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The huge magnetic field that surrounds the Earth, protecting it from radiation and charged particles from space – and that many animals even use for orientation purposes – is constantly changing, c & # 39; that's why geoscientists are constantly monitoring it. The ancient well-known sources of the Earth's magnetic field are the Earth's core – up to 6,000 kilometers deep inside the Earth – and the Earth's crust: in other words, the soil on which we stand. The Earth's mantle, extending from 35 to 2,900 kilometers below the surface of the Earth, has so far been considered largely "magnetically dead". An international team of German, French, Danish and American researchers has now shown that a form of iron oxide, hematite, can retain its magnetic properties even deep within the Earth's mantle. This occurs in relatively cold tectonic plates, called slabs, which are found mostly under the western Pacific Ocean.
"This new knowledge of the Earth's mantle and the highly magnetic region of the Western Pacific could light up the Earth's magnetic field from one day to the next," said the mining physicist. and first author, Dr. Ilya Kupenko from the University of Münster (Germany). The new discoveries could, for example, be relevant for any future observations of magnetic anomalies on the Earth and on other planets such as Mars. Indeed, Mars no longer has a dynamo and therefore no source to build a powerful magnetic field from the nucleus such as that of the Earth. It might be useful now to take a more detailed look at his coat. The study was published in the "Nature"newspaper.
Context and methods used:
At the bottom of the Earth's metallic core, it's a liquid iron alloy that triggers electrical flows. In the outer crust of the Earth, the rocks cause a magnetic signal. In deeper regions of the Earth's interior, however, it was thought that rocks lose their magnetic properties due to very high temperatures and pressures.
Researchers have now taken a closer look at the main potential sources of magnetism in the Earth's mantle: iron oxides, which have a high critical temperature, ie the temperature above which the material is exposed. Is more magnetic. In the Earth's mantle, iron oxides are found in slabs buried in the earth's crust, deeper into the mantle, as a result of tectonic shifts, a process called subduction. They can reach a depth of between 410 and 660 km inside the Earth – the so-called transition zone between the upper mantle and the lower mantle of the Earth. Previously, however, no one had succeeded in measuring the magnetic properties of iron oxides in the extreme pressure and temperature conditions encountered in this region.
Now scientists have combined two methods. Using a so-called diamond anvil cell, they pressed micrometric samples of iron oxide hematite between two diamonds and heated them with the help of lasers to reach pressures of up to 90 gigapascals. and temperatures above 1000 ° C (1300 K). The researchers associated this method with so-called Mössbauer spectroscopy to probe the magnetic state of samples by means of synchrotron radiation. This part of the study was carried out at the ESRF synchrotron in Grenoble, France, which allowed to observe the modifications of the magnetic order in iron oxide.
The surprising result is that the hematite remained magnetic up to a temperature of about 925 ° C (1200 K), prevailing temperature in the subducted slabs located under the western part of the island. Pacific Ocean at the depth of the Earth's transition zone. "As a result, we are able to demonstrate that the mantle of the Earth is not as magnificently" deadly "magnetically as we have supposed until now," said the Professor Carmen Sanchez-Valle of the Institute of Mineralogy of the University of Münster. "These findings could justify other conclusions relating to the entire Earth's magnetic field," she adds.
Relevance for investigations of the Earth's magnetic field and pole motion
By using satellites and studying the rocks, researchers observe the Earth's magnetic field, as well as local and regional changes in magnetic force. Context: The geomagnetic poles of the Earth – not to be confused with the geographical poles – are constantly in motion. As a result of this movement, they have in fact changed their position every 200,000 to 300,000 years in the recent history of the Earth. The last pole reversal took place 780 000 years ago, and scientists in recent decades report an acceleration of the magnetic poles movement of the Earth. The tipping of magnetic poles would have a profound effect on modern human civilization. The factors that control the movements and reversal of the magnetic poles, as well as the directions they follow when reversing, are not yet understood.
One of the polar routes observed during flips crosses the western Pacific, which corresponds very clearly to the electromagnetic sources proposed in the Earth's mantle. Researchers are therefore studying the possibility that magnetic fields observed in the Pacific with the help of rock recordings do not represent the migration path of the poles measured on the Earth's surface, but come from the electromagnetic source up to Then unknown rocks containing hematite in the Earth's mantle under the West Pacific.
"What we now know, that there are magnetically ordered materials in the Earth's mantle, should be taken into account in any future analysis of the Earth's magnetic field and pole motion," says the co-author, the teacher. Leonid Dubrovinsky at the Institute for Research in Experimental Geochemistry and Geophysics of the University of Bayreuth in Bavaria.
Source of the story:
Material provided by University of Münster. Note: Content can be changed for style and length.
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