ASU researchers discover new mineralogy of the deep Earth

October 19, 2022

What is the structure of the Earth? For starters, it consists of several layers: the crust, the upper and lower mantle, and the core.

The mantle makes up most of our planet’s volume — 84%. The lower mantle represents 55% of the Earth’s volume; it is also hotter and denser than the upper mantle.  Graphic illustration of a mixture of gray, pyramid-like structures and blue and yellow spheres, representing minerals found in Earth's lower mantle. Atomic-scale crystal structures of mantle perovskites. From left to right: Bridgmanite (magnesium rich), new mantle perovskite with both magnesium and calcium, Davemaoite (calcium rich). Credit: Crystal structure images courtesy Dan Shim; background image courtesy iStock/Getty Images. Download Full Image

The lower mantle has played an important role in the Earth’s evolution, including how Earth has cooled over billions of years, how materials have been circulated, and how water is stored and transported from and to the deep interior over a geologic time scale.  

For more than seven decades, the mineralogy of the lower mantle has been studied extensively. The decades of studies, including laboratory experiments, computational simulations and the study of inclusions in deep diamonds, led to the conclusion that the lower mantle consists of three main minerals: bridgmanite, ferropericlase and davemaoite.  

In a study recently published in Nature, a team of scientists — including Byeongkwan Ko, former PhD student at Arizona State University and now a postdoctoral researcher at Michigan State University, and Dan (Sang-Heon) Shim, professor at ASU's School of Earth and Space Exploration and a Navrotsky Professor of Materials Research at ASU, have completed a new high-pressure experiment employing some different styles of heating to reveal an additional mineral residing in the lower mantle.

Among these three main minerals, two minerals — bridgmanite and davemaoite — have both so-called perovskite-type crystal structures. This structure is also widely known in physics, chemistry and materials engineering, as some materials with the perovskite-type structure have shown superconductivity.

At shallow depths, minerals with similar crystal structures often merge and become single minerals, typically under a high-temperature environment. For example, mineral diopside has both calcium and magnesium, and is stable in the crust. Despite the structural similarity, however, existing studies have shown that davemaoite, rich in calcium, and bridgmanite, rich in magnesium, remain separate throughout the lower mantle. 

“Why davemaoite and bridgmanite do not merge to one despite the fact that they have very similar atomic-scale structures? This question has fascinated researchers over two decades,” Shim said. “Many attempts have been made to find conditions where these two minerals merge, yet the answer from experiments has been consistently two separate minerals. This where we felt we need some fresh new ideas in experiments.”

The new experiment was an opportunity for the research group to try various heating techniques to compare methods. Instead of increasing temperature slowly in conventional high-pressure experiments, they increased temperature very fast to the high temperature related to the lower mantle, reaching 3,000 to 3,500 degrees Fahrenheit within a second. The reason for this was that once two perovskite-structured minerals form, it becomes very difficult for them to merge, even if they enter into temperature conditions where single perovskite mineral should be stable.  

By heating the samples fast to target temperatures, Ko and Shim were able to avoid formation of two perovskite-structured minerals at low temperatures. Once they reach the temperature of the lower mantle, they monitor what minerals form for 15 to 30 minutes using X-ray beams at the Advanced Photon Source. They found that only single perovskite mineral forms, unexpected from the previous experiments. They found that at sufficiently high temperatures, greater than 3,500 F, davemaoite and bridgmanite become a single mineral in the perovskite-type structure.  

“It has been believed that a large size difference between calcium and magnesium, the major cations of davemaoite and bridgmanite, respectively, should hinder these two minerals from merging,” Ko said. “But our study shows that they can overcome such difference in hot environments.”

The experiments suggest that the deeper lower mantle with sufficiently high temperature should have a mineralogy different from the shallower lower mantle. Because the mantle was much warmer in early Earth, the group’s new results indicate that most of the lower mantle had a single perovskite-structured mineral then, which means the mineralogy differed from the present-day lower mantle. 

This new observation has a range of substantial impacts on our understanding of the deep Earth. Many seismic observations have shown that the deeper lower mantle properties are different from the shallower lower mantle. The changes are reported to be gradual. The merge of bridgmanite and davemaoite is shown to be gradual in the research group’s experiments. Also, the properties of a rock with three main minerals — bridgmanite, ferropericlase and davemaoite — does not match well with the properties of the deeper lower mantle. Ko and collaborators predict that these unresolved problems can be explained by a merge of bridgmanite and davemaoite to a new single perovskite-structured mineral.

