Radiocarbon Dating History: Early Days, Questions, and Problems Met

Abstract

W F Libby's new dating method from the 1940s, based on experience in physics and chemistry, opened possibilities to check and revise chronologies built on other principles than radioactive decay. Libby's method initially implied collaboration with archaeologists to demonstrate that it worked but also with physicists to improve the technique to measure low β– activities. Chemists, geophysicists, botanists, physiologists, statisticians, and other researchers have contributed to a prosperous interdisciplinary development. Some pitfalls were not recognized from the beginning, although issues such as contamination problems were foreseen by Libby. Pretreatment of samples was discussed very early by de Vries and collaborators, among others. This subject has not yet been abandoned. Closely related to pretreatment is the choice of fraction to be dated and chemicals to be used, especially for accelerator mass spectrometry (AMS) measurements. Calibration against tree rings and comparison with dates obtained using other methods as well as intercomparison projects are partly history but still very actual. The impact by man and climate is also studied since the early days of the method. Also, the carbon cycle has been of great interest. The tools for measurements and statistical analysis have been improved during these first 3 or 4 decades, allowing interpretations not possible earlier. δ13C determinations are mostly very important and useful, but sometimes they have been misleading in discussions of the origin of carbon, especially for human tissues—the metabolism was not yet fully understood. The history and development of the method can only be illustrated by selected examples in a survey like this.

Carbon Cycling and Organic Radiocarbon Reservoir Effect in a Meromictic Crater Lake (Lac Pavin, Puy-de-Dôme, France)

“…The choice of sample pretreatment procedure may be critical on 14 C results (Olsson 2009) but was not explored in detail during this study. Since sediment material in Lac Pavin is mostly composed of autochthonous material, humic-like fractions extracted by hydroxide will not reflect terrestrial contamination but rather will contain the information that is being sought.…”

“…Bulk sediment (accounting for sediment organic carbon SOC), sediment-trap (POC sink ), and macro-remains samples were analyzed either at the Saclay LMC14 facility or at the PoznaÒ Radiocarbon Laboratory after acid-alkali-acid (AAA) pre-treatment (Goslar and Czernik 2000). AAA pretreatment applied to bulk biogenic sediment may cause the weight losses of a large proportion of the organic as well as of the bulk siliceous material (Olsson 2009). Humics from soils in the watershed of the lake are thought to make a very minor contribution to Lac Pavin and humic-like compounds present in sediment have rather a planktonic origin.…”

Astronomical forcing of sub-Milankovitch climate oscillations during the late Quaternary

“…Heinrich, 1988). With the link between patterns in tree rings and 14 C variations confirmed, wiggle matching is now important in matching floating pieces of chronology to a chronological framework (e.g., Blaauw et al, 2004;Olsson, 2009;Wieder et al, 2010).…”

“…Around 70% of natural variability has been attributed to heliomagnetic and geomagnetic activity, and the remainder to climate effects . Anthropogenic causes include the Industrial Revolution, atomic bomb blasts, and the burning of fossil fuels (Libby, 1960;Damon and Sonett, 1991;Olsson, 2009;Suess, 1953Suess, , 1955Taylor and Bar Yosef, 2014). Natural causes include changes in the strength and intensity of the geomagnetic dipole, astrophysical forcing, and changes in ocean circulation and global wind speeds (Blackwell and Buck, 2008;Damon and Sonett, 1991;Lal and Lingenfelter, 1991;Hathaway, 2010;Stuiver et al, 1991;Tiwari and Rao, 1998;Suess, 1986;Taylor and Bar Yosef, 2014).…”

“…However, by 1962 the length of this half-life was challenged based on further experimentation and found to be 3% too young, with the "true" value deemed to be 5730±40 yrs called the Cambridge half-life (Bowman, 1990;Olsson, 2009;Taylor and Bar Yosef, 2014). At the Pullman Conference in 1965 (later upheld at other conferences since the early seventies), it was decided that, because of the large number of radiocarbon dates already published, the Libby half-life would continue to be used (Bowman, 1990;Chiu et al, 2007;Hughen et al, 1998;Olsson, 2009;Taylor and Bar Yosef, 2014).…”