Carbon dating doesn t work
Preserved leaves in the cores — “they look fresh as if they’ve fallen very recently”, Bronk Ramsey says — yielded 651 carbon dates that could be compared to the calendar dates of the sediment they were found in.
The recalibrated clock won’t force archaeologists to abandon old measurements wholesale, says Bronk Ramsey, but it could help to narrow the window of key events in human history.
By measuring the ratio of the radio isotope to non-radioactive carbon, the amount of carbon-14 decay can be worked out, thereby giving an age for the specimen in question.
But that assumes that the amount of carbon-14 in the atmosphere was constant — any variation would speed up or slow down the clock.
Carbon-14 dating is a way of determining the age of certain archeological artifacts of a biological origin up to about 50,000 years old.
It is used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities.
The clock was initially calibrated by dating objects of known age such as Egyptian mummies and bread from Pompeii; work that won Willard Libby the 1960 Nobel Prize in Chemistry.
But even he “realized that there probably would be variation”, says Christopher Bronk Ramsey, a geochronologist at the University of Oxford, UK, who led the latest work, published today in Science.
Take the extinction of Neanderthals, which occurred in western Europe less than 30,000 years ago.The technique hinges on carbon-14, a radioactive isotope of the element that, unlike other more stable forms of carbon, decays away at a steady rate.Organisms capture a certain amount of carbon-14 from the atmosphere when they are alive.“If you have a better estimate of when the last Neanderthals lived to compare to climate records in Greenland or elsewhere, then you’ll have a better idea of whether the extinction was climate driven or competition with modern humans,” says Paula Reimer, a geochronologist at Queen’s University in Belfast, UK.She will lead efforts to combine the Lake Suigetsu measurements with marine and cave records to come up with a new standard for carbon dating.
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