Geophysicists have found that their favored dynamo theory for Earth’s magnetic field is less sustainable than thought, leaving them wondering how our planet retained its magnetic field for “geologic time.”

Nature wrote, “New calculations show that the electrical resistance of Earth’s liquid-iron core is lower than had been thought. The results prompt a reassessment of how the planet’s magnetic field has been generated and maintained over time.”  This is from Bruce Buffett,1 reporting on a paper by Pozzo et al. in the same issue.2  They said their findings have significant implications:

Revised estimates of σ and k calculated directly at core conditions have fundamental consequences for the thermochemical evolution of the deep Earth. New estimates of the power requirements for the geodynamo suggest a CMB [core-mantle boundary] heat flux in the upper range of what is considered reasonable for mantle convection unless very marginal dynamo action can be sustained, while a primordial inner core is only possible with a significant concentration of radiogenic elements in the core. There are objections to a high CMB heat flux and also to radiogenic heating in the core, but one of the two seems inevitable if we are to have a dynamo. If the inner core is young, these high values of conductivity provide further problems with maintaining a purely thermally driven dynamo. A thermally stratified layer at the top of the core also appears inevitable. Viable thermal history models that produce thin stable layers and an inner core of age ~1 Gyr are likely to require a fairly rapid cooling rate and some radiogenic heating. The presence of a stable layer, and the effects associated with an increased electrical conductivity, have significant implications for our understanding of the geomagnetic secular variation.

This makes it sound like the geodynamo is a “theory in crisis” with two requirements, both of them undesirable to maintain the dynamo for the assumed age of the Earth….

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