The rotating, solid inner core of the Earth can slow down by a minimal amount, according to evidence from earthquakes.
Researchers Yang Yi and Song Xiaodong from Peking University in China looked at measurements of seismic waves passing through the Earth as a result of nearly identical earthquakes dating back to the 1960s.
These waves should be the same in some respects wherever they occur if the Earth had a consistent structure throughout. Differences in wave patterns and travel time, however, provide clues about the much-discussed processes and activities that take place deep inside the Earth over several decades.
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The study published (opens in a new tab)in the journal Nature Geoscience found that the planet’s solid iron core 3,200 miles (5,150 kilometers) below our feet had been rotating slightly faster than Earth’s mantle. But since 2009, there has been little difference in the travel time of waves through the Earth, suggesting that its spin has slowed, and soon, if we could see down to its core, could appear to rotate in the opposite direction to us (not actually changing direction). Previous studies suggested a steady rotation of the inner core.
However, this is not an earth-shattering event. For example, it will not have a major impact on the Earth’s magnetic field, which is generated by the movements of the molten outer core.
There is also evidence that this apparent slowing down, speeding up and oscillation of the rotation of the inner core is part of a cycle that lasts about 70 years, probably due to gravitational coupling between the Earth’s inner core and the much more massive mantle.
The authors conclude that the fluctuation of the rotation of the inner core coincides with changes in the Earth’s surface system, such as small fluctuations in the length of a day and magnetic field. “As such, our finding may implicate dynamic interactions between the deepest and shallowest layers of the solid Earth system,” the authors write.
Still, there is some disagreement about what the data represents, and despite headlines claiming that the Earth’s inner core can change direction, there are some earth scientists and science communicators. encourage a more sensible choice (opens in a new tab) on the course.
“The inner core doesn’t stop,” Hrvoje Tkalcic, a geophysicist at the Australian National University, told CNN.com (opens in a new tab). Instead, Tkalcic said, the finding simply indicates “that the inner core is now more in sync with the rest of the planet than it was a decade ago when it was spinning a little faster.”
“Nothing catastrophic happens,” he added.
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