Berkeley — Verso powerful geologic dating technique called argon-argon dating has pegged the 79 Verso
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 sopra 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 esatto date many recent important fossil finds, from the highly touted human ancestor dubbed “Lucy” and the major Ethiopian codice promozionale asiandate 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 preciso 1,700 degrees Celsius
Argon-argon dating also has been used puro establish the age of meteorites several billion years old, mass extinctions, climate changes and other geologic events mediante the last several hundred million 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 Civetta of the Department of Geophysics and Vulcanology at the University of Naples. Civetta also is head of the Vesuvian Vulcanological Observatory.
Orsi and Fraschetta are working with the center sicuro obtain argon-argon dates for numerous past volcanic eruptions sopra the Campi Flegrei or Phlegraean Fields surrounding Naples, con search of clues esatto 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 preciso volcanic hazard.
According sicuro the Roman historian Pliny the Younger, Vesuvius erupted in the early afternoon of Aug. 24, 1,918 years ago, destroying Pompeii, Herculaneum and other Roman cities.
The certainty of the date tempted the gruppo to esame the ability of the argon-argon dating technique sicuro 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 per 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, per technique limited sicuro organic material such as wood or bone.
Onesto everyone’s surprise the date given by the argon-argon dating technique was 1,925 years spillo — off by only seven years. The scientific error on the estimate was plus or minus 94 years.
“We nailed the date sicuro five percent on our first attempt, so we could probably get the error down preciso one percent or less,” Renne says.
The result is so amazing because every dating technique invokes assumptions or involves uncertainties that limit its ability onesto pinpoint dates with extreme precision. With carbon-14, for example, the changing ratio of carbon-12 onesto carbon-14 in the atmosphere over time puts per limitation on how precise verso 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 onesto argon-40 with verso 1.25 billion year half-life.
Durante an older method known as potassium-argon dating the quantity of each isotope per the sample was measured esatto obtain an estimate of the its age.
Durante argon-argon dating, first developed at UC Berkeley con the 1960s, samples are irradiated with neutrons onesto convert potassium-40 sicuro argon-39, which is normally not present per nature. The ratio of argon-40 esatto argon-39 gives a measure of the age of the sample less subject onesto experimental error.
Thanks sicuro 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 a new carbon dioxide laser allows gradual heating of small samples, sopra per 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 preciso date even younger samples, perhaps per mere 1,000 years old with 10 percent accuracy
“With potassium-argon dating you had sicuro garantit that any argon trapped mediante the sample had the same isotopic composition as the atmosphere at the time of formation,” Sharp says. “Argon-argon dating allows us to correlate with other air isotopes onesto tell if there is any deviation from that caused by non-atmospheric argon, such as contamination from argon con the rocks.”
For this experiment the researchers obtained samples of potassium-rich sanidine, a type of feldspar, from verso recent excavation of the Campagna di Poppea at Pompeii, and brought them sicuro Berkeley for analysis.