Geology Reference
In-Depth Information
Graph showing first test of radiocarbon dating in a plot of known sample age versus the rate of carbon-14 (
14
C) decay
and the close fit between measured values (data points) and values predicted (curve) by radiocarbon decay
(
based on
a figure in Arnold, J. R., and Libby, W. F., 1949, Age determinations by radiocarbon content: Checks with samples of
known age,
Science
, v. 110, p. 678-680
).
The development of radiocarbon dating was revolutionary, as it enabled scientists to reli-
ably date deposits from the last few tens of thousands of years. The method was developed
by Willard Libby at the University of Chicago's Institute for Nuclear Studies and is based
on measuring the rate of decay of the naturally occurring unstable radioactive isotope
14
C
(carbon-14). Collisions between cosmic ray protons and particles in the atmosphere pro-
duce secondary neutrons that are captured by nitrogen nuclei in the N
2
gas that forms most
of the atmosphere. This fusion creates
14
C, which decays to the normal stable nitrogen iso-
tope (
14
N) with a characteristic half-life of about 5,720 years, the time it takes for half of
the amount remaining to decay. When plants convert atmospheric carbon dioxide (CO
2
) in-
to organic matter during photosynthesis, a small amount of
14
C is incorporated in propor-
