The young man was found dead in a small room near the entrance to the Hall of the Augustales, a civic order of freedmen, a bit like a freemason lodge. Perhaps he was a security guard. He’s been nicknamed the Guardian for that reason. Alternatively, he might also have come from outside, running panicked through the city of Herculaneum as it was overtaken by black ash and poisonous fumes following the eruption of Mount Vesuvius in 79 CE, with no idea where he was but seeking shelter in a place everyone else had evacuated, finally collapsing face down on the wooden bed.
The last mortal remains of his fellow residents of Herculaneum were found mostly where they fell, several hundred crowded onto the beach and in beach-front chambers, presumably in hopes of escaping the pyroclastic currents that soon engulfed them, preserving them and the details of their life 2,000 years ago: papyrus scrolls, bread, olives, bronze pitchers, furniture, fresh and dried fruit — all under an avalanche of volcanic deposits.
The mostly charred, bony remains of the young man who stayed were found in 1960 by the superintendent of the archeological site that is what’s left of the ancient city. Along with volcanic ash, his brain and spinal cord were found to contain a mysterious archeological treasure: tiny, gleaming shards of black glass.
Not till 2020, around 1,941 years after he breathed he breathed his last, did scientists demonstrate that the unfortunate volcano victim’s brain, or parts of it, had literally turned to a glass-like material — vitrified — in a truly unique example of natural alchemy. As described last week in Nature Scientific Reports, the so-called guardian of Herculaneum continues to offer up his secrets, providing us with not just an image, but a mental movie of how the Vesuvius disaster may have gone down.
A fragment of the organic glass found inside the skull of the deceased individual in Herculaneum. (Pier Paolo Petrone)“We demonstrate experimentally that the process of vitrification occurred [as a result of ] the very early arrival of a dilute ash cloud that invaded Herculaneum leaving just a few centimeters of ash and very little to no structural damages, but at temperatures higher than 510° C that killed instantaneously all inhabitants. The ash cloud then dissipated and the brain could cool down quickly to ambient temperature, transforming into glass,” Dr. Guido Giordano, lead author of the new study and adjunct professor in the department of science at Roma Tre University in Rome, told Salon in an email.
"The ash cloud then dissipated and the brain could cool down quickly to ambient temperature, transforming into glass."
After demonstrating that the glass-like substance found in the guardian’s brain was organic in origin and in fact was vitrified brain tissue, Dr. Pierpaolo Petrone and others used scanning electron microscopy and image processing tools to visualize the man’s actual brain cells, incredibly well-preserved, even as the rest of him was charred to mostly ash.
In the skull, they found fatty acids suggestive of brain triglycerides (proteins typical of brain tissue) and fatty acids typical of human hair fat — all vitrified. None of these substances were found outside the skull, in the volcanic ash in which the carbonized, skeletal remains were buried. The rest of the skeleton, other than the tibia, which was partly vitrified and generally preserved, was “completely charred and burst from being subjected to the intense heat of the pyroclastic ash surge, a high-speed turbulent cloud rich in hot gases, ash and steam,” as Petrone eloquently described it.
The shards, or clasts, have a glassy luster, making them look a lot like obsidian, a glass formed from lava when it cools very quickly. Like obsidian, in fact, their edges are sharp but the shards have an almost twirly shape and lack the crystalline structure of black-colored minerals like augite or tourmaline. Whatever process occurred to do this preserved the original brain tissue so well that individual neurons can actually be seen using a scanning electron microscope. It certainly looks like glass. But is it really?
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“To demonstrate that a material is really a glass,” Giordano told Salon, “you need to demonstrate first that it was formed across a ‘glass transition temperature’ and then investigate what physical processes were involved. Both the glass transition and the processes responsible are the focus of this new paper, which is then an absolute ‘prémiere.'”
He’s not kidding. Giordano and his colleagues describe an entirely unique, never-before-seen process that could indeed have resulted in glass being formed from a human brain. The temperature of the pyroclastic flows that buried Herculaneum and Pompeii was several hundreds of degrees Celsius, hot enough to easily burn and destroy soft tissue. This new analysis is both experimental and analytical, attempting to explain how you could possibly have achieved the quick cooling, or quenching, required to turn brain tissue into glass, when the environment was one of extremely hot volcanic activity.
Nothing so evocative usually happens. Other human remains found elsewhere in Herculaneum had iron oxide deposits in the skull, suggesting that the fluids in the skull were vaporized by the heat, leaving only traces of degraded heme proteins.
Annotated image of the remains of the deceased individual in situ in their bed in the Collegium Augustalium, Herculaneum. This is a section of Fig. 1 from the published article. (Guido Giordano et al./Scientific Reports)Even less poetically, if cerebral tissue is ever found in archeological finds, it’s usually not vitrified, but saponified — that is, the brain triglycerides are transformed into glycerol and fatty acids. Most of us know this as soap.
