Friday, January 27, 2023

Earth’s core has slowed down

Earth’s core — a ball of pure iron more than 5,000 kilometers deep that is hotter than the Sun — may have slowed down and is spinning away from the planet’s surface, according to a study published this Sunday. nature geology, This pause can have global effects, such as shortening days by fractions of a second and affecting climate and sea levels.

Two of the paper’s authors are Yi Yang and Xiaodong Song from the Institute of Theoretical and Applied Geophysics of Peking University in China. Both have tried to solve an existing puzzle because, a few decades ago, it was confirmed that Earth contained one planet inside another.

The smallest would be the inner core: a solid sphere about 1,200 kilometers in diameter that spins freely in a sea of ​​molten iron and other metals known as the outer core. The free rotation of this massive sphere is like a dynamo that generates Earth’s magnetic field, which shields it from cosmic radiation and allows life to exist on its surface. The Earth’s mantle extends around this core with a thickness of about 3,000 kilometers, and finally, the outer crust, with an average thickness of only 40 kilometers.

Reaching the center of the Earth is an impossible challenge. In the late 1970s, Soviet scientists began drilling a well on the Kola Peninsula in northern Russia. After years of work, they reached a depth of 12 kilometers, the maximum ever dug into the bowels of the planet. It seems impossible to go much further without collapsing under the pressure of the walls of the hole.

The common method of understanding what happens in the deep regions is to analyze earthquakes. The variation of seismic waves as they pass through the planet reveals the internal structure of the core and its rate of rotation.

the days are getting shorter

In 1996, Xiaodong Song, working in the United States, was one of the authors of an important study that analyzed seismic signals and showed that the Earth’s inner core rotates faster than the crust. In 2005, this scientist confirmed these observations and elaborated that approximately once every 900 years the core rotates more than the rest of the planet. This lack of synchronicity is partly due to the fact that the progressive distance of the tides and the Moon is slowing the crust, meaning that days do not last exactly 24 hours—1,400 million years ago, a day was less than 19 hours. – In parallel with this phenomenon, the day has been getting shorter by fractions of a second for some years without anyone knowing why.

Now Song analyzed nearly 200 earthquakes in the South Sandwich Islands, a remote Atlantic archipelago near the South Pole, between 1960 and the present day. These earthquakes occurred in pairs and generated similar waves. But when they were caught at stations in Alaska near the North Pole, their waves came out slightly out of step if, while passing through the nucleus, it rotated faster than the crust.

Analysis of these shocks, along with computer models that reconstruct the entire Earth, show that Earth’s core slowed down in 2009 and has since slowed down slightly compared to the crust. This observation has an unusual implication. “Viewed from space, the core rotates at roughly the same speed as the rest of the planet. But from the perspective of the surface, where the seismic stations are, the core is now rotating in the opposite direction; to the west”, explains Song El Pais.

Scientists have also discovered that a similar break already occurred in the mid-1970s. “We estimate that there is an oscillation cycle that lasts about seven decades,” Song explains. “It shows that there is a resonance that connects all the layers of the Earth that happen with that rhythm,” he details.

The incident could have global implications. “In recent years, the days are getting shorter and it is possible that this is partly due to the Earth’s core,” he argues. They say the main anomaly is now one thousandth of a second smaller than it was in 1970. “The rotation of the inner core within the outer also changes the internal gravity field and causes distortions on the surface, which in turn can affect sea level. These changes can also affect the global temperature of the planet”, Geologist’s suggestion.

In early 2022, John Widale and Wei Wang of the University of Southern California analyzed the shockwaves caused by a pair of nuclear bombs detonated by the Soviet Union between 1971 and 1974. The results suggested that Earth’s inner core had stopped and started over in that period. For rotation in the opposite direction with respect to the crust, results similar to the present study. Vidal now cautions, “The new study is great, but it is still difficult to confirm what it proposes.” The problem is that the number of earthquakes valid for these analyzes is limited. Furthermore, these jobs require extensive computing time with powerful computers to fully simulate Earth. “It is possible that in 5 or 10 years, with more data and better simulations, we will be able to know whether the Earth’s core seems to follow these cycles,” says the American scientist.

Puy Ayarza, director of the Department of Geology at the University of Salamanca, believes the new work is “novel and provocative.” What was observed by the Chinese geologists, he says, “fits well with contrary 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 core within the outer core, so it may be true that it is rotating more slowly. It seems that the speed of the inner core may not be as uniform as we thought.” The work is a step ahead and provides a lot of data. We will see if their findings hold true”, he added.

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