Accelerator radiocarbon dating at the molecular level

Abstract

Molecular level 14C dating is the isolation of specific classes of molecules for their 14C dating by accelerator mass spectrometry (AMS). Complex matrices such as fossil bone are difficult to date due to their extreme chemical heterogeneity. By isolating individual amino acids, contaminants (humates) are removed and crystalline amino acids result. Bones with ≥0·1–0·2% N and collagenous compositions can be dated accurately because structural collagen is present; contaminants are removable with XAD resin. Bones with ⩽0·1% N and non-collagenous compositions yield dates hundreds to thousands of years too young because most of the preserved organic matter is exogenous. Accelerator 14C dates on collagenous and non-collagenous bones are not comparable due to intrinsic dating inaccuracies. AMS 14C dating of amino acids demonstrated that (1) post 10,800 year ages for North American megafauna are due to sample contamination, not Holocene ages on extinct fauna, (2) a Clovis age (10,900 years) was established for a human fossil from the Anzick site, Montana, (3) Holocene ages cannot be established absolutely for many North American human fossils because the bones were non-collagenous, (4) accurate ages are attainable on vertebrate fossils as small as passerine birds from Pacific Island localities, (5) well preserved bones are datable without their destruction by extracting protein with water at high temperatures, and (6) stratigraphic anomalies to 45,000 years in European Upper Paleolithic rock shelters are recognizable by dating bone directly.