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Like most of us, the earth has many things below the surface – even in what could have once been its most modest layer.
The coat, an area between the thin crust of our planet and the melted nucleus, includes 1,800 miles (2,900 kilometers) of mainly solid rock, with a consistency as a thickened caramel that scientists have long hypothetical were uniformly mixed. But non -mixed massive regions have been found persistent in the coat, like pieces of chocolate in a cookie, and new discoveries are barely to reveal their secrets.
Among the pieces of enigmatic coat, there are two huge “supercontinents” buried thousands of kilometers under the crust in the middle of the remains of old tectonic plates. A supercontinent lies under Africa, and the other lies deeply under the Pacific Ocean. By using a new method to analyze data from earthquakes, researchers have recently discovered unknown details before on these vast regions of the island, revealing that they can serve as anchors in the coat of our planet and that They could be much older than we thought before.
The discovery adds to an increasing number of evidence suggesting that the rocky coat is not as well interrupted by the internal barattage of the earth as believed once. And hidden structures or pockets of unixed materials, such as these supercontinents, can shape the activity of the mantle, including the movement of plates, in a way that remains to be understood, scientists reported on January 22 in the journal Nature.
“These results will contribute to a better understanding of the convection of the mantle and the tectonics of the plates, and, consequently, of the phenomena that we live on the surface like earthquakes and volcanism,” said Claire RichardsonA doctoral student at the School of Earth and Space Exploration of the Arizona State University, which was not involved in the new research.
“To solve the physical, thermal and chemical properties of rocks ~ 3000 km (1,864 miles) under our feet, at temperatures and extreme pressures, is a difficult problem to say the least,” Richardson told CNN in an email . “Open questions abound, and each new study brings us closer to understanding what is really going on there.”
The researchers first spotted underground supercontinents about 50 years ago when they appeared as anomalies in the seismic data generated by earthquakes powerful enough to send reverberations via the planet. When seismic waves encounter unusual structures in the mantle, the changes in the speed of waves provide sismologists with the deep interior of the earth.
Over the decades, seismic data have revealed that these supercontinents represent approximately 20% of the border of the Napshot. Each of the buried islands covers hundreds of thousands of kilometers, and in certain places, they dominate nearly 600 miles (965 kilometers). However, we knew little about what they were done when they sank and what role they could play in the flow of the mantle, known as convection, said Dr Sujania Talavera-SozaMain author of the new study and researcher geosciences and seismology at the University of Utrecht in the Netherlands.
“Their origin and if these are long -life structures – it is widely debated,” said Talavera -Soza.
Previous research has focused on the speed of seismic waves, showing that the speed of waves slowed about 2% when arriving at the supercontinents. This slowdown in seismic waves led geologists to name the regions of large provinces of low shear speed, or LLSVPS.
The loss of speed in seismic waves suggested that these coat areas were warmer than the rocks around them, said Talavera-Soza. But we did not know if the LLSVPs were structurally different from neighboring regions. Scientists did not know if the supercontinents were actively involved in convection, or if they were “dense heaps that would simply be seated there,” said the co -author of the study Dr Arwen DeussProfessor of structure and composition of the deep interior of the earth at the University of Utrecht.
“There was no information about it,” said Deuss. “We only knew that the seismic waves slowed down.”
In the new study, the authors used a different approach to study LLSVP to see if they could disentangle details on the composition and activity of the areas. They looked at the attenuation or the intensity of the seismic signals while they were traveling through the coat to see the amount of energy the vibrations of earthquakes lost.
In music, attenuation is comparable to the damping of a tone that produces a lower volume, said Deuss. Examination of the attenuation of the waves – as well as changes in the speed of waves – could provide unpublished clues to the makeup of LLSVPs. The best data for this come from waves produced by earthquakes which are magnitude 7.8 or more, added Talavera-Soza.
The speed of the waves and the loss of energy were known to be affected by the size of the mineral grains as well as the temperature, so that the authors used a model of physics which linked seismology and mineral physics. The waves are more amortized when they meet smaller grain material; If a lot of grains are packed together, there are more limits between the grains that can undermine the energy of a wave.
Other Revealed studies that the supercontinents had company in the deep mantle. Around them were “slab“Lounge tectonic plates,” said Deuss. They were cooler than the LLSVP, so the seismic waves crossed them more quickly.
However, the new model has shown that if the speed of seismic waves has dropped when they reached LLSVP, the waves have not lost much energy. In comparison, there was a significant damping between the cooler cemeteries around LLSVP.
Researchers think that these differences come down to the comparative ages of structures. Over millions of years, while the rocky material descends through the border between the upper and lower coat, the mineral crystals are compressed and reformed in more tiny grains which then repel over time. The younger regions therefore have smaller crystals, which suck more energy from seismic waves, therefore the amount of damping in a region suggests its age.
“The fact that LLSVP show very little damping, which must be made up of much larger grains than their environment,” said Talavera-Soza. According to the study, the greatest mineral grains suggested that supercontinents were significantly older than tectonic cemeteries around them, because their grains had to have more time to develop, according to the study. More important construction blocks would also make the supercontinents more rigid, keeping them separated from the convection of the mantle or the movement of the materials in this layer because of the transfer of heat.
“Our study indicates that LLSVPs are long-term characteristics, at least half a billion years, perhaps even older,” said Talavera-Soza. “This implies that they act as anchors at the base of the border of the basic mantle and have survived the convection of the coat, which means that the coat is not well mixed.”
This discovery follows another recent revelation on even more “worlds pushed” which contradict the notion of mixed coat. The plates buried in tectonic cemeteries tend to accumulate in alignment with the areas of subduction of the earth – regions where the edges of two plates meet, and where one slides under the other. But earlier this year, Another team of scientists Identified tectonic slabs flowed from these limits in places under the interiors of the continents and under the oceans, where pressed plates had never been found before.
“Apparently, such areas in the terrestrial mantle are much more widespread than we thought before,” said Thomas SchoutenPrincipal author of this survey and researcher at the Geological Institute of Eth Zurich, the Federal Institute of Swiss Technology, in a declaration.
The model of the new study – The first 3D attenuation model for the entire mantle – will help seismologists better understand what is thousands of kilometers below the surface of the earth, said Richardson, the doctoral student.
“He maps the regions of the earth which weaken seismic energy, ultimately affecting the measures that many seismologists use to understand other physical and chemical properties from the interior of the earth,” she said.
The results could transform the understanding of the researchers of the plates tectonics and the way in which the movement of the plaques could be shaped by these ancient and fixed anchors near the heart of the earth, said Deuss. A more in-depth analysis of the supercontinents could also reveal if they are the source of geochemical elements almost as old as the earth itself which is in the lava from certain types of volcanoes, she added.
“These LLSVPs have been there for a long time – if they have been there for a billion years, they could also have been there for 4 billion years. They may well be this hidden reservoir where these primordial chemical elements could be located. We cannot prove it now, but geochemists can investigate this, “said Deuss.
“According to this study, I think there will be a lot of additional research that could answer many unanswered questions that have confusing scientists for ages.”
Mindy Weisberger is a scientific writer and media producer whose work has appeared in Live Science, Scientific American and How It Works Magazine.