Silicates relatively uncommon deep within the Earth, finds study

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Washington, May 11 (ANI): Using quantum mechanics, scientists have discovered that silicates, the most common minerals on Earth, are relatively uncommon deep within the planet.

Researchers, led by a team of physicists led by Ohio State University, have been able to simulate the behavior of silica in a high-temperature, high-pressure form that is particularly difficult to study firsthand in the lab.

Silica makes up two-thirds of the Earth's crust, and we use it to form products ranging from glass and ceramics to computer chips and fibre optic cables.

Ohio State doctoral student Kevin Driver, who led this project for his doctoral thesis, said: "Silica is all around us.

"But we still don't understand everything about it. A better understanding of silica on a quantum-mechanical level would be useful to earth science, and potentially to industry as well."

Silica takes many different forms at different temperatures and pressures -- not all of which are easy to study, Driver pointed out.

He said: "As you might imagine, experiments performed at pressures near those of Earth's core can be very challenging. By using highly accurate quantum mechanical simulations, we can offer reliable insight that goes beyond the scope of the laboratory."

Over the past century, seismology and high-pressure laboratory experiments have revealed a great deal about the general structure and composition of the earth.

For example, such work has shown that the planet's interior structure exists in three layers called the crust, mantle, and core.

The outer two layers - the mantle and the crust - are largely made up of silicates, minerals containing silicon and oxygen.

Still, the detailed structure and composition of the deepest parts of the mantle remain unclear.

These details are important for geodynamical modelling, which may one day predict complex geological processes such as earthquakes and volcanic eruptions.

Even the role that the simplest silicate - silica - plays in Earth's mantle is not well understood.

Driver said: "Say you're standing on a beach, looking out over the ocean. The sand under your feet is made of quartz, a form of silica containing one silicon atom surrounded by four oxygen atoms. But in millions of years, as the oceanic plate below becomes subducted and sinks beneath the Earth's crust, the structure of the silica changes dramatically."

Driver, his advisor John Wilkins, and their team used a quantum mechanical method to design computer algorithms that would simulate the silica structures.

When they did, they found that the behaviour of the dense, alpha-lead oxide form of silica did not match up with any global seismic signal detected in the lower mantle.

This result indicates that the lower mantle is relatively devoid of silica, except perhaps in localized areas where oceanic plates have subducted, Driver explained.

The physicists used a method called quantum Monte Carlo (QMC), which was developed during atomic bomb research in World War II.

To earn his doctorate, Driver worked to show that the method could be applied to studying minerals in the planet's deep interior.

Wilkins said: "This work demonstrates both the superb contributions a single graduate student can make, and that the quantum Monte Carlo method can compute nearly every property of a mineral over a wide range of pressure and temperatures."

He added that the study will "stimulate a broader use of quantum Monte Carlo worldwide to address vital problems."

The study has appeared in the early online edition of the Proceedings of the National Academy of Sciences (PNAS). (ANI)

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