On October 13, 1988, the world’s press gathered at the British Museum in London for the release of the carbon-14 test results. When they entered the room, they saw the blackboard, above.
In 1988, an international team of scientific experts performed radiocarbon dating on snippets of the Shroud of Turin. The results showed that the famous cloth did not date back to the time of Christ’s crucifixion in the first century A.D. In fact, the cloth seemed to have been manufactured sometime between 1260 and 1390 A.D. The team concluded the Shroud was nothing more than a medieval hoax.
In the years since the stunning announcement, Shroud experts and other investigators have called into question the accuracy of the dating. Some have even argued that damage to the border of the Shroud in December 1532 during a fire in the chapel of the Dukes of Savoy in Chambery, France, might in some way have changed the chemical composition of the cloth and skewed the testing results. Stephen J. Mattingly, a Professor of Microbiology and Immunology at the University of Texas Health Sciences Center in San Antonio, also doubts the 1988 radiocarbon results — though he blames not fire, but microbes.
Professor Stephen J. Mattingly at work in his laboratory, demonstrating that bacteria could have influenced the accuracy of the carbon-14 dating of the Shroud
Despite the lingering controversy, the basic science behind radiocarbon dating is disarmingly straightforward. The element carbon exists naturally on Earth in two stable forms, or isotopes, known as carbon-12 and carbon-13; in carbon-13, the nucleus of the atom contains one extra sub-atomic particle called a neutron. A third isotope of carbon with two extra neutrons, known as carbon-14, is produced in the atmosphere when atoms of nitrogen are blasted by high-energy cosmic rays streaming in from space. The atom is unstable — radioactive — and eventually decays back into nitrogen-14. Because some of the radioactive atom always exists at a low level in the atmosphere and on Earth, however, it gets incorporated at a predictable rate into the cells and tissues of all living things, from bacteria to plants to people, when, for example, the organisms suck up C-14 containing carbon dioxide molecules as part of their natural metabolic processes.
After things die, they no longer take in C-14, and so as the isotope decays back to nitrogen-14, its relative abundance steadily decreases over time. Measuring the amount of C-14 in something originally derived from organic material, then — a wooden artifact, say, or the fibers of a linen cloth, which are made from flax plants — tells the amount of time that has passed since the organism it came from was last alive.
What that means, however, is that any contamination with an object that was more recently alive will raise the relative abundance of C-14 atoms, producing an apparently younger age. In the case of the Shroud of Turin, says Mattingly, the younger contaminants were bacteria. “You might imagine that over hundreds of years or several thousand, the Shroud has come in contact with many thousands of species of bacteria and fungi and some were able to grow for short or long periods of time,” he explains. “Some of these organisms would be more recent and be incorporating more recent radiocarbon material. The microbes are not digesting the linen, they are eating one another so to speak. As long as they can grow and incorporate carbon dioxide, which many microbes can do, they are actually making the Shroud appear more recent as time continues.”
This strip was removed from the Shroud in 1988 when scientists used carbon-14 dating to test the age of the cloth
In fact, Mattingly and his colleague Leoncio Garza-Valdes have found several different species of bacteria colonizing pieces of the Shroud, including some organisms that had never been seen before.
They tested samples from an outside strip of the cloth removed during the 1988 dating effort. Giovani Riggi, the scientific caretaker of the Shroud at the time, kept the strip and later provided samples to Mattingly and Garza-Valdes. “The Catholic Church did not sanction the removal and giving of the material to us and would not certify that the pieces were authentic. Nevertheless, we know that they are authentic,” Mattingly says.
Intriguingly, one of the microbe species seems to be producing an unusual material that coats the linen threads “with a brittle plastic-like material that made the linen difficult to cut, much like trying to cut through dry pasta,” Mattingly says. “It appears that this polymer may have actually helped preserve the Shroud linen through time.” Similar coatings on other artifacts — the linen wrappings on mummies, for example — could also be affecting their radiocarbon ages.
Mattingly also suspects that bacteria are responsible for the Shroud’s ethereal image. His idea is that as the crucified man was dying, bacteria such as the common skin microbe Staphylococcus epidermi would have colonized and multiplied in his bloody wounds, creating a thin layer called a biofilm. A biofilm can soak up water like a sponge. After the man died and his body was washed, the biofilm would have absorbed water and become extremely sticky. When the burial shroud was later placed over the body, it would have adhered fast, allowing the transfer of the microbes to the fibers of the cloth. Over time, the degradation of the microbes would have produced a faint yellow imprint of the face and body that slowly darkened like a photographic image. “I have observed the drying of bacteria on surfaces before and noticed that they leave a straw yellow color similar to that observed with the Turin Shroud,” he says. Key to the color change are unsaturated fatty acids normally found within the membranes of all types of cells, including bacteria. The addition of oxygen atoms to the fatty acids molecules — or oxidation — changes their chemical make-up, giving rise to the yellow color. Similarly, says Mattingly, “the yellowing seen in ‘ring around the collar’ is due to fatty acids from the body and bacteria that have rubbed off onto the collar.”
In a series of ongoing experiments to prove his theory, Mattingly has taken samples of bacteria from his own skin and grown them in culture to produce a biofilm. After killing the bugs to prevent infection, he slathers the film back on his skin and drapes it with a linen cloth. The cloth readily adheres, but, more importantly, a photograph-like image forms on the cloth as the bacteria oxidize. In images he has created of his own hand, Mattingly’s wedding ring is clearly visible. The image, he says, is “not perfect, but darn close! The hand is great to use, because it is mainly skin and bone. When you get to the face, there is fatty tissue around the cheeks that cause the image to be flatter, because the linen attaches so strongly to the skin. Take away the fatty tissue and hydrated tissue, as you have in an individual who has lost virtually all of his body fluid, and you would have skin on bone, thereby getting a much better image.” Mattingly is now conducting tests to isolate the chemical compounds responsible for the yellow color. He is also trying to improve the quality of the facial images.
