From Costa Rica's Great Balls to Death Valley's wandering rocks: The 10 bizarre phenomenon that still have scientists baffled

Scientists have spent centuries uncovering the many mysteries of the natural world, yet some phenomenon still baffle even the sharpest of scientific minds, The Daily Mail reports.

From strange lights in the sky following earthquakes to rocks that spontaneously glide across the ground, these naturally-occurring events from around the world seem to have no purpose or meaning.

Science Uncovered's Hayley Birch has compiled a list of the top 10 most strange, cryptic and incredible naturally-occurring events from around the world.


For mystery, controversy and epic scale, nothing beats earthquake lights - the unexplained illuminations in the sky that can accompany a seismic shudder. The various theories include heat caused by friction, radon gas and piezoelectricity - an electric charge accumulating in quartz rocks as tectonic plates move


Covering a 450km expanse of coastal desert, the Nazca Lines are oversized artworks etched into the Peruvian plains, pictured. They are thought to have been created by the Nazca people over a 1,000-year period between 500BC and 500AD, but no one knows why


Millions of monarch butterflies, pictured, migrate 2,000 miles every year. In 1976, zoologists found them at the top of the 'Mountain of Butterflies' in Mexico. While scientists know the monarchs target 12 to 15 Mexican mountain sites, they don't know how they navigate there


The phenomenon of ball lightning has generally been described as being a luminous sphere that appears during or after a thunderstorm. Some theories suggest ball lightning, pictured, is a plasma, others that it is the result of a chemiluminescent process - light that occurs due to a chemical reaction


At Racetrack Playa in the Death Valley, California, pictured, heavy rocks appear to move across the floor while no one is looking. Scientists believe the movement may be caused by the ice stuck to the bottom of the stones, which are then moved in the wind. However, no-one has caught the stones in the act


An unidentified hum is a low-frequency noise that's been heard from Bristol to Bondi. Scientists have attributed this drone to tinnitus, distant waves crashing, pictured, industrial noise and singing sand dunes. In 2006, one New Zealand scientist claimed to have recorded the sound


In 2013, cicadas emerged from the ground after not being seen since 1996. Scientists have no idea how they knew when it was the right time to leave the ground


Scientists are sceptical about animal rain. Odzaci, in Serbia, has supposedly been pelted by frogs, and perch have fallen on Lajamanu, Australia. After tadpoles rained on the Japanese cities of Nanao and Hakusan in 2009, it was suggested birds dropped them but this has never been proved


The great balls of Costa Rica, pictured, were found in the 1930s. Some are as large as two metres in diameter. Now dated to between 600 and 1000 AD, the balls are known locally as Las Bolas. Yet, there are no written records of the culture of the people who created them


Fossilis uncovered in geographical regions and archaeological time zones they don't belong to have fuelled creationist arguments. Some of these have yielded new information about our ancestry. Others have been revealed as fakes. Recently, a human skull unearthed in Sussex was found to be a forgery