Not stone or dust: scientists explain how a hot ash cloud turned brain tissue into glass
Learn how the eruption of Mount Vesuvius in AD79 transformed one unfortunate victim’s brain into organic glass
The archaeological site of Herculaneum in Ercolano, near Naples, Italy. Photo: AFPA young man was lying in bed when a viciously hot cloud of ash swept down from the erupting Mount Vesuvius and turned his brain to glass almost 2,000 years ago.
That is the theory put forward by Italian scientists to explain the strange case of the ancient Roman’s brain. They have said it is the only human tissue ever known to have naturally turned to glass.
One of history’s most famous natural disasters
Mount Vesuvius – near the modern-day Italian city of Naples – erupted in the year and buried the cities of Pompeii and Herculaneum in a fast-moving blanket of rock and ash called a pyroclastic flow.
Thousands of bodies have been discovered at the sites effectively frozen in time, offering a glimpse into the daily life of ancient Rome. This unique brain could rewrite the story and prepare us for future volcanic eruptions, the scientists have suggested.
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A little-understood phenomenon
In the 1960s, the charred remains of a man aged roughly 20 were found on a wooden bed in a Herculaneum building dedicated to the Roman Emperor Augustus.
But Italian anthropologist Pier Paolo Petrone, the co-author of a new study, noticed something shimmery in the shattered skull. What was left of the man’s brain had been transformed into fragments of shiny black glass.
These “chips” are up to a centimetre wide, vulcanologist Guido Giordano, the lead author of the new study in Scientific Reports, told Agence-France Presse.
When the scientists studied the glass using an electron microscope, they discovered an “amazing, truly unexpected thing”, he said. According to the study, complex networks of neurons, axons and other identifiable parts of the man’s brain and spinal cord were preserved in glass.
How it may have happened
The Roman’s brain preserved in glass is the “only such occurrence on Earth” ever documented for human or animal tissue, the study said.
The scientists determined that the brain must have been exposed to temperatures soaring above 510 degrees Celsius. That is hotter than the pyroclastic flow that buried the city, which peaked at around 465 degrees.
Then the brain needed to rapidly cool down – and all this had to happen before the flow arrived.
The “only possible scenario” was that an ash cloud emitted by Vesuvius delivered an initial hot blast before quickly dissipating, the study said. This theory is supported by a thin layer of ash that settled in the city shortly before it was smothered.
This would mean the people of Herculaneum were actually killed by the ash cloud – not the pyroclastic flow as had long been thought. Giordano hoped the research would lead to more awareness about the threat these hot ash clouds pose, which remain “very poorly studied” because they leave little trace behind.
A unique fate
Unlike Pompeii, Herculaneum had some time to respond to the eruption. All the other bodies discovered there were clearly trying to flee into the Mediterranean Sea. The man is thought to have been the guardian of the Collegium building and stayed in bed in the middle of town. He may have been the first hit.
Why is it practically impossible for the human brain to turn into glass?
Glass rarely forms in nature because it requires extremely hot temperatures to cool so rapidly that there is no time for crystallisation. It is usually caused by meteorites, lightning or lava.
Lava is rich in a rock material called silica. When it cools down rapidly, it forms obsidian, a type of natural volcanic glass. This is very unlikely to happen to human tissues because they are mostly made of water.