Radiocarbon dating calibration involves
(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.
Familiar to us as the black substance in charred wood, as diamonds, and the graphite in “lead” pencils, carbon comes in several forms, or isotopes.
One rare form has atoms that are 14 times as heavy as hydrogen atoms: carbon-14, or C ratio gets smaller.
Radiocarbon dating—also known as carbon-14 dating—is a technique used by archaeologists and historians to determine the age of organic material.
In recent years, dating methods based on cosmogenic isotopes other than carbon (such as beryllium-10 and chlorine-36) have been developed, which allow for the dating of a wider variety of objects over much longer time scales.We will deal with carbon dating first and then with the other dating methods.Carbon has unique properties that are essential for life on Earth.Conversely, contamination by newer plant matter carried by flowing water or intruding plant roots may result in a date that is much too young. The original technique was based on counting the number of individual radioactive decay events per unit of time, using a device similar to a Geiger counter.Archaeologists are acutely aware of these and other potential difficulties, and take extreme care in the selection and handling of objects to be dated. In the 1970s a new technique was developed called Accelerator-based Mass Spectrometry (AMS), which counts the number of carbon-14 atoms directly.