Earth's core runs ahead of crust

BBC NEWS: "US scientists claim to have confirmed that the Earth's core is spinning faster than its outer layers. The team compared seismic waves being produced by pairs of earthquakes occurring at the same location on the planet, but at different times. Waves from these nearly identical quakes passed through the Earth's core, they explain in Science magazine. The results show that the inner core is rotating faster than the rest of the planet by about 0.009 seconds per year. Earth has a solid inner core made of iron and nickel that is about 2,400km in diameter and a fluid outer core about 7,000km in diameter. The inner core plays an important role in the dynamo that generates Earth's magnetic field. An electromagnetic torque from this dynamo is thought to drive the inner core to rotate relative to the mantle and crust. Xiaodong Song, of the University of Illinois at Urbana-Champaign, and Paul Richards, of Columbia University, argued that the inner core was spinning faster than the rest of the planet in 1996. But their findings were greeted with widespread scepticism."