Glassified in Time

In 2020, researchers found pea-sized chunks of black glass inside the skull of a young man who died when Mt. Vesuvius erupted in 79 AD and engulfed entire villages in southern Italy.

They realized that the glass was actually the remains of the brain of a man of about 20 years of age. But they couldn’t explain how organic matter became glass.

Now they can, thanks to a new study in which researchers show how an extremely hot cloud of ash enveloped the brain and immediately cooled down, turning the organ into glass.

“This is a unique finding,” lead study author Guido Giordano told the BBC, adding that it is the only known instance of an organic material naturally turning into glass.

Scientists now believe that the initial surge of hot ash from Vesuvius was the primary cause of most deaths in the area of Pompei and Herculaneum, near modern-day Naples, where as many as 20,000 people lived about 2,000 years ago.

As the volcano erupted, a fast-moving current of hot gas and volcanic material – a pyroclastic flow – then swept through the area, burying it. Experts suggest that the intense heat of the initial ash cloud is what caused the man’s brain to turn into glass, as the pyroclastic flow would not have been hot enough and would have cooled too slowly.

Glass requires specific temperature conditions to form and rarely occurs naturally, which is why researchers think it is unlikely, but not impossible, to find other similar remains.

To vitrificate – namely, turn into glass – a substance must cool rapidly from its liquid state to avoid crystallization, and it must be at a much higher temperature than its surroundings.

Using X-ray and electron microscopy, the researchers determined that the brain had been exposed to temperatures of at least 950 degrees Fahrenheit before undergoing rapid cooling.

“The glass that formed as a result of such a unique process attained a perfect state of preservation of the brain and its microstructures,” explained researchers.

This process occurred in the brain because only materials containing some liquid can undergo vitrification. As a result, the bones could not have vitrified. Meanwhile, the extreme heat likely destroyed other soft tissue before it could cool enough to turn into glass.