Scientists have been baffled for years by the mysteries of our world, from giant movements under the ocean to how the oceans themselves originated. Today, we have the answers to some of these questions.

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10 The Secret Of Death Valley’s Sailing Stones

Fron the 1940s till recently, the Racetrack Playa, a dry lake bed with a flat surface in Death Valley National Park, was the setting for a “sailing stones” mystery that left people scratching their heads. With years or even decades between each occurrence, an unseen force appeared to move hundreds of rocks across the ground at the same time, leaving long parallel trails in the dried mud. These sailing stones weighed up to 300 kilograms (700 lb) each.

No one had even seen the stones in motion as far as scientists knew. So a team of US researchers decided to investigate in 2011. They set up time-lapse cameras and a weather station to measure wind gusts. Then they installed motion-activated GPS tracking units in 15 limestone rocks and set them on the playa.

It could have been a decade or more before anything happened, but they got lucky. In December 2013, the team was there in person when the stones sailed—and the mystery was solved.

Heavy rain and snow had left 7 centimeters (3 in) of water on the playa. It froze at night into thin sheets of ice that broke up into larger floating panels under the midday sun. Light winds of about 15 kilometers (10 mi) per hour were needed for the accumulated ice to push the rocks across the playa, leaving tracks in the mud beneath the icy surface. The trails became visible months later when the lake bed dried out.

The rocks will only move if conditions are perfect. Not too much wind, sun, water, or ice. Not too little, either. “It’s possible that tourists have actually seen this happening without realizing it,” says researcher Jim Norris. “It is really tough to gauge that a rock is in motion if all the rocks around it are also moving.”

9 How Giraffes Stay Upright On Their Bony Legs








Giraffes weigh about 1,000 kilograms (2,200 lb) but have incredibly thin leg bones for their size. Yet they don’t collapse or appear to get hurt.

To find out why, researchers from the Royal Veterinary College tested giraffe limbs donated from European Union zoos. The limbs were from animals that had died of natural causes in captivity or had been euthanized. The researchers placed the limbs in a rigid frame then used masses of up to 250 kilograms (550 lb) to simulate a giraffe’s weight on its legs. Each limb stayed stable and upright without any problem. In fact, the giraffe legs would have been able to successfully tolerate even greater forces.

The reason is a suspensory ligament (fibrous tissue that holds bones together) that resides in a groove running the length of leg bones in a giraffe. These leg bones are similar to the metatarsal bone in a human foot and the metacarpal bone in a human hand. But in a giraffe, these bones are much longer.

The suspensory ligament doesn’t generate any force on its own. It provides passive support only because it’s elastic tissue, not muscle. That lessens fatigue for the animal because it doesn’t have to use its muscles as much to bear its weight. This ligament also protects the giraffe’s foot joints and prevents the collapse of its feet.





8 The Singing Sand Dunes



There are 35 known sand dunes that emit a loud rumble that sounds like the low moan of a cello. The sound may last as long as 15 minutes and can travel up to 10 kilometers (6 mi) away. Some dunes sing occasionally, others daily. It happens when grains of sand slide down these particular dunes.

At first, scientists thought the tones came from vibrations in the dunes’ subsurface layers. But researchers found that they could recreate the sound in a lab by letting sand slide down an incline. That proved that the sand, not the dune, was singing. The sound came from the vibrations of the grains themselves as they cascaded down the dune or an inclined lab structure.

Next, the researchers investigated why some singing sand dunes produced multiple notes at once. For this, they studied sand from two dunes—one in southwestern Morocco and the other in southeastern Oman.

The Moroccan sand always produced sound at about 105 Hertz, which is similar to a G-sharp two octaves below middle C. The Omani sand produced a range of nine notes, from about F-sharp to D, with frequencies from 90 to 150 Hertz.

The researchers discovered that the size of the grains was responsible for the pitch of the notes. The Moroccan grains were all about the same size, 150–170 microns (0.006–0.0065 in). They consistently sounded like a G-sharp. But the Omani grains ranged from 150 to 310 microns in size (0.006–0.012 in), which accounted for their broader range of nine notes. When scientists isolated some of the Omani grains by size, their narrower range vibrated at one frequency to produce the same note.

The speed of the moving sand was also a factor. When the grains were all close in size, they moved at similar speeds and consistently produced the same pitch. When the grains varied in size, they moved at different speeds, causing a greater range of notes.

