The level is affected by variations in the cosmic ray intensity, which is, in turn, affected by variations in the Earth’s magnetosphere.
In addition, there are substantial reservoirs of carbon in organic matter, the ocean, ocean sediments, and sedimentary rock.
A man called Willard F Libby pioneered it at the University of Chicago in the 50's. This is now the most widely used method of age estimation in the field of archaeology.
Changes in the Earth’s climate can affect the carbon flows between these reservoirs and the atmosphere, leading to changes in the atmosphere’s carbon 14 fraction.
Finally, although radiocarbon dating is the most common and widely used chronometric technique in archaeology today, it is not unfailing. Whenever possible multiple samples should be collected and dated from associated sections.
In 1960, Libby was awarded the Nobel Prize in Chemistry for this work.
He demonstrated the accuracy of radiocarbon dating by accurately estimating the age of wood from a series of samples for which the age was known, including an ancient Egyptian royal barge of 1850 BCE.