TECHNOLOGY

Radiocarbon Dating

1949 CE

History · Contemporary · Holocene · Meghalayan

Radiocarbon dating, established by Willard Libby and James Arnold in 1949, reads the age of anything once alive from the slow decay of carbon 14, whose half-life is about 5,700 years.

Radiocarbon dating rests on a radioactive isotope present in the atmosphere, assimilated by living organisms throughout their existence and whose quantity thereafter decreases at a constant rate, the half-life being about 5,700 years. Willard Libby and James Arnold established its application in 1949, and verified the method on Egyptian objects of historically known age; Libby received the Nobel Prize in Chemistry in 1960. The reach of the method today attains about fifty thousand years. Raw measurements must be corrected, atmospheric production of carbon-14 not being constant.

Why it matters

Before this method, prehistoric chronology rested on relative sequences, established by comparison of styles and stratigraphies, with no possibility of relating distant sites to a common scale. Radiocarbon made such comparisons possible and invalidated several models of technical and cultural diffusion then accepted. A substantial part of the dates appearing in this edition proceeds from it.

Dating & uncertainty

The founding publications date from 1949. Correction of the measurements is necessary because carbon-14 is produced in the upper atmosphere by cosmic rays, and that production varies with solar activity and the terrestrial magnetic field, atmospheric content therefore not being constant over time. Correction is effected by means of wood whose exact year is established by ring counting, each ring supplying simultaneously its date and the content of its period; the calibration curves so constituted convert a measurement into a calendar date.

Our species’ history as one day

23:59:3821.1 s before midnight

if the 315,000 years of Homo sapiens were compressed into a single day