How Can Quantum Physics Help Researchers Understand the Deep Earth?
For Earth Day, learn about how science at its smallest scale is applied to the depths of our planet.
April 22, 2022
Our planet is full of mysteries. How exactly did Earth form and evolve to its current state? Why do some places in its interior seem hotter or colder, rising or sinking? For answers, geoscientists experiment on materials expected to be found in Earth’s interior, but these exist at immense pressures and temperatures that are impractical to reproduce in the lab. Renata Wentzcovitch, a condensed matter physicist, says quantum simulations can help.
“Nature is quantum,” said Wentzcovitch, a professor at Columbia Engineering and the Lamont Doherty Earth Observatory.
Quantum mechanics is a theory concerned with the wave-like motion of minuscule particles, like electrons circling an atom. Atoms and their electrons combine into molecules that form materials that make up the Earth—all of which have quantum properties. Although quantum mechanical equations can be applied to any material, they are most often invoked to describe phenomena that cannot be understood with classical physics, she said.
During her PhD, Wentzcovitch studied the quantum nature of hard materials, like diamond and graphite, and how extreme temperatures and pressures can change a material’s electronic and structural properties. She then developed quantum simulation methods in her postdoc years to address complex materials. Where else can complex materials subject to extreme conditions be found? The deep Earth.
To understand the deep Earth’s evolution and current state, researchers must combine information about its material composition with the effects of external forces like temperature and pressure. There, Wentzcovitch applies techniques she helped develop in condensed matter physics to study the nearly 4,000 miles of material below our feet.
For example, last fall, she and colleagues combined more than 15 years of work on a quantum property called the spin state, which occurs in materials containing iron. Combining those results with seismological evidence, the team identified the signature of a spin transition deep within the Earth's mantel. This strictly quantum phenomenon changes the speed at which sound travels in solids and helps explain the mysterious pattern of seismic velocities observed 1,200 kilometers below ground.
In January, she and her team revealed that Earth’s molten iron core solidified upon cooling in a two-step process, rather than one. This result is another step towards solving a long-standing paradox that says it should have taken longer than the Earth’s age, 4.5 billion years, for its inner core to solidify.
She and her group are currently working with seismologists and geodynamicists on a reference model of the distribution of mineral phases and their compositions in the Earth’s mantle. All to shed light on the deep Earth’s evolution with the help of quantum simulations.