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Apparent Anomalies in the Decay of Archeological Samples

Herbert C. Sorensen

1973

Processes of decay are familiar phenomena to experimental investigators; their empirical measurement and theoretical descriptions have frequently been useful. Information about the rate and type of decay is of value in assessing modes of disintegration as well as types and magnitudes of forces promoting the dissolution process. The objective of the following preliminary report is to provide empirical information on the decay of archeological samples. This information may be of use to gauge certain factors effecting the decay.

Because of the availability of reliable data for analysis, this study has been arbitrarily limited to archeological samples containing carbon which have been dated by radiocarbon means. During the years of 1950 through 1965, more than 10,000 such samples were studied (1) . These materials were collected on a worldwide basis and studied in more than fifty laboratories located on every continent except Antarctica. This information about the data qualifies the results obtained, however, under the circumstances it is a satisfactory initial approach.

The samples were catalogued by centuries of radiocarbon age. The data was arrayed as age (centuries) vs. number of samples of that age (N). Consideration of the probable type of decay suggested that there would be an exponential relationship between the variables:

N/N0 = e-lt

The validity of this hypothesis is illustrated in Figure I where data on samples between 20 and 60 centuries of age is displayed. The number of samples parameter and age parameter exhibit a high degree of correlation (R = -.95).
 

Figure I.  The logarithmic "decay" of recent carbonaceous materials.  The least squares analysis yields a half-life of 18.5 centuries.
 

Least squares analysis of this subset of data yields a half life of 18.5 centuries. Factors likely to be represented in this number are:

1. Rate of formation of archeological samples.

2. Rate of deposition.

3. Internal forces of decay.

4. External forces of decay - climatic, oxidation, etc.

5. Sample selection and collection.

 No attempt has been made to distinguish the individual contribution of these or other factors. However, the regularity of the data suggests that there is not erratic variation in any of the factors during this specific time period.

A presentation of the data on samples between zero and 250 centuries of age is given in Figure II.

Figure II.  The "decay" of carbonaceous materials.
 

Examination of this data reveals four distinct subsets of data. They are partially characterized in Table I.
 
Epoch Centuries Half-life (centuries)
Correlation (number/age)
I
20-60
18.5
-.95
II
60-115
20.8
-.40
III
115-140
8.7
-.90
IV
140-250
8.7x10**-5
-.17
Table I.

It is significant that there appear to be anomalies in the decay of archeological samples. Moreover, these are not simply random and erratic variations, but changes in the "decay" behavior occur at three points, i.e., 60, 115, and 140 centuries of age. An obvious conclusion is that one or more of the enumerated factors affecting the half-life was altered at those times. The nature of the samples (worldwide) seems to preclude the possibility that only local changes were involved.

It is not possible with the data at hand to give a full explanation of the results, however, there may be some relationship between these observations and known geomagnetic reversals. A reversal 124 centuries ago might in fact coincide with the observed discontinuity at 115 centuries (2) . Further studies may adequately account for the observed anomalies.

References:

(1) Radiocarbon Measurements: Comprehensive Index, 1950- 1965; E.S. Deevey, R.F. Flint, J. Rouse, eds. Yale University, New Haven, Connecticut, 1967.

(2) N. -A. Morner, J.P. Lanser, J. Hospers, Nature Phys. Sci.Dec. 27 (1971)