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G. Brent Dalrymple: Deep time in a tarpaper shack

In 1963, Brent Dalrymple embarked on a journey through time that would set the course of his life. For the work he accomplished in geochronology, which started with dating rocks in a homemade lab and ended as dean of a major oceanographic institution, Dalrymple received the National Medal of Science on March 14.

G. Brent Dalrymple received the National Medal of Science on March 14 for his lifetime’s work dating Earth. Courtesy of Judy Scott, Oregon State University.

Fresh out of graduate school at the University of California, Berkeley, Dalrymple was recruited by Richard Doell and Allan Cox of the U.S. Geological Survey (USGS) in Menlo Park. Cox and Doell were among the first to recognize that rocks might carry signatures of the planet’s magnetic field, and that they might record times in the past when Earth’s magnetic pole switched from north to south. The scientists were eager to date the rocks they had sampled from around the world, to determine whether a polarity reversal would be a one-time event, regularly occurring, or random and unpredictable — information that they thought might help solve the question of continental drift.

In the space of six months, Dalrymple and his co-workers built a mass spectrometer dating laboratory at the USGS campus in Menlo Park, in a tarpaper shack that had been an annex for the hospital of an old army installation. In that flimsy leftover structure, the research team set up a state-of-the-art facility — which at that time, meant building it from scratch.

“You couldn’t buy mass spectrometers that were nearly sensitive or clean enough to do that kind of work,” says Dalrymple, who is now retired and living in Corvallis, Ore., with his wife. “You couldn’t even buy a high voltage power supply” stable enough, he says. “Now you can buy those things off the shelf.”

Dalrymple and his lab mates used a special glass mass spectrometer tube created by physicist John H. Reynolds of the University of California at Berkeley, to measure potassium/argon ratios in the rock samples. Dalrymple presented a complete magnetic polarity reversal time scale for the past 3.5 million years for the first time in 1965, in a talk at a Geological Society of America meeting, co-authored by Cox and Doell.

That year, “people were really starting to think about seafloor spreading and magnetic stripes,” Dalrymple says. “It was an exciting period of time — everybody was discovering things and plugging them in” to the current picture of Earth.

After seeing Dalrymple’s data, Fred Vine, a geophysicist at Princeton, connected the dots to show that the record of reversals in the ocean floor, a mirrored pattern of ribbon-like flip-flops, matched the pattern of dated magnetic reversals. Older rocks that matched specific magnetic polarities lay farther away from the ocean-bottom spines, hinting that mid-ocean ridges were spreading zones. The discovery led directly to what would become the modern theory of plate tectonics.

Over a decade later, Dalrymple’s work drew him into the evolution debate. In 1979, a California deputy attorney general approached him to be a witness at a trial that challenged the teaching of evolution in public schools. His testimony on Earth’s multi-billion-year age led to a phone call from the American Civil Liberties Union, asking him to testify in two larger federal cases, along with several other scientists, including Stephen Jay Gould. “We weren’t defending science,” Dalrymple says. “We were trying to show that the creationists’ ideas about the age of Earth and evolution were wrong, and not scientific.” The case from Louisiana eventually landed in the Supreme Court, which decided that laws requiring creationism in science education are unconstitutional (see Political Scene).

But Dalrymple has not limited himself to dating rocks and defending evolution. With USGS colleagues, he tackled the Hawaiian-Emperor volcanic chain, presenting age measurements that support its formation by the Pacific plate’s movement over a hotspot (see story, this issue). He has explored the Geysers geothermal field in California, lunar impacts and a variety of other scientific topics.

While conducting research, Dalrymple also served as USGS Assistant Chief Geologist for the Western Region for three years. David Howell, an oceanographer and former head of the USGS Pacific Marine Geology Branch, who worked with him, describes Dalrymple as “very serious,” “approachable,” “no nonsense” and an administrator who “got things done,” he says, but often with a sense of humor. In 1994, the Oregon State University at Corvallis offered Dalrymple the position of dean of the College of Oceanic and Atmospheric Sciences. After 31 years at the USGS, Dalrymple says, “it was a chance to do something else.” Mike Freilich, who was a faculty member during Dalrymple’s deanship and is now the college’s associate dean, calls Dalrymple “unflappable,” and says it’s no surprise that a geochronologist would become an oceanographer. “The ocean basins have preserved the record of deep-time history far better than land structures, which are constantly being eroded,” Freilich says.

“Brent has really clear vision,” says Duane Champion, who worked with Dalrymple in later incarnations of the tarpaper shack. He “could always walk into the candy store and pick up three nice gumballs and walk out and enjoy them. A lot of us get stuck in the candy store,” trying to tackle too many problems at once.

That focus and accompanying precision paradoxically has helped Dalrymple have a large impact on a wide variety of earth science issues, says Gary Greene, a former USGS geophysicist who worked with Dalrymple on research cruises, and who remembers first meeting Dalrymple in a trailer surrounded by glass pipes to capture the gas for measuring isotopic ratios. “I can’t think of someone who deserves the National Medal of Science more than Brent.”

Naomi Lubick

Links:

"Creationism: Back in Kansas Again," Political Scene, Geotimes, April 2005
"New dates defy fixed hotspots," Geotimes, April 2005

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