Ar-Ar Refined
Thursday April 24, 2008
A paper published in Science today reports a major improvement in the precision of the argon-argon dating method (see the press release). More formally known as the 40Ar-39Ar method, it's an ingenious self-calibrating technique for measuring the minuscule quantities of argon-40 produced by the radioactive decay of potassium-40 in certain minerals. By using high-precision measurements of a sequence of rocks with ages that are accurately known through astronomical orbital cycles, the argon-argon technique was improved to allow ages to be gauged with uncertainties of 0.25 percent. Thus 4-billion-year-old meteorites, for instance, can be dated to within a mere 10 million years. A million here, a million there, you might be thinking, but compared to what we had before it's fantastic. More notably, the infamous K-T boundary, marking the time the last of the dinosaurs died in an asteroid crash, is now put at 65.95±0.04 million years by the research team.
Comments
Andrew,
Shouldn’t we be using “K-P” boundary now that the “Tertiary” has been scrapped? (i.e. the period formerly-known-as-the-Tertiary has been subdivided into Paleogene and Neogene periods)
Amelin et al. (Science, Vol 297, 2002), dated differences in formation ages of chondrules (in a CR chondrite) and CAIs (in a CV chondrite) to 2.5 Ma ±1.2 Ma, using Pb-Pb dating. The CR and CV chondrites are obviously >4.56 Ga in age, so this new Ar-Ar dating method isn’t so hot with longer dates when compared with Pb-Pb. But as you noted with the KT impactor, the shorter the timeframe, the more accurate the dating, so this is a very exciting development for more “recent” events.
That’s right, uranium-lead methods are still the gold standard in dating, but now argon-argon is a more meaningful adjunct.