A new study published on Friday in the journal Science indicates that the Earth's core is spinning marginally faster than its crust.
Scientists at Columbia University's Lamont-Doherty Earth Observatory and at the University of Illinois at Urbana-Champaign came up with the surprising findings after measuring the difference between earthquake measurements over a period of years.
The scientists compared the time it took seismic waves generated by nearly identical earthquakes to travel through the Earth's inner core.
The findings appear to end a nine-year debate over whether the Earth's inner core is undergoing changes that can be detected on a human timescale, the journal said.
The Earth's core consists of a solid inner core about 2,400km in diameter that spins independently in a fluid outer core about 7,000km across. The new information might yield important data about how the Earth generates its magnetic field, the authors said.
The study was based on the evaluation of identical earthquakes that took place over 35 years.
One comparison focused on two almost identical earthquakes that occurred in the South Atlantic in 1993 and 2003.
The scientists found that the seismograms were almost identical for waves that had travelled only in the mantle, or Earth's crust, and outer core.
But waves that had traveled through the inner core looked slightly different. The waves made the trip through the center of the Earth one-tenth of a second faster in 2003 than in 1993.
The team calculated that the difference was caused by the core's rotating approximately 0.3-0.5 degrees faster than the rest of the Earth. Over a period of 700 to 1,200 years, the inner core appears to make one full extra spin.
"For decades, people thought of the Earth's interior as changing very slowly over millions of years," said study co-author Paul Richards, Mellon Professor of the Natural Sciences at Columbia.
"This shows that we live on a remarkably dynamic planet. It also underscores the fact that we know more about the moon than about what's beneath our feet. Now we need to understand what is driving these changes," he said.
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