For approximate analysis it is assumed that the cosmic ray flux is constant over long periods of time; thus carbon-14 could be assumed to be continuously produced at a constant rate and therefore that the proportion of radioactive to non-radioactive carbon throughout the Earth's atmosphere and surface oceans is constant: ca. For more accurate work, the temporal variation of the cosmic ray flux can be compensated for with calibration curves.
If these curves are used, their accuracy and shape will be the limiting factors in the determination of the radiocarbon age range of a given sample.
The highest rate of carbon-14 production takes place at altitudes of 30,000 to 50,000 feet, and at higher geomagnetic latitudes, but the carbon-14 spreads evenly throughout the atmosphere and reacts with oxygen to form carbon dioxide.
Carbon dioxide also permeates the oceans, dissolving in the water.
The K-Ar and uranium decay series are used in dating older objects (see Radiometric dating).
is a radiometric dating method that uses the naturally occurring isotope carbon-14 to determine the age of carbonaceous materials up to ca. Within archaeology it is considered an absolute dating technique.
The technique was discovered by Willard Frank Libby and his colleagues in 1949.
In addition, there are tiny amounts of the unstable isotope carbon-14 (14C) on Earth.
Carbon-14 has a half-life of just under 6000 years and would have long ago vanished from Earth were it not for the unremitting cosmic ray impacts on nitrogen in the Earth's atmosphere, which forms more of the isotope.
Later a more accurate figure of 5730 -40 years was measured, which is known as the Cambridge half-life.