The Earth is surrounded by a huge magnetic field that protects it from radiation and charged particles from space. Many animals use it to orient themselves, as it is constantly changing, a reason that leads geoscientists to keep it under surveillance. What causes this natural shield? For as far as we know the terrestrial nucleus, up to 6,000 kilometers deep, and the crust, the terrain in which we are. And even there, because the mantle of the planet, which extends from 35 to 2,900 km below the surface had been considered until now "magnetically dead". Well, we were wrong. As published by an international team of researchers from Germany, France, Denmark and the United States in the journal "Nature", a form of iron oxide, hematite, can retain its magnetic properties even in this gigantic geological sandwich. They have discovered it under the waters of the Pacific and can influence how we interpret the inversion movement of the poles.
Deep in the Earth's metallic core, there is a liquid iron alloy that triggers the electric flows. In the outermost crust, the rocks cause a magnetic signal. In the deeper regions of the interior, however, it was believed that rocks lost their magnetic properties due to high temperatures and pressures.
The researchers closely analyzed the main potential sources of magnetism in the Earth's mantle: iron oxides, which have a high critical temperature, above which the material is no longer magnetic. In the mantle, iron oxides are produced in slabs that are buried from the earth's crust to the interior as a result of tectonic changes, a process called subduction. They can reach a depth of between 410 and 660 kilometers, the so-called transition zone between the upper and lower mantle of the Earth. Previously, however, no one had managed to measure the magnetic properties of iron oxides in the extreme conditions of pressure and temperature found in this region.
At more than a thousand degrees
Now scientists have combined two methods to do it. Using what is called a diamond anvil cell, they squeezed micrometric samples of iron oxide hematite between two diamonds, and heated them with lasers to achieve pressures of up to 90 gigapascals and temperatures of more than 1,000 ° C. They combined this method with the so-called Mössbauer spectroscopy to test the magnetic state of the samples by means of synchrotron radiation. This part of the study was carried out in the facilities of the ESRF synchrotron in Grenoble, France.
The surprising result was that the hematite remained magnetic up to a temperature of around 925 ° C, which prevails in the slabs subducted below the western part of the Pacific, in the depth of the transition zone of the Earth. "As a result, we can show that the Earth's mantle is not as magnetically dead as it has been assumed until now," says Professor Carmen Sánchez-Valle, of the Institute of Mineralogy at the University of Münster. "These findings could justify other conclusions related to the entire magnetic field of the Earth," he adds.
Investment of the poles
By using satellites and studying rocks, researchers observe the Earth's magnetic field, as well as local and regional changes in magnetic force. In this way they know that the geomagnetic poles, which should not be confused with the geographical poles, move constantly. As a result of this movement, they have changed positions with each other every 200,000 or 300,000 years in the recent history of the Earth. The last pole shift occurred 780,000 years ago, and in recent decades scientists have seen an acceleration in the movement of the magnetic poles. This investment would have a profound effect on modern human civilization. The factors that control the movements and the rotation of the magnetic poles, as well as the directions that follow during the rollover are still unknown.
One of the routes of the poles observed during the turns runs through the western Pacific, corresponding remarkably to the electromagnetic sources proposed in the mantle of the Earth. Therefore, researchers are considering the possibility that the magnetic fields observed in the Pacific do not represent the path of migration of the poles measured on the surface of the Earth, but rather they originate from the electromagnetic source hitherto unknown to us. rocks that contain hematite in the mantle of the earth below the western Pacific.
The mantle of Mars
"What we now know, that there are magnetically ordered materials down there in the mantle of the Earth, must be taken into account in any future analysis of the Earth's magnetic field and the movement of the poles," says co-author Leonid Dubrovinsky of the Bavarian Research Institute of Geochemistry and Experimental Geophysics at the University of Bayreuth.
"This new knowledge about the Earth's mantle and the strongly magnetic region in the western Pacific could shed new light on any observation of the Earth's magnetic field," says the study's first author, Ilya Kupenko, a physicist at the University of Münster. (Germany). And not only that. The new findings could, for example, be relevant to any future observations of magnetic anomalies on other planets such as Mars. This is because Mars no longer has a dynamo and, therefore, no source that allows a strong magnetic field originating in the nucleus to be built like Earth's. But perhaps it would be worth taking a closer look at his cloak. . (tagsToTranslate) magnetism (t) earth