For years, one of the ocean’s strangest mysteries fueled speculation that a massive creature could be hiding somewhere in the deepest parts of the sea. The mysterious sound, known as the “Bloop,” was so powerful that some people jokingly connected it to the extinct Megalodon, the enormous prehistoric shark believed to have reached around 24 meters in length. The idea captured people’s imaginations, especially because so little of the deep ocean has been explored. However, there are several reasons why a living Megalodon would be extremely unlikely. A predator of that size would require enormous amounts of food, while its teeth would also likely be discovered regularly if it were still alive. Scientists therefore had a much different explanation for the strange underwater noise.

The mystery was eventually investigated using underwater microphones known as hydrophones. Researchers working with NOAA eventually traced the source of the sound to Antarctica, where they discovered that it had nothing to do with a giant shark or a sea monster. Instead, the Bloop was caused by enormous ice movements. According to NOAA, the sound came from an “icequake,” produced when huge icebergs cracked, shifted or broke away from Antarctic glaciers. The discovery finally put the Megalodon theory to rest, although the story remains a fascinating example of how mysterious sounds can inspire extraordinary theories. Rather than an ancient predator lurking beneath the waves, the terrifying noise was actually produced by powerful natural forces involving Antarctic ice. The ocean may still contain plenty of mysteries, but this particular one has a far more scientific—and chilling—explanation.