As a rule, carbon dates are younger than calendar dates: a bone carbon-dated to 10,000 years is around 11,000 years old, and 20,000 carbon years roughly equates to 24,000 calendar years.The problem, says Bronk Ramsey, is that tree rings provide a direct record that only goes as far back as about 14,000 years. Climate records from a Japanese lake are set to improve the accuracy of the dating technique, which could help to shed light on archaeological mysteries such as why Neanderthals became extinct.

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’re trying to look at archaeological sites at the order of 30,000 or 40,000 years ago, the ages may shift by only a few hundred years but that may be significant in putting them before or after changes in climate,” he says.

Take the extinction of Neanderthals, which occurred in western Europe less than 30,000 years ago.

A very common claim of young earth creationists in trying to reject the evidence for an old earth is to loudly proclaim that radiometric dating methods “makes assumptions” and that these “assumptions” are somehow fatally flawed or not supported by evidence.

These claims generally land in three different categories: (1) radiometric dating assumes that initial conditions (concentrations of mother and daughter nuclei) are known, (2) radiometric dating assumes that rocks are closed systems and (3) radiometric dating assumes that decay rates are constant.

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.

Surely, if some daughter nuclei left the rock or parent nuclei entered the rock, the dates would come out all wrong! Follow Debunking Denialism on Facebook or Twitter for new updates.

While this is technically true, there are several mini-industries dedicated developing methods and techniques to make sure that there is no contamination and check to see if the rocks where disturbed between forming and being tested by scientists. On of the great things about many forms of radiometric dating is that they are self-checking.

As time goes on, the ratio of the parent to daughter nuclei will change and decrease (as more parent nuclei decay into daughter nuclei, the former decreases and the latter increases).