any “new” field, and perhaps only one out of every ten attempts at such a reversal is successful.
Magnetic anomalies
It should be emphasized that, although these results are fascinating in themselves, it is not known whether they can be attributed to the real Earth. However, we have mathematical models of the magnetic field of our planet over the past 400 years with early data based on observations of sailors from the merchant and navy. Their extrapolation to the internal structure of the globe shows the growth over time of the regions of the reverse flow at the boundary of the core and mantle. At these points, the compass needle is oriented, in comparison with the adjacent areas, in the opposite direction - inward or out of the nucleus. These sections with a reverse flow in the southern Atlantic Ocean are primarily responsible for weakening the main field. They are also responsible for the minimum tension called the Brazilian Magnetic Anomaly, whose center is located under South America. In this area, high-energy particles can come closer to Earth, causing an increased radiation risk for satellites in low Earth orbit.
Much remains to be done to better understand the properties of the deep structure of our planet. This is a world where the pressure and temperature are similar to the parameters of the surface of the Sun, and our scientific understanding reaches its limit.