Fractionation radiocarbon dating
In addition to permitting more accurate dating within archaeological sites than previous methods, it allows comparison of dates of events across great distances.
Histories of archaeology often refer to its impact as the "radiocarbon revolution".
The results were summarized in a paper in Science in 1947, in which the authors commented that their results implied it would be possible to date materials containing carbon of organic origin.
Libby and James Arnold proceeded to experiment with samples of wood of known age.
The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by radiocarbon dating are around 50,000 years ago, although special preparation methods occasionally permit dating of older samples.The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age.Other corrections must be made to account for the proportion of throughout the biosphere (reservoir effects).For example, two samples taken from the tombs of two Egyptian kings, Zoser and Sneferu, independently dated to 2625 BC plus or minus 75 years, were dated by radiocarbon measurement to an average of 2800 BC plus or minus 250 years. Carbon dioxide produced in this way diffuses in the atmosphere, is dissolved in the ocean, and is taken up by plants via photosynthesis.Animals eat the plants, and ultimately the radiocarbon is distributed throughout the biosphere.
It was soon discovered that in the atmosphere by neutrons from cosmic rays that had been slowed down by collisions with molecules of atmospheric gas.