Clearly, various centers of civilization arose independently of one another even if the Near Eastern one remains the oldest on record.
) and is instantantly mixed throughout the atmosphere.
There are also significant plateaus in the curves, such as the one from 11000 to 10000 radiocarbon years BP, which is believed to be associated with changing ocean circulation during the Younger Dryas period.
The accuracy of radiocarbon dating is lower for samples originating from such plateau periods. Originally a Carbon-14 half-life of 5568 -30 years was used, which is now known as the Libby half-life.
The level is maintained by high energy particles interacting with the earth's upper atmosphere, which may be affected by changes in the earth's magnetic field or in the cosmic ray background, e.g. In addition there are substantial reservoirs of carbon in organic matter, the ocean, ocean sediments (see methane hydrate), and sedimentary rocks; and changing climate can sometimes disrupt the carbon flow between these reservoirs and the atmosphere.
This is the number of radiocarbon years before 1950, based on a nominal (and assumed constant - see "calibration" below) level of carbon-14 in the atmosphere equal to the 1950 level.
labs generally report an uncertainty, e.g., 3000 -30BP indicates a standard deviation of 30 radiocarbon years.
are traditionally made by counting the radioactive decay of individual carbon atoms by gas proportional counting or by Liquid scintillation counting, but this is relatively insensitive and subject to relatively large statistical uncertainties for small samples (below about 1g carbon).
If there is little carbon-14 to begin with, a half-life that long means that very few of the atoms will decay while their detection is attempted (4 atoms/s/mole just after death, hence e.g. Sensitivity has since been greatly increased by the use of accelerator-based mass-spectrometric (AMS)techniques, where all the 14C atoms can be counted directly, rather than only those decaying during the counting interval allotted for each analysis.