A memorial service is planned this spring for Garnis H. Curtis, a pioneering geologist at UC Berkeley who used radioactive elements to determine crucial dates in the long timeline of human evolution. Mr. Curtis died Dec. 18 in Orinda. He was 93.
The dating method he and his colleagues developed was based on the decay time of potassium isotopes into argon and revealed in the fossil bones of our early human ancestors and the volcanic rocks around them that they had lived more than a million years ago.
Mr. Curtis and his colleague, seismologist Jack F. Evernden, first rocked the world of anthropology with their method in 1960. They used it to discover that a pre-human called Zinjanthropus, found in Africa's Olduvai Gorge by anthropologist Mary Leakey, was 1.85 million years old. The discovery pushed back the age of that era by a million years.
He also teamed up with Berkeley geologist Carl Swisher to discover that the million-year-old human ancestor called Homo erectus had survived in Asia until about 50,000 years ago. The controversial discovery meant the creature had actually existed in the region at the same time as Homo sapiens, our early modern humans.
Mr. Curtis retired from the UC faculty in 1989 and went on to work with paleoanthropologist Donald Johanson at the Institute of Human Origins. He then established a laboratory in Berkeley that dated ancient fossils, volcanic eruptions and the impacts of comets and asteroids. The lab, now called the Berkeley Geochronology Center, is among the most important dating labs in the world.
Mr. Curtis also helped refine the technique of potassium-argon dating into another new method known as argon-argon dating. The technique was used to establish the age of Johanson's famed fossil Lucy, Australopithecus afarensis, at 3.2 million years old, and has determined the age of UC Berkeley anthropologist Tim D. White's nearly as famous fossil Ardi, Ardipithecus ramidus, at 4.4 million years old.
Born in San Rafael, Mr. Curtis obtained his first degree in mining engineering from UC Berkeley in 1942. After working as a geologist for copper and oil companies, he returned to Berkeley to complete his doctorate in geology in 1951 and immediately joined the UC faculty.
He is survived by his brother Ralston; his daughters Penelope of Grass Valley and Ann of Orinda; his son Robin of San Rafael; seven grandchildren; and five great-grandchildren. His wife of 45 years, Dorette Davis Curtis, died in 1987.
Donations in Mr. Curtis' memory may be made to the Berkeley Geochronology Center, 2455 Ridge Road, Berkeley CA, 94709; the California Audubon Society, 4225 Hollis Street, Emeryville, CA 94608; or The Nature Conservancy, 4245 N. Fairfax Drive, Suite 100, Arlington, VA 22203.