"This will have a big impact on radio-isotopic dating in general."Mundil and his colleagues, including BGC director Paul Renne, adjunct professor of earth and planetary science at UC Berkeley, used this improved U/Pb technique to establish a more accurate date for the end of the Permian period and the beginning of the Triassic period - 252.6 million years ago, plus or minus 200,000 years.
This boundary coincides with the largest extinction of life on Earth, when most marine invertebrates died out, including the well-known flat, segmented trilobites.
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.
In addition there is another stable isotope, lead 204, that is entirely primordial and does not form via radioactive decay at all.
Thus any of the radioactive isotopes and its lead daughter product can be used for dating, or a combination may be used.
Zircon is especially useful because it frequently contains uranium in substitution for zirconium, but does not incorporate lead (as shown by the absence of Lead-204).Uranium 238 can only be used to date volcanic rocks of a very old age.The uranium and thorium decay systems offer a multitude of radiometric dating options.The amount of carbon-14 in the atmosphere has not changed in thousands of years.Even though it decays into nitrogen, new carbon-14 is always being formed when cosmic rays hit atoms high in the atmosphere.