Conductivity measurements to help scientists map water in Earth's mantle

Scientists at Lawrence Livermore National Laboratory believe their improved understanding of electrical conductivity inside Earth's mantle will help them map the distribution of water inside Earth.

Earth is the only planet in the solar system to develop plate tectonics and large liquid water oceans on its surface. Planetary scientists believe the distribution of significant amounts of water inside Earth's mantle is linked with the two phenomena.

Understanding the diffusion of hydrogen in the mantle is key to measuring the distribution of water inside Earth. Hydrogen plays an important role in encouraging electric conductivity, but researchers haven't been able to accurately quantify the relationship between hydrogen and conductivity.

To do so, scientists looked to olivine, the most abundant mineral in the upper mantle.

"We approached the problem from a different perspective, using new hydrogen diffusion measurements to infer what the contribution of hydrogen would be to electrical conductivity," lead researcher Wyatt Du Frane, a scientists at LLNL, said in a news release. "Our experiments on olivine indicated a larger temperature dependence than previously thought to occur for this phenomenon. The contribution of hydrogen to electrical conductivity, while modest at lower temperatures, becomes quite large at the temperatures expected to occur in the mantle."

Not only does the diffusion of hydrogen help explain the high conductivity measured in the upper mantle, it also confirms the significant concentration of dissolved water in Earth's interior.

"The amount of hydrogen required to match geophysical measurements of electrical conductivity inside Earth are in line with the concentrations that are observed in oceanic basalts," Du Frane said. "This demonstrates that geophysical measurements of electrical conductivity are a promising tool for mapping out water distributions deep inside the Earth."

Scientists detailed their analysis of hydrogen diffusion and conductivity in olivine in the journal Scientific Reports.