Carbon 14 dating be
(Since humans have only existed in the Americas for approximately 12,000 years, this is not a serious limitation to southwest archaeology.) Radiocarbon dating is also susceptible to contamination.
If the ground in which an object is buried contains particles of coal or other ancient sources of carbon, radiocarbon testing may indicate that the object is far older than it really is.
First, the older the object, the less carbon-14 there is to measure.
Radiocarbon dating is therefore limited to objects that are younger than 50,000 to 60,000 years or so.
There are eight AMS laboratories currently operating in the Unites States.
(The numbers 12, 13 and 14 refer to the total number of protons plus neutrons in the atom's nucleus.
Deemed the gold standard of archaeology, the method was developed in the late 1940s and is based on the idea that radiocarbon (carbon 14) is being constantly created in the atmosphere by cosmic rays which then combine with atmospheric oxygen to form CO2, which is then incorporated into plants during photosynthesis.
When the plant or animal that consumed the foliage dies, it stops exchanging carbon with the environment and from there on in it is simply a case of measuring how much carbon 14 has been emitted, giving its age.
The proportion of carbon-14 to carbon-12 in the atmosphere therefore remains relatively stable at about 1.5 parts per billion.
One of the implied assumptions in radiocarbon dating is that levels of atmospheric carbon-14 have remained constant over time.