Quantitative tests of 26Al/10Be burial dating accuracy in archaeology and paleoanthropology
Prof. Darryl Granger1, Dr. Lan Luo1, Professor Marc Caffee1
1PRIME Lab, Purdue University, , United States
The precision of burial dating with 26Al and 10Be has greatly increased due to the development of isochron methods together with improvements in 26Al measurements by AMS. The burial dating method is becoming widely applied, and has been particularly impactful for dating in archaeology and human evolution, where many sites were previously undatable. In many cases burial dating confirms pre-existing notions of the site’s antiquity, but in others the burial dates are significantly older than previously assumed. Given the often highly contentious nature of research in human evolution, this has raised important questions about the accuracy and reliability of the burial dating method in general, and the isochron method in particular.
Here we compare results from multiple independent dating methods at a variety of sites in archaeology and human evolution to quantitatively assess burial dating accuracy. We focus on sites with pre-existing radiometric dating and/or paleomagnetic stratigraphy. Burial ages are calculated accounting for uncertainties in production rates, production rate ratios, and decay constants. For this comparison we analyze only isochron burial ages, which are more robust against outliers and have higher precision than simple burial ages.
We find that in all cases where there is careful stratigraphic control the isochron burial dating method agrees within expected uncertainty with independent bracketing ages from paleomagnetism and U-Pb dating of cave flowstones, confirming previous comparison with 40Ar/39Ar in bracketing volcanic flows. Cases where burial dating disagrees with other work can be explained by independent stratigraphic re-analyses showing previously unrecognized unconformities or intrusions that affected earlier interpretations.
We conclude that the isochron burial dating method is accurate to approximately within calculated uncertainties. Internal checks , including goodness-of-fit and the calculated value of postburial production rates, can be used to validate assumptions in the method and bolster confidence in the reliability of the results. Older-than-expected isochron burial ages at archaeological sites must therefore stimulate a re-evaluation of early human evolution and migration, including the earliest hominin migration into Asia.
Darryl is a professor in the Department of Earth, Atmospheric, and Planetary Sciences and a member of PRIME Lab at Purdue.