What was believed to have been the underwater remnants of an ancient, long lost Greek city is actually the result of a natural geological phenomenon that occurred during the Pliocene era, up to five million years ago, according to new research published on Friday.
Several years ago, CNN and the New York Times explained, divers discovered what appeared to be paved floors, courtyards and other evidence of a long-forgotten city off the coast of the Greek island Zakynthos that would have been swallowed up when tidal waves washed over it.
However, writing in the latest edition of the journal Marine and Petroleum Geology, researchers from the UK’s University of East Anglia and the University of Athens in Greece revealed that it was not a man-made metropolis, but actually built by microbes, not humans, and were produced as a byproduct of their efforts to break down methane gas for energy.
“We investigated the site, which is between two and five meters under water, and found that it is actually a natural geologically occurring phenomenon,” lead author Professor Julian Andrews of the UEA School of Environmental Sciences, who along with his colleagues analyzed the mineral content and texture of the site, said in a statement.
Methane release similar to fracking spurred on the process
When divers first discovered the size near Alikanas Bay, they found structures that looked as if they could have been man-made, such as circular column bases and paved floors. However, they were puzzled by the lack of other signs of human activity, including pottery or other artifacts.
That led scientists to conduct a preliminary set of mineralogical and chemical analyses, then turn to the UoA and UEA researchers for help. Andrews’ team used a combination of microscopy, X-ray and stable isotope techniques to closely examine the remains, and found that the location was something known as a “cold seep” in which methane within the ocean floor moved upward via a series of faults and seabed sediments, where it was then consumed by microbes.
“The disk and doughnut morphology, which looked a bit like circular column bases, is typical of mineralization at hydrocarbon seeps,” Andrews explained in a statement. “We found that the linear distribution of these doughnut shaped concretions is likely the result of a sub-surface fault which has not fully ruptured the surface of the sea bed.”
“The fault allowed gases, particularly methane, to escape from depth,” he added. “Microbes in the sediment use the carbon in methane as fuel. Microbe-driven oxidation of the methane then changes the chemistry of the sediment forming a kind of natural cement, known to geologists as concretion. In this case the cement was an unusual mineral called dolomite which rarely forms in seawater, but can be quite common in microbe-rich sediments.”
The professor noted that this type of event rarely occurs in shallow water, and most phenomena like it are often discovered several hundred to thousands of meters below sea level. However, he said that the process, though natural, was similar to the effects of fracking – in both cases, natural methane leaks from rocks in hydrocarbon reservoirs, but in the latter instance, humans are simply speeding up the release of the gas.
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Image credit: Credit: University of Athens
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