Model Shows How Iron Was Distributed in the Early Earth Core

In a mind-boggling piece of engineering achievement, experts at the University of California in Davis (UCD) used a supercomputer to model the early stages of the Earth's crust, back in the days when the planet was just solidifying from an incandescent ball of red-hot lava. The goal of the simulation was to understand how iron-bearing minerals spread through the inner and outer layers of the planet, and how different isotopes of the metal were spread all over the globe at the very beginning. In order to do that, the computer application had to mimic the conditions that existed at the time, and to subject virtual iron-rich minerals to high pressures and lava currents.

The results obtained by the UCD team could usher in a new wave of research dedicated to the planet's mantle, the 1,800-mile-deep layer inside Earth, that stretches all the way from the thin crust made up by the tectonic plates to the metallic core at the center. “Now that we have some idea of how these isotopes of iron were originally distributed on Earth, we should be able to use the isotopes to trace the inner workings of Earth's engine,” Chancellor's fellow and UCD Professor of Geology James Rustad explains. He is also the senior author of a new study detailing the results of the simulation, published online Sunday, June 14th, in the ahead-of-print issue of the journal Nature Geoscience.

Despite the fact that the mantle may appear to be still to the human eye, it's actually moving, albeit over millions and hundreds of millions of years, in a motion similar to that taking place in a bowl of thick soup, placed over a low-intensity flame. That slow motion is the engine behind the movement of the tectonic plates, rocky formations just miles thick, on which continents and oceans reside. The plates simply float on top of the mantle, and are driven into each other (such as in the Pacific Circle of Fire), or away from each other (such as in the mid-Atlantic rift) at slow, but constant, speeds.

Some of the major sources of information that geologists have at their disposal for analyzing iron distribution around the planet are four isotopes of the element, which can be found in various configurations in lava coming out of the crust either in Hawaiian volcanoes or in Atlantic rifts. Some experts hypothesize that the magma carrying these isotopes could be originating at the core-mantle divide, some 1,800 miles under the surface. “Geologists use isotopes to track physico-chemical processes in nature the way biologists use DNA to track the evolution of life,” UCD Associate Professor of Geology Qing-zhu Yin, a co-author of the new paper, adds.

According to the results supplied by the 144-processor computer used in the research, the heavier isotopes of the metal were concentrated near the bottom of the crystallizing mantle, which was at the time just starting to take shape. By using lasers and a tool called a diamond anvil, the researchers now hope to take their experiments to the next level, and to determine how iron isotopes vary in pure chemicals located at the core-mantle boundary. The tools can mimic the required temperatures and pressure conditions. “Much more fun work lies ahead. And that's exciting,” Yin says.