When searching for treasure, there's no knowing what you might find. That was the case for Swedish divers who stumbled across something very strange in the Baltic Sea in 2011.
While using sonar to scan the seabed, they saw a strange shape. The scans were blurry, so it was hard to make out what this unidentified object might be, but it was circular and around 60 metres in diameter — around the size of a Ferris wheel.
What was it? No one knew, and media speculation went wild. People suggested it might be a meteorite or a UFO that had crashed in the ocean and was now sitting 90 metres deep on the seabed. Some even suggested that the mythical lost city of Atlantis had been found.
Peter Lindberg, one of the treasure hunters on the diving team that found the anomaly, said in a press release that the media had speculated about everything from UFOs to spaceships.
Things got weirder when the divers suggested that something near the object — dubbed the Baltic Sea Anomaly — was causing technology to malfunction. When they were above the anomaly, they said their electrical equipment didn't work.
But before you get excited that we've discovered proof of extraterrestrial life, hold your horses. There's probably a more logical explanation.
According to Live Science, Volker Brüchert, a geology professor at Stockholm University, said most of the samples brought up from the sea bottom were granites, gneisses and sandstones, along with a piece of basalt, which forms when lava cools and solidifies.
The basin of the Baltic Sea was carved out by glaciers during the last ice age, and these rocks may be remnants of that process. Brüchert told Live Science that both the feature and the rock samples were likely to have formed through glacial and postglacial processes.
Although experts have offered a geological explanation, many people have remained intrigued by the Baltic Sea Anomaly over the years — after all, a spaceship is more exciting than a glacial deposit. It isn't the only time a strange geological formation has looked like something else: researchers once found what resembled the Wizard of Oz's yellow brick road 1,000 metres deep in the Pacific Ocean, created by ancient volcanic activity.