SECTION OF GEOLOGY AND MINERALOGY: SAMPLE CONTAMINATION AND RELIABILITY OF RADIOCARBON DATES*

Abstract

During the ten years that have passed s i n c e W. F. Libby proposed t h e radiocarbon method of age determination several thousand d a t e s have been reported. Although the large majority of these measurements s e e m to provide accurate estimates of absolute a g e of events that have occurred $uring the past 40,000 years, a few of t h e s e measurements are clearly anomalous. One of three explanations may account for the apparent errors: (1) sample radiocarbon concentration h a s been wrongly measured;(2) the sample dated d o e s not represent the event it is supposed to date; or (3) the basic assumptions of the radiocarbon a g e method do not apply to the particular sample.Since the adoption of gas-counting techniques by most radiocarbon laboratories, the first source of errornamely, faulty activity measurementhas almost disappeared. Enough cross-checks between laboratories have been carried out to substantiate this conclusion; in addition, internal electronic checks and duplicate measurements of each sample keep a laboratory in day-to-day contact with the performance of i t s equipment.

Structural Characterization of Charcoal Exposed to High and Low Ph: Implications for 14C Sample Preparation and Charcoal Preservation

“…The method commonly used for removing contaminants from charcoal samples is the so-called acid-base-acid (ABA) pretreatment (Olson and Broecker 1958). The basic ideas behind this treatment are that the initial acid treatment primarily removes soluble carbonates and other minerals; the alkali treatment removes the humic substances; and the final acid treatment removes the dissolved carbon dioxide.…”

Miami Natural Radiocarbon Measurements II

“…In addition to the dating of marine carbonate materials, however, we have extended our methods to the dating of wood and peat samples. All dated peat and wood samples have been given a standard pretreatment by successive washings with dilute HCl and 2% NaOH solution for removal of carbonates and humic acids (Olson and Broecker, 1958). Where sufficient alkali-soluble "humic acid" was recoverable for analysis, this fraction was dated separately and is included with the date obtained from either the wood or peat.…”

Who's That Lying in My Coffin? An Imposter Exposed by 14C Dating

“…This treatment was initially devised to remove carbonates, fulvic acids, and humic acids from soils, sediments, charcoal, and buried materials (Olson and Broecker 1958). Materials such as mummy linen are unlikely to require AAA treatment as contaminates such as fulvic acids and humic acids are unlikely to affect textiles that have not been buried in soil.…”