Scientists eye whirlpool in Earth's core By O. Baker Heat-driven circulation of liquid iron in Earth's fluid core constitutes the geodynamo believed to produce the planet's magnetic field. A rock mantle surrounds the core. 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. 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.