Magazine article Science News

Scientists Eye Whirlpool in Earth's Core

Magazine article Science News

Scientists Eye Whirlpool in Earth's Core

Article excerpt

Reaching back to the compass readings of early polar explorers, geophysicists have now pieced together evidence of a slowly whirling vortex within Earth's liquid-iron interior. This result suggests that a long-nurtured theory of Earth's magnetism is on target.

Einstein described geomagnetism as one of the chief unsolved puzzles of physics. Neither Earth's liquid outer core nor its solid, yet superhot, inner core has struck scientists as likely sources of its magnetic field. Heat cooks the magnetism out of magnets, and liquefaction melts it away. Physicists were flummoxed.

Over several decades, an idea has emerged: Earth's core acts like a giant dynamo. Heat causes churning in the liquid outer core, which Earth's rotation transforms into a liquid whirlpool that swirls around the planet's axis. This circulation produces a magnetic field roughly aligned with that axis.

Basic physics says that electric currents give rise to magnetic fields and moving magnets generate electric currents. These two effects enable a churning outer core to magnify the small magnetic field that the planet captured from its surroundings as it formed. As opposing streams of molten iron, carrying tiny magnetic fields, sweep past one another, each induces currents in the other. This creates more magnetism, which induces more currents, and so on.

Supercomputer simulations suggest that dynamo motions could indeed arise within the core and create a field like Earth's. The simulations fall short of nailing the matter down, however. "You have to make approximations," says geophysicist Bruce A. Buffett of the University of British Columbia in Vancouver. "We really don't know how accurate these simulations are," he says.

In the Nov. 11 NATURE, however, geophysicists at Johns Hopkins University in Baltimore report that a whirlpool slowly spins in the liquid outer core far below the North Pole, much as the simulations predict. …

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