Lead uranium dating
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.Therefore, we can assume that the entire lead content of the zircon is radiogenic.Where this is not the case, a correction must be applied.The zircons were obtained from ash layers located in central and southeastern China.The Meishan section in the latter region is accepted as the type locality for the Permian/Triassic boundary.The new U/Pb date, though about 2.5 million years older than Renne reported nine years ago based on Ar/Ar dating, nevertheless confirms his conclusion that the Permian extinction occurred at the same time as a major series of volcanic eruptions in Siberia.
The term 'U-Pb dating' normally implies the coupled use of both decay schemes.
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.
Despite these treatments, the U/Pb method still produced a wide range of dates for zircons from the same layer of ash.
Mattinson's idea was to first heat or anneal the zircons, sealing off the least damaged areas of the crystal, then using a strong reagent, hydrofluoric acid, to eat away the heavily damaged areas.