For several thousands of years, ancient Egypt dominated the Mediterranean world—and scholars across the globe have spent more than a century trying to document the reigns（统治，支配） of the various rulers of Egypt's Old, Middle and New Kingdoms. Now, a detailed radiocarbon（放射性碳） analysis of short-lived plant remains from the region is providing scientists with a long and accurate chronology（年代） of ancient Egyptian dynasties that agrees with most previous estimates but also imposes some historic revisions（校订，修正） . Although previous chronologies have been precise in relative ways, assigning absolute dates to specific events in ancient Egyptian history has been an extremely contentious（有争议的） undertaking. This new study tightly constrains those previous predictions, especially for the Old Kingdom, which was determined to be slightly older than some scholars had believed. The study will also allow for more accurate historical comparisons to surrounding areas, like Libya and Sudan, which have been subject to many radiocarbon dating techniques in the past.

Christopher Bronk Ramsey and colleagues from the Universities of Oxford and Cranfield in England, along with a team of researchers from France, Austria and Israel, collected radiocarbon measurements from 211 various plants—obtained from museum collections in the form of seeds, baskets, textiles（纺织品） , plant stems and fruits—that were directly associated with particular reigns of ancient Egyptian kings. They then combined their radiocarbon data with historical information about the order and length of each king's reign to make a complete chronology of ancient Egyptian dynasties.

Their research will be published in the June 18 issue of Science, the peer-reviewed（同行评议） journal published by AAAS, the nonprofit science society.

"My colleague, Joanne Rowland, went to a lot of museums, explaining what we were doing and asking for their participation," Bronk Ramsey said. "The museums were all very helpful in providing material we were interested in—especially important since export of samples from Egypt is currently prohibited. Fortunately, we only needed samples that were about the same size as a grain of（一粒） wheat."

The researchers' new chronology does indicate that a few events occurred earlier than previously predicted. It suggests, for example, that the reign of Djoser in the Old Kingdom actually started between 2691 and 2625 B.C. and that the New Kingdom began between 1570 and 1544 B.C.

Bronk Ramsey and his colleagues also found some discrepancies（差异） in the radiocarbon levels of the Nile Valley, but they suggest that these are due to ancient Egypt's unusual growing season, which is concentrated in the winter months.

For the most part, the new chronology simply narrows down the various historical scenarios that researchers have been considering for ancient Egypt.

"For the first time, radiocarbon dating has become precise enough to constrain the history of ancient Egypt to very specific dates," said Bronk Ramsey. "I think scholars and scientists will be glad to hear that our small team of researchers has independently corroborated（证实，使坚固） a century of scholarship in just three years."