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.In a stratigraphical context objects closer to the surface are more recent in time relative to items deeper in the ground.Although relative dating can work well in certain areas, several problems arise.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.As long as there is organic material present, radiocarbon dating is a universal dating technique that can be applied anywhere in the world.
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!
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.
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.