Have you ever heard of the geodynamo? Perhaps not, but its presence has certainly had a huge impact on your life. The theory describes how Earth's magnetic field is generated and maintained by convective flow in the Earth's fluid outer core. According to physicists, this convection is driven by gravitational energy from secular cooling and differentiation of the Earth. A lot of big words, right? And an even bigger significance, because the magnetic field generated by the geodynamo is what allows our planet to deflect harmful ionizing particles from the solar wind and cosmic rays. So why do we know so little about the geodynamo’s origin?
Well, new research published in Nature Communications by an international collaboration of investigators suggests that the presence of lighter elements in the principally iron core could influence the geodynamo's genesis and sustainability. The team was led by current and former Carnegie scientists Alexander Goncharov, Nicholas Holtgrewe, Sergey Lobanov, and Irina Chuvashova.
While we know that Earth’s core is predominately iron, seismic data suggests that during the formation of our planet, some lighter elements like oxygen, silicon, sulfur, carbon, and hydrogen dissolved into it.
The presence of these elements amongst others, including silicon, could affect the thermal conductivity of the geodynamo. In order to investigate this idea, the research team utilized lab-based mimicry of deep Earth conditions to simulate how they would affect the transmission of heat from the planet's iron core out into the mantle.
"The less thermally conductive the core material is, the lower the threshold needed to generate the geodynamo," Goncharov explained. "With a low enough threshold, the heat flux out of the core could be driven entirely by the thermal convection, with no need for the additional movement of material to make it work."
The presence of silicon turned out to be hugely significant. From their simulations, the researchers discovered that with a concentration of about 8 weight percent silicon, the geodynamo could have functioned on heat transmission alone for the planet's entire history!
The researchers plan to continue their investigations in order to determine the influences of oxygen, sulfur, and carbon in the core.