Comments on a new carbon 14 calibration

Comments on a new carbon 14 calibration

July 5, 2001

I do set My bow in the cloud

An article "Extremely Large Variations of Atmospheric 14C Concentrations During the Last Glacial Period" in 29 June 2001 Science pages 2453-2458 gives evidence of large variations in the concentration of carbon 14 in the last 50,000 years. The article concludes that the true ages may be older than conventionally assumed on the basis of carbon 14 dates, in some cases. This article discusses the dating of a submerged stalagmite using 230Th and 14C dating. Absolute ages were inferred from the 230Th dates and from these the 14C time scale was revised. The 230Th dates and 14C dates both grow progressively older as one goes deeper and deeper in the stalagmite, as one would expect if these dates were correct.

The purpose of this article is to evaluate the strength of this evidence from a short chronology creationist viewpoint. If these dates are not correct, then how does one explain the observed pattern of dates?

The initial 230Th/232Th ratio was estimated using isochron techniques. The value computed was much larger than the value commonly used for such calculations. However, this value did not have much effect on the computed dates because of low initial 232Th concentrations. This latter fact might indicate that the ages computed were little more than model ages computed from a daughter to parent substance ratio.

After the initial 230Th/232Th ratio was estimated, the 230Th dates were apparently evaluated as model ages, inferring the initial 230Th concentration from the 230Th/232Th ratio. Thus the individual 230Th ages were apparently not computed using isochrons.

What process could account for the observed pattern of ages? Suppose that the water seeping into this cave passed through rock that "looked old," both in terms of its carbon 14 age and its 230Th age. Initially, most of the substances entering this cave would derive from the "old" rock. As more and more "young" water seeped into the cave, less "old" substance would remain and so the composition of the substances entering the cave would more and more approximate that of the "young" water. Thus we would obtain a pattern of ages with the oldest ages on the bottom, both for 230Th and 14C, and the youngest ages on top.

Why would the rock "look old" initially? This depends on one's model of the creation. If one assumes an old universe and a young earth, some of the substance in the earth could be old. Perhaps the earth existed in a primordial state, unlike the current earth, before the creation week. Perhaps rates of decay were faster in the past.

How do we explain the agreement between the 14C and 230Th ages? It is interesting that a DCF (dead carbon fraction) was inferred in order to make these ages agree. The authors are actually quite frank about this. The dead carbon fraction indicates the amount of carbon present at the beginning.

The resulting 14C ages are compared with 14C ages from a number of other chronologies, with good agreement back to about 30,000 years ago but poor agreement before this. Why would there be good agreement back to about 30,000 years? This can be partly explained by the use of the DCF to make the ages agree with standard chronologies. It appears to me from the tables that a zero DCF value would introduce a considerable error into these tables at least in the 10,000 to 20,000 year range.

The fact that the various chronologies differ in their 14C ages before 30,000 years ago is also significant. The authors suggest a number of causes for this. It is also interesting that the Carbon 14 chronology should be so significantly revised by this paper, indicating that the previous chronologies were unreliable.

The authors also infer that there were dramatic fluctuations in the concentration of 14C in the past. If this is indeed true, it could of course invalidate all 14C dating in prehistoric periods.

At first sight this article appears to give powerful evidence for the correctness of isotopic dating in the past 50,000 years. However, on closer examination, this evidence appears less compelling.

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