Árbók Hins íslenzka fornleifafélags - 01.01.2010, Blaðsíða 28

Summary
The 14C dating method has been used successfully on archaeological samples since the
method was first established by Libby and his co-workers around 1950. Sometimes
disagreement between the 14C dates and traditional timeframe has risen. If such a
disagreement still remains after repeated measurements, a careful examination of the
samples and their living environment as well as of the assumptions integrated in the
14C dating technique is needed before the traditional timeframe is rejected.
The time of settlement of Iceland has for many years been subject of intense debate,
fuelled by the fact that radiocarbon dates of early human occupation often give an
older age by 100-150 years than the historical tradition (late 9th century). The old 14C
dates are invariably from samples of birch and other indigenous wood species, that may
have some age prior to use and do therefore not give the true age of the archaeological
context.
It is argued that the following four criteria have to be fulfilled in order for 14C
dating to ref lect the precise and true age of archaeological finding: 1) The dating
laboratories have to pre-treat the carbon samples by modern, proven methods
and be able to measure the 14C concentration both precisely and accurately. 2) The
carbon sample has to be closely associated with the event to be dated, but often good
knowledge and experience are needed to understand this connection. 3) Careful
thoughts have to be given to what could possibly inf luence the carbon sample in such
a way that its 14C concentration does not ref lect its true age and make corrections and
calibrations accordingly. 4) The event to be dated has to have occurred at a time when
the calibration curve is steep and free of “wiggles”. The first criterion is solely in the
hands of the dating laboratory, the second in the hands of those who do the sampling,
the ones that interpret the 14C dates are responsible for the third one and the fourth is
beyond our control and depends on the shape of the calibration curve at the time the
samples was formed. In the paper each of these criteria is discussed.
It is well known that 14C age determination does not always give the true
calendar age though the 14C concentration is precisely and accurately measured. The
main reasons for this, such as reservoir effects, volcanic/geothermal effects and age
of the archeological finding prior to its use, are discussed as well as the corrections
and calibrations that have to be performed in order to get as precise 14C dating of
archaeological findings as possible.
¹4C ALDURSGREININGAR OG NÁKVÆM TÍMASETNING FORNLEIFA 27
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