NYT — When snorkelers discovered what appeared to be pieces of ancient stonework, including columns and doughnut-shaped disks that might have been column bases, in a bay off the Greek island of Zakynthos several years ago, government archaeologists were sent in to investigate. The debris might have been the ruins of a city, the scientists reported and, if so, a rare discovery of a Greek archaeological site in shallow waters.
But oddly, the archaeologists found nothing else — no shards of pottery or other flotsam and jetsam of everyday existence — that would suggest that people had once lived there (and perhaps had been forced to flee by rising sea levels).
Scientists have now discovered the reason there were no signs of human habitation at the site. The columns and other objects, they say, are not stonework at all, but a natural byproduct of the breakdown of methane gas. And they were made by an ancient civilization of microbes, not people.
Julian Andrews, a geochemist at the University of East Anglia in England and the lead author of a paper in the journal Marine and Petroleum Geologyabout the work, said that the area was a “cold seep” where methane in deep formations moved upward through faults and then through sediments in the seabed. Those sediments contain bacteria that consume methane for energy.
All that consumption of methane, Dr. Andrews said, changed the chemistry of the seawater that saturated the sediments. That caused dissolved minerals to precipitate out of the water as a rock called dolomite. And the dolomite cemented the sediment particles in place, forming concretions. The columns and other shapes resulted from the methane spreading in different ways through the sediments as it flowed upward.
Dr. Andrews said the researchers’ analysis suggested that the concretization might have occurred several million years ago deeper in the sediments and that the objects had been exposed over time as the seabed eroded.
