Based on the speed of earthquake waves passing through the earth, geophysicists have calculated the Earth's inner core, which is a solid iron ball larger than the moon, spins faster than the rest of our planet. They claim the inner core appears to be making one full extra spin over a period of 700 to 1,200 years.
Over the course of a day, the earth spins around once, or 360 degrees. The new research indicates that over a year, the inner core spins an extra 0.3 to 0.5 degrees compared with the rest of the planet.
There was also a similar research in 1996 which found a difference of 1.1 degrees per years. However, the new research is more precise. Read on at New York Times