Buzz
For years, experts were perplexed by some of Earth's greatest riddles, from the colossal shifts beneath the ocean to the very origins of our seas. Today, many of these mysteries have been solved.
10. The Enigma of Death Valley’s Moving Stones
From the 1940s until recent years, Death Valley National Park's Racetrack Playa, a vast dry lakebed with a smooth surface, became the site of a baffling mystery involving “sailing stones.” These stones seemed to move across the ground by some invisible force, leaving long parallel trails in the cracked mud. Some of these rocks weighed as much as 300 kilograms (700 lb) each.
Despite no one ever observing the stones in motion, scientists were determined to uncover the truth. In 2011, a team of US researchers launched an investigation. They set up time-lapse cameras and installed a weather station to monitor wind gusts. Additionally, they equipped 15 limestone rocks with motion-activated GPS tracking units and placed them on the playa.
Although it could have taken decades for any action, fortune favored the researchers. In December 2013, they were present when the stones finally moved, solving the long-standing mystery.
After heavy rain and snow, 7 centimeters (3 in) of water accumulated on the playa, which froze into thin sheets of ice overnight. Under the midday sun, the ice broke into larger floating panels. Light winds of about 15 kilometers (10 mi) per hour were just enough to push the rocks across the surface, leaving tracks in the mud beneath the ice. The tracks were visible once the playa dried out.
The rocks only move under perfect conditions—just the right amount of wind, sun, water, and ice. Too much or too little of any factor would prevent the movement. “It’s possible that tourists have actually witnessed this phenomenon without realizing it,” says researcher Jim Norris. “It’s difficult to notice when a rock is moving if all the surrounding rocks are also in motion.”
9. The Secret Behind How Giraffes Keep Their Balance On Thin Legs
Despite weighing around 1,000 kilograms (2,200 lb), giraffes have surprisingly slender leg bones for their size. Yet, they manage to stand tall without collapsing or showing any signs of injury.
To uncover the secret, researchers from the Royal Veterinary College examined giraffe limbs donated by European Union zoos. These limbs came from animals that passed away from natural causes or were euthanized. The researchers placed the limbs in a rigid frame and applied weights of up to 250 kilograms (550 lb) to simulate the giraffe's weight. Remarkably, the limbs stayed stable, and even higher forces could have been withstood.
The key to their strength is a suspensory ligament, a fibrous tissue that holds the bones together. This ligament runs along a groove in the giraffe’s leg bones, which resemble the metatarsal bone in the human foot and the metacarpal bone in the human hand. However, in giraffes, these bones are much longer.
The suspensory ligament doesn’t produce any force on its own. Instead, it offers passive support due to its elastic tissue, unlike muscle. This reduces fatigue for the giraffe since it doesn’t have to rely on its muscles as much to support its weight. Additionally, the ligament helps safeguard the giraffe’s foot joints and prevents the collapse of its feet.
8. The Musical Sand Dunes
There are 35 known sand dunes that produce a deep rumbling sound, akin to the low moan of a cello. This sound can last up to 15 minutes and travel as far as 10 kilometers (6 mi). Some dunes hum occasionally, while others sing every day. The sound is triggered when sand grains slide down the dunes.
Initially, scientists believed that the sound came from vibrations deep within the dune layers. However, researchers discovered they could recreate the sound in a lab by allowing sand to slide down an incline. This confirmed that it was the sand, not the dune itself, that was creating the sound. The noise came from the vibrations of the grains themselves as they slid down the dune or the lab's incline.
Next, the researchers explored why certain singing sand dunes produced multiple notes at once. To understand this, they analyzed sand samples from two dunes—one in southwestern Morocco and the other in southeastern Oman.
The sand from Morocco consistently produced a sound around 105 Hertz, similar to a G-sharp two octaves below middle C. Meanwhile, the sand from Oman generated a range of nine different notes, from about F-sharp to D, with frequencies ranging from 90 to 150 Hertz.
Researchers discovered that the size of the grains determined the pitch of the notes. The Moroccan sand grains were uniform, ranging from 150–170 microns (0.006–0.0065 in), and they consistently produced a G-sharp. In contrast, the Omani grains varied in size from 150 to 310 microns (0.006–0.012 in), creating a broader range of notes. When the Omani grains were sorted by size, those with a narrower range of sizes vibrated at a single frequency to produce the same note.
The speed at which the sand moved also played a role. When the grains were of similar size, they moved at comparable speeds, producing a consistent pitch. However, when the grains varied in size, they moved at different speeds, resulting in a greater variety of notes.
