Carbon dating methodology
So every living thing has a certain amount of radiocarbon within them.
After an organism dies, the radiocarbon decreases through a regular pattern of decay. The time taken for half of the atoms of a radioactive isotope to decay in Carbon-14’s case is about 5730 years.
Since plankton is the foundation of the marine food chain, Carbon-14 is spread throughout aquatic life.
Shellfish remains are common in coastal and estuarine archaeological sites, but dating these samples require a correction for the “reservoir effect” a process whereby "old carbon" is recycled and incorporated into marine life especially shellfish inflating their actual age in some cases several centuries.
Radiocarbon is produced in the upper atmosphere after Nitrogen-14 isotopes have been impacted by cosmic radiation.
Radiocarbon is then taken in by plants through photosynthesis, and these plants in turn are consumed by all the organisms on the planet.
Plants are not the only organism that can process Carbon-14 from the air.
The Mayan calendar used 3114 BC as their reference.For example, Christian time counts the birth of Christ as the beginning, AD 1 (Anno Domini); everything that occurred before Christ is counted backwards from AD as BC (Before Christ).The Greeks consider the first Olympic Games as the beginning or 776 BC.One good example would be the elevated levels of Carbon-14 in our atmosphere since WWII as a result of atomic bombs testing.Therefore, radiocarbon dates need to be calibrated with other dating techniques to ensure accuracy.