A man who died in the catastrophic eruption of Vesuvius nearly 2,000 years ago seems to have found a unique way to shuffle off this mortal coil.
A new analysis of his remains reveals that a lump of dark-colored glass rattling around in his skull was once his brain, vitrified in an extremely rare set of circumstances that have only ever occurred once that we know of – in the city of Herculaneum in 79 CE.
“Our comprehensive chemical and physical characterization of the material sampled from the skull of a human body buried at Herculaneum by the 79 CE eruption of Mount Vesuvius,” writes a team led by volcanologist Guido Giordano of Roma Tre University in Italy, “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 nor any other kind.”
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Theoretically, anything that is able to melt can turn into glass… but, in reality, the conditions under which this could happen for organic matter are so rare that the Herculaneum remains mark the only time it has ever been seen.
When the remains were revealed a few years ago, the researchers who published a correspondence about it – that is, a short commentary on the discovery itself in a letter to The New England Journal of Medicine – could only conclude one explanation for why a man’s skull might contain a lump of glass.
They received a hefty dose of skepticism from other scientists, not least of which was a lack of analysis or methodology. Well, Giordano and his colleagues have now performed that analysis, and their conclusion remains the same. Not only that, they have discovered a way in which the vitrification could have occurred.
The main problem with the vitrification of organic materials is that it needs to heat quickly, and cool quickly, before the hardening material has the opportunity to arrange its atoms into a crystalline structure. Glass is what we call an amorphous solid, one in which the atoms are set in a higgledy-piggledy disarray.
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The researchers retrieved samples of the glass from the skull and spinal column of the Herculaneum victim, and subjected it to a number of analytical techniques, including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and energy dispersive X-ray spectroscopy (EDS).
Under SEM, the sample yielded well-preserved neurons, axons, and other neural structures, the researchers said, consistent with earlier findings published in 2020.
The DSC – a technique for determining the thermal transitions of a given material as it is heated – revealed the temperatures required to create the glass as the researchers heated samples past melting point in a series of experiments. And the other techniques also revealed the fine structure of the material, information that helped the researchers reconstruct how it was heated, and the evolution of the temperature changes.
They determined that the brain of the man had to have been heated to temperatures of at least 510 degrees Celsius (950 Fahrenheit) quickly, and cooled quickly very soon after. This means that the pyroclastic outflows from the eruption – a fast-moving, high-density mixture of volcanic gas, ash, and other materials – could not be the cause of the vitrification, since they reached a maximum temperature of just 465 degrees Celsius.
However, there’s another kind of pyroclastic outflow that could have produced a glass brain. Based on observations of volcanic eruptions in the modern day, the first devastating event from the eruption may have been a super-heated ash cloud that spread out from Vesuvius and dissipated within minutes, catching the unfortunate victim as it went.
This cloud, the researchers say, could have exceeded the 510-degree threshold required to vitrify the victim’s brain without destroying it completely, and then dissipated quickly enough to enable rapid cooling – thus leaving behind evidence of this rare set of circumstances buried under the ash at Herculaneum.
Indeed, this is consistent with a 2023 paper that found initial temperatures that hit Herculaneum were somewhere between 500 and 555 degrees Celsius.
“The brain tissue studied here is the only known case of preserved vitrification of human tissue as a result of cooling after heating to very high temperature,” the researchers write.
“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.”
Their findings have been published in Scientific Reports.
