Radiocarbon dating was invented in the late 1940s. It has been continuously improved to provide more accurate measurements. It is the standard techniques for identifying the dates of artifacts in archeology and other scientific disciplines.
Stuart Manning is the Goldwin Smith Professor of Classical Archaeology in the College of Arts and Sciences at Cornell University. Manning says, "If it's organic and old -- up to 50,000 years -- you date it by radiocarbon." Manning is the lead author of a new paper published in March in the journal Science Advances. In his paper, Manning makes a case for the need to further refine the radiocarbon dating technique. The results of his research have great relevance for understanding Mediterranean history and prehistory.
Carbon-14 is an unstable radioactive isotope of carbon. It is created by cosmic radiation and it is present in all organic matter. The flux of cosmic radiation is not constant. In order to take into account fluctuations in cosmic radiation in the atmosphere of the Earth, scientists use the radiocarbon content of tree rings whose ages are known going back thousands of years. Radiocarbon dating measures the decomposition of Carbon-14.
The wide use of radiocarbon dating began around 1970. In 1986, scientists developed a standard calibration curve. The curve is updated every few years as more data is accumulated. Manning said, “A single Northern Hemisphere calibration curve has formed the basis of radiocarbon dating in Europe and the Mediterranean for five decades, setting the time frame for prehistory. However, as measurement precision increases, there is mounting evidence for some small but substantive regional (partly growing season) offsets in the same-year radiocarbon levels.”
In the study conducted by Manning and his team, they raised the question of the accuracy of using a single calibration curve for all of the Northern Hemisphere. One laboratory collected information to control for interlaboratory variations. With this data, Manning and his team compared radiocarbon dating from Germany and Central Turkey in the first and second millennia B.C. The researchers found that there were small but critical periods of variation for the radiocarbon dating of these two locations. Other laboratories had taken samples from central Italy and northern Turkey which confirmed the consistency of the variations between these two areas.
One reason for the variation involves the growing season according to Manning’s report. The radiocarbon level on Earth depends on the season. There is a winter low level and a summer high level. The carbon in a tree ring is related to the time that the tree is photosynthesizing. This process involves the tree in absorbing carbon dioxide from the atmosphere. Manning said, “In northern Europe or in North America, a tree is going to be doing this in April through September. But a tree in Jordan or Israel does that October through April -- almost the opposite time of the year.” These variations are small but they can affect the calendar dates for prehistorical artifacts by as much as a few decades.
Even date offsets of fifty years or less can have a significant effect on constructing the timeline of the Mediterranean region. This region was a hotbed of related cultures in the last two centuries B.C. The dates adjusted by the research of Manning have helped to synchronize previously discordant dates for some historically important events. These events include the death and burial for the Egyptian Pharaoh Tutankhamun. This happened between 1320 and 1310 B.C. according to recent work in Egyptology.
Manning’s research has also contributed to a debate over the date of a huge volcanic eruption on the Greek island of Santorini. This event has been extensively studied and is currently dated around 1500 B.C. by archeologists but is dated to between 1630 and 1600 B.C. by scientists. According to Manning, his work indicates that the eruption could not have occurred around the 1500 B.C. date. The 1630 to 1600 B.C. period is still possible with respect to Manning’s new dating but a later date in the 1600 to 1550 B.C. period is also possible and this is more in accord with existing archaeological and historical records.
Manning’s research also has important implications for which ancient culture influenced both the Minoans and the Mycenaeans. These cultures were the foundation for the culture of ancient Greece. Manning said, "Getting the date right will rewrite and get our history correct in terms of what groups were significant in shaping what then became classical civilization. An accurate timeline is key to our history.”
Manning predicts that follow-up studies will lead to more regionally specific regional calibration for the Northern Hemisphere. This should lead to more adjustments of the dates for historical artifacts.
Grants from the U.S. National Science Foundation and the Canadian Social Science and Humanities Research Council funded Manning’s research.