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.Dates up to this point in history are well documented for C14 calibration.For object over 4,000 years old the method becomes very unreliable for the following reason: Objects older then 4,000 years run into a problem in that there are few if any known artifacts to be used as the standard.
Since its conception by Willard Libby in 1949, it has been invaluable to the discipline.
Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years.
The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age.
by Helen Fryman Question: What about radiocarbon dating? Response: I asked several people who know about this field. (1.) C14 dating is very accurate for wood used up to about 4,000 years ago.
This is only because it is well calibrated with objects of known age.