A new study has determined that the inner core of our planet is slowing down, or backtracking, relative to the surface of the planet. The findings have been reported in Nature, although the implications are unclear.
For decades, scientists have debated about Earth's inner core movement. Some studies have determined that the inner core has a faster rotation than the surface. However, this study has provided evidence that the inner core began to slow down around 2010, and got slower than the surface's rotation. This is the first time in forty years that the core has backtracked and reversed enough to be rotating slower than the Earth's mantle.
"When I first saw the seismograms that hinted at this change, I was stumped," said John Vidale, a Professor at the University of Southern California . "But when we found two dozen more observations signaling the same pattern, the result was inescapable. The inner core had slowed down for the first time in many decades. Other scientists have recently argued for similar and different models, but our latest study provides the most convincing resolution."
The inner core is about 3,000 miles (4,828 kilometers) below the surface of the planet, and is made of iron and nickel. This sphere of metal is surrounded by an outer core made of liquid iron and nickel. The outer core generates the planet's magnetic field. Researchers can only study this feature of the planet by using seismic recordings to extrapolate data about the core's movement.
Repeating earthquakes are seismic events that happen at the same place, generating identical seismograms. These seismic events and waveforms were used to study the core for this research. Data that was recorded around the South Sandwich Islands between 1991 and 2003, for example, captured 121 repeating earthquakes. Another instance of twin Soviet nuclear tests in 1971 and 1974 were also used, along with some other data from other nation's nuclear tests.
The work indicated that the outer, liquid iron is causing the slowdown. This outer core can affect gravity in dense regions of the mantle.
So what does this slowdown mean? Scientists can only speculate at this stage. The length of days might be changed, but only at minuscule timescales, or fractions of a second. "It's very hard to notice, on the order of a thousandth of a second, almost lost in the noise of the churning oceans and atmosphere," said Vidale.
The investigators want to know more about why these changes are occurring. "The dance of the inner core might be even more lively than we know so far," Vidale said.
Sources: University of Southern California, Nature