A group of scientists suggested that the inner core of the Earth, a hot and dense ball of solid iron that hides more than 5,000 kilometers deep,
could have recently stopped and is reversing its internal rotation.
The results of the research, based on the analysis of dozens of earthquakes, are published in the journal Nature Geoscience, and, according to its authors, this variation is correlated with small changes in geophysical observations on the Earth's surface, such as the magnetic field or the increase or decrease in the length of days
.
It is the most inaccessible point on planet earth.
The article is signed by
Xiaodong Song and Yi Yang, from Peking University
in China, who say they were "quite surprised."
The results could help unravel the many mysteries deep within Earth, such as
the role the inner core plays in maintaining the
planet's magnetic field and in the rate of rotation, and thus the length of the day, he explains. Nature in your news section.
"But they are just the latest installment in a long effort to explain the unusual rotation of the inner core, and they may not be the last word on it," they added.
The study of the heart of the planet is controversial
The Earth is made up of several layers: the crust, the mantle, the outer core, and the inner core.
The latter, the deepest layer, is a solid iron ball somewhat larger than Pluto that is surrounded by a liquid outer core, allowing it to spin differently from Earth's own rotation.
The spin of the inner core is driven by the magnetic field generated in the outer core and balanced by the gravitational effects of the mantle.
Knowing how the solid inner core rotates could clarify how the Earth's layers interact, explain the authors who, however, point out that the speed of this rotation and whether it varies
has been the subject of debate among the scientific community for years.
An analysis of earthquakes, the key to explaining the phenomenon
It is not easy to study the inaccessible center of the Earth, due to its depth and extreme conditions, but
seismology is an alternative method
for this: earthquakes generate seismic waves that propagate through the interior of the planet and some pass through the core.
The layers of the earth.
Photo: Wikipedia
To conduct their research, Yang and Song analyzed seismic waves from nearly identical earthquakes that have traversed Earth's inner core following
similar trajectories since the 1960s.
They found that, since about 2009, trajectories that previously showed significant temporal variation have seen little change, suggesting that
the inner core's rotation has stopped.
They also found that this may be related to a reversal of the inner core's rotation as part of
a seven-decade oscillation.
These changes could link the inner core to broader geophysical phenomena, such as the increase or decrease in the length of the day on Earth.
By analyzing seismic wave data over the past six decades, Xiaodong Song and Yi Yang concluded that core rotation
"almost stopped around 2009 and then turned in the opposite direction."
"We think that the central nucleus is, with respect to the Earth's surface, rotating in one direction and then in the other, like a swing," they told AFP.
"
A complete cycle (in one direction and in the other) of this movement lasts about seven decades
," according to the researchers.
The last rotation change, before this one in 2009, had occurred in the early 1970s. And the next one will take place in the mid-2040s, completing the cycle, according to Chinese scientists.
How seismic movements traverse the earth.
This movement would more or less adjust to the changes in the length of the day, minute variations in the exact time that the Earth needs to rotate on its axis, they add.
To date, there are few indications about the influence of this rotation on the Earth's surface.
But the two authors are convinced that there are physical links between all the layers that make up the Earth.
The researchers also conclude that this oscillation in the rotation of the inner core
demonstrates the interaction between the different layers of the Earth
, sums up the magazine.
The findings could help deepen our understanding of how deep Earth processes affect its surface.
With information from AFP and EFE
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