Washington, D.C.— Lyman Thomas Aldrich, 95, who worked as a geophysicist and geochemist at the Carnegie Institution for Science’s Department of Terrestrial Magnetism (DTM) for 34 years, including a stint as its acting director, died Wednesday, May 1, at a retirement community in Mitchellville, MD.

 

Aldrich was known for his work as part of a research team that pioneered the development of methods and instruments for determining the ages of rocks through dating their constituent minerals. Aldrich’s efforts were seminal to the group’s work, which created many fundamental techniques that would be used by geochemists around the world for the next 50 years or more.

 

The work of the research group was accomplished using high accuracy measurements of the isotope ratios of naturally occurring, long-lived radioactive decays such as potassium decaying to argon, rubidium decaying to strontium, and uranium decaying to lead. The accomplishments of this group and its postdoctoral fellows are the stuff of legend among geologists and geochemists.

 

Despite this focus on isotope geochemistry, it was common at that period of time in DTM history for staff scientists to be involved in a range of studies across different disciplines. Considering himself more a geophysicist, Aldrich became involved with seismic studies of the earth’s crust as a participant in the Carnegie expedition to study the crust of the central Andes in 1957.

 

Afterward, he took a more active role as a team leader for DTM explosion seismic experiments. Aldrich participated in several large-scale seismic experiments in the U.S. in the 1960s, including in Maine, Lake Superior, and the East Coast On-shore Off-shore experiment off the coasts of Virginia and North Carolina in 1965. He also served as the “shooter” for several international projects in the Andes in the early to mid-1970s, assembling and detonating charges of 1 to 5 tons in Andean lakes in order to generate seismic signals that were used to study crustal and upper mantle structure across the high Andes.

 

In 1967 Aldrich joined in studies to determine electrical conductivity as a function of depth in the crust and upper mantle beneath the Altiplano of southern Peru, and he continued that research even into retirement.

 

Aldrich served as DTM’s Assistant Director from 1965-1966, Associate Director from 1966-1974 (with Ellis Bolton as Director), and Acting Director from September 1974-March 1975. He retired as a member of the scientific staff in 1984.

 

He is remembered at DTM for being fearless around equipment--including fixing and building mass spectrometers--and for his view that procrastination rarely makes things better. He was also an unfailing supporter of the Carnegie postdoctoral program, and always willing and eager to engage in international collaborations.

 

Aldrich received his PhD from the University of Minnesota in 1948, where he studied with the well-known physicist Al Nier. He researched radiogenic Argon in potassium-bearing minerals, as well as making some of the first measurements on the elements Strontium and Helium.

 

He worked as an assistant professor at the University of Missouri from 1948-1950.

 

He started his career at the Naval Ordnance Laboratory during WWII, where he met former-DTM Director Merle Tuve, who eventually recruited him to come to DTM.

 

Aldrich was a member of the Seismological Society of America and a fellow of the American Physical Society, the American Association for the Advancement of Science, and the American Geophysical Union, for which he was president of the Volcanology/Geochemistry/Petrology section from 1968-1970.

 

He is survived by his two daughters, three granddaughters, and nine great-grandchildren.
 

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