Where did our planet's magnetic field come from? According to new research, Earth's mantle, not its core, may have generated the planet's early magnetic field. The Earth's mantle is made of silicate material that is normally a very poor electrical conductor.
Therefore, even if the lowermost mantle were liquid for billions of years, rapid fluid motions inside it wouldn't produce large electrical currents needed for magnetic field generation, similar to how Earth's dynamo currently works in the core.
Liquid silicate more electrically conductive?
In a study appearing in the journal Earth and Planetary Science Letters, Scripps Oceanography researchers Dave Stegman, Leah Ziegler and Nicolas Blanc provide new estimates for the thermodynamics of magnetic field generation within the liquid portion of the early Earth's mantle.
Stegman's team asserted the liquid silicate might actually be more electrically conductive than what was generally believed. "Currently we have no grand unifying theory for how Earth has evolved thermally," Stegman said. "We don't have this conceptual framework for understanding the planet's evolution. This is one viable hypothesis."
New research lends credence to an unorthodox retelling of the story of early Earth first proposed by a geophysicist at Scripps Institution of Oceanography at University of California San Diego. It has been a bedrock tenet of geophysics that Earth's liquid outer core has always been the source of the dynamo that generates its magnetic field.
Mantle may have provided young its first magnetic shield
In another paper, Arizona State geophysicist Joseph O'Rourke applied Stegman's concept to consider whether it's possible that Venus might have at one point generated a magnetic field within a molten mantle.
Magnetic fields form on Earth and other planets that have liquid, metallic cores, rotate rapidly, and experience conditions that make the convection of heat possible. If Stegman's premise is correct, it would mean the mantle could have provided the young planet's first magnetic shield against cosmic radiation.
It could also underpin studies of how tectonics evolved on the planet later in history. "If the magnetic field was generated in the molten lower mantle above the core, then Earth had protection from the very beginning and that might have made life on Earth possible sooner," Stegman said.
