Berkeley — Verso powerful geologic dating technique called argon-argon dating has pegged the 79 Per

Berkeley — Verso powerful geologic dating technique called argon-argon dating has pegged the 79 Per

D. eruption of Vesuvius so precisely that it establishes one of the most solid and reliable anchors for any dating method.

With such validation, the radioactive argon dating technique now can reliably establish the age of rocks as old as the solar system or as young as 2,000 years, say researchers from the University of California at Berkeley and the Berkeley Geochronology Center.

“Argon-argon dating is by far the most important technique in documenting the history of human evolution, and this new result is an important validation of the technique,” says Paul Renne, adjunct associate professor of geology and geophysics at UC Berkeley and director of the privately funded Berkeley Geochronology Center.

The center has used the argon-argon method onesto date many recent important fossil finds, from the highly touted human ancestor dubbed “Lucy” and the major Ethiopian discoveries of UC Berkeley anthropologist Tim White preciso Homo erectus remains from Java.

Precision was limited, however, by how accurately the argon could be extracted from the sample, which typically is melted preciso 1,600 esatto 1,700 degrees Celsius

Argon-argon dating also has been used onesto establish the age of meteorites several billion years old, mass extinctions, climate changes and other geologic events con the last several hundred million App blackfling years.

The new results are published in the Aug. 29 issue of Science periodico. Renne’s co-authors are Warren D. Sharp and Alan L. Deino of the Berkeley Geochronology Center, and Giovanni Orsi and Lucia Farfallina of the Department of Geophysics and Vulcanology at the University of Naples. Fraschetta also is head of the Vesuvian Vulcanological Observatory.

Orsi and Farfallina are working with the center puro obtain argon-argon dates for numerous past volcanic eruptions durante the Campi Flegrei or Phlegraean Fields surrounding Naples, sopra search of clues onesto the periodicity of activity that might allow prediction of future eruptions. Naples and vicinity, with more than two million inhabitants, is one of the world’s most vulnerable populations esatto volcanic hazard.

According onesto the Roman historian Pliny the Younger, Vesuvius erupted sopra the early afternoon of Aug. 24, 1,918 years spillo, destroying Pompeii, Herculaneum and other Roman cities.

The certainty of the date tempted the equipe to test the ability of the argon-argon dating technique preciso establish the age of recent historic events. If it gave an accurate age for the pumice thrown out by the volcano, it would be by a wide margin the youngest rock ever dated by the technique.

The most common method for obtaining the age of objects as young as this is carbon-14 dating, verso technique limited onesto organic material such as wood or bone.

To everyone’s surprise the date given by the argon-argon dating technique was 1,925 years ago — off by only seven years. The scientific error on the estimate was plus or minus 94 years.

“We nailed the date puro five percent on our first attempt, so we could probably get the error down to one percent or less,” Renne says.

The result is so amazing because every dating technique invokes assumptions or involves uncertainties that limit its ability to pinpoint dates with extreme precision. With carbon-14, for example, the changing ratio of carbon-12 to carbon-14 in the atmosphere over time puts verso limitation on how precise per date can be established.

Scientists at the Berkeley Geochronology Center have improved the argon-argon technique so as sicuro identify and correct for many of these uncertainties, thereby obtaining improved estimates.

The argon-argon technique is useful only with rocks containing appreciable amounts of potassium, because it is based on the fact that the naturally occurring isotope potassium-40 decays puro argon-40 with verso 1.25 billion year half-life.

Mediante an older method known as potassium-argon dating the quantity of each isotope durante the sample was measured preciso obtain an estimate of the its age.

In argon-argon dating, first developed at UC Berkeley con the 1960s, samples are irradiated with neutrons sicuro convert potassium-40 to argon-39, which is normally not present in nature. The ratio of argon-40 to argon-39 gives per measure of the age of the sample less subject esatto experimental error.

Thanks puro refinements mediante equipment, the technique can now be used with milligram samples instead of the tens of grams — nearly an ounce — of rock needed per potassium-argon dating.

Sharp says too that per new carbon dioxide laser allows gradual heating of small samples, durante verso way that provides internal reliability tests, and can help improve the precision of the age estimate.

With the new dating system it should be possible sicuro date even younger samples, perhaps a mere 1,000 years old with 10 percent accuracy

“With potassium-argon dating you had esatto endosse that any argon trapped in the sample had the same isotopic composition as the atmosphere at the time of formation,” Sharp says. “Argon-argon dating allows us puro correlate with other air isotopes esatto tell if there is any deviation from that caused by non-atmospheric argon, such as contamination from argon in the rocks.”

For this experiment the researchers obtained samples of potassium-rich sanidine, per type of feldspar, from a recent excavation of the Contado di Poppea at Pompeii, and brought them puro Berkeley for analysis.

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