Toshiko K. Mayeda, mastered the measurement of oxygen radioisotopes

Toshiko K. Mayeda

Toshiko Kuki Mayeda, a Japanese-born chemist, was born in Tacoma, Washington, in 1923. However, she spent most of her childhood in Yokkaichi and Osaka, Japan, returning to her hometown after high school.

Her love of science led her to study chemistry at Wilbur Wright College, then at the University of Chicago, where she graduated in 1949. This degree allowed her to interview for a job in the laboratory of Harold Urey (Nobel Prize in Chemistry in 1934 for the discovery of a heavy isotope of hydrogen, which he called deuterium) at the University of Chicago. Initially hired to wash glassware, she soon moved on to more important and enriching work.

When Mayeda came to Urey's lab as an assistant, the small group of researchers, led by the Nobel laureate, were working to develop an "oxygen thermometer". The work began with the observation that the natural process of calcium carbonate shell secretion in marine mollusks incorporates the stable isotopes of oxygen in proportions that depend on temperature. When the temperature changes, so does the ratio. Urey hoped that determining oxygen isotope ratios in dated marine fossil strata could provide information about the prehistoric temperature record of the oceans.

Mayeda gradually moved from cleaning glassware to mastering the mass spectrometry methods that Urey and his team had developed, becoming the leading operator of the large but precise instruments. Her contributions to the research carried out in Urey's lab earned her the respect of her collaborators and she continued to grow as a chemist. In addition, she worked with the students and postdocs who passed through the lab teaching the methods of mass spectrometry.

In 1958, after Urey's transfer to the University of California, Robert Clayton took over the laboratory and persuaded Mayeda to stay on as a collaborator. The result was a great deal of work that they would do together over two decades.

Robert N. Clayton

Clayton became interested in the early history of the solar system and what oxygen isotopes could reveal about it. So, together with Mayeda, they carried out many studies of oxygen isotope ratios in the solar system, examined all the meteorites that fell into their hands and analyzed about 300 lunar samples. This allowed them to determine the temperatures at which these rocks had formed and to discover that the meteorites included pre-solar system oxygen. Together they developed the Clayton-Mayeda model of oxygen isotope abundance in the solar system.

2002 he was awarded the Merit Award of the Geochemical Society of Japan. In the same year, an asteroid was named after him.

Mayeda continued to work with Clayton until he died in 2004. He died of cancer on 13 February, in Chicago, Illinois.

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