Two Columbia University scientists announced today they had detected and measured the motion of the Earth's inner core for the first time and found that it rotates faster than the planet itself.

They told a news conference their finding had implications for resolving what Albert Einstein considered one of the most important unresolved problems in physics: how Earth's magnetic field has been generated and maintained for 3.5 billion years.

They said the precise techniques they used to reach their finding about the solid iron inner core would also help seismologists better understand earthquakes.

"We need to locate them better, we need to measure them better, we need to get their depth. And all that technical work will get a lift because people will be reminded again of the importance of being able to make very precise measurements," said Paul G. Richards, who along with fellow seismologist Xiaodong Song made the discovery at Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y. They report the findings in Thursday's issue of the journal Nature.

The Earth's solid iron inner core, which was discovered by seismological methods in 1936, is estimated at roughly three-quarters the size of the moon. It rotates independently because it is surrounded by a much larger liquid-iron outer core; together, the two form a giant electrical motor.

Richards, standing beside a clear plastic model of the inner parts of the planet, told reporters they had found that the inner core rotates in the same direction as the Earth but completes its once-a-day rotation faster.

He said a point on the equator of the inner core would move 12 miles a year farther than a similar point on the equator of the Earth's slower-moving crust. Over the past 100 years that has given the core a quarter-turn on the planet as a whole, a motion that is considered remarkably fast for a geological process.

The scientists said the inner core's motion is about 100,000 times faster than the drift of continents.

Richards said the discovery was made possible by advances over the last few years in measuring earthquake-generated seismic waves passing through the inner core. He said he and Song had used seismic waves to view the rotating inner core of the Earth in much the same way that doctors use sound waves to observe a moving fetus inside a mother. The scientists used data from seismic waves from some 50 earthquake locations and from locations of large nuclear test explosions from 1967 to 1995.

In measuring the speed of seismic waves from quakes near the South Sandwich Islands at the southern tip of the planet, which traveled up through the inner core to Alaska, for example, they found the waves arrived three-tenths of a second faster in the 1990s than they did in the 1960s. In contrast, the arrival times of waves that merely passed through the outer core remained constant over the period studied.