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Precision of radioactive argon dating improved

Date: 04-May-08
Author: University of California at Berkeley

Scientists at the University of California, Berkeley, and the Berkeley Geochronology Center have pinpointed the date of the dinosaurs' extinction more precisely than ever thanks to refinements to a common technique for dating rocks and fossils.

The argon-argon dating method has been widely used to determine the age of rocks, whether they're thousands or billions of years old. Nevertheless, the technique had systematic errors that produced dates with uncertainties of about 2.5 percent.

Paul Renne, director of the Berkeley Geochronology Center, and his colleagues in Berkeley and in the Netherlands now have lowered this uncertainty to 0.25 percent and brought it into agreement with other isotopic methods of dating rocks, such as uranium-lead dating.

Scientists studied sediment layers at Zumaia in the Basque country of northern Spain to obtain a higher precision for the radioactive argon dating method. Courtesy: AAAS Science

As a result, argon-argon dating today can provide more precise absolute dates for many geologic events, ranging from volcanic eruptions and earthquakes to the extinction of the dinosaurs and many other creatures at the end of the Cretaceous period and the beginning of the Tertiary period. That boundary had previously been dated at 65.5 million years ago, give or take 300,000 years.

According to a paper by Renne's team in the April 25 issue of Science, the best date for the Cretaceous-Tertiary, or K/T, boundary is now 65.95 million years, give or take 40,000 years.

Full story: Improved rock-dating method pinpoints dinosaur demise with unprecedented precision

Related links:

• Geologic Time: Radiometric Time Scale
• Dating the Earth