Carbon dating accuracy called into question after major flaw discovery
When news is announced on the discovery of an archaeological find, we often hear about how the age of the sample was determined using radiocarbon dating, otherwise simply known as carbon dating.
Deemed the gold standard of archaeology, the method was developed in the late 1940s and is based on the idea that radiocarbon (carbon 14) is being constantly created in the atmosphere by cosmic rays which then combine with atmospheric oxygen to form CO2, which is then incorporated into plants during photosynthesis.
When the plant or animal that consumed the foliage dies, it stops exchanging carbon with the environment and from there on in it is simply a case of measuring how much carbon 14 has been emitted, giving its age.
But new research conducted by Cornell University could be about to throw the field of archaeology on its head with the claim that there could be a number of inaccuracies in commonly accepted carbon dating standards.
If this is true, then many of our established historical timelines are thrown into question, potentially needing a re-write of the history books.
In a paper published to the Proceedings of the National Academy of Sciences, the team led by archaeologist Stuart Manning identified variations in the carbon 14 cycle at certain periods of time throwing off timelines by as much as 20 years.
The possible reason for this, the team believes, could be due to climatic conditions in our distant past.
This is because pre-modern carbon 14 chronologies rely on standardised northern and southern hemisphere calibration curves to determine specific dates and are based on the assumption that carbon 14 levels are similar and stable across both hemispheres.
However, atmospheric measurements from the last 50 years show varying carbon 14 levels throughout. Additionally, we know that plants typically grow at different times in different parts of the northern hemisphere.
The paper: (open access) http://www.pnas.org/content/early/2018/05/23/1719420115
Fluctuating radiocarbon offsets observed in the southern Levant and implications for archaeological chronology debates
We observe a substantive and fluctuating offset in measured radiocarbon ages between plant material growing in the southern Levant versus the standard Northern Hemisphere radiocarbon calibration dataset derived from trees growing in central and northern Europe and North America. This likely relates to differences in growing seasons with a climate imprint. This finding is significant for, and affects, any radiocarbon application in the southern Levant region and especially for high-resolution archaeological dating—the focus of much recent work and scholarly debate, especially surrounding the timeframe of the earlier Iron Age (earlier Biblical period). Our findings change the basis of this debate; our data point to lower (more recent) ages by variously a few years to several decades.
Considerable work has gone into developing high-precision radiocarbon (14C) chronologies for the southern Levant region during the Late Bronze to Iron Age/early Biblical periods (∼1200–600 BC), but there has been little consideration whether the current standard Northern Hemisphere 14C calibration curve (IntCal13) is appropriate for this region. We measured 14C ages of calendar-dated tree rings from AD 1610 to 1940 from southern Jordan to investigate contemporary 14C levels and to compare these with IntCal13. Our data reveal an average offset of ∼19 14C years, but, more interestingly, this offset seems to vary in importance through time. While relatively small, such an offset has substantial relevance to high-resolution 14C chronologies for the southern Levant, both archaeological and paleoenvironmental. For example, reconsidering two published studies, we find differences, on average, of 60% between the 95.4% probability ranges determined from IntCal13 versus those approximately allowing for the observed offset pattern. Such differences affect, and even potentially undermine, several current archaeological and historical positions and controversies.