The core of the Earth recoils | Science | EUROtoday

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A research has simply confirmed that the Earth's interior core is receding with respect to the floor, based on new analysis printed within the journal Nature.

Scientists have been debating the motion of the interior core for many years. Some analysis signifies that the innermost a part of the planet rotates sooner than the floor, and others preserve the other. The new research gives “the strongest evidence” that the interior core started slowing down round 2010 and is now slower than the Earth's floor, based on its authors.

“When I first saw the seismograms that hinted at this change, I was stunned,” mentioned John Vidale, a researcher on the University of Southern California and co-author of the work, in a press launch. “But when we found two dozen more observations that pointed to the same pattern, the result was undeniable. The inner core has slowed down for the first time in many decades. “Other scientists have recently argued in favor of similar and different models, but our latest study provides the most convincing resolution,” says the researcher.

Last year, similar work by Chinese scientists raised alarms that the Earth's inner core, a sphere of nearly pure iron more than 5,000 kilometers deep, was spinning more slowly than the outer crust. This means that from the point of view of someone who is in that cortex, the nucleus rotates in the opposite direction. Researchers call it backtrack in English, which means to go back or retreat. The effects of this phenomenon on the daily lives of Earthlings are imperceptible, although it can modify the length of the days in fractions of a second and even deform the Earth's crust.

The inner core is considered to be receding relative to the planet's surface because it is moving slightly slower than the mantle for the first time in about 40 years, according to the new work. Relative to its speed in previous decades, the inner core is slowing down.

Previous studies have revealed that this lack of rhythm follows something similar to cycles, and that a couple of decades ago it was the nucleus that rotated faster than the cortex. Just starting in the 2010s the phase changed and the inner core began to rotate slower than the outer one.

The inner core is a large ball of iron and nickel surrounded by the outer core, made of the same material, but in a liquid state. The core is about the same size as the Moon. Understanding it presents a huge challenge because it is not accessible. Scientists use seismic waves from earthquakes to create representations of the movement of the inner core.

Vidale and his colleague Wei Wang of the Chinese Academy of Sciences have analyzed the waves produced by 143 pairs of identical earthquakes that occur in the same place and produce identical seismograms.

In this study, the researchers compiled and analyzed 121 earthquakes recorded around the South Sandwich Islands that occurred between 1991 and 2023. They have also used tremors caused by identical nuclear bomb explosions detonated by the Soviet Union between 1971 and 1974, as well as French and American repeated nuclear tests of other inner core studies. The work agrees that the core of the planet rotated faster than the surface between 2003 and 2008. From that year to the present, the speed of the core was reduced about three times and is now going in the opposite direction with respect to the crust.

Vidale believes that the slowdown of the inner core is explained by friction with the outer core, made of liquid metal. This process is essential for life on Earth, as it produces a dynamo effect that generates the Earth's magnetic field, which protects the planet from radiation from space. In addition, the stoppage that the denser regions of the cortex can print influences, the scientist added.

Researcher Xiadong Song, from the Institute of Theoretical and Applied Geophysics at Peking University and author of the first study on the retreat of the core in 2023, explains that this new work confirms his results and “provides a clear demonstration that the retreat is really happening. It should be noted that we are talking about the rotation of the inner core in relation to the Earth's surface; That is, the inner core was spinning slightly faster than Earth's rotation before 2009, was synchronized around 2009, and has been spinning slightly slower since 2009. The finding is a stunning demonstration that our planet is so dynamic that its profound movement can be vividly revealed to our human eyes,” he provides.

The implications of this modification in interior core movement for the Earth's floor are a matter for hypothesis. Vidale factors out that the retreat of the interior core can alter the size of a day by fractions of a second: “It is very difficult to notice, on the order of a thousandth of a second, almost lost in the noise of the oceans and the atmosphere in agitation.” “The dance of the inner core could be even more lively than we know so far,” he added.

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https://elpais.com/ciencia/2024-06-19/el-nucleo-de-la-tierra-recula.html