Mount Vesuvius turned this ancient brain into glass. Here’s how

The eruption of Mount Vesuvius in A.D. 79 is perhaps most famous for entombing the Roman city of Pompeii. But in nearby Herculaneum, also buried in the eruption, the preserved skeleton of a young man lying in bed contained a surprising find: glass remnants of his brain.

When researchers studied the shiny samples, they saw what appeared to be nerve cells. A new study now uncovers more details into how the glass may have formed, the team reports February 27 in Scientific Reports.

Glass forms when a liquid — usually molten sand — is quickly cooled. That’s how manufacturers make windows and cups. The process can also occur naturally, like when lighting strikes a sandy desert, forming lumps of glass called fulgurites. Before the young Roman’s brain remnants were discovered, however, glassy biological soft tissues had not been found in nature, the researchers say.

“When we realized that there was really a glassy brain, the scientific question was: how is it possible?” says Guido Giordano, a geologist and volcanologist at Roma Tre University.

Giordano and colleagues used a technique called differential scanning calorimetry, which involved heating the already glassy brain shards, to determine the temperature at which the glass had formed. The shards underwent structural changes at temperatures over 510° Celsius (950° Fahrenheit), suggesting that’s the temperature the brain tissue hit originally to turn to glass.

The researchers reasoned that the swift onslaught of hot volcanic ash, rock and gas that entombed Herculaneum could not have been responsible for turning the brain chunks to glass. Similar pyroclastic flows have been found to max out at 465° C and would not have cooled fast enough to turn brain to glass. Instead, a much hotter ash cloud probably hit the young man and dissipated fast, allowing for the necessary cooling. Only later were the remains buried in the thick volcanic debris, the team says.

So why didn’t the young man’s brain completely disintegrate in the extreme heat? His skull may have had something to do with it, the researchers suggest. The bones may have protected against direct contact with the ash cloud.