Advantages and disadvantages of carbon dating
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.
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.
Half-lives vary according to the isotope, for example, Uranium-238 has a half-life of 4500 million years where as Nitrogen-17 has a half-life of 4.173 seconds!
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.
Plankton absorbs, Carbon-14 from the ocean much like terrestrial plants absorb Carbon-14 from the air.
Since plankton is the foundation of the marine food chain, Carbon-14 is spread throughout aquatic life.