Several more riddles that previously seemed insoluble have been solved. "Moving stones", strange giraffe feet, singing sand dunes and other amazing mysteries of nature that we have been able to solve over the past few years.
1. The Secret of "Moving Stones" in Death Valley
From 1940 until recently, Racetrack Playa, a dry, flat-bottomed lake in Death Valley in California, was the site of the "moving rocks" phenomenon. Many people puzzled over this secret. For years or even decades, some force seemed to move the stones along the surface of the earth, and they left long furrows behind them. These "moving stones" weighed approximately 300 kg each.
No one has ever seen exactly how they move. Experts saw only the end result of this phenomenon, and nothing more. In 2011, a group of American researchers decided to deal with this phenomenon. They installed special cameras and a weather station to measure wind gusts. They also installed a GPS tracking system and waited.
It could take ten or more years before anything happened, but the researchers were lucky and it happened in December 2013.
Due to snow and rain, a layer of water of about 7 cm has accumulated on the dried bottom. At night, frost hit, and small groups of ice floes appeared. A weak wind, whose speed was about 15 km / h, was enough for the ice to start moving and pushing boulders along the bottom of the lake, and the boulders left furrows in the mud. These furrows became visible only a few months later, when the bottom of the lake dried up again.
Lumps only move when conditions are perfect. They need not too much (but not too little) water, wind and sun to move them.
“Perhaps tourists have seen this phenomenon more than once, but simply did not understand it. It is really difficult to notice that a boulder is moving if the boulders around it are also moving, ”said researcher Jim Norris.
2. How can giraffes stand on such thin legs?
A giraffe can weigh up to one ton. But for this size, giraffes have incredibly thin leg bones. However, these bones do not break.
To find out why, researchers at the Royal Veterinary College examined the limb bones of giraffes donated by EU zoos. These were the limbs of giraffes that died of natural causes. The researchers installed the bones in a special frame, and then attached a weight of 250 kg to them to mimic the weight of the animal. Each bone was stable and no signs of fracture were observed. Further, it turned out that bones can carry even more weight.
The reason turned out to be in fibrous tissue, which is located in a special groove along the entire length of the giraffe's bones. The giraffe's leg bones are a bit like the metatarsal bones in human feet. However, in a giraffe, these bones are much longer. By itself, the fibrous ligament in the giraffe's bone does not create any effort. It only provides passive support because it is flexible enough, although it is not muscle tissue. This, in turn, reduces the animal's fatigue, since it does not need to use its own muscles too much to move its weight. Also, the fibrous tissue protects the giraffe's legs and prevents fractures.
3. Singing Sand Dunes
There are 35 sand dunes in the world that emit a loud sound that is a bit like the low sound of a cello. The sound can last 15 minutes and can be heard 10 km away. Some dunes "sing" only occasionally, some - every day. This happens when grains of sand begin to slide down the surface of the dunes.
At first, the researchers thought the sound was caused by vibrations in sandy layers close to the dune's surface. But then it turned out that the sound of the dunes could be recreated in the laboratory by simply letting the sand slide down the slope. This proved that the sand "sings", not the dunes. The sound was due to the vibration of the grains of sand themselves as they cascaded down.
Then the researchers tried to find out why some dunes play several notes at the same time. To do this, they studied sand from two dunes, one of which was in eastern Oman, and the other in southwestern Morocco.
Moroccan sand produced a sound with a frequency of about 105 Hz, which was similar to G sharp. Sand from Oman could produce a wide range of nine notes, from F sharp to D. Sound frequencies ranged from 90 to 150 Hz.
It was found that the pitch of the notes depends on the size of the grains of sand. Grains of sand from Morocco were about 150-170 microns in size, and always sounded like a G sharp. The grains from Oman were 150 to 310 microns in size, so their range of sound consisted of nine notes. When scientists sorted the grains of sand from Oman by size, they began to sound at the same frequency, and played only one note.
The speed of the sand movement is also an important factor. When the grains of sand are about the same size, they move about the same distance at the same speed. If the grains of sand differ in size, they move at different speeds, as a result of which they can reproduce a wider range of notes.
4. Pigeon Bermuda Triangle
This mystery emerged in the 1960s, when a professor at Cornell University was studying the remarkable ability of pigeons to find their way home from places they had never been before. He released pigeons from various locations throughout New York State. All the pigeons returned home except one, which was released into Jersey Hill. The pigeons released there were lost almost every time.
On August 13, 1969, these pigeons finally found their way home from Jersey Hill, but they seemed disoriented and were flying around in complete chaos. The professor was never able to explain why this happened.
Dr. Jonathan Hagstrum of the US Geological Survey believes he may have solved this mystery, although his theory is controversial.
“Birds navigate using a compass and a map. The compass, as a rule, is the position of the Sun, or the magnetic field of the Earth. And they use the sound as a map. And all of this tells them how far from home they are. "
Hagstrum believes that pigeons use infrasound, which is a very low frequency sound that the human ear cannot hear. Birds can use infrasound (which can be generated, for example, by ocean waves, or small vibrations on the Earth's surface) as a locator beacon.
When birds were lost in Jersey Hill, air temperature and wind caused the infrasonic signal to travel high in the atmosphere, and the pigeons did not hear it near the surface of the earth. However, on August 13, 1969, the temperature and wind conditions were excellent. Thus, the pigeons were able to hear the infrasound and found their way home.
5. Unique origin of Australia's only volcano
Australia has only one volcanic region that stretches for 500 km, from Melbourne to Mount Gambier. Over the past four million years, about 400 volcanic events have been observed there, and the last eