Imagine Earth’s inner core—the dense center of our planet—as a heavy metal dancer. This iron-rich dancer is capable of pirouettes at ever-changing speeds.
That core could be about to make a big change. Seismologists recently reported that after brief, but peculiar pauses, the inner core changes the way it spins—relative to the motion of Earth’s surface—perhaps once every two to three decades. And, right now, one of those changes could be in the works.
But there’s nothing to worry about: nothing apocalyptic will result from this planetary spin cycle, which may have been going on for eons.
The inner core is like “a planet within a planet, so how it moves is obviously very important,” said Xiaodong Song, a seismologist at Peking University in Beijing and one of the study’s authors.
In 1936, the Danish seismologist Inge Lehmann discovered that the Earth’s liquid outer core envelops a solid metal marble.
Scientists suspect that this mostly iron and nickel ball is 2,446 kilometers long and as hot as the surface of the Sun.
But if the core were inert, the almost identical journeys of sinking waves into the core from earthquakes and nuclear explosions would never change—yet they do over time.
One explanation: the inner core is spinning, deflecting these waves. In the mid-1990s, Song suggested that the core might be spinning at a different speed than the Earth’s surface. Since then, seismologists have found evidence to suggest that the core’s spin can speed up and slow down.
What is happening? One idea is that two titanic forces are in battle. 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 layer below the Earth’s crust, whose immense gravitational field traps the inner core and slows its spin.
By studying core-dipping seismic waves recorded from the 1960s to the present, Song and Yi Yang, another Peking University seismologist and co-author of the study, posit that this enormous push and pull causes the inner core to rotate. backwards and forwards in a cycle of about 70 years.
If it exists, this 70-year rhythm could have a tangible effect on parts of the deepest bowels of the Earth. But it may only be able to cause comparatively little turbulence closer to the surface — perhaps by causing subtle changes in the planet’s magnetic field.
Due to its inaccessibility, this nether realm may forever elude explanation.
By: ROBIN GEORGE ANDREWS
BBC-NEWS-SRC: http://www.nytsyn.com/subscribed/stories/6551457, IMPORTING DATE: 2023-01-30 23:10:07
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