The Earth’s core is “braking” and scientists question whether the direction of rotation has changed – News

The inner core is the most inaccessible place on our planet, with extreme conditions: its temperature can even exceed that of the Sun’s surface. It is a solid sphere of iron and nickel that rotates, like the other layers of the Earth, and it is the subject of the question: has this rotation stopped? The answer is no.

according to one article recently published in the journal “Nature Geoscience” and led by Xiaodong Song and Yi Yang of Peking University, it has slowed down and is slightly “shifted” relative to the rotation speed of the rest of the planet. Although in this study the scientists speak of a “recent stop” and that the rotation of the core may have been “reversed”, this does not mean that it has suddenly stopped or is in the opposite direction from the surface of the Earth.

There are nuances, and one of them is that these are relative velocities (relative to another object) and trend reversal, said Maurizio Mattesini, professor of Earth Physics at the Complutense University of Madrid and researcher at the Institute of Geosciences. EFE Organization (IGEO) of the National Research Council of Spain (CSIC).

According to him, “analysis of the inner core is important to understand the dynamics of the planet and its state of health.”

What is the inner core?

The Earth is made up of different layers and at the center, at a depth of 5,000 kilometers, there is a sphere almost entirely made of iron. It is the inner core, with a radius of 1,220 kilometers – slightly larger than Pluto – and is surrounded by a layer 2,260 kilometers thick of a similar composition, but in a molten state, a kind of “layer”.

The inner core was discovered in 1936 by Danish seismologist Inge Lehmann when she analyzed seismic waves.

Convective motions in the liquid outer core, combined with Earth’s rotation, create the magnetic field, which shields Earth from highly energetic particles from the Sun and space, explain Alberto Molina, Marina Puente and Pablo Rivera, also from the IGEO.

Surrounding the core is the mantle, about 2,900 kilometers thick, and above that is the Earth’s crust.

How is the inner core studied?

Analyzing the deepest layer of the Earth is difficult. Drilling to collect samples is impossible, said Mattesini, who recalls that the deepest hole ever drilled is less than 12 kilometers deep.

CT still has technological limitations, so the alternative is seismology.

Earthquakes create seismic waves that propagate through the interior of the planet, and some pass through the inner core, from where they emerge at the Earth’s surface. That’s when seismographs record a signal that contains information from the center of the Earth.

The planet rotates and it takes about 24 hours to make a complete rotation. Until now, it was thought that the inner core was continuing at the same pace as recorded in the last decade, i.e. rotating slightly faster than the mantle and crust, called “hyperrotation”, so that it advanced by about a tenth. one degree each year.

scientific controversy

The first research that talked about oversteer is from 1996 – Song also participated – although later studies have said the opposite (there is even a minority who argue that there are no discriminations in the rotation). There is enough data, but the differences are so subtle that they are open to interpretation and scientific debate.

What does the latest Nature Geoscience study conclude? The core, as of 2009, would have slowed to the same spin rate as the outer layers, or even slightly slower.

These differences in relative velocities are very small, the IGEO scientists explain in their paper.

For example, a car traveling at 120 kilometers per hour overtakes a car traveling at 121 kilometers per hour. “From the window we will see that it is slowly passing us. If the other vehicle slows down to 120 kilometers per hour, we will see it “stopped” next to our car, although it is still moving, just like us. “

Similarly, the core would have slowed down and now, rotating at the same speed as the Earth’s surface mantle and crust, we would see it standing still.

Thanks to the geological record, as IGEO explained on Twitter, we know that years in the geological past were longer in days, meaning the Earth rotated faster and therefore the days were shorter (in the Mesozoic, they were 23 hours long).

This is because the Moon is moving away from us at a rate of 3.82 centimeters per year, and its effect is a slowing down of the rotation, imperceptible on a human scale.

The new study found that the speed at which the Moon brakes showed anomalous values. Using seismic wave propagation from earthquakes, it was discovered that this could be due to the differential rotation of the core.

it’s not the first time

This small change in core rotation is not the first time: the data shows another similar event in 1970.

This suggests that the phenomenon repeats with a periodicity of about 2 to 3 decades, or even 7, depending on the authors, and it seems that the same frequency occurs in other observable geophysical phenomena, such as the geomagnetic field, the length of the day – one millimeter of a second give or take, depending on the shot – or the weather, which suggests they may be related.

But that’s just a hypothesis, Mattesini cautioned, noting that there is no scientific evidence yet.

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Of course, the actual time it takes the Earth to complete one rotation varies slightly – which is important for coordinating navigation systems – and the days are getting longer again.

To learn what lies behind this and the complex dynamics of the Earth, we must continue to investigate.

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