Article:Marking time is a science at Berkeley center / It devis:/c/a/2004/09/27/MNGNP8VHS31.DTL Article:Marking time is a science at Berkeley center / It devis:/c/a/2004/09/27/MNGNP8VHS31.DTL advertisement | your ad here SFGate [BUTTON] Back to Article SFGate Marking time is a science at Berkeley center It devises ways to date nearly everything David Perlman, Chronicle Science Editor Monday, September 27, 2004 Director Paul R. Renne (right) and lab director Timothy A... When chemist Willard F. Libby discovered unexpected evidence that all the plants on Earth, both living and dead, were faintly radioactive, he opened an era of age-dating that has since seen extraordinary new techniques emerge to tell how old everything might be -- from mountains to fossil microbes. Would you like to know how long ago the Pharaoh Sesostris III of Egypt sailed to the land of the dead aboard his funerary boat? Libby's "atomic clock" determined it almost exactly: It was 3,676 years ago, give or take a decade or two. Do you want to know how long ago our earliest relatives on the human family tree lived in Africa's Great Rift Valley? Geochronologists in Berkeley can tell you that one branch of hominids inhabited a once-verdant site in now arid Ethiopia about 5.8 million years ago -- among the earliest prehuman remains discovered so far. And do you know when our ancestors first used stone tools? They were flaking volcanic rocks into choppers and scrapers to prepare their meat as far back as 2.6 million years ago -- the earliest known artifacts made by our distant relatives. Libby's discovery a half-century ago had limitations. But using the newest dating technologies, developed by scientists at the Berkeley Geochronology Center, geologists and physicists can now date the drifting of continents, the past eruptions of extinct volcanoes, the history of quakes along the San Andreas Fault, the age of lunar samples brought back to Earth by the Apollo astronauts and even the age of Earth itself (4.6 billion years). Housed in a few basement rooms of the Church Divinity School of the Pacific on a leafy street near the University of California campus, the independent nonprofit center is now 10 years old. It is financed largely by $1 million annual grants from the Ann and Gordon Getty Foundation, plus funds from the National Science Foundation. "What we're really trying to establish is the timing of major events and the causal relationships between them," says Paul R. Renne, the center's director and adjunct professor of geology at UC Berkeley. "If species go extinct, we want to know what caused them to vanish. If new hominid species arrive on the scene, we want to know why. "We're so often left with puzzles in science where timing is critical -- whether it's in archaeology or cosmology, and the most critical question is the rate at which everything happens. Time is of the essence, and determining when events occur is crucial to understanding Earth's history." Libby, who won the 1960 Nobel Prize and died in 1980, was an early researcher into nuclear energy who helped develop the gaseous diffusion technique for enriching uranium to fuel atom bombs. He also found traces of radioactivity in living plants -- and realized it must have come as the plants absorbed a radioactive form of carbon from the atmosphere's carbon dioxide. And he discovered that the radioactive carbon, an isotope called carbon-14, gave up its radioactivity by decaying into stable nitrogen at a rate that could be measured. Half of it, in fact, decayed every 5,568 years. Because dead plants stop absorbing carbon-14 from the air, Libby realized that by counting the second-by-second decay rate of the remaining carbon-14 in a dead plant, he could calculate its age. Thus was born Libby's atomic clock, and archaeologists, art historians and scientists studying any object containing carbon left over from living objects -- a rotting bison-hide tepee, the timbers of a ship sailed by African slave traders, or the carcasses of long-extinct birds -- could reveal their age by measuring the decay rate of the remaining carbon-14. Radiocarbon dating is valid only for the past few thousand years, however, and scientists need to date objects back for millions and even billions of years. They can and do -- using the known decay rates of other radioactive elements into stable forms. Radioactive uranium decays into stable lead at a known rate, for example. The artificially radioactive form of the gaseous element argon decays into a more stable form of the same element at a different rate in what scientists term argon-argon dating. An unstable element decays by emitting particles from its nucleus, and the time period it takes for it to decay by half is known as its "half-life." Knowing that half-life is the key to calculating any ancient date. The rates can be extraordinarily slow -- millions of years, sometimes. In uranium-to- lead dating, uranium's half-life is just about 4.5 billion years; its well- calibrated presence in a rock can yield the secret of the rock's age. Fast forward to last week, when geologist Roland Mundil and a team of scientists at the Geochronology Center reported in the journal Science that they have developed a highly specialized new technique -- using microscopic samples of the mineral zircon, found in volcanic ash from central and southeastern China -- to perfect the uranium-to-lead dating method. The new method has allowed them to refine long-standing estimates for the age of the greatest mass extinction of life that has ever occurred on Earth. Nearly all the world's marine invertebrate species and 70 percent of the land organisms perished in that single brief geologic spasm, which took less than a million years from start to finish. That spasm, Mundil and his colleagues have determined, happened 252.6 million years ago, plus or minus 200,000 years, between the end of the geologic time known as the Permian Period and the beginning of its successor, the Triassic. The extinctions included almost all the well-known segmented trilobites; most of the reef-building corals and the sponges; the larger organisms like the earliest heavily armed fish with jaws -- ancestors of the sharks ; and the dominant land animals, huge sail-backed reptiles like Dimetrodons. The new date Mundil established, using zircon samples measured in trillionths of a gram, is 2.5 million years older than an estimate that center director Renne had arrived at only nine years ago using an earlier argon dating method. "Further application of Mundil's approach will make the geologic time scale more accurate," Renne said, "letting us calibrate extinctions and important events in Earth's history, ranging from 100 million to several billion years ago, with unparalleled accuracy." Mundil and his colleagues also dated a vast deposit of basalt left over from the most monstrous outpouring of lava from deep in the Earth's crust that the world has ever experienced. Known as the Siberian Traps, the flood basalts from that volcanic eruption still cover at least 1.5 million square miles of central Russia -- more than nine times the area of California. They dated the volcanic event at 252.6 million years ago, exactly as old as the catastrophic Permian extinction. Many scientists are convinced the lava flood caused the mass extinction -- although some believe it could have been triggered by the impact of some giant asteroid that crashed to Earth at that same time. One of the Berkeley center's most important achievements has been the continued and precise dating of the troves of hominid fossils that have been discovered in the volcanic highlands of Ethiopia's Awash River region, where the rock formations date back many millions of years. "The geochronologists are beginning to establish clearly the timing of our human origins, from millions of years ago to the emergence of our direct ancestors," said Tim D. White, the UC Berkeley anthropologist who has led annual fossil-hunting expeditions to the Awash region and has recruited, trained and encouraged some of Ethiopia's foremost paleoanthropologists. On their most recent expedition, White said, he and his Ethiopian colleagues found some "fantastic" fossils. "But we don't know how old they really are," he continued. "That's what the folks at the Geochronology Center will do for us. Their work is crucially important, and they're a huge asset for science." E-mail David Perlman at dperlman@sfchronicle.com. http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/09/27/MNGNP8VHS31.DT L This article appeared on page A - 4 of the San Francisco Chronicle © 2004 Hearst Communications Inc. | Privacy Policy | Feedback | RSS Feeds | FAQ | Site Index | Contact Quantcast