Needless to say, trying to solve even one of the myriad of unresolved world mysteries takes plenty of time, but these ten global riddles have already become open secrets.
'Sailing Stones' of Death Valley
Between 1940 and 2013, this mystery puzzled many researchers from all across the globe. Littered across the surface of a dry lake in California's Death Valley, hundreds of heavy rocks appeared to have been dragged across the ground, leaving synchronised trails that stretch for hundreds of metres.
In this April 11, 2010, file photo, tourists walk along a ridge at Death Valley National Park, Calif.
© AP Photo / Brian Melley
In December 2013, US researchers found that the movement of 320-kg (700-pound) rocks was caused by a rare combination of events. The scientists figured out that during the mild winter, rain collects in Death Valley to form a shallow lake, which subsequently freezes when the temperatures plummet at night.
When the morning closes in, the Sun warms the ice, which then breaks into small plates. If a plate is under a rock, wind and flowing water slowly pushes it, prompting the rock to leave a trail in the mud.
Giraffe Legs
Now take a look at giraffes, whose leg bones are under high levels of mechanical stress and are never broken despite each animal typically weighing about 1,000 kg (2,204 pounds).
Researchers from the Royal Veterinary College (RVC) of London found that it is supportive ligament, protected by a groove in the animals' lower leg bones, which "plays an important role".
This groove is much deeper in giraffes than in other animals, something that "adds great stiffness to giraffe limbs" and helps the animals support their body weight, according to RVC scientists.
'Singing' Sand Dunes
Lots of scientists have repeatedly wondered why sand grains shuffling down the slopes of certain sand dunes produce a deep hum that reverberates for miles.
In 2012, a team of Parisian biophysicists tracked down a pair of singing dunes, one in Morocco, and another in Oman, that could even "sing" more than one note at a time.
The researchers finally discovered that it's not necessarily the motion of the sand that determines the pitch of the note - it's the size of the grains that matters. According to the biophysicists, "the size of the grain controls the actual sound", which they claimed also depends on the grains of sand's speed of movement.
Pigeons' 'Bermuda Triangle'
One more breakthrough pertains to the mystery of the so-called "Bermuda Triangle" of the homing pigeon. Scientists have been in the dark for years as to why homing pigeons - usually excellent navigators - get lost when released from a particular site in New York State.
Research released in 2013 suggested that the birds are using "infrasound", low frequency sounds to find their way around, and that they were unable to hear such vibes in the abovementioned US location, which were affected by changes in the atmosphere.
Referring to the discovery, Jonathan Hagstrum from the US Geological Survey, who was lead author of the study, argued the pigeons were creating "acoustic maps" of their surroundings.
"The way birds navigate is that they use a compass and they use a map. The compass is usually the position of the Sun or the Earth's magnetic field, but the map has been unknown for decades. I have found they are using sound as their map […] and this will tell them where they are relative to their home", the scientist claimed.
Secret of Australia's Volcanoes
Another resolved mystery concerns Australia's east coast, littered with the remnants of hundreds of volcanic eruptions, the most recent being just a few thousand years old. Scientists have been baffled as to why there was so much volcanic activity in the eastern parts of an otherwise stable continent.
In 2020, Ben Mather, lead author of a study, revealed that in the area scientists found "a special volatile mix of molten rock that bubbles up to the surface through the younger, thinner east coast Australian crust".
Referring to peaks of activity 20 million and two million years ago, researchers suggested that "most of these eruptions are not caused by Australia's tectonic plate moving over hot plumes in the mantle under the Earth's crust" and that "instead, there is a fairly consistent pattern of activity, with a few notable peaks".
"From there it is being slammed into the transition zone between the crust and the magma at depths of about 400 to 500 kilometres. This material is then re-emerging as a series of volcanic eruptions along Australia's east coast, which is thinner and younger than the centre and west of the continent", in a process called subduction, according to Mather.
Fish in Polluted Waters
Researchers have repeatedly tried to explain why the Atlantic Fundulus fish paid little attention to the polluted waters in the New Bedford harbour in Massachusetts, continuing to thrive and reproduce in the area.
It was really a mystery given that from 1940 to 1970, factories dumped waste containing polychlorinated biphenyls (PCBs) directly into the harbour, which was finally declared an ecological disaster zone due to hazardous levels of PCBs.
At the end of the day, scientists found that the Atlantic Fundulus was able to genetically adapt itself to the toxins, which enables the fish to successfully resist the polluted environment.
Giant Underwater Waves
Scientists have always tried to understand the origin of huge internal waves that are hidden entirely within the ocean and that can have a significant effect on climate and ocean ecosystems.
These waves are hard to detect, which is why studying them directly in the ocean is a formidable task. In 2014, Thomas Peacock from the Massachusetts Institute of Technology and his colleagues conducted large-scale laboratory experiments to explore the origin of internal waves in the Luzon Strait located between Taiwan and the Philippines.
The experiments showed that internal waves had been generated by the entire ridge system of the area's seafloor rather than a localised hotspot within the ridge. According to Peacock, the discovery is "an important missing piece of the puzzle in climate modelling".
Why a Zebra is Striped
Here's one more mystery solved regarding a zebra's black and white stripes. Researchers previously suggested that this animal print served as camouflage to shun massive predators, an identity signal to other zebras or sort of wearable air conditioner. Now, however, many scientists share a view that the stripes' goal is to tackle biting flies that may carry deadly diseases.
Zebra
© Photo : Pixabay
Tim Caro from the University of California, co-author of a study published in 2019, observed horse flies trying to bite zebras, stressing that "something is stopping the fly from realising that it's close to making a landing [on a zebra's body]". According to him: "We don't know what that is, but stripes are exerting an effect to the very last second".
Biggest-Ever Mass Extinction
In 2014, scientists appeared to have resolved the mystery of the biggest mass extinction in history that took place 252 million years ago, which, they say, was caused by climate-changing microbes.
The researchers believe that a chief perpetrator was a microscopic methane-producing life form, Methanosarcina, that bloomed drastically in the oceans. This single-celled organism generated enormous quantities of methane, a potent greenhouse gas, which prompted higher temperatures, also acidifying the seas. Unable to adapt quickly enough, about 90 percent of species then vanished from the Earth, the scientists claim.
Origin of Earth's Oceans
Water covers about 70% of our planet's surface and scientists previously believed that at the time of Earth's formation there was no water on it. Earlier theories claimed that water emerged on our planet much later, as a result of collisions with asteroids and wet comets.
The most recent research, however, claims that water was in place on the Earth at the stage of its formation about 4.6 billion years ago, when meteorites brought the substance to the planet's surface.