Earth’s core is a roiling furnace, where temperature and pressure exist at extremes that alter the basic behavior of solid matter. These physical extremes cause changes in matter down to the molecular level, where complex crystals form and unusual atomic interactions take place. These behaviors are normal deep inside the earth, but stay hidden under miles of rock. Thus, to learn about matter at environmental extremes, those extremes must be created in a lab—and doing so may hold lessons about Earth and its celestial neighbors.
Enter Natalia Dubrovinskaia, a full professor at the University of Bayreuth in Germany, and pioneer in the field of high-pressure studies. In the pursuit of extreme pressure studies, Dr. Dubrovinskaia developed special diamond anvils used to create ultrahigh pressures in a lab setting. Using this technique, she has learned about iron in Earth’s core and created pressures so high, they only exist in giant planets.
Using the diamond anvils, Dr. Dubrovinskaia’s group first generated gigapascal pressures, which approximate the conditions in Earth’s core. The pascal is the metric unit for pressure, and a gigapascal is one billion of them. For comparison, a human bite registers at about one megapascal, or 1000 times weaker than a gigapascal.
The diamond anvils focus pressure the same way a knife does. A cook applies relatively low pressure to the handle of a knife, but its thin, sharp blade multiplies that pressure, thereby easily slicing a tomato or cucumber. The diamond anvils work in a similar way. Jewlrey-quality diamonds, similar to those found in an engagement ring, are flattened on the tip to provide an area for squeezing matter. Then, a small diamond “semiball” (essentially a sphere cut in half) is added to the flattened area. This essentially sharpens the blade, in turn multiplying the force enormously. These are called double-stage anvils, where one stage is the large diamond and the second stage is its attached semiball.
The ability to apply such high pressure to matter has yielded fascinating results. Using diamond anvils, Dr. Dubrovinskaia squeezed iron oxide, a compound which makes up a major portion of the Earth’s crust and mantle. When treated with the incredible pressure and temperature found in Earth’s mantle, iron oxide formed highly complex crystals not found at “normal” temperature and pressure, releasing oxygen in the process. By exposing iron oxide to such extreme conditions, Dr. Dubrovinskaia bent the rules of solid matter. In doing so, she found that a large reservoir of oxygen may reside under the surface of the earth, participating in oxygen cycling on a global scale.
Most recently, Dr. Dubrovinskaia’s group achieved pressures never before generated by humans. When squeezing iron oxide, her group achieved gigapascal pressures. In their most recent work, her group blew past that and achieved terapascal pressures—1,000 times greater than a gigapascal. This high pressure mark was hit by compressing gold in the special double-stage anvils. While the current study is a proof of principle, the new technology is significant: humans have never squeezed anything this hard before. Indeed, pressures at or above 1 terapascal don’t even naturally occur on Earth—you have to travel to the core of huge planets to find these pressures.
When asked what we might learn about celestial bodies from her research, Dr. Dubrovinskaia demurs; space isn’t her specialty. She is more focused on why matter organizes the way it does, and pressure is one of the basic factors that determines that organization. Placing materials under extreme conditions can lead to technological innovation, as in the case of MRI machines, which rely on superconducting magnets kept extremely cold by liquid helium. On the way to technological innovation, however, we find unusual phenomena. Observation of these phenomena “contribute[s] to our global understanding of solid matter,” says Dr. Dubrovinskaia. This helps us better understand our world, and why its unique beauty developed exactly the way it did.
The Inner Life of Life 