C14 radiocarbon dating
It is naturally unstable and so it will spontaneously decay back into N-14 after a period of time.
For example, Christian time counts the birth of Christ as the beginning, AD 1 (Anno Domini); everything that occurred before Christ is counted backwards from AD as BC (Before Christ).C-14 is produced in the upper atmosphere when nitrogen-14 (N-14) is altered through the effects of cosmic radiation bombardment (a proton is displaced by a neutron effectively changing the nitrogen atom into a carbon isotope).The new isotope is called "radiocarbon" because it is radioactive, though it is not dangerous.Theoretically, if one could detect the amount of carbon-14 in an object, one could establish that object’s age using the half-life, or rate of decay, of the isotope.In 1946, Libby proposed this groundbreaking idea in the journal Physical Review.
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There are two techniques for dating in archaeological sites: relative and absolute dating.