Argon argon dating
The method relies on satisfying some important assumptions: Given careful work in the field and in the lab, these assumptions can be met.
The rock sample to be dated must be chosen very carefully.
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 , the best date for the Cretaceous-Tertiary, or K/T, boundary is now 65.95 million years, give or take 40,000 years.
Nevertheless, the technique had systematic errors that produced dates with uncertainties of about 2.5 percent, according to Paul Renne, director of the Berkeley Geochronology Center and an adjunct professor of earth and planetary science at UC Berkeley.
At Zumaia in the Basque country of northern Spain, sediments laid down around the end of the Cretaceous period show layers of light limestone and dark marl reflecting warm and cool periods, respectively, in Earth's climate.
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The potassium-argon (K-Ar) isotopic dating method is especially useful for determining the age of lavas.
That is, a fresh mineral grain has its K-Ar "clock" set at zero.
"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 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.