On February 19, 2021, the journal Science published an article by an international team of researchers entitled “An environmental crisis 42,000 years ago”. It revealed, for the first time in history, the effects caused by a change in the Earth’s magnetic poles. Thanks to precise carbon-14 dating of New Zealand kauri trees (a species of conifer endemic to the North Island), a drop in the intensity of the Earth’s magnetic field has been linked to a cascade of environmental crises – changes in weather patterns, large mammal extinctions, and even modifications in human behavior – just before and during the Laschamp event , a magnetic field reversal (magnetic north pole became south pole) that happened 41,400 years ago, at the end of the last ice age The inversion lasted 440 years and the recovery of the initial magnetic field needed another 250 years.
Until now, it was believed that geomagnetic changes had no appreciable impact, mainly because the geomagnetic event could not be correlated with other types of records. However, analysis of the rings of kauri trees preserved in the Ngawha Swamp has revealed that there was an increase in the amount of carbon-14 in the atmosphere (and from there into the trees) over the time that the Laschamp event lasted.
According to the computer simulation, our having a weakened magnetic field could have altered weather patterns. In fact, it suggests that the increase in charged subatomic particles reaching the atmosphere increased the production of nitrogen oxides, which tend to consume ozone. Atmospheric changes also affected how much sunlight is absorbed by different layers of the atmosphere, leading to large-scale changes that cooled the planet. Surprisingly, the most intense effects did not occur during the pole reversal but in the previous hundreds of years, from about 42,300 to 41,600 years ago: during the reversal the magnetic field was reduced to 28% of the current one, but during the transition period, the field intensity fell to approximately 6% of its current value.
This fact temporarily coincides with some extinctions , such as that of the Australian megafauna -which included the disappearance of Diprotodon (the largest known marsupial) and that of the giant kangaroo Procoptodon goliah- . And not only that. By this time humans made greater use of the caves , in which are found an uncanny abundance of handprints made of red ochre, a pigment believed to have been used as sunscreen. Are we facing a response from our ancestors to a more intense Sun due to a significant loss of the ozone layer? According to the French Jean-Pierre Valet, from the Institute of Globe Physics in Paris, and Hélène Valladas, from the Laboratory of Climate and Environmental Sciences, the Laschamp event had an important effect on the evolution of human beings . These scientists have studied the disappearance of the Neanderthals, which happened around then. According to their work, the drop in stratospheric ozone associated with the sudden drop in the magnetic field caused the Neanderthals to weaken enough that they could not survive the ice age.
Now, why does the Earth’s magnetic field reverse? And more importantly, can we predict it? A step towards understanding it was taken in 2016, when a team of scientists from the University of Leeds (Great Britain) and the Technical University of Denmark discovered that between Alaska and Siberia there is a peculiar river that runs from east to west some 3000 km from depth, and it is nothing like those that run on the surface of our planet: it is made of cast iron. It has a width of 420 km and carries a speed of 5 meters per hour or 50 km in a year. With a temperature similar to that of the Sun’s surface, it has tripled its speed in less than two decades and is heading towards Europa.
In essence, the heart of our planet is a solid composed mainly of iron at 5400º C and two-thirds the size of the Moon. Around it is a 2000 km layer (the so-called outer core) of liquid iron and nickel where differences in temperature, pressure and composition produce currents and eddies. The river discovered by these scientists is part of these currents, which contribute to producing the magnetic field thanks to the dynamo effect , a mechanism first proposed in 1919 by the Irishman Joseph Larmor. The dynamo requires the pre-existence of an initial magnetic field and a rotating electrically conductive material (the iron core) to convert the rotational energy into magnetic energy. Once the dynamo starts, the initial magnetic field can disappear; no longer needed. And best of all, this is a self-maintaining system as long as it stays in rotation.
Scientists know that for the past two millennia the north magnetic pole has been wandering around the geographic north pole , something that has been puzzling geophysicists ever since James Clark Ross first measured it in 1831 in the Canadian Arctic. In the mid-1990s, it increased its speed, going from 15 kilometers per year to almost 55. By 2001 it had entered the Arctic Ocean and in 2018 it crossed the international date line on its way to Siberia. And even more, the intensity of the magnetic field has been reduced by 10% since 1860: nobody knows why or what will happen in the future, if it will continue to weaken or will disappear completely.
It’s also unclear why that river of molten iron is accelerating , although it is suspected that it is part of an internal cycle of the Earth, which causes the magnetic field to disappear and reverse. The best theory we have to explain this inversion is that at depths of 3000-5000 km in certain areas a magnetic field appears that opposes the general field. This is what seems to be happening in the so-called South Atlantic Anomaly, an area that runs from Zimbabwe to Chile where the Earth’s magnetic field is particularly weak. If those areas grow large enough, the global magnetic field is affected, and then one of two things can happen: either the original field wins the battle, or a reversal occurs.
According to geological data, a complete magnetic reversal takes between 1,000 and 20,000 years to occur, but the process is not gradual and smooth. What happens is that the magnetic field breaks into pieces and other smaller ones appear, so that we can find several magnetic poles scattered around the planet. Are we currently in an investment process? Geophysicists think that what is happening today with the Earth’s magnetic field is similar to what happened in the Laschamp event: the field intensity is rapidly decreasing, the areas of the outer core with reverse magnetization are growing, and in a few hundred years we will find ourselves with a period in which our magnetic protective shield will be practically non-existent. Some scientists have dared to put a date on the disaster: if what is happening in the Earth’s core does not change by 2034, the collapse of the magnetic field will be inevitable . And just like in the Leschamp event, the intensity of the field will be reduced by more than 90%, and over centuries or millennia high-energy particles that were previously deflected by the field will reach the Earth’s surface. And then what will happen?
A strong and stable magnetic field is essential for our civilization, as it protects us from high-energy particles from space . That they reach the surface in sufficient quantity is a risk to cause damage to computers and everything that works with electricity, which is practically everything. John Tarduno, a geophysicist at the University of Rochester, points out that a decrease in our magnetic shielding would also have effects on the atmosphere: “more holes could develop in the ozone layer due to the action of cosmic rays”. Obviously under those holes the increase in skin cancer would be a fact. We need to start thinking about how to protect both ourselves and our technology from a civilizational collapse.