| Going faster
London, Aug. 26: The Earth’s inner core is rotating faster than the rest of the planet, scientists have found.
An ingenious comparison of earthquakes has revealed that the solid ball of iron and nickel at the centre of the planet is spinning about half a degree more quickly than its upper layers.
While the excess spin is very small, it means that over 900 years the very centre of the Earth will complete one more revolution than the rest.
The findings settle a scientific controversy that has raged for nine years, since Paul Richards of Columbia University in New York and Xiaodong Song of the University of Illinois at Urbana-Champaign first proposed the core’s odd behaviour.
Their 1996 study was widely disputed, with many researchers suggesting that the apparent extra spin was in fact caused by measurement errors.
While the core is poorly understood ' the great physicist Richard Feynman once said we know more about the centre of the Sun than the centre of the Earth ' it is critical to the make-up of the planet, and indeed to life on Earth.
Currents in the core create a vast dynamo that generates the planet’s magnetic field. Without this, the surface would be exposed to radioactive cosmic rays and plasma from solar flares that would make the existence of complex life all but impossible.
In the new study, details of which are published in the journal Science, a team led by Song and Richards made use of earthquakes in the South Sandwich Islands, in the Pacific Ocean.
Two earthquakes, in 1993 and 2003, occurred no more than half a mile apart and generated precisely the same patterns of peaks and troughs on seismographs thousands of miles away in Alaska.
The seismic waves from the 2003 earthquake, which passed through the Earth’s core, arrived at the Alaska monitoring station about a tenth of a second more quickly than they did in 1993.
Only an inner core spinning faster than other parts of the Earth can explain this.
The most likely explanation is electromagnetic coupling, the phenomenon that drives electric motors. “The magnetic field generated in the outer core diffuses into the inner core, where it generates an electric current,” Song said.
“The interaction of that current with the magnetic field causes the inner core to spin.”