Radiocarbon dating of pollen by accelerator mass spectrometry
Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years.
In addition to permitting more accurate dating within archaeological sites than previous methods, it allows comparison of dates of events across great distances.
We are attempting to resolve whether this is due to contamination of the pollen or the presence of significant quantities of old reworked pollen.
Pollen dates from lake sediments associated with Mazama Ash were consistent with other published ages; however, replicate dates on pollen samples from above the ash were consistently older than the surrounding sediment.
Other corrections must be made to account for the proportion of throughout the biosphere (reservoir effects).
Additional complications come from the burning of fossil fuels such as coal and oil, and from the above-ground nuclear tests done in the 1950s and 1960s.
By contrast, methane created from petroleum showed no radiocarbon activity because of its age.