Despite these findings, scientists are still puzzled as to why the tones produced by the sand sound musical. Their working theory is that the vibrations of the sliding grains synchronize, compressing the air in a way similar to how a loudspeaker diaphragm works.
7. The Bermuda Triangle of Homing Pigeons
This puzzle dates back to the 1960s, when a professor from Cornell University began studying the incredible navigational skills of homing pigeons. He released the birds from various locations around New York State, and they generally had no trouble finding their way back. However, pigeons released from Jersey Hill kept getting lost. On August 13, 1969, they successfully made their way home, but on every other occasion, they seemed confused and flew around aimlessly. The professor couldn’t figure out what caused this odd behavior.
Dr. Jonathan Hagstrum from the US Geological Survey believes he may have cracked the mystery, though his theory has sparked some debate. “The birds navigate using both a compass and a map. The compass typically relies on the Sun’s position or the Earth’s magnetic field,” he explained. “They also use sound as their map… this helps them determine their position relative to their home.”
Hagstrum theorizes that the pigeons are using infrasound, low-frequency sound that humans cannot hear. This type of sound may have been utilized in ancient soundscapes to influence the mental states of our ancestors during religious rituals.
The pigeons may be using infrasound (which in this case is created by subtle vibrations on the Earth's surface caused by deep ocean waves) as a homing beacon. At Jersey Hill, the infrasound signal was pushed high into the atmosphere due to temperature and wind conditions, rendering it undetectable to the birds. However, on August 13, 1969, the weather conditions were just right, allowing the pigeons to hear the infrasound and navigate their way home.
6. The Mysterious Origin of Australia’s Sole Active Volcano
Australia is home to just one active volcanic region, stretching 500 kilometers (300 mi) from Melbourne to Mount Gambier. Over the past four million years, there have been about 400 volcanic events, with the most recent eruption occurring around 5,000 years ago. Scientists had long been puzzled about why eruptions took place in this part of the world, where volcanic activity is otherwise rare.
However, researchers have now cracked the case. Most volcanoes form along the edges of tectonic plates, which constantly shift at small rates (measured in centimeters per year) above the Earth's mantle. But in Australia, variations in the continent’s thickness create mantle currents that bring heat to the surface. Coupled with Australia’s gradual northward drift at 7 centimeters (3 in) per year, a hotspot formed in this region, producing magma.
“Around 50 other similarly isolated volcanic regions exist worldwide, and we may now be able to explain many of them,” says Rhodri Davies from the Australian National University.
5. The Fish Flourishing in a Superfund Cleanup Site
From the 1940s to the 1970s, manufacturing plants discharged polychlorinated biphenyls (PCBs) into New Bedford Harbor in Massachusetts. The Environmental Protection Agency labeled the harbor as a Superfund cleanup site due to PCB contamination levels that were more than four times what was considered safe. Yet, this harbor also holds a biological mystery that researchers may have just unraveled.
Amid such hazardous pollution, Atlantic killifish have managed to thrive in New Bedford Harbor. These small prey fish tend to remain in the same waters throughout their entire lives, often staying within a few hundred yards of where they were born.
Typically, when a fish digests PCBs, the byproducts become even more toxic than the original PCBs themselves. However, killifish have essentially deactivated a genetic pathway that would normally cause this toxic transformation. They’ve adapted to survive PCB pollution, though some scientists worry that this genetic change could make them more vulnerable to other pollutants. There’s also concern that, once the waters are cleaned, these fish may struggle to survive in a restored, healthier environment.
Killifish serve as prey for larger fish like striped bass and bluefish, many of which are part of our diet. So, despite the killifish's apparent resistance to PCB toxins, they can still pass these harmful substances up the food chain, ultimately reaching us.
4. The Formation of Underwater Waves
Underwater waves, or internal waves, remain below the ocean’s surface, out of sight from us. They can slightly lift the water’s surface by just a few inches, making them challenging to detect unless using satellite technology. The largest internal waves are found in the Luzon Strait, between Taiwan and the Philippines. These waves can rise up to 170 meters (560 ft) high and travel at a pace of only a few centimeters per second, covering vast distances.
Scientists believe that understanding how internal waves are created is essential, as they could play a significant role in global climate change. These waves mix the ocean's warmer, less salty surface water with the colder, saltier deeper layers. They help drive vast amounts of salt, heat, and nutrients throughout the ocean, acting as the primary mechanism for transferring heat from the upper ocean to the lower depths.
