Abstract
The initial C14 contents of dendrochronologically dated tree rings have been determined for samples covering the entire range of the present tree-ring chronology which extends back to 3750 B.C. The initial C14 content is within ±15‰ of the 1850 A.D. value during the Christian era, except for the period between 1500 and 1700 A.D. (T1/2 = 5730 years). During that time Δ fluctuates between about 0 and +30‰. There is a steady increase of about 4 mille per 100 years from 100 B.C. and continuing through the oldest dendrochronologically dated tree rings (California bristlecone, 3755 B.C.). The key date for the Egyptian Middle Kingdom astronomical chronology is the seventh year of the reign of Pharaoh Sesostris III of the Twelfth Dynasty. Wood samples associated with the reign of Sesostris III indicate a Δ value greater than 35‰, which is consistent with the contemporaneous bristlecone pine tree ring Δ value of 67‰. There no longer seems to be reasonable doubt concerning the reality of the fluctuation of the C14 content of the atmosphere during historic time. The extent of variation during prehistoric time has yet to be established and the causal factors remain obscure. There appears to be a correlation between initial C14 and climate.
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