But that assumes that the amount of carbon-14 in the atmosphere was constant — any variation would speed up or slow down the clock.
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.
The more accurate carbon clock should yield better dates for any overlap of humans and Neanderthals, as well as for determining how climate changes influenced the extinction of Neanderthals.
“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.
The levels of 14C present in a specimen can be measured in a variety of ways; however the invention of accelerator-based mass spectrometric techniques have drastically increased measurement accuracy, as it provides a count of the number of 14C atoms present in a sample.
It has been used to date specimens up to 60,000 years in age.
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.Take the extinction of Neanderthals, which occurred in western Europe less than 30,000 years ago.Archaeologists vehemently disagree over the effects changing climate and competition from recently arriving humans had on the Neanderthals' demise.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.
Various geologic, atmospheric and solar processes can influence atmospheric carbon-14 levels.
When an organism dies, the intake of 14C ceases, and what was left in the organism begins a measurable disintegration.