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"We've finally narrowed it down to where we are talking about fractions-of-a-percent revisions in the future, at most."Klaudia Kuiper, the lead author of the Science paper, was a Ph. student in Amsterdam working with study coauthors Wijbrans, Hilgen and Wout Krijgsman when the study was initiated. and Dutch National Science Foundations and the Ann and Gordon Getty Foundation.She also conducted lab work with Renne and Alan Deino, a geochronologist with Renne at the Berkeley Geochronology Center who was also one of the study's coauthors. "The importance of the argon-argon technique is that it is the only technique that has the dynamic range to cover nearly all of Earth's history," Renne said."What this refinement means is that you can use different chronometers now and get the same answer, whereas, that wasn't true before."Renne noted that the greater precision matters little for recent events, such as the emergence of human ancestors in Africa 6 million years ago, because the uncertainty is only a few tens of thousands of years."Where it really adds up is in dating events in the early solar system," Renne said.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.Renne's group had proposed using the astronomical tuning approach to calibrate the argon-argon method as early as 1994, but lacked ideal sedimentary sequences to realize the full power of this approach.
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.Wijbrans of the Free University in the Netherlands to obtain convincing evidence.Wijbrans and his Dutch colleagues were studying a unique series of sediments from the Messinian Melilla-Nador Basin on the coast of Morocco that contain records of cycles in Earth's climate that reflect changes in Earth's orbit that can be precisely calculated.Any alteration or fracturing means that the potassium or the argon or both have been disturbed.The site also must be geologically meaningful, clearly related to fossil-bearing rocks or other features that need a good date to join the big story.