A "lost city" discovered by snorkelers off the Greek island of Zakynthos isn't an underwater metropolis after all. "We investigated the site, which is between [6.5 to 16 feet] underwater, and found that it is actually a natural geologically occurring phenomenon," Julian Andrews, lead author of research published in the Marine and Petroleum Geology journal, says in a press release. Instead of the paved floors and circular column bases that divers initially thought they had discovered, mineral and chemical tests by a joint team of University of Athens and University of East Anglia scientists show those formations were actually created by Mother Nature during the Pliocene era, some 2.6 million to 5 million years ago. "The suggestion that they were archaeological remains was brought about by tourists who were swimming around and saw these things and thought they were stonework," Andrews tells CNN.
Oddly, there were no coins, pottery, or "other flotsam and jetsam of everyday existence," as the New York Times puts it. After more complete testing was carried out, the researchers theorized that a sub-surface fault allowed gases—chief among them methane—to leak out into the sediment. Microbes in the sediment then fed off the gas and the sediment was chemically altered in a way that created a mineral called dolomite; erosion ultimately exposed the structures. Smithsonian.com explains that a big methane leak typically produces slab-like structures, but when the leak is small and the microbes are forced to concentrate around it, they may "make column-like and doughnut-shaped formations" as seen here. Andrews says one of the reasons scientists were duped at first is that this type of natural event doesn't often happen in such shallow waters. "Most similar discoveries tend to be many hundreds and often thousands of meters deep underwater." (This sunken find looks like it's the real deal.)