But scientists still don’t understand why these tones sound like music. Their theory is that the vibrations of the moving grains synchronize, pushing air together like the diaphragm in a loudspeaker.

7 The Homing Pigeon Bermuda Triangle



This mystery started in the 1960s, when a Cornell University professor studied homing pigeons’ remarkable ability to find their way home from locations previously unknown to them. He released the pigeons from a variety of locations throughout New York State. They all did fine except for birds released from Jersey Hill. Those pigeons got lost almost every time. On August 13, 1969, they found their way home from Jersey Hill, but every other time, they seemed to be disoriented and flew around randomly. The professor couldn’t explain why that happened.

Dr. Jonathan Hagstrum from the US Geological Survey thinks he may have solved the mystery, although his theory is controversial. “The way the 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,” he said. “They are using sound as their map . . . and this will tell them where they are relative to their home.”

Hagstrum believes the pigeons are using infrasound, low-frequency sound inaudible to humans. As we talked about once before, that type of sound may have been used in ancient soundscapes to alter our ancestors’ mental states when they participated in religious ceremonies.

The birds may be using infrasound (which is generated in this case by small vibrations on the Earth’s surface from deep ocean waves) as a homing beacon. When the birds got lost at Jersey Hill, the temperature and wind caused the infrasound signal to move high into the atmosphere. The pigeons couldn’t sense it on the ground. But on August 13, 1969, the temperature and wind conditions were perfect. So the pigeons could hear the infrasound and find their way home.





6 The Unique Origin Of Australia’s Only Active Volcano



Australia has only one active volcanic area, which extends 500 kilometers (300 mi) from Melbourne to Mount Gambier. In the past four million years, there have been around 400 volcanic events, with the last eruption about 5,000 years ago. Scientists had been baffled by what caused these eruptions in a part of the world that otherwise has almost no volcanic activity.

Now, researchers have solved the mystery. Most volcanoes on Earth occur on the edges of tectonic plates, which constantly move small distances (in centimeters per year) on top of the Earth’s mantle. But in Australia, variations in the continent’s thickness cause currents in the mantle below to draw heat to the surface. Combined with Australia’s northward drift at 7 centimeters (3 in) per year, a hotspot evolved in the area, creating magma.

“There are around 50 other similarly isolated volcanic regions around the world, several of which we may now be able to explain,” says Rhodri Davies of Australian National University.

5 The Fish That Thrive In A Superfund Cleanup Site

From the 1940s to the 1970s, manufacturing plants dumped polychlorinated biphenyls (PCBs) as waste into New Bedford Harbor in Massachusetts. The Environmental Protection Agency declared the harbor a Superfund cleanup site because the amount of PCB pollution was more than four times the level believed to be safe. But the harbor is also home to a biological puzzle that researchers may have finally solved.

In the midst of such toxic pollution, Atlantic killifish have thrived in New Bedford Harbor. A type of prey fish, killifish remain in the same waters within a few hundred yards of their birthplace for their entire lives.

Normally, when a fish digests PCBs, some of the metabolized chemicals become more toxic to the fish than the initial PCBs are. But killifish have flipped an off switch on this genetic pathway, stopping the metabolized toxins from forming. They’ve adapted to PCB pollution, but some scientists believe this genetic change may leave the killifish more susceptible to the harmful effects of other pollutants. It’s also possible that these fish won’t be able to live in a healthy environment when the waters are cleaned up.

Killifish are prey for striped bass, bluefish, and other fish that we eat. So even though the killifish appear to be immune to PCB toxins, they can pass those pollutants up the food chain all the way to us.





4 How Underwater Waves Are Produced



Underwater waves, also called internal waves, stay beneath the ocean surface, hidden from our view. They raise the ocean’s surface water by inches, which makes them difficult to detect except by satellite. The largest internal waves appear in the Luzon Strait, between Taiwan and the Philippines. They can tower 170 meters (560 ft) and move at only a few centimeters per second across great distances.

Scientists believe we must understand how these waves are generated because they may be an important contributor to global climate change. Internal waves mix the ocean’s less salty, warmer, upper water with its saltier, colder, lower water. They drive large volumes of salt, heat, and nutrients through the ocean. It’s the primary way that heat is transferred from the upper ocean to the lower waters.

