"Zircons have produced complicated data that are hard to interpret, though people have pulled dates out," said Mundil, a former UC Berkeley postdoctoral fellow now at the BGC, a non-profit scientific research institute dedicated to perfecting dating techniques for establishing the history of Earth and life on Earth.
The age of a rock can be calculated if its ratio of uranium to lead is known.
This is unstable and eventually decays to lead, which is stable.
– A new study by geologists at the Berkeley Geochronology Center and the University of California, Berkeley, improves upon a widely used dating technique, opening the possibility of a vastly more accurate time scale for major geologic events in Earth's history.
In a paper published this week in Science, geochemist Roland Mundil of the Berkeley Geochronology Center (BGC) and his colleagues at BGC and UC Berkeley report that uranium/lead (U/Pb) dating can be extremely accurate - to within 250,000 years - but only if the zircons from volcanic ash used in the analysis are specially treated.
Based on the improved U/Pb technique, the team also established that the argon/argon (Ar/Ar) isotopic dating technique that Renne employed for an earlier study of the Permian-Triassic boundary consistently gives younger dates, by about 1 percent.
Renne ascribes this to a lack of a precise measurement of the decay constant of potassium.The technique is based on the fact that the naturally occurring isotope potassium-40 decays to argon-40 with a 1.25 billion year half-life.To date, zircons - known to many as a semiprecious stone and December's birthstone - have often produced confusing and inaccurate results.A secondary electron microscopy image of a zircon from volcanic ash, about four thousandths of an inch (100 microns) across.The zircon has been cut and polished, then treated with high-temperature annealing and chemical abrasion with hydrofluoric acid.The crystal interior parts affected by lead loss have been "mined out" in the process, allowing uranium/lead dating to provide a more accurate measure of its age.