Ancient sunken ruins off the Greek coast have turned out to be anything but the man-made objects they were thought to be. It has been found the ruins are microbial poop.

In 2013, snorkellers off the Greek Island Zakynthos discovered formations very much like columns and paved streets. Archaeologists couldn’t find the usual accompanying antique pottery shards or artifacts, though.

Samples collected by Julian Andrews (a geochemist from the University of East Anglia in the UK) and his colleagues revealed that the “ruins” were actually sediment laid down by methane-consuming microbes over millions of years. Apparently, microbes living in vents on the ocean floor ingest methane from enriched fluids that reach the surface of the vents. It turns out that, over millions of years, the microbes’ excrement produced carbonate minerals that compacted to create the hollow structures spotted by divers.

The study detailing the process and its discovery will be published in the Journal of Marine and Petroleum Geology later this year.

Source: Science News