A new study suggests that the Earth’s inner core may have stopped and reversed its rotation.
Earthquakes and nuclear explosions can send seismic waves through a mysterious solid iron core.
These waves indicate that the core changed direction in the 1970s and may be undergoing another reversal today.
Living on the surface of the Earth, we see only about 0.5% of the planet. Deep beneath the crust, then the hot rock mantle, and then the liquefied outer core, lies one of our planet’s greatest mysteries: a solid iron core at the center.
This iron ball – Earth’s inner core – may have recently stopped rotating and then changed direction for no apparent reason, according to a new study.
This may sound apocalyptic, but don’t worry. Scientists don’t think it significantly changed life on the surface, except to stun them.
“It’s probably benign, but we don’t want things we don’t understand deep down on Earth,” John Vidale, a geophysicist at the University of Southern California, told The Washington Post.
Published Monday in the journal Nature Geoscience, the peer-reviewed study suggests that Earth’s solid inner core may experience changes in its rotation every few decades.
Traces of earthquakes and nuclear explosions indicate a change around 2009
Scientists can’t look directly at the inner core, but they can get clues about its activity from massive earthquakes and Cold War-era nuclear weapons tests that sent seismic waves bouncing off the Earth’s center.
These deep seismic waves showed that the core is composed mostly of pure, solid iron and nickel and can rotate slightly faster than the rest of the Earth.
If the inner core were neutral and spinning in unison with the outer layers of the planet, similar waves should travel through it along similar paths. But over time, the motion of these waves changes, indicating that the nucleus itself is changing. Spinning is one of the main explanations for these seismic mismatches.
A new study throws a wrench into the core spin. It looks closely at seismic waves from the 1960s to the present day. Scientists discovered a quirk that began in 2009: in the last decade, the paths of similar seismic waves have not changed. This suggests that the inner core may have stopped rotating around this time.
Data from two pairs of nuclear explosions show a similar break around 1971, after which the core rotated eastward, leading scientists to believe that the inner core may stop and reverse its rotation roughly every 70 years.
The theory is that the Earth’s magnetic field attracts the inner core and causes it to spin, while the mantle’s gravitational field creates an opposing force, pulling the inner core. Every few decades, one force may prevail over the other, changing the spin of the great iron ball.
The inner core is a great mystery and we may never solve it
Explaining these quirks in the seismic record is difficult and speculative because there is so little information about the inner core.
Another explanation is that the surface of the inner core changes over time, rather than the entire iron ball rotating. Lianxing Wen, a seismologist at Stony Brook University, discussed this theory in a 2006 paper and still holds to it. He told The Washington Post that this explains the interruptions in 1971 and 2009.
“This study misinterprets seismic signals that are caused by episodic changes in the inner surface of the Earth’s core,” said Wen Post.
A new study may help shed further light on the mysterious nature of the inner core and how it interacts with Earth’s other layers. However, it may be a long time before scientists piece together the full picture – if they ever do.
“It’s certainly possible we’ll never know,” Vidale told The New York Times.
Still, he said, “I’m an optimist. One day the pieces will fall into place.”
Until then, Vidale and his colleagues will just listen to the seismic waves that travel from one side of the planet to the other, straight through an iron core that the researchers themselves will never reach.
Read the original article in Business Insider