Garniss Curtis, pioneer of precision fossil dating, has died at 93

Geologist Garniss H. Curtis, a professor emeritus of earth and planetary science at the University of California, Berkeley, whose pioneering use of radioactive isotopes to date relatively young rocks provided the first solid timeline for human evolution, died Dec. 18 in Orinda, Calif., at the age of 93. Curtis collaborated with late UC Berkeley professors John Reynolds, a physicist, and Jack Evernden, a seismologist, to take advantage of the radioactive decay of potassium into argon in volcanic rock to determine how long ago the rock formed. Using this potassium-argon method, they established precise dates for recent geologic time periods that allowed Curtis to assign dates to fossilized human remains and prove they were much older than once thought. "Reynolds developed a precise way to date meteorites in the 1950s, but it was Garniss who adapted the technique to work on geological problems," said G. Brent Dalrymple, emeritus professor and former dean of the College of Earth, Ocean and Atmospheric Sciences at Oregon State University in Corvallis. He first met Curtis while obtaining his Ph.D. at UC Berkeley in the 1960s.