Professor of Geology James Rustad and his co-author Associate Professor Qing-zu Ying used a supercomputer to examine how heat and pressure similar to that present at the time when the Earth solidified affects iron-bearing minerals. By heating and squeezing these materials, they were able to map how different isotopes of iron were distributed during the initial formation of the solid structure of the planet. Scientists can use this information along with knowledge of the current distribution of these same isotopes on the surface at geological hotspots like volcanos and deep ocean ridges to explore how the iron rose to the surface over time.
Modeling the effects of pressure and heat on the iron is not as straightforward as it might sound. Temperatures in the region of the mantle near the core are estimated to reach 4500 degrees Kelvin. At that extreme heat the differences between the isotopes are minuscule. In addition, the pressure from thousands of feet of solid rock alters the basic structure of the iron atom. Rustad handled this by calculating the effects of a range of temperatures, pressures, and electron spin states on the minerals ferroperovskite and ferropericlase which contain the vast majority of iron found in the lower mantle region.
Even with a 144-processor computer, these calculations were so complex it took scientists a month to complete each run. In the end, results showed that nearly all of the iron in the Earth’s mantle originated in the region near the core. The iron rose toward the surface of the planet slowly over time thanks to the slow churn of the mantle caused by heat from the molten core and the radioactive decay of other elements within the mantle.
The scientists say they hope to one day verify these conclusions with actual samples from the lower levels of the mantle, but such experiments are still far from reality. In the meantime, Ranstad and Yin plan to model the heat and pressure conditions found during the mantle crystallization process in the laboratory setting using lasers and a diamond anvil.
TFOT has previously reported on other discoveries related to planetary evolution and planetary science including an MIT study showing that young planets remain hot longer than expected, short National Geographic documentaries on the Earth’s atmosphere and the evolution of oceans, and recent discoveries about the chemistry and geology of Mercury prompted by data from NASA’s Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft.
Read more about these efforts to model iron in the Earth’s interior in this University of California at Davis news article.
Icon image credit: NASA, Johns Hopkins University Applied Physics Laboratory, and Carnegie Institution of Washington.