The hunt has been on for a source of extra power to account for the dynamo that generates the Earth's magnetic field. A synthesis of computation and experiment now suggests that the search may not be necessary after all. The Earth's magnetic field originates in the core, a fluid region almost 3,000 km below our feet of which the main constituent is molten iron. The basic mechanism of field generation is generally accepted―it is a dynamo process, in which the magnetic field is maintained by convection of the highly electrically conducting fluid. But the details are less clear. For example, how much power is required to drive the geodynamo? With current estimates, the inferred heat flow from the core is not enough to drive a dynamo over most of Earth's history, as is required from measurements of a strong magnetic field recorded in ancient rocks. One possible explanation lies in a re-evaluation of the composition of the core―could it contain more potassium, which would provide an additional heat source from radioactive decay? Some geochemists are coming round to this idea, but it remains controversial. On page 169 of this issue, Christensen and Tilgner offer an alternative―they argue that less power than previously estimated is required to drive the geodynamo, and that no additional heat sources are necessary.
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