One radioactive, or unstable, carbon isotope is C14, which decays over time and therefore provides scientists with a kind of clock for measuring the age of organic material.
The earliest experiments in radiocarbon dating were done on ancient material from Egypt. Libby’s team obtained acacia wood from the 3rd Dynasty Step Pyramid of Djoser to test a hypothesis they had developed.
However, cosmic radiation constantly collides with atoms in the upper atmosphere.
Part of the result of these collisions is the production of radiocarbon (C, pronounced "c fourteen"), carbon atoms which are chemically the same as stable carbon, but have two extra neutrons.
Libby reasoned that since the half-life of C years, the Djoser sample’s C14 concentration should be about 50% of the concentration found in living wood (for further details, see Arnold and Libby, 1949). Subsequent work with radiocarbon testing raised questions about the fluctuation of atmospheric C14 over time.
Scientists have developed calibration techniques to adjust for these fluctuations.
The samples included animal remains, shells, plant material and charcoal.
"Nobody had ever done that before." The team analyzed organic material from artifacts obtained from museum collections that were not in good enough shape to go on display.
The numbers of C14 atoms and non-radioactive carbon atoms remain approximately the same over time during the organism’s life.
The accession of King Aha to the throne is often thought to define the start of the Egyptian state, with the new study suggesting (with 68 percent probability) that he became king between 3111 B. [See Photos of Egypt's Great Terrace of God] To create a more reliable timeline, archaeologists based at the University of Oxford have developed the most comprehensive chronological analyses of Early Egypt artifacts yet based on a computer model of existing and newly measured radiocarbon dates. Other existing settlements at the time were isolated city-states, but Egypt developed into a more complex and expansive settlement similar to modern countries today, Dee said.
The analyses suggest the rise to statehood occurred between 200 and 300 years faster than previously thought, beginning between 3800 B. The team hopes that their results will help inform future research on Early Egypt culture, but does not have plans to produce more dates from Egypt.
The most precise chronology of Early Egypt yet suggests the country formed much more quickly than previously thought. Existing timelines of Egypt's transition from a nomadic community along the Nile River to a permanent state are mainly based on changes in pottery artifacts found at various locations around the country. The findings, which also suggest the preceding Neolithic period lasted longer than thought, are detailed Sept. The resulting dates for each ruler were accurate to within 32 years, and with 68 percent probability, the researchers said. Only very small quantities of material were needed for the analyses, ranging from roughly 10 milligrams – about the size of a fingernail clipping – for plant material, to as much as 0.5 grams (0.02 ounces) for bone.
The new finding reveals a robust timeline for the first eight kings and queens of Egypt, including, in order of succession Aha, Djer, Djet, Queen Merneith, Den, Anedjib, Semerkhet and Qa'a. However, such timelines are flawed due to the subjectivity required to distinguish one pottery style from another, and because styles might vary from site to site without signifying a change in time period. The dates revealed King Djer ruled from about 3073 B. Egypt was, by some standards, the world's first country as countries are known today.