Other contributing authors on this study are Eran Greenberg, University of Chicago; Vitali Prakapenka, University of Chicago; E. Ercan Alp, Argonne National Laboratory; Wenli Bi, University of Alabama at Birmingham; Yue Meng, Argonne National Laboratory; Dongzhou Zhang, University of Chicago and University of Hawai’i at Mano.

Media Relations and Marketing Manager, School of Earth and Space Exploration


2 ASU professors appointed as first-ever Navrotsky Professors of Materials Research

May 3, 2022

Last year, Alexandra Navrotsky, the director of Arizona State University’s Navrotsky Eyring Center for Materials of the Universe, made a $10 million gift bequest to the university to ensure the long-term growth of materials science. As part of these efforts, two ASU professors have recently been appointed the first-ever Navrotsky Professors of Materials Research.

Candace Chan, an associate professor in the School for Engineering of Matter, Transport and Energy, and Dan (Sang-Heon) Shim, a professor in the School of Earth and Space Exploration, were selected for the professorship based on their significant contributions in the field of materials research. Side-by-side portraits of ASU professors Candace Chan (left) and Dan (Sang-Heon) Shim. Candace Chan (left) and Dan (Sang-Heon) Shim. Download Full Image

“The Center for Materials of the Universe is at the forefront of materials science research, and home to some of the brightest minds in the field,” said Kenro Kusumi, dean of natural sciences in The College of Liberal Arts and Sciences. “The Navrotsky Professorships will provide the opportunity for these outstanding faculty members to not only innovate in their research but also grow in their careers. As the first two to receive this prestigious appointment, I am eager to see what exciting new discoveries professors Chan and Shim make in the next two years.”

Through the Navrotsky Professorship of Materials Research, Chan and Shim will serve to build the field of solid state science and materials research at ASU. The funding they receive will also enable them to step into a leadership role, while encouraging materials research innovation and collaborations that bridge the Department of Physics, the School of Molecular Sciences, the School of Earth and Space Exploration and the School for Engineering of Matter, Transport and Energy.

“It is thrilling to honor such wonderful colleagues,” Navrotsky said.

During the two-year term, they will pursue and promote new ideas, discoveries and technologies, advocate for and seek new funding opportunities and provide outreach to expand research in the broad field of materials.

“Dr. Navrotsky’s research has left an indelible mark on the field of materials science, and we are extremely grateful for her generosity to ensure the future of the discipline,” said Lenore Dai, director of the School for Engineering of Matter, Transport and Energy in the Ira A. Fulton Schools of Engineering. “We are excited for the positive impacts this professorship will continue to have at ASU and in the scientific community at large through stimulating research collaborations, continuous innovation and opportunities for workforce development.”

“I congratulate professors Chan and Shim on their selection as the inaugural awardees for the Navrotsky Professorships,” said Meenakshi Wadhwa, director of the School of Earth and Space Exploration. “These professorships will provide these faculty the ability to widen the aperture for the kinds of exploratory research projects that are not easily funded by federal agencies, but have the potential for being transformational for materials research.”

The Navrotsky Eyring Center for Materials of the Universe unites cosmology, astrophysics, astronomy, planetary science and exploration, and mineralogy and petrology with materials science and engineering, chemistry, physics and biology to address grand questions of the complex chemistries and evolution of planets. The center strives to attract and inspire scientists across all science, technology, engineering and mathematics (STEM) fields to explore alien and extreme conditions and environments with the expectation of discovering new, useful materials and understanding the formation and evolution of planets.

“The idea of the Center for Materials of the Universe by Professor Navrotsky is revolutionary in that we can understand distant planets outside of our solar system by studying chemistry under a wide range of pressure, temperature and composition,” Shim said. “I have been extremely lucky to participate in the exciting intellectual journey in the Center for Materials of the Universe from the beginning. The Navrotsky professorship will allow me to pursue some of the new research directions identified from the first few years of the Materials of the Universe initiative.”

“I am truly honored to receive this appointment. Professor Navrotsky has touched all areas of materials research with her innovative methods for understanding the fundamental thermodynamic properties of materials. Indeed, it seems like she has studied all the materials that exist in the universe at one point or another,” Chan said. “I look forward to working with her and the other members of the Center for Materials of the Universe on the challenges that face us as we strive toward engineering materials solutions for decarbonization, sustainable and clean energy, and critical materials needed for technologically important applications.”

Emily Balli

Manager of marketing and communications, New College of Interdisciplinary Arts and Sciences