Greece

The lost (microbe) colony: bacteria make underwater 'ruins' off Greek island

Site near Zakynthos predates civilization by millions of years and bears striking resemblance to Hellenic structures but is result of process called concretion

What were thought to be ancient remains of a lost Greek city were in fact created by a naturally occurring microbes.
What were thought to be ancient remains of a lost Greek city were in fact created by a naturally occurring microbes. Photograph: University of Athens

Columns strewn across the seafloor, detached from their familiar circular bases; tiles as from an ancient Greek courtyard above the water’s reach on an island nearby. A sunken city – or so the snorkelers thought.

Greek archaeologists who dove to the site near Alikanas Bay, off the island of Zakynthos, were baffled by the eerie scene they found 7-15ft (2-4 meters) down. Though the sunken debris looked like paved floors and colonnades, the divers could see no other signs of life: no pottery, coins, or shards of sculpture or art.

“They tried to decide whether they’re actually Hellenic stonework,” said Julian Andrews, a professor at the University of East Anglia (UEA) who assisted the research, “but couldn’t find any evidence that it was other than these rather bizarre structures [which] looked like superficially like stonework.”

In fact, the site predates civilization entirely. The “ruins” were created as long as 3m years before mankind is thought to have left Africa – 5m years before Troy, Athens or Alexander.

Microbes did it.

In a study published on Thursday by a joint team from the University of Athens and UEA, the researchers write that the site is not a lost city at all, but a natural if strange phenomenon.

Not the base of a column.
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Not the base of a column. Photograph: University of Athens

The team used microscopy and x-rays to study the mineral content and texture of the formations. They found that methane had jetted, oozed and flowed from within the earth, through a subsurface fault still hidden by the seabed.

“The earth’s crust is a rather leaky reservoir,” Andrews said. “It’s almost like a kind of plumbing system, if you like, in the sediment.”

Bacteria that use the carbon in methane as fuel clustered near the tubes and cracks, consuming the gas and gradually leaving behind a calcium byproduct. Its reaction with oxidizing methane created a kind of natural cement, in a process called concretion.

The cylindrical “doughnut” shape of the column-like structures, Andrews said, was the result of microbes gathered round a central, gas-spewing hole.

The tile-like floor, he said, was caused by a slower, more diffuse seepage of methane. The reaction between the microbes living in the sediment and the gas was consequently more diffuse, creating a flat and seemingly paved texture on the seafloor.

The scientists published their findings in the journal Marine and Petroleum Geology.

Andrews said dolomite, the particular mineral contained in the cement, rarely creates such formations in shallow seas but they can be common to microbe-rich regions of the deep.

Not tiled floor.
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Not a tiled floor. Photograph: University of Athens

“They’re found pretty much in all the oceans, in the Pacific, particularly off the west coast of the US,” he said, adding that such formations are also found in the Atlantic and the Mediterranean.

“The microbes do much the same thing whether they’re in deep or shallow settings. But the majority of the cases that have been reported are relatively deep water, sort of 100 meters down.”

Natural gas is more likely to bleed out of the earth in deep water, and most undersea oil fields are found in the deep, making such formations more likely far below the range of divers.

Though this process is natural, Andrews said, it has an analogy to what humans do on land with hydraulic fracking. Through fracking, he said, “humans essentially speed up or enhance the phenomena”.