When a group of tourists came ashore after a day of snorkeling in 2013, claiming to have discovered the submerged ruins of an ancient city, Greece took them seriously. After all, the place is a hotbed of antiquities. The snorkelers reported what appeared to be the remains of a city in the shallow emerald waters off the coast of the Ionian island of Zakynthos — and so archaeologists got right on that.
And it was true that what the snorkelers found appeared to have humanity's grubby fingerprints all over it: rows of giant cylindrical structures rising from a bed of flat, interlocking rectangular stones could once have been the courtyards and colonnades of a bustling seaside city. However, other than the structures themselves, researchers found the site completely devoid of signs of human habitation (like pottery or coins). As a paper published in the journal Marine and Petroleum Geology reminds us: "Columns and pavements in the sea, not always antiquities will be."
While it would have been cool if those snorkelers had found the next lost city of Atlantis, they didn't. Not even close. Science has known since soon after their discovery that the structures were natural, but the exact process wasn't understood; that's what this new research clarifies. Though the underwater structures weren't man-made, they were created by somebody — and that somebody just happens to be bacteria.
The research team has determined the pipe-like structures that bear such a resemblance to ancient Greek columns are really geologic formations created around 5 million years ago, when microbes began to cluster around methane vents in the sea floor. As the bacteria metabolized the gas, they turned the sediment at the mouth of the vent into the mineral dolomite. This happened through a chemical process called concretion. Because the methane escaped into the sea along a fault line, these structures arranged themselves accordingly in a nice row. Over the millennia the sea floor around the structures has worn away, leaving tourist-fooling slabs and pillars of rock.
Although undersea structures like these are not uncommon, they generally exist in much deeper waters. As it is, though, what was thought to have been a "lost city" acts as a reef in the shallow waters off Zakynthos, providing a city for fish and other sea life — just not now, or ever, for humans.