However, this prompts the question of how one might determine this prior to using carbon dating to determine the age.
They further argue that dating much older items will result in anomalous dates, which might fall within the range that carbon dating can measure.
Claims have been made of the method being calibrated back to 10,000 years using dendrochronology, C ratios the same as the atmosphere.
For example, it is well known that carbon dating cannot be used on many types of marine life due to reservoirs of "old" carbon held in sedimentary rocks.
Most man-made chemicals are made of fossil fuels, such as petroleum or coal, in which the carbon-14 has long since decayed.
However, oil deposits often contain trace amounts of carbon-14 (varying significantly, but ranging from 1% the ratio found in living organisms to undetectable amounts, comparable to an apparent age of 40,000 years for oils with the highest levels of carbon-14).
The initial C-14 level for the calculation can either be estimated, or else directly compared with known year-by-year data from tree-ring data (dendrochronology) to 10,000 years ago, or from cave deposits (speleothems), to about 45,000 years of age.
That is, samples with dates known from historical records can be used to check the accuracy of the method.
Despite this, however, caution is still necessary in accepting dates derived from carbon dating.
When cosmic rays enter the atmosphere, they undergo various transformations, including the production of neutrons.
The resulting neutrons ( The highest rate of carbon-14 production takes place at altitudes of 9 to 15 km (30,000 to 50,000 feet) and at high geomagnetic latitudes, but the carbon-14 readily mixes and becomes evenly distributed throughout the atmosphere and reacts with oxygen to form radioactive carbon dioxide.