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New theory suggests magnesium could be the key to understanding Earth's magnetic field





Two types of chemical convection in Earth's core. Precipitating a thin layer of magnesium-rich minerals at the top of the core provides as much energy for the magnetic field as forcing silicon and oxygen out of the entire inner core. Credit: Joseph O'Rourke


A pair of planetary scientists has come up with a new theory to help explain the mechanism behind the generation of the Earth's magnetic field. In their paper published in the journal Nature, Joseph O'Rourke and David Stevenson, both with the California Institute of Technology, suggest that magnesium that made its way to the core of the planet during its early history could be the key to understanding how the magnetic field was generated in the past and what drives it in the present. Bruce Buffett with the University of California offers a News & Views piece on the work done by the team in the same journal issue.


For many years, scientists have believed that the Earth's  is likely generated by energy that is released as the core cools and material solidifies, and radioactive decay—causing churning, the essence of the geodynamo. But, there is a problem with that idea, scientists also believe that the core did not cool enough to form an inner core, until approximately one billion years ago—that begs the questions of what caused the magnetic field to come about before there was sufficient cooling? The research pair with this new effort suggest it has to do with —they propose that it was introduced to the core during the time when the Earth was being formed, by collisions with other protoplanets, approximately 3.4 to 4.2 billion years ago.
They further suggest that magnesium could make up as much as 1 percent of the material in the core, and because magnesium is only soluble in iron at very high temperatures, they believe that it is slowly precipitating out to the boundary between the core and the mantle. That process, the team notes, would leave the iron behind denser, which would cause the release of energy, which they suggest could explain the power source behind the dynamo. Their theory would explain how it is that the magnetic field has been present for so long—it would also suggest that it continues to play at least a part in how the field is generated today—with magnesium possibly driving iron convection from the top part of the core while the release of light elements from the inner would drive convection from the bottom side.
The team used computer models in developing their theory which means experiments will have to be conducted to help bolster their ideas.
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