Scientists have long wanted to solve the mystery of how the huge internal waves in the Luzon Strait are generated. They’re hard to see in the ocean, although instruments can detect the difference in density between an internal wave and its surrounding water. Nevertheless, scientists decided to conduct their tests in a 15-meter (50 ft) wave tank. The internal waves were generated by pushing cold bottom water over two ridges on the simulated seafloor. It appears that these huge internal waves are produced by the spacing of the ridges in the Luzon Strait, not by one feature on a ridge such as a high mountain.

“It’s an important missing piece of the puzzle in climate modeling,” says Thomas Peacock of MIT. “Right now, global climate models are not able to capture these processes. You get a different answer . . . if you don’t account for these waves.”

3 Why Zebras Have Stripes



There are many theories on why zebras have stripes. Some think the stripes act as camouflage or a way to confuse predators. Others believe the stripes help zebras regulate body heat or choose their mates.

Scientists at the University of California at Davis decided to find the answer. They studied where the species (and subspecies) of zebras, horses, and asses lived. They gathered information on the color, location, and size of stripes on the bodies of the zebras. Then they mapped the locations of tsetse flies and tabanids like horseflies and deer flies. A few other variables, some statistical analysis, and voila. They had their answer.

“I was amazed by our results,” said researcher Tim Caro. “Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.”

Zebras are more vulnerable to biting flies because their hair is shorter than that of similar animals like horses. These blood-sucking flies can carry deadly diseases, so it’s important for zebras to avoid this risk.

Other researchers from the University of Sweden found that flies avoid zebra stripes because they’re the right width. If they were wider, the zebras wouldn’t be protected. In that study, more flies were attracted by black surfaces, fewer by white surfaces and the fewest by stripes.





2 The Mass Extinction Of About 90 Percent Of Earth’s Species



About 252 million years ago, around 90 percent of the species on our planet were wiped out in the end-Permian extinction, also known as the “Great Dying,” the worst mass extinction on Earth. It’s an ancient whodunit, with suspects ranging from asteroids to volcanoes. But it turns out the killers can’t be seen without a microscope.

According to MIT researchers, the culprit was a single-celled microbe called Methanosarcina that eats carbon compounds and produces methane as waste. This microbe exists today in garbage dumps, oil wells, and the guts of cows. In the Permian period, scientists believe Methanosarcina underwent a gene transfer from a bacterium that allowed Methanosarcina to process acetate. Once that happened, the microbe could consume large piles of organic matter containing acetate that were sitting on the ocean floor.

The microbe population exploded, spewing huge amounts of methane into the atmosphere and acidifying the ocean. Most plants and animals on land perished, along with fish and shellfish in the sea. But the microbes would have needed nickel to multiply so wildly. Based on their sediment analysis, the researchers believe Siberian volcanoes belched the large amounts of nickel needed by the microbes.

“I would say that the end-Permian extinction is the closest animal life has ever come to being totally wiped out, and it may have come pretty close,” says researcher Greg Fournier. “Many, if not most, of the surviving groups of organisms barely hung on, with only a few species making it through, many probably by chance.”

1 The Origin Of Earth’s Oceans



Water covers about 70 percent of our planet’s surface. Initially, scientists believed that Earth formed dry, with a molten surface created by the impacts of other objects from space. Collisions with asteroids and wet comets supposedly brought water to our planet much later. “Some people have argued that any water molecules that were present as the planets were forming would have evaporated or been blown off into space,” said geologist Horst Marschall. “[Scientists thought that] surface water as it exists on our planet today must have come much later—hundreds of millions of years later.”

But a new study shows that Earth had water on its surface when it formed, enough for life to have evolved earlier than originally believed. The same may be true for other planets in our inner solar system before their environments turned hostile.

To determine when water arrived on Earth, researchers compared two sets of meteorites. The first set, carbonaceous chondrites, are the most ancient meteorites ever identified. They came into existence about the same time as our sun, before any planets developed. The second set of meteorites are believed to have come from Vesta, a big asteroid that formed in the same general area as Earth about 14 million years after our solar system was born.

The two types of meteorites share the same chemistry and contain a lot of water. For that reason, the researchers believe that Earth formed with water on its surface from the carbonaceous chondrites about 4.6 billion years ago.