The extra neutrons in Carbon-14’s case make it radioactive (thus the term, radiocarbon).Radiocarbon is produced in the upper atmosphere after Nitrogen-14 isotopes have been impacted by cosmic radiation.The Mayan calendar used 3114 BC as their reference.More recently is the radiocarbon date of 1950 AD or before present, BP.The Greeks consider the first Olympic Games as the beginning or 776 BC.The Muslims count the Prophet’s departure from Mecca, or the Hegira, as their beginning at AD 662.Therefore, radiocarbon dates need to be calibrated with other dating techniques to ensure accuracy.Plants are not the only organism that can process Carbon-14 from the air.
The numbers refer to the atomic weight, so Carbon-12 has 6 protons and 6 neutrons, Carbon-13 has 6 protons and 7 neutrons, and Carbon-14 has 6 protons and 8 neutrons.
Rodents, for example, can create havoc in a site by moving items from one context to another.
Natural disasters like floods can sweep away top layers of sites to other locations.
In fact, levels of Carbon-14 have varied in the atmosphere through time.
One good example would be the elevated levels of Carbon-14 in our atmosphere since WWII as a result of atomic bombs testing.