Mantle, not core, may have produced Earth's earliest magnetic field

March 16 (UPI) -- New research suggests Earth's early magnetic field may have been generated by the liquid portion of the young planet's mantle.

The research, published this week in the journal Earth and Planetary Science Letters, considers a trio of studies that could help scientists better understand the geologic evolution of early Earth.

"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."

Geoscientists have long credited Earth's liquid outer core and its molten convection, or dynamo, with generating the planet's magnetic field. In 2007, however, researchers in France published research suggesting Earth's lower mantle wasn't always solid, but was molten. They called it the "the basal magma ocean."

The authors of the latest study, Scripps Oceanography researchers Dave Stegman, Leah Ziegler, and Nicolas Blanc, first published research in 2013 showing a magma ocean in the lower mantle could have been large enough to produce a magnetic field.

Critics claimed that because Earth's mantle is rich in silicate material, a poor conductor of electricity, it's unlikely a liquid mantle could have generated a magnetic field.

For one of the studies reviewed in the latest paper, the scientists set out to determine whether liquid silicate might be more electrically conductive.

"Ziegler and Stegman first proposed the idea of a silicate dynamo for the early Earth," UCLA geophysicist Lars Stixrude said in a news release. "[Results] showed that a silicate dynamo was only possible if the electrical conductivity of silicate liquid was remarkably high, much higher than had been measured in silicate liquids at low pressure and temperature."

Models designed to simulate the electrical properties of silicates inside the basal magma ocean revealed the potential for much greater conductivity than previously estimated.

In another study, Arizona State geophysicist Joseph O'Rourke used the model to show the flowing mantle of Venus could also generate a magnetic field.

"The pioneering studies of Dave Stegman and his collaborators directly inspired my work on Venus," said O'Rourke. "Their recent paper helps answer a question that vexed scientists for many years: How has Earth's magnetic field survived for billions of years?"

If the new hypothesis can gain wider acceptance among geoscientists, it could help researchers develop a theory for how early Earth protected itself from cosmic radiation, allowing for the development of life. The hypothesis could also inspire scientists to rethink the evolution of tectonics on early Earth.

"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.

"Ultimately, our papers are complementary because they demonstrate that basal magma oceans are important to the evolution of terrestrial planets," said O'Rourke. "Earth's basal magma ocean has solidified but was key to the longevity of our magnetic field."