For years, scientists have been eager to unlock the mystery of how the enormous internal waves in the Luzon Strait form. Though difficult to observe directly, specialized instruments can detect the density differences between the internal waves and surrounding water. To study this, researchers set up an experiment in a 15-meter (50 ft) wave tank, where cold bottom water was pushed over two ridges on a simulated seafloor. Their findings suggest that these massive internal waves are generated by the spacing of ridges in the Luzon Strait, rather than a singular feature on a ridge like a mountain.
“It’s a crucial missing piece in climate modeling,” says Thomas Peacock from MIT. “Current global climate models fail to account for these processes. The results change significantly if you don’t factor in the impact of these waves.”
3. The Mystery Behind Earth’s Oceans
Water makes up about 70 percent of the Earth's surface. Early scientists believed the planet began dry, with a molten surface formed from impacts by space objects. It was thought that collisions with asteroids and water-rich comets later introduced water to Earth. Geologist Horst Marschall explained, “Some people argued that any water molecules present during the planet's formation would have evaporated or been blown into space. Surface water as we know it today must have arrived much later—hundreds of millions of years after Earth’s formation.”
However, a recent study challenges this view, suggesting that Earth already had water on its surface when it first formed. This discovery implies that life may have evolved sooner than previously thought, and that other inner solar system planets may have experienced similar conditions before becoming inhospitable.
To pinpoint when water arrived on Earth, scientists compared two types of meteorites. The first, carbonaceous chondrites, are the oldest meteorites known, originating around the same time as the Sun, before planets had formed. The second type is believed to be from Vesta, a large asteroid formed 14 million years after our solar system's birth.
Both types of meteorites share a similar chemical makeup and are rich in water. Based on this, the researchers propose that Earth formed with water on its surface, brought by the carbonaceous chondrites about 4.6 billion years ago.
2. The Extinction Event That Wiped Out 90 Percent of Earth’s Species
Around 252 million years ago, a catastrophic event known as the end-Permian extinction, or the 'Great Dying,' erased about 90 percent of Earth's species. It remains the most severe mass extinction in history. The cause of this event has puzzled scientists, with theories ranging from asteroid impacts to volcanic activity. However, the true culprits were much smaller—and invisible to the naked eye.
MIT researchers have identified a tiny but deadly microbe, Methanosarcina, as the main perpetrator. This single-celled organism consumes carbon compounds and produces methane as a byproduct. Today, Methanosarcina can be found in landfills, oil wells, and the digestive systems of cows. During the Permian period, a gene transfer from another bacterium allowed Methanosarcina to process acetate. This breakthrough enabled the microbe to consume large amounts of organic matter that had accumulated on the ocean floor.
The population of these microbes exploded, releasing vast amounts of methane into the atmosphere and acidifying the oceans. This environmental shift led to the extinction of most land plants and animals, as well as marine life. However, the microbes required nickel to proliferate at such a rapid rate. Researchers suggest that the volcanic activity in Siberia released the large quantities of nickel necessary for this process.
Greg Fournier, one of the researchers, commented, 'The end-Permian extinction is the closest animal life has ever come to being completely wiped out, and it may have been on the brink.' He added, 'Many of the surviving species barely made it, with only a few organisms managing to survive, likely by chance.'
1. Why Zebras Have Stripes
The purpose of zebra stripes has long been a topic of debate. Some believe the stripes offer camouflage or confuse predators. Others suggest the stripes help with temperature regulation or even play a role in mate selection.
A team of scientists at the University of California, Davis set out to uncover the truth. They examined the habitats of zebras, horses, and donkeys, collecting data on the color, pattern, and size of stripes on zebras. They then mapped the locations of tsetse flies and other biting insects like horseflies and deer flies. After analyzing this data with a bit of statistical rigor, they found their answer.
'I was truly surprised by the results,' said researcher Tim Caro. 'Time and time again, we observed more stripes in regions where zebras faced more intense irritation from biting flies.'
Zebras are particularly susceptible to biting flies due to the fact that their hair is shorter compared to other similar species like horses. These flies, which can transmit harmful diseases, pose a significant risk to the zebras, making it crucial for them to avoid these pests.
A separate study by researchers at the University of Sweden discovered that flies tend to avoid zebra stripes because of their specific width. If the stripes were broader, zebras wouldn't enjoy the same level of protection. In their experiments, they found that black surfaces attracted more flies, white surfaces drew fewer, and stripes were the least appealing to the insects.
