A colossal earthquake shook the earth under the Indian Ocean on the morning of Dec. 26, triggering a tsunami that ravaged a dozen countries and killed more than 150,000 people.
It was one of the worst natural disasters in history, and its ramifications are still uncertain. Beyond the physical toll, however, the tragedy exposed a vitally important, and often under-recognized, scientific field: geoscience.
In Princeton's geosciences department, faculty members study the earth as a whole, from its atmosphere to oceans to core.
Though chair of the department Tony Dahlen is a world-renowned seismologist, when searching for the origin of earthquakes, professor Tom Duffy perhaps provides the deepest answers.
What Duffy studies is the earth's interior, the inaccessible deeps where tectonic activity originates. "It's all connected," Duffy said. "From the plate tectonics, we understand why earthquakes occur in certain areas. But now we're moving to the next level of inquiry: what is the driving force behind the movement of these plates? Ultimately, it's processes in the deep interior."
And just as earthquakes continue to evade accurate prediction, the constitution of the deep interior remains an open question.
Duffy, an associate professor who came to the University in 1997, seeks to understand the composition of planets by studying the properties of materials under extremely high pressures and temperatures.
Since there is no hole deep enough to reach the Earth's core, scientists can never make direct observations of the planet's interior.
Duffy's method, then, is to take materials that are likely constituents of the interior and subject them to the conditions that exist there.
In his lab in Guyot Hall and in a federal x-ray facility outside Chicago, Duffy compresses minuscule quantities of minerals between the faces of two gem-quality diamonds.
This process creates pressures more than a million times greater than atmospheric pressure, approximately equivalent to balancing the Eiffel tower on a quarter, Duffy said.
Simultaneously, Duffy uses a high-powered laser to heat the samples to between 2,000 and 3,000 degrees.
These conditions simulate the environment at the boundary between the Earth's mantle and core, about 2,900 kilometers below the surface.
The physical and chemical properties of materials can change drastically under such conditions, Duffy said. Graphite, normally the soft, slippery substance found in pencil lead, can change to diamond under high temperature and pressure. Insulators can become metals.
The radically different structures formed after such experiments can lead to new models for the bulk composition of Earth.
In the past year, Japanese researchers discovered that a major constituent of the Earth's lowest mantle suddenly becomes denser at 300 km above the boundary between the mantle and core.
Previously, scientists believed that the material — silicate perovskite — remained stable all the way to the core.
This discovery is significant because the region where the material changes has been studied for decades due to the strange properties of its seismic waves. The region contributes vitally to hot spots like Hawaii, Duffy said, and to dynamic surface behavior as a whole.
Using high temperatures and pressure, Duffy and his students have recently been able to synthesize this new phase of perovskite in the laboratory and recover it at ambient conditions.
This provides an unprecedented opportunity to study the properties of this region of the Earth's interior.
"It's exhausting, really, and exciting," said Duffy, who pursued graduate students in geosciences only after working at a blue-collar job in a food warehouse. "We've put all the earlier projects on the backburner, and devoted all we can to this new one."
"We're just scratching the surface of the implications of this new phase," he added. "We're changing how we understand the deepest part of Earth."
And while it may not give direct answers about the causes of devastating earthquakes, Duffy's research provides a framework for further study.
"You need to understand the entire earth to understand the surface," he said. "It's a question of fundamental interest."
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