Silica makes up two-thirds of the Earth’s crust, and is used to create products ranging from glass and ceramics to computer processors and fibre optic cables.

"Silica is all around us," said doctoral student Kevin Driver of Ohio State University.

"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."

"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."

Earth’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 -- mineral compounds that contain silicon and oxygen.

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

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

"Say you’re standing on a beach, looking out over the ocean," said Driver.

"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 co-authors used a quantum mechanical method to design computer algorithms that would simulate these silica structures.

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 indicates that the lower mantle is relatively devoid of silica, except perhaps in localised areas where oceanic plates have subducted.

The researchers used a method called quantum Monte Carlo (QMC) that was developed during World War II as part of the effort to create an atomic bomb.

"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," said Wilkins.

Image credit: http://commons.wikimedia.org/wiki/User:CharlesC / CC BY-SA 3.0