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[tab:A Date for Life]

A Date for Life

Radiocarbon is by far the most common dating method in use today. Carbon-14 has a half-life of “only” 5,730 years, which lends itself to dating relatively recent material – the sort of material that might be uncovered by an archaeologist, for instance.

Even better, carbon-14 occurs naturally in all living things. The cycle begins in the upper atmosphere with cosmic radiation bombarding nitrogen, which then turns into carbon-14. Plants take up carbon during photosynthesis, and animals eat the plants. As long as an organism is alive, the decaying carbon-14 will be replaced from the environment. When the plant or animal dies, carbon-14 will shrink relative to the stable isotope of carbon-12. The ratio of the two isotopes, together with the half-life of carbon-14, will be used to calculate the age of the sample.

Production, uptake, and decay of radiocarbon

Production, uptake, and decay of radiocarbon

Of course, with increasing age it becomes increasingly difficult to detect the presence of radioactive carbon. The best labs use atomic mass spectrometers (AMS), but even these state-of-the-art devices can only handle samples with a maximum theoretical age of around 50,000 years. In practice, radiocarbon dating tends to be used on wood, bone, shells and other organic materials that are only a few thousand years old.

All of this sounds very rosy, until we start looking into the major assumptions of radiocarbon dating:

  1. The half-life of carbon-14 has remained constant.
  2. The production of carbon-14 in the atmosphere has remained constant.
  3. All organisms take up carbon-12 and carbon-14 in exactly the same ratios.

For a long time now, people working with radiocarbon on a day-to-day basis have acknowledged problems with the second and third assumptions (and some have questioned the first assumption as well [1]). Against the second assumption it is known that cosmic radiation varies over time, and so the production of carbon-14 varies too. And against the third assumption, it is known that some organisms absorb the lighter carbon-12 at higher rates than the heavier carbon-14. It is also known that some parts of the world have higher concentrations of carbon-14 than other parts of the world. These are all significant sources of error for something that is touted as an “absolute” dating method.

[tab:Choosing the Date]

Choosing the Date

The favorite “fix” is to adjust radiocarbon years to tree-ring years. Researchers will bore a tiny hole into a very old tree, count the rings, and then measure the carbon-14 for each ring. The resulting plot of carbon-14 age versus tree-ring age will be used to “calibrate” every other radiocarbon measurement.

Unfortunately, tree-ring dating is not without its assumptions. Researchers have to assume, for instance, that trees add no more, and no less, than one ring per year. Further, the oldest living trees – the bristlecone pines of California – only have a few thousand rings. Building a longer record involves some guess work in matching the rings from living specimens with the rings from fallen logs. Given all the variation in radiocarbon production and concentration, the calibration curve will have plenty of “wiggles” and “plateaus” that can frustrate the conversion of radiocarbon values into meaningful calendar years.[2]

C14-calibration

Plateau problems: A radiocarbon date of 2460 years, no matter how accurate the measurement may be, would “fit” the calibration curve over several centuries (based on Guilderson, et al., 2005).

Attempts to calibrate radiocarbon dates beyond the available tree-ring records rely on sediment layers, ice layers, coral rings and other deposits that are supposed to have accumulated on an annual basis. These methods with all their assumptions, plus the tree-ring data with all its assumptions, plus “some fancy statistical treatments” (as one science reporter put it), have now been used to construct a 50,000-year radiocarbon calibration curve.[3]

Naturally, those of us who take the Biblical record at face value are pretty skeptical about the entire radiocarbon enterprise. However, it turns out to be something of a mixed bag. To illustrate this point I would like to draw on some examples that are relevant to Biblical studies.

[tab:Case Study: Tel Rehov]

Case Study: Tel Rehov

The remains of this Canaanite and (later) Israelite city are located in the Beth-Shean valley. It has already yielded a wealth of data on everyday life in the ancient Near East. An industrial beekeeping operation on the site confirms that this was, indeed, a land flowing with honey (Exodus 3:8).[4]

A series of occupations at the site straddle several critical episodes in the history of the Hebrew people. As usual, the chronology of these events as portrayed in Scripture has come under attack. For instance, Israel Finkelstein has argued vigorously against the consolidation of power during the reigns of Saul, David and Solomon. On his account, the glories of Solomon are a later fiction invented to prop up Josiah’s claims to rule in the north as well as the south.[5]

What, then, can we make of pharaoh Shishak’s invasion during the reign of Solomon’s immediate successor, Rehoboam (1 Kings 14:25)? Why would Shishak mount a substantial military campaign if there was nothing much to attack? Finkelstein thinks these accounts are simply bogus. However, recent high resolution radiocarbon results of a destruction layer from Tel Rehov are consistent with the traditional Biblical chronology, which places Shishak’s invasion in 925 BC.[6]

This is obviously good news for Bible believers, but what happens if the results are overturned by another set of radiocarbon tests? We need to be cautious about placing our confidence in what is, after all, a very shaky piece of corroborating evidence.

