By KENNETH CHANG

As the earth turns, the center of the earth turns even faster. Confirming assertions first made in 1996, a team of geophysicists are presenting data in the journal Science today showing that the earth’s inner core, a ball of solid iron larger than the moon, spins faster than the rest of the planet. Over a period of 700 to 1,200 years, the inner core appears to make one full extra spin.”

This is not unexpected, but still interesting. If it’s true, the differential rotation is probably caused by convection currents in the core. Those convection currents which move radially while at the same time traveling in the same direction as the Earth’s rotation are what folks have guessed is causing the Earth’s magnetic field.

The only difficult question here is there is no obvious mechanism that would explain the weakening and flipping of the Earth’s magnetic field which seems to occur every few hundred thousand years or so.