Earth’s inner core, the dense center of our planet, is like a heavy, metal ballerina. This ballerina, made of iron, is capable of pirouettes at ever-changing speeds.
Well now that core may be on the cusp of a big change.according to researchers.
A group of seismologists reported Monday in the journal nature geoscience that after brief but peculiar pauses, the inner core changes the way it spins—relative to the motion of Earth’s surface—once every few decades.
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And it is possible that, at this moment, one of those changes is being made.
This may sound like the plot of a blockbuster movie in which we witness the destruction of the world.
But calm down, since we should not worry, since nothing apocalyptic will result from this cycle of planetary spinwhich may have been going on for eons.
The researchers proposing this speculative model seek to advance the understanding of Earth’s innermost sanctuary and its relationship to the rest of the world.
The inner core is like “a planet within a planet, so the way it moves is obviously very important”said xiaodong songseismologist of the Peking University and one of the study authors.
In 1936, the Danish seismologist Inge Lehman discovered that Earth’s liquid outer core envelops a solid metal core, and that has baffled scientists ever since.
“It is strange that there is a solid iron ball floating in the middle of the Earth”said John Vidale, a seismologist at the University of Southern California, who was not involved in the study.
Scientists believe the core crystallized from a soup of molten metal sometime in Earth’s not too distant past, after the planet’s inner hell had cooled sufficiently.
The inner core cannot be analyzed directlybut energetic seismic waves emanating from the powerful earthquakes and nuclear weapons tests of the Cold War era have ventured through the inner core, illuminating some of its properties.
Scientists suspect that this ball of iron and nickel is about 2,446 kilometers long and almost as hot as the surface of the sun.
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But these waves also created a puzzle. If the core were inert, the travel of waves plunging into the core from earthquakes and nuclear explosions would never change; however, over time, they do.
One explanation is that the inner core is spinning, and it deflects these waves.
In the mid-1990s, Song was one of the first scientists to suggest that the inner core might be spinning at a different speed than Earth’s surface. Since then, seismologists have found evidence that the spin of the inner core can speed up and slow down.
Why is that?
One idea is that two titanic forces are fighting for control of the heart of the world.
Earth’s magnetic field, generated by swirling iron currents in the liquid outer core, is pulling on the inner core, causing it to spin. That momentum is counteracted by the mantle, the slime layer above the outer core and below the Earth’s crust, whose immense gravitational field traps the inner core and slows its spin.
By studying core-immersion seismic waves recorded from the 1960s to the present, Song and Yi Yanganother Peking University seismologist and study co-author, they postulate that this tremendous tug-of-war causes the inner core to spin back and forth in a roughly 70-year cycle.
In the early 1970s, compared to someone standing on Earth’s surface, the inner core was not spinning. Since then, the inner core has gradually rotated faster to the east, outpacing the rotation rate of the Earth’s surface. Subsequently, the spin of the inner core slowed until it appeared to stop sometime between 2009 and 2011.
The inner core is now beginning to gradually turn west relative to the Earth’s surface.
It is likely to speed up and then slow down again, coming to another standstill in the 2040s and completing its last cycle of turning east and west.
This 70-year rhythm, if it exists, could have a tangible effect in some of the deepest parts of the Earth.
But it may only be able to cause comparatively minor turbulence closer to the surface, perhaps causing subtle changes in the planet’s magnetic field, or even very slightly changing the length of a day, which is known to wax and wane at a fraction of a millisecond every six years.
This is just one of several models that seek to explain the erratic travel of waves reaching the nucleus. It is also possible that the innermost layer of the Earth is wobbling. Or, conversely, the ferrous core could have a metamorphic surface, twisting any seismic waves that pass through it.
“No matter which model you like, there is data that does not agree”Vidale said.
Due to its inaccessibility, the explanation of this nether realm could elude us forever.
“Certainly, we may never find out”Vidale said.
But, he added, “I’m optimistic. The pieces will fit together one day.”.
With information from The New York Times