It was over a meal aboard the Vema, the research vessel of Columbia University’s Lamont Geological Observatory, sometime during the International Geophysical Year of 1957–1958 that Taro Takahashi had a conversation that would profoundly change his career and help spur the creation of the field of mineral physics.
The conversation was between Taro, then a postdoctoral researcher at Lamont (known today as the Lamont-Doherty Earth Observatory), and Maurice “Doc” Ewing, Lamont’s director. Both were on the Vema pursuing their research interests: Ewing was overseeing the collection of seismic data to learn about the rock below the ocean floor, whereas Taro, to whom Ewing had offered the position at Lamont so he could join the cruise, was collecting data on the carbon dioxide content of seawater.
Taro was primarily a geochemist, but he had a keen interest in geophysics, especially in the compositions and properties of Earth’s deep interior. As the two scientists were enjoying their meal, Taro asked Doc what he thought explained the Mohorovičić discontinuity (or Moho), the boundary separating crustal rock that conducts seismic signals at about 6 kilometers per second from the upper mantle rock below that conducts seismic signals at about 8 kilometer per second. Doc replied that there were two possible explanations: The Moho represented either a change in the composition or a change in the physical properties of the rock.
It was clear at that time that the available observations that could shed light on this question were simply too few and too poorly understood to allow a more definitive answer. To address such questions, much more needed to be known about the properties of materials at high pressures and temperatures.
Developing Diamond Anvil Cells
When Taro’s 2-year postdoc at Lamont was up, he sought a permanent position. Recalling how Doc had answered his question about the Moho, Taro decided he wanted an academic position in which he could turn his attention to investigating the physical properties of minerals thought to occur in Earth’s interior. In about 1959, he accepted a faculty appointment at Alfred University in upstate New York, where he installed a large tetrahedral apparatus to analyze physical properties of minerals at high pressures.
I originally knew Taro from our time together at Columbia, where I completed my Ph.D. in 1959. Following a postdoctoral appointment at Brookhaven National Laboratory, I took a position in the Geology Department at the University of Rochester, about 100 kilometers north of Alfred, in 1961. After I had settled into my new job, my department chair asked who I thought the department should add to its faculty next. Without hesitation I said, “Taro Takahashi.” Taro came for an interview and was soon offered a position at Rochester as well as generous space to carry on his research into the effects of high pressure on minerals.
Taro and I frequently discussed how best to produce high pressures in the lab so we could use X-rays and other analytical techniques to examine mineral properties under these conditions. One day in about 1963, Taro saw the notice of a paper to be given at a conference in New York City describing a new instrument, only centimeters in size, in which samples of minerals or other materials could be compressed to extremely high pressures between flat faces of two small diamonds. The instrument, called a diamond anvil cell (DAC), also allowed a person to look directly at a sample through the diamonds using a microscope [Bassett, 2009]. That sounded ideal for achieving our research interests, so we drove to New York City and listened while Alvin Van Valkenburg of the National Bureau of Standards talked about the DAC and showed pictures taken while samples were compressed in the apparatus. If visible light could be used to observe samples at high pressures, could other types of radiation such as X-rays also be used?
Soon after the conference, we visited Van’s lab in Washington, D.C., and learned that Charlie Weir, one of Van’s colleagues, was already using X-rays with the DAC. We asked if they would object if we made our own DAC at Rochester to study minerals at high pressure with X-rays, and they said, “No problem.” We next visited an old brick factory in Hornell, N.Y., where transmissions for U.S. Army tanks were once manufactured to see if Taro’s machinist friend, Phil Stook, would make DACs for us. He was glad to have the job.
After mounting the first DAC on our X-ray generator, we set to work analyzing mineral samples. We also bought three more X-ray generators and established a machine shop at the University of Rochester so Phil could produce new DACs right there as we redesigned them. Our students fell into a ritual of developing the X-ray films of their microscopic samples at the end of each weeklong exposure. And soon the data were flowing as fast as we could interpret them.
Taro was very capable in guiding our students to squeeze information from their data using solid-state physics, thermodynamics, and math. I loved dreaming up new designs for the DACs.
High Temperatures Needed
One day, over lunch, we were discussing the need to be able to produce very high temperatures—ranging from several hundred to several thousand degrees Celsius—in addition to high pressures if we hoped to simulate all the conditions in Earth’s interior. Taro said, “Maybe we could use a laser.” The idea instantly appealed to me, although lasers were so new at the time that we had to wait until the Howard Hughes Medical Institute produced a ruby laser that was powerful enough for our needs.
Eventually, that happened, and in 1967 we bought one. It proved to be an excellent way to promote sluggish mineral phase transitions in silicates and to measure pressure-temperature boundaries between phases.
A Versatile Scientist
Taro and I liked writing papers together, usually with me at the typewriter and Taro looking over my shoulders. We took turns composing and critiquing. The absence of a delete button sometimes resulted in pages that were 90% crossed out. But we loved the process. Together with our students, we published 22 papers. Most of these studies reported on the effects of pressure on the crystal structures and molar volumes of the most important materials in Earth’s deep interior, such as iron alloys and spinel structure silicates [e.g., Takahashi et al., 1968; Mao et al., 1969].
Following a sabbatical year spent at the California Institute of Technology in 1970 to further his mineral physics research, Taro decided the time had come to return to his geochemical pursuits at Lamont, as he had told Doc he would. After 10 years of working together and with our very talented students, he felt we had significantly advanced the kind of research needed to solve questions about Earth’s interior by finding ways to measure physical properties that influence seismic velocities as well as other geophysical field observations. It was the very sort of work he had discussed with Doc Ewing aboard the Vema years earlier.
Today, Taro may be better known for his contributions to the geochemistry of carbon dioxide, but prior to much of his work on that subject, he was very instrumental in launching mineral physics as a discipline. I have emphasized his contributions to that field, so the scientific community has a chance to learn about Taro’s important contributions beyond geochemistry.
I will sorely miss Taro, as will his family, his colleagues, and his friends the world over. It was an honor to work so closely with such a remarkable and versatile research scientist.
Bassett, W. A. (2009), Diamond anvil cell, 50th birthday, High Pressure Res., 29, 163–186, https://doi.org/10.1080/08957950802597239.
Takahashi, T., W. A. Bassett, and H. K. Mao (1968), Isothermal compression of the alloys of iron up to 300 kilobars at room temperature: Iron-nickel alloys, J. Geophys. Res., 73, 4,717–4,725, https://doi.org/10.1029/JB073i014p04717.
Mao, H. K., et al. (1969), Effect of pressure and temperature on the molar volumes of wustite and three (Fe,Mg)2SiO4 spinel solid solutions, J. Geophys. Res., 74, 1,061–1,069, https://doi.org/10.1029/JB074i004p01061.
William A. Bassett ([email protected]), Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, N.Y., retired