Dr. Garniss H. Curtis, a UC Berkeley professor emeritus of earth and planetary science, died Dec. 18 in Orinda, California at the age of 93.

Curtis’ work with other UC Berkeley professors and seismologists pioneered a new form of radioactive dating that worked on relatively young rocks and helped establish the first solid timeline for human evolution. Using vacuum systems and mass spectrometers, Curtis and his colleagues were able to measure the tiny amounts of radioactive decay products in the sample rocks and precisely date their creation. This helped establish references for geological periods and allowed scientists to have a more precise idea of the exact timeline of human evolution.

One of the many major discoveries yielded from this method was the now well-established knowledge that the million-year-old human ancestor Homo erectus and modern humans, Homo sapiens, coexisted. Other breakthroughs revolutionized the accepted dates of many major geological periods in our planet’s history by millions of years.

Curtis was well-known at UC Berkeley and admired for mentoring students. After almost 40 years of work with the UC Berkeley geology faculty, Curtis retired and established the Berkeley Geochronology Center to continue his work and refine his new method of radioactive dating. He and his colleagues provided dates for discoveries of human ancestors in Africa and the laboratory is one of the top facilities for radioactive dating in the world today.

Throughout his life, Curtis accumulated a number of honors, including the Newcomb Cleveland Award of the American Association for the Advancement of Science.