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.
The Mayan calendar used 3114 BC as their reference.
More recently is the radiocarbon date of 1950 AD or before present, BP.
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.
Absolute dating represents the absolute age of the sample before the present.
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!
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.
As long as there is organic material present, radiocarbon dating is a universal dating technique that can be applied anywhere in the world.
It is good for dating for the last 50,000 years to about 400 years ago and can create chronologies for areas that previously lacked calendars.
Plankton absorbs, Carbon-14 from the ocean much like terrestrial plants absorb Carbon-14 from the air.