Brain of glass Study: Hot Vesuvian ash cloud really did turn a brain to glass Fresh analysis with calorimetry, X-rays, electron microscopy lend support to hotly debated theory. Jennifer Ouellette Feb 27, 2025 11:00 am | 7 Remains of a Vesuvius victim, still in bed in the Collegium Auguistalium at Herculaneum. Credit: Pier Paolo Petrone Remains of a Vesuvius victim, still in bed in the Collegium Auguistalium at Herculaneum. Credit: Pier Paolo Petrone Story textSizeSmallStandardLargeWidth *StandardWideLinksStandardOrange* Subscribers only Learn moreFor several years now, we've been following a tantalizing story indicating that the high heat of the ash cloud generated when Mount Vesuvius erupted in 79 AD was sufficiently hot to turn one of the victim's brains into glass. It remains a matter of debate in the archeological community, but a fresh analysis of the physical properties of the glass-like material found in the remains lends more evidence to the hypothesis, as detailed in a new paper published in the journal Scientific Reports.As previously reported, the eruption of Mt. Vesuvius released thermal energy roughly equivalent to 100,000 times the atomic bombs dropped on Hiroshima and Nagasaki at the end of World War II, spewing molten rock, pumice, and hot ash over the cities of Pompeii and Herculaneum in particular.The vast majority of the victims died of asphyxiation, choking to death on the thick clouds of noxious gas and ash.But a 2001 studyin Nature, co-authored by Petrone, estimated a temperature of 500 Celsius (932 Fahrenheit) for the pyroclastic surge that destroyed Pompeii, sufficient to kill inhabitants in fractions of a second. Back in 2018, we reportedon Petrone's conclusion that inhabitants of Herculaneum may have suffered a similar fate. There was fracturing in the bones and "cracking and explosion" of the skullcaps, consistent with forensic cases where skulls burst from extreme heat.In 2020, we reported on Petrone's follow-up study, which offered additional evidence that extreme heat killed many victims. He and several colleagues completed an analysis of one victim's skull in particular, first excavated in the 1960s from Herculaneum. The body was found on a wooden bed, buried in volcanic ash, and there was evidence of brain matter remains in the skull. He is believed to have been the guardian of the Collegium Augustalium, a public building dedicated to the worship of Caesar Augustus, where the remains were found.According to Petrone et al., usually such brain matter would be "saponified" by the extreme heatthat is, turned to soap (glycerol and fatty acids). But this particular victim's brain matter had been vitrified, i.e., fused into glass. Petrone et al. estimated that temperatures could have been as high as 520 Celsius (984 Fahrenheit) based on evidence gleaned from charred wood at the site.V is for vitrification A fragment of the organic glass found inside the skull of the deceased individual in Herculaneum. Pier Paolo Petrone A fragment of the organic glass found inside the skull of the deceased individual in Herculaneum. Pier Paolo Petrone A sample of the organic glass under direct light. Guido Giordano et al./Scientific Reports, 2025 A sample of the organic glass under direct light. Guido Giordano et al./Scientific Reports, 2025 Using scanning electron microscopy (SEM), forensic archaeologists found evidence of human neurons in 2020. Pier Paolo Patrone Using scanning electron microscopy (SEM), forensic archaeologists found evidence of human neurons in 2020. Pier Paolo Patrone A sample of the organic glass under direct light. Guido Giordano et al./Scientific Reports, 2025 Using scanning electron microscopy (SEM), forensic archaeologists found evidence of human neurons in 2020. Pier Paolo Patrone Later that same year, Petrone struck again, claiming the discovery of preserved human neurons in the victim with the "glassified" brain. He looked at the genetic expression of previously identified proteins and also included the results of using scanning electron microscopy (SEM) to image vitrified brain and spinal cord remains. They found that the images revealed distinctive features typical of the human central nervous system, including evidence for neurons and white matter axons.Brain tissue does sometimes preserve; there are around 1,300 samples worldwide dating back to the mid-16th and mid-17th centuries. But the Vesuvian preserved brain studied by Petrone et al. is both very old (although not the oldest) and unusual in terms of the hypothesis proposed about the precise mechanism by which it was preserved. Another 2020 paper documented the preservation of neurocytoarchitecture in a 2,600-year-old Iron Age human skull excavated in Heslington, York, albeit via a different mechanism than the vitrification claimed by Petrone et al.So this claim was met with some skepticism by others in the archaeological community, particularly since the raw data was not available. An alternative theory is that the victims at Herculaneum may have been essentially "baked" by lower-intensity heat, like roasting a joint in the oven. The archaeological site of Herculaneum, with Mount Vesuvius visible in the background. Pier Paolo Petrone The archaeological site of Herculaneum, with Mount Vesuvius visible in the background. Pier Paolo Petrone Annotated image of the remains of the deceased individual in situ in their bed in the Collegium Augustalium. Guido Giordano et al./Scientific Reports, 2025 Annotated image of the remains of the deceased individual in situ in their bed in the Collegium Augustalium. Guido Giordano et al./Scientific Reports, 2025 FE-SEM images of brain samples shown at different magnifications. Guido Giordano et al./Scientific Reports, 2025 FE-SEM images of brain samples shown at different magnifications. Guido Giordano et al./Scientific Reports, 2025 Annotated image of the remains of the deceased individual in situ in their bed in the Collegium Augustalium. Guido Giordano et al./Scientific Reports, 2025 FE-SEM images of brain samples shown at different magnifications. Guido Giordano et al./Scientific Reports, 2025 Now Petrone, Guido Giordano of the University of Roma Tre, and several other colleagues are back with a fresh analysis using various techniques to investigate the specific properties of samples taken from the glass-like material: field emission scanning electron microscopy, 3D scanning tomography, Raman spectroscopy, energy dispersive X-ray spectroscopy, and differential scanning calorimetry.The results: "Our comprehensive chemical and physical characterization of the material sampled from the skull of a human body buried at Herculaneum... shows compelling evidence that these are human brain remains, composed of organic glass formed at high temperatures, a process of preservation never previously documented for human or animal tissue, neither brain or any other kind," the authors wrote.Given these findings, the authors propose the following scenario. When Vesuvius erupted, the first "deadly event" was a very hot ash cloud that surrounded its victims, including the guardian at Herculaneum. This heated the guardian's brain to well above 510 Celsiusthe glass transition temperaturewhich likely badly damaged the brain but did not destroy it. Rather, the brain fell into smaller pieces (which matches what has been found at the site). It's possible that the guardian's thick skull bones and spine offered a little protection from the extreme heat, which likely vaporized the soft tissues of other victims at Herculaneum.Once the ash cloud dissipated, temperatures returned to ambient conditions, resulting in the "fast cooling" that turned the brain fragments into glass. The bodies would have been exposed to open air at first, as the ash cloud would have deposited only a few centimeters of ash on the ground. The bodies were subsequently buried by thick pyroclastic flows at lower temperatures, preserving the guardian's vitrified brain. Per the authors, "This is the only way by which such a glass type can be preserved in the geological or archaeological record and explains why this is a unique occurrence and preserves the ultra-fine neural structure of the brain."DOI: Scientific Reports, 2025. 10.1038/s41598-025-88894-5 (About DOIs).Jennifer OuelletteSenior WriterJennifer OuelletteSenior Writer Jennifer is a senior writer at Ars Technica with a particular focus on where science meets culture, covering everything from physics and related interdisciplinary topics to her favorite films and TV series. Jennifer lives in Baltimore with her spouse, physicist Sean M. Carroll, and their two cats, Ariel and Caliban. 7 Comments