Based on their experimental work, heating samples of shards from the skull to different temperatures to determine how the material changed and exactly where the glass transition occurred. Their temperature must be higher than the ambient temperature, and the faster the cooling takes place, the higher the glass transition temperature.
The researchers propose that very early on that terrible day, a dilute ash cloud invaded Herculaneum. It would have left just a few centimeters of ash and caused little or perhaps no structural damage. But this brief invader brought with it incredibly high temperatures, above 510º C, perhaps higher even 600º C, killing everybody in an instant. The odd bit of tissue, protected by bone, may have survived though. In the case of the guardian, his skull provided enough protection to prevent the destruction of that tissue, the researchers suggest.
“The ash cloud then dissipated and the brain could cool down quickly to ambient temperature, transforming into glass,” Giordano told Salon. Although there is no way to experimentally verify the rate at which cooling actually occurred, the volcanic deposits that ultimately buried the remains must have been much cooler than the glass fragments, or they would have returned to a soft tissue state, and disintegrated.
So the researchers posit that the only possible scenario is that fast dissipation of the ash cloud allowed for very quick cooling, ensuring that the shards were vitrified before being buried. Only later, perhaps after some hours had passed, were the town and the bodies of all of its inhabitants buried by the hot pyroclastic flow deposits, more physically destructive but not as hot as that quick and deadly cloud of ash.
Is there any other possible explanation? “Really do not think so,” Giordano wrote to Salon.
Even though we’re talking about human tissue, the physical principles that turn brain to glass are not different from those that create glass anywhere else. The quenching that occurred inside the skull of a single human victim of Vesuvius may be unique and have required an extraordinarily rare set of conditions, but the process itself is used routinely in glassmaking, when a sheet of glass is heated to around 620 degrees Celsius in a tempering oven, then quickly cooled with high-pressure blasts of air. The outside cools much faster than the inside, creating compressive stress on the material and tempering it — making it stronger — by creating a structure in which the center is in tension but the exterior is being compressed.
Dr. Robert Mann, a forensic anthropologist at the University of Hawaii, has examined somewhere between 15,000 and 20,000 human skulls and skeletons over a storied career, mostly focusing on modern remains. This has included the first victim of serial killer Jeffrey Dahmer and victims of Apichai Ongwisit, the so-called Thai Ted Bundy; the Unknown Soldier from the Vietnam War, ultimately identified as Air Force 1st Lt. Michael Joseph Blassie; and victims of 9/11. But he has a keen interest in ancient skeletons as well, and last summer examined skeletal remains from Pompeii, the ancient Roman city more famously buried and preserved under volcanic ash, like Herculaneum, when Vesuvius erupted. Mann is fascinated by the finding that brains could be vitrified and identification of the complex set of conditions needed to cause the phenomenon — and cautions that it's always possible that there's some other factor or possible scenario we haven't thought of — yet.
"The histology, the microscopy work, indicates that there is brain matter in there that's turned into glass but I guess what people would wonder about, and may speculate about and come up with their own scenarios. And maybe this is not the right explanation. What is the formation itself? Not what the findings are, but how did it come to be, and these are really difficult things to figure out," Mann told Salon in a video interview, after exhibiting an orange 3D-printed model of his own skull. (He also currently trying to figure out what conditions resulted in certain little bony formations stuck like barnacles to the inside of the skull, a previously unrecorded phenomenon he's now found in just seven people.)
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Once we know that vitrified brain tissue is a thing we can look out for, it's possible that we'll start finding more examples of this currently unique process, Mann said. And then there's always a possibility that some other scenario, beyond the admittedly convincing quick ash cloud one, might then come to mind that is supported by other evidence.
"I always marvel that we've been doing human anatomy and gross anatomy for hundreds of years, and we still stumble on something, even today, we go 'Well, we've never seen this before,' and before you stumble upon it, there's no way to know that it even exists, right?" Mann explained.
Giordano's research is not only relevant to colleagues like volcanologists, but also materials and forensics scientists, he said. It might also be valuable to emergency planners. As Petrone wrote in a 2019 review of the effects of the eruption on Herculaneum residents, there are “crucial implications for the present-day risk of a similar outcome to around three million people living close to the volcano, including metropolitan Naples.”
This is not all doom (or boom!) and gloom though.
“By understanding the process of formation I think there is a great lesson also for the present,” Giordano said. “In active volcanic areas while it is essential to evacuate all people possibly in the way of pyroclastic flows, it is also essential to fit houses as shelters able to resist heat, such as is done for wildfires. This way, should anyone be caught in a dilute hot ash cloud, [as] was the case of the unfortunate ancient Roman in Herculaneum, there could be a possibility to survive and wait for rescue.”
It does sound magical that a human being could turn into glass, but far better if studying the Guardian can prevent vaporizing, volatilization and vitrification — or saponification — of anyone else.
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