How has Earth’s magnetic field survived for billions of years? Is it a question that has long tormented the scientists. And that can now be answered.
Researchers Dave Stegman, Leah Ziegler, and Nicolas Blanc have worked to prove that the old theory saying that the magnetic field of our planet was generated by the solid core of it is, in fact, wrong. They say it’s the liquid portion of the early Earth’s mantle that did it.
Earth’s magnetic field, or the geomagnetic field, extends from the Earth’s interior out into space. There, it interacts with the solar wind. The magnetic field is generated by electric currents due to the motion of convection currents of molten iron in the Earth’s outer core.
These convection currents are caused by heat escaping from the core, a natural process called a geodynamo.
Earth’s outer core is a fluid layer about 2,400 km thick and composed of mostly iron and nickel that lies above Earth’s solid inner core and below its mantle.
The transition between the inner core and outer core is located approximately 5,150 km beneath the Earth’s surface. Unlike the inner (or solid) core, the outer core is liquid.
The mantle is responsible for the Earth’s magnetic field, not the core
It was believed that the Earth’s mantle has remained entirely solid since the very beginnings of the planet. But in 2007, French researchers claimed that it was not so. They say that the core was initially molten. And that it was so for half of the planet’s age.
That’s over 2 billion years the core was a basal magma ocean. Magma oceans exist during periods of a planet’s accretion when the planet is completely or partly molten.
In 2013, Dave Stegman went further and claimed that the basal magma ocean was the source of the geomagnetic field.
The only issue, at that time, was that the mantle could produce just a silicate dynamo, and silicate material is a very poor electrical conductor. So, the only way Stegman’s theory could sustain was if the electrical conductivity of silicate liquid was remarkably high.
For the first time, quantum-mechanical computations to predict the conductivity of silicate liquid at basal magma ocean conditions were made possible by Lars Stixrude, from UCLA.
And Sixtrude concluded: “We found very large values of the electrical conductivity, large enough to sustain a silicate dynamo.”
Another study, from Arizona State University, made by geophysicist Joseph O’Rourke, applied Stegman’s concept to consider if Venus might have generated a magnetic field within a molten mantle.