MADRID.- The core of the Earth –a sphere of almost pure iron more than 5000 kilometers deep that is hotter than the Sun– has slowed down and may be spinning in the opposite direction to the planet’s surfaceAccording to a study published today in Nature Geoscience. This halt can have global effects, like shortening the days by a few fractions of a second and influencing the climate and sea level.
Both authors of the work They are Yi Yang and Xiaodong Song, from Peking University’s Institute of Theoretical and Applied Geophysics, in China. Both have tried to solve a current enigma since, a few decades ago, it was confirmed that the Earth contains a planet inside another.
The smallest would be the inner core: A solid sphere about 1,200 kilometers in diameter spinning freely in a sea of molten iron and other metals, known as the outer core. The free rotation of this gigantic sphere is like a dynamo that generates the Earth’s magnetic field, which protects it from space radiation and allows life to exist on its surface. Around this nucleus extends the earth mantlewith a thickness of almost 3000 kilometers, and finally, the outer crust, with only about 40 kilometers of average thickness.
Getting to the center of the Earth is an impossible challenge. In the late 1970s, Soviet scientists began digging a well on the Kola Peninsula in northern Russia. After years of work they reached a depth of 12 kilometers, the most that has been achieved dig into the bowels of the planet. It seems impossible to go much further without the walls of the hole collapsing under the pressure.
The usual method to understand what happens in deeper areas is to analyze earthquakes. The variation of seismic waves as they pass through the planet reveals the internal composition of the core and its rate of rotation.
In 1996, Xiadong Song, then working in the US, was one of the authors of a groundbreaking study that analyzed seismic signals and proved that the inner core of the Earth spins faster than the crust. In 2005, this scientist confirmed these observations and detailed that the core goes around one more time than the rest of the planet every 900 years, approximately. This lack of synchrony is partly due to the fact that the tides and the progressive distance of the Moon have been slowing down the crust, which means that the days do not last exactly 24 hours. – 1400 million years ago, a day had less than 19 hours. Parallel to this phenomenon, the days have been shortening by a few fractions of a second for a few years without anyone knowing why.
Now Song has analyzed nearly 200 earthquakes in the South Sandwich Islands, a remote Atlantic archipelago near the South Pole, between the 1960s and the present. These quakes happened in pairs and produced identical waves. But when they were captured in stations in Alaska, near the North Pole, their waves arrived slightly out of step if, when passing through the nucleus, it rotated faster than the crust.
Analysis of these tremors with computer models that reconstruct the entire Earth show that In 2009 the Earth’s core slowed down and since then it has rotated a little slower than the crust.. This observation has an unusual implication. “Seen from space, the core rotates at almost the same rate as the rest of the planet. But from the point of view of the surface, where the seismic stations are, the nucleus now rotates in the opposite direction; westward”, explains Song to THE COUNTRY.
Scientists have also detected that in the mid-1970s there was already a similar brake. “We infer that there is an oscillation cycle that lasts about seven decades,” Song explains. “This suggests that there is a resonance that connects all the layers of the Earth that occurs with that cadence,” she details.
This phenomenon may have global effects. “In recent years, the days are getting shorter, and it may be partly due to the Earth’s core,” reasons. Core anomaly makes a day one thousandth of a second shorter now than it was in 1970, details. “The rotation of the inner core within the outer one also alters the inner gravitational field and causes deformations on the surface, which in turn can influence sea level. These changes could also affect the global temperature of the planet”, suggests the geologist.
In early 2022, John Vidale and Wei Wang of the University of Southern California analyzed tremors caused by pairs of nuclear bombs detonated by the Soviet Union between 1971 and 1974. The results suggested that in this period the Earth’s inner core had stopped and began to rotate in the opposite direction with respect to the crust, a result similar to that of the current study.. “The new study is very good, but even so it is difficult to confirm if what it proposes is true,” Vidale now warns. The problem is that the number of valid earthquakes for these analyzes is limited. In addition, these jobs require extensive computing time with powerful computers to fully simulate the Earth. “It is possible that in five or 10 years, with more data and better simulations, we can know if, as it appears, the Earth’s core follows these cycles,” adds the American scientist.
Puy Ayarzadirector of the Department of Geology at the University of Salamanca, believes that the new work “it is novel and provocative”. What was observed by the Chinese geologists, he says, “fits well with contrasting facts such as that the Earth’s magnetic field has been changing very rapidly in recent decades and its dipole character is weakening.” [con polos norte y sur]”. “This dipole character is given by the differential rotation of the inner nucleus within the outer one, so it could be true that it is rotating more slowly. It seems that the movement of the inner core may not be as uniform as we thought. The work is a step forward and provides a lot of data. We will see if his conclusions are true, ”he adds.
By Nuno Dominguez
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