The interior of the Earth is a mystery, especially at greater depths (> 660 km). Researchers only have seismic tomographic images of this region, and to interpret them they need to calculate seismic (acoustic) velocities in minerals at high pressures and temperatures. With these calculations, they can create 3D speed maps and determine the mineralogy and temperature of the observed regions. When a phase transition occurs in a mineral, such as a change in crystal structure under pressure, scientists observe a change in speed, usually a strong discontinuity in the seismic speed.
In 2003, scientists observed in the laboratory a new type of phase change in minerals: a change in the spin of iron in ferropericlase, the second most abundant component of the Earth’s lower mantle. A spin change, or spin crossover, can occur in minerals like ferropericlase under an external stimulus, like pressure or temperature. In the following years, experimental and theoretical groups confirmed this phase change in both ferropericlase and bridgmanite, the most abundant phase of the lower mantle. But no one really knew why or where this was happening.
In 2006, Columbia engineering professor Renata Wentzcovitch published her first paper on ferropericlase, providing a theory for the spin crossing in this mineral. His theory suggested that this had happened over a thousand kilometers in the lower mantle. Since then, Wentzcovitch, who is a professor in the Department of Applied Physics and Applied Mathematics, Earth and Environmental Sciences, and the Lamont-Doherty Earth Observatory at Columbia University, has published 13 papers. with his group on this topic, studying the speeds in all possible situations. of the spin crossing in ferropericlase and bridgmanite, and predict the properties of these minerals throughout this crossing. In 2014, Wenzcovitch, whose research focuses on computational quantum mechanical studies of materials under extreme conditions, particularly planetary materials, predicted how this spin-shift phenomenon could be detected in seismic tomographic images, but seismologists still couldn’t see it.
Working with a multidisciplinary team from Columbia Engineering, University of Oslo, the The Tokyo Institute of Technology and Intel Co., Wenzcovitch’s latest article details how they’ve now identified the spin-crossing signal for ferropericlase, a quantum phase transition deep in the Earth’s lower mantle. This was done by examining specific regions of the Earth’s mantle where ferropericlase is expected to be abundant. The study was published on October 8, 2021 in Nature Communication.
“This exciting discovery, which confirms my previous predictions, illustrates the importance for materials physicists and geophysicists to work together to learn more about what is happening deep in the Earth,” said Wentzcovitch.
The spin transition is commonly used in materials such as those used for magnetic recording. If you stretch or compress only a few nanometer-thick layers of a magnetic material, you can change the magnetic properties of the layer and improve the recording properties of the medium. Wentzcovitch’s new study shows that the same phenomenon occurs over thousands of kilometers inside the Earth, going from the nanoscale to the macro scale.
In addition, geodynamic simulations have shown that the intersection of spins stimulates convection in the Earth’s mantle and the movement of tectonic plates. We therefore believe that this quantum phenomenon also increases the frequency of tectonic events such as earthquakes and earthquakes. volcanic eruptions ”, notes Wentzcovitch.
There are still many regions of the mantle that researchers do not understand, and the change in spin state is essential for understanding velocities, phase stabilities, etc. Wentzcovitch continues to interpret seismic tomographic maps using seismic velocities predicted by ab initio calculations based on density functional theory. She is also developing and applying more accurate material simulation techniques to predict seismic velocities and transport properties, especially in regions rich in iron, molten, or near melting temperatures.
“What’s particularly exciting is that our material simulation methods are applicable to strongly correlated materials – multiferroics, ferroelectrics, and high temperature materials in general,” says Wentzcovitch. “We will be able to improve our analyzes of 3D tomographic images of the Earth and learn more about how the overwhelming pressures from within the Earth’s interior indirectly affect our lives above, on the Earth’s surface.”
Constrain the composition of the Earth’s interior with mineral elasticity
Grace E. Shephard et al, Seismological expression of the spin crossing of iron in ferropericlase in the Earth’s lower mantle, Nature Communication (2021). DOI: 10.1038 / s41467-021-26115-z
Provided by Columbia University School of Engineering and Applied Science
Quote: Quantum phase transition detected globally deep in the Earth (2021, October 12) retrieved October 12, 2021 from https://phys.org/news/2021-10-quantum-phase-transition-global -scale.html
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