It is well known that the Earth’s magnetic field does not remain static, but moves, and its intensity increases and decreases. In fact, the north magnetic pole is currently moving rapidly from Canada to Siberia – so much so that scientists have had to prematurely update the magnetic declination model that facilitates global navigation.
This dynamism has caused that, throughout the history of our planet, the magnetic poles have been reversed several times, and the last episode is known as the Brunhes-Matuyama magnetic inversion. Studying this geological phenomenon is fascinating, and can provide clues to help elucidate when and how the next inversion will occur.
But do not panic: this phenomenon, if it occurs at a time when the human species continues to live on Earth, will not produce an apocalypse or the collapse of civilization, as some predict. It is true that, surely, it would affect navigation and telecommunications systems, but what we are clear is that it will not occur overnight, so there will be time to adapt, and the study of the operation of the magnetic field and the Past investments will help you better predict future changes.
In this particular study, published in the journal Science Advances , it is concluded that the last magnetic reversal, which happened about 770,000 years ago, took at least 22,000 years to complete , which is much longer than previously calculated.
How are changes in the magnetic field studied?
The magnetic field is caused by the movements of the liquid materials that make up the core of the Earth. In the new rocks that are formed – generally in the form of volcanic lava flow or sediments deposited on the bottom of the sea – the characteristics of the magnetic field are recorded at that very moment, so that scientists can analyze the past by looking for these traces in rocks, as if it were a fossil record. This record is much clearer in the case of the most recent investment, that of Brunhes-Matuyama.
In this case, the scientists analyzed lava flows deposited in Chile, Tahiti, Hawaii, the Caribbean and the Canary Islands. “Lava flows represent an ideal record of the magnetic field. They have many minerals with a high iron content and, when they cool down, they are blocked in the direction of the field ”, explains Brad Singer, a geologist at the University of Wisconsin-Madison (USA) and one of the authors of the work. The problem is, since there are no regular volcanic eruptions, the work must be very meticulous to correctly date the records.
The team of researchers combined magnetic readings and radioisotope dating of samples from seven lava flow sequences to recreate the magnetic field over a span of approximately 70,000 years, focusing on the Brunhes-Matuyama inversion.
The lava flow data was corroborated by magnetic readings of the seabed. In addition, the researchers used Antarctic ice cores to track the deposition of beryllium , which is produced by cosmic radiation colliding with the atmosphere. When the magnetic field reverses, it weakens and allows more radiation to hit the atmosphere, producing more beryllium.
Magnetic inversion could last 22,000 years
The results revealed that the final reversal was fast on the geological scale, lasting only about 4,000 years. But, previously, this geological phenomenon was preceded by a very long period of instability that included partial and temporary reversals and that could last 18,000 years . This is an estimate that would double the time estimated by previous hypotheses, and which state that the reversals would occur in a period of 9,000 years.
When will the next magnetic reversal take place?
Since the scientific community became interested in the magnetic field, its strength has decreased by around 5% every century. Records carried out by the US team indicate that a weakened magnetic field may be the precursor to an eventual reversal, although it is not clear that it is imminent.
In any case, and as we have already commented, this study reinforces the idea that human society would have, in the event of this effect, several generations to adapt to this potential period of magnetic instability. Our civilization is much more likely to collapse for reasons other than the magnetic field.
“I’ve been working on this problem for 25 years,” says Singer, who ‘stumbled upon’ paleomagnetism when he realized that the volcanoes he was studying served as a good record of Earth’s magnetic fields. “And now we have a much richer and better dated record of the last magnetic reversal.”
