Radiocarbon dating tools
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.
Therefore, radiocarbon dates need to be calibrated with other dating techniques to ensure accuracy.
The Muslims count the Prophet’s departure from Mecca, or the Hegira, as their beginning at AD 662.
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.
In recognition of this problem archaeologists have developed regional reservoir correction rates based on ocean bottom topography, water temperature, coastline shape and paired samples of terrestrial and marine objects found together in an archaeological feature such as a hearth.
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.
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.