The Bloop

During the summer of 1997, the US National Oceanic and Atmospheric Administration (NOAA) detected an ultra low frequency underwater several times that they could not identify. So named for the sound made, the source of the "Bloop" remains unknown.

The Bloop originated off the southwest coast of South America. It was picked up several times using US Navy equipment designed to detect Soviet submarines. The Bloop rose in frequency for over a minute and was strong enough to be heard from over 5,000 km. The scientists who have heard the Bloop say that it matches the audio profile of a living being, however, there is no known animal large enough to have made the noise. If it did come from an animal, the creature would have to be bigger even than the largest known animal on Earth, the Blue Whale.

Hear the Bloop here.