The Devonian period (420-360 million years ago) is full of scientific questions. One of the great enigmas of that geological stage, in which the Earth’s continents were changing their configuration and were different from the current ones, is why the rocks of this period of time do not seem to have traces of the Earth’s magnetic field? For a long time, scientists have assumed that this is because the rocks for some reason lost their “magnetic memory” or fossil magnetism (alignment or arrangement of tiny crystals in the rock, determined by the Earth’s magnetic field at each time). .
“According to many studies, it seems that the Earth’s magnetic field was really weak at that time. And that is the reason why the rocks do not have these traces,” explains paleomagnetist Annique van der Boon of the Center for Evolution and Earth Dynamics at the University of Oslo, UiO (www.uio.no), in Oslo (Norway).
THE GEOMAGNETIC FIELD.
Explain that the Earth’s magnetic field plays an important role in our daily lives. It protects us from solar storms that consist of energetic charged particles and can be harmful to modern technology and our satellites. “The magnetic field extends out into space. The stronger it is, the more it spreads and the better it protects us from harmful radiation coming from our sun. The place where the magnetic field and the solar wind balance is called a magnetopause”, explains van der Boon.
He adds that “the interaction between the Earth’s magnetic field and solar storms is what creates the aurora borealis”, a natural phenomenon that manifests itself as a multicolored light show in the night sky, whose appearance and intensity vary, and which can be seen in Norway.
Earth’s magnetic field also protects our atmosphere, and today it’s strong, stable and protective, but it wasn’t always that way in the past, he says.
When studying a set of Devonian rocks collected in Canada in his laboratory, Van der Boon found that it was very difficult to obtain and interpret their paleomagnetic data (records of the Earth’s magnetic field in the past that are recorded in the rocks through physical-chemical processes).
What if this were so because the magnetic field was then too weak to affect those records? the researcher wondered. Her findings point in that direction.
All paleomagnetic data from the Devonian are highly problematic, according to Van der Boon.
THE MEMORY OF THE ROCKS.
Scientists have suggested that rocks from this period could have been heated when the continents collided with each other around this time. This is something that could have affected the magnetic memory, he explains.
Yet the very lack of reliable Devonian paleomagnetic data makes it difficult to understand how continental plates (large blocks into which the planet’s outermost layer is divided) have moved through time.
Their research shows that even those rocks that should have “a good memory” of the Earth’s magnetic field offer problematic information.
Van der Boon believes that the lack of reliable paleomagnetic data pertaining to the Devonian could be because the Earth’s magnetic field was very weak at that time, for reasons that are still unknown.
“Now we are trying to understand when the field weakened and how long it was weak,” explains Van Der Boon.
“During the Devonian, plants appeared. There is scientific evidence that these plants were damaged by UV-B radiation at the end of this geological period. This fits with the idea of a “weak magnetic field” (which would not have provided sufficient protection against harmful solar radiation).
“We know very little about the Earth’s magnetic field over long time scales and why it behaves the way it does,” admits Van der Boon.
Paleomagnetists can study rocks millions or even billions of years old to learn more about Earth’s magnetic field at that time, he says. This can provide insights into the position of continental plates in the past and the inner workings from Earth to greater depths, he says.
Van der Boon’s research suggests that the Earth’s magnetic field was very weak in the Devonian, but this has opened up other questions, such as why it was so weak and how did this affect life on Earth…?
Regarding the possible cause of the weakening of the geomagnetic field in the Devonian, the researcher explains in an interview with EFE that two hypotheses are being explored.
On the one hand, it is believed that this phenomenon could be related to the influence of the formation of the solid inner core of the Earth, which seems to exert a strong influence on the strength and behavior of the Earth’s magnetic field, but about which there is still much. uncertainty.
The second hypothesis is that the Earth’s magnetic field goes through cycles in which its strength alternates between strong and weak, and that are repeated every 200 million years, in a phenomenon influenced by the internal heat flow of the planet and the cycle of the tectonic plates (movement of the continental plates), as explained to EFE.
“And a third explanation for the possible cause of the weak field in the Devonian is that it is due to something completely different, which we have not yet discovered,” he highlights.
Daniel Galilee
EFE Reports