Argon argon dating
– 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.
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The potassium-argon (K-Ar) isotopic dating method is especially useful for determining the age of lavas.
The collaboration brought together all the appropriate expertise to bring this approach to fruition, he said."The problem with astronomical dating of much older sediments, even when they contain clear records of astronomical cycles, is that you're talking about a pattern that is not anchored anywhere," Renne said.
"You see a bunch of repetitions of features in sediments, but you don't know where to start counting."Argon-argon dating of volcanic ash, or tephra, in these sediments provided that anchor, he said, synchronizing the methods and making each one more precise.
The ratio of argon-40 to argon-39 then provides a measurement of the age of the sample."This should be the last big revision of argon-argon dating," Renne said.Renne 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.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."The evolution of the early solar system - the accretion of planetessimals, the differentiation of bodies by gravity while still hot - happened very fast.Argon-argon dating is now no longer at odds with that evidence, but is very consistent with it."Renne has warned geologists for a decade of uncertainty in the argon-argon method and has been correcting his own data since 2000, but it took a collaboration that he initiated in 1998 with Jan R.
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Wijbrans' colleague Frits Hilgen at the University of Utrecht, a coauthor of the study, has been one of the world's leaders in translating the record of orbital cycles into a time scale for geologists, according to Renne.