Tel Rehov

Aerial view of Tel Rehov (rehov.org)

[tab:Case Study: Shroud of Turin]

Case Study: The Shroud of Turin

This remarkable piece of cloth bears the image of what appears to be a man with long hair and a beard. Various features of the image match descriptions of Jesus’ crucifixion and burial. Roman Catholics have revered the object as the actual burial cloth of Christ for many centuries. Just this past May, Pope Benedict XVI stood in front of the cathedral in Turin and affirmed that the relic did, indeed, wrap “the remains of a crucified man in full correspondence with what the Gospels tell us of Jesus.”[7] Even non-Catholics have embraced the Shroud as possible evidence for the resurrection.[8]

A panel of researchers in 1978 found no evidence of forgery. However, the team avoided radiocarbon dating because the method, at that time, would have required a destructively large sample. The arrival of AMS technology allowed testing on tiny fragments of the Shroud. In the late 1980s, three labs independently converged on dates in the 13th through 14th centuries AD.[9]

Today it is common to hear the Shroud dismissed as a medieval forgery based entirely on the radiocarbon dating results. Of course, there are other reasons to doubt the authenticity of this object. Researchers do not believe, for instance, that the complex twill weave of the Shroud’s fabric could be found in Palestine of Jesus’ day.[10]

[tab:Art vs. Science / Endnotes]

Art vs. Science

Whether we use radiocarbon dates to confirm the Biblical text (Tel Rehov) or throw doubts on controversial claims (Shroud of Turin), we are going to have make up our minds about the reliability of the method. Perhaps we are justified in using radiocarbon dates on occasion, especially for relatively recent objects that map onto the more reliable sections of the tree-ring calibration curve. In the end, however, radiocarbon dating is more of an art than a science. Subjective decisions sneak in at every step of the process from sample collection to interpretation of the final results. In all likelihood the radiocarbon method can never, by itself, settle any debate about the historical reliability of Scripture.

[A version of this article appeared originally in Think, August 2010, pp. 20-21.]

Endnotes

[1] John R. Baumgardner, “14C Evidence for a Recent Global Flood and a Young Earth,” in Larry Vardiman, et al., eds., Radioisotopes and the Age of the Earth, Volume II. El Cajon, CA: Institute for Creation Research, 2005, pp. 597-630.

[2] Tom P. Guilderson, et al., “The Boon and Bane of Radiocarbon Dating,” Science, Jan. 21, 2005, pp. 362-364.

[3] Michael Balter, “Radiocarbon Daters Tune Up Their Time Machine,” Jan. 15, 2010. [Online] http://news.sciencemag.org/sciencenow/2010/01/15-03.html

[4] Amihai Mazar and Nava Panitz-Cohen, “It Is the Land of Honey: Beekeeping at Tel Rehov,” Near Eastern Archaeology, Dec. 2007, pp. 202-219.

[5] Israel Finkelstein, “Patriarchs, Exodus, Conquest: Fact or Fiction?,” in The Quest for the Historical Israel. Atlanta: SBL, 2007, pp. 54-55.

[6] Hendrik J. Bruins, et al., “14C Dates from Tel Rehov: Iron-Age Chronology, Pharaohs, and Hebrew Kings,” Science, April 11, 2003, pp. 315-318.

[7] Nick Squires, “Pope Benedict says Shroud of Turin Authentic Burial Robe of Jesus,” May 3, 2010. [Online] http://www.csmonitor.com/World/Europe/2010/0503/Pope-Benedict-says-Shroud-of-Turin-authentic-burial-robe-of-Jesus

[8] Gary Habermas, Ancient Evidence for the Life of Jesus. Nashville, TN: Thomas Nelson, 1984, p. 159.

[9] P.E. Damon, et al., “Radiometric Dating of the Shroud of Turin,” Nature, Feb. 16, 1989, pp. 611-615.

[10] Mati Milstein, “Shroud of Turin Not Jesus’, Tomb Discovery Suggests,” Dec. 17, 2009. [Online] http://news.nationalgeographic.com/news/2009/12/091216-shroud-of-turin-jesus-jerusalem-leprosy.html

[tab:END]

© 2010 – 2011, Trevor Major. All rights reserved.

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