Working with no small degree of dexterity, the 30-year-old Marquardt simulated the Earth’s lower mantle – the layer surrounding the Earth’s core – in a lab setting for his dissertation at Freie Universität Berlin. His research findings pave the way for conclusions regarding the spread of seismic waves and for determining temperatures deep within the Earth’s mantle, which have been largely unknown to date. For his work, the Körber Foundation has now awarded Marquardt its prestigious German Dissertation Prize (Deutscher Studienpreis) for 2010 in the field of natural science and technology.
In his lab at the German Research Centre for Geosciences (GFZ) in Potsdam, Marquardt literally worked under extreme pressure: The lower reaches of the Earth’s mantle are located at depths of between 660 and 2900 kilometers below the surface of the Earth, and pressure in the center of the mantle can reach about 800,000 bars. “That’s equivalent to the pressure you would feel if you could balance the Eiffel Tower on the tip of one finger,” Marquardt says. Tectonic plates, whose movements are the trigger behind many earthquakes, reach all the way down to these depths.
To simulate the Earth’s mantle, Marquardt needed to produce a synthetic version of the mineral ferropericlase, which is present in the lowermost region of the mantle. He couldn’t use natural ferropericlase, because no one has ever been able to drill far enough down to reach the lower mantle. “The deepest holes that have been drilled thus far go to about twelve kilometers,” Marquardt says.
Marquardt applied pressure to the crystal with two diamonds cut to a point. He used a needle to place the tiny ferropericlase crystal atop one of these diamond points. To ensure that the sharp points did not simply crush it, the crystal was enclosed in a metal ring. Rubies also placed within the ring served as pressure sensors.
With increasing pressure, the speed at which sound waves travel changes. As in any solid object, there are sound waves present within crystals, because they are made up of atoms. The atoms are always in motion, and it is these tiny movements that trigger the acoustic waves. “The speed at which sound travels through minerals is of particular interest to Earth scientists, because it can be compared to the speed at which seismic waves spread,” Marquardt says.
The scientist also studied the crystal’s atomic structure. He discovered that the speed at which seismic waves travel changes depending on how the atoms are arranged with respect to one another. He also found that there is one particular spatial alignment of crystals in the lower mantle that is most prevalent. This alignment of mineral deposits in turn affects the spread of seismic waves.
Marquardt’s data serve as a basis for achieving a better understanding of the movements of acoustic and seismic waves, thereby perhaps also giving scientists tools to predict earthquakes with greater accuracy someday. The research findings also show an unexpected connection between the temperatures present in the lower mantle and the speed at which seismic waves travel: “This could be used to create the concept for a kind of thermometer for the Earth’s lowermost mantle, but more detailed lab data and more precise seismic records are needed before we can accomplish that.”