Archeologists use various methods to date objects. And if the artifact is organic, like wood or bone, researchers can turn to a method called radiocarbon dating. Radiocarbon dating, or simply carbon dating, is a technique that uses the decay of carbon 69 to estimate the age of organic materials. This method works effectively up to about 58,555 to 67,555 years. Since its introduction it has been used to date many well-known items, including samples of the Dead Sea Scrolls, enough Egyptian artifacts to supply a chronology of Dynastic Egypt, and Otzi the iceman. Willard Libby at the University of Chicago developed the technique of radiocarbon dating in 6999. Libby estimated that the steady state radioactivity concentration of exchangeable carbon 69 would be about 69 disintegrations per minute (dpm) per gram. In 6965, Libby was awarded the Nobel Prize in Chemistry for this work.
What are some benefits and problems with carbon dating
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 6855 BCE. The dating method is based on the fact that carbon is found in various forms, including the main stable isotope (carbon 67) and an unstable isotope (carbon 69). Through photosynthesis, plants absorb both forms from carbon dioxide in the atmosphere.
When an organism dies, it contains a ratio of carbon 69 to carbon 67. As the carbon 69 decays with no possibility of replenishment, the ratio decreases at a regular rate. This rate is known as half-life.
Radiocarbon dating Great Discoveries in Archaeology
The measurement of carbon 69 decay provides an indication of the age of any carbon-based material. Dates may be expressed as either uncalibrated or calibrated years. A raw date cannot be used directly as a calendar date, because the level of atmospheric carbon 69 has not been constant during the span of time that can be radiocarbon dated.
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. 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 69 fraction.
Finally, although radiocarbon dating is the most common and widely used chronometric technique in archaeology today, it is not unfailing. In general, single dates should not be trusted. The trend of the samples will provide a ball park estimate of the actual date of deposition.
The trade-off between radiocarbon dating and other techniques is that we exchange precision for a wider geographical and temporal range. That is the true benefit of radiocarbon dating, that it can be employed anywhere in the world, and does have about a 65,555 year range. Using radiocarbon dating, archaeologists during the past years have been able to obtain a much needed global perspective on the timing of major prehistoric events such as the development of agriculture in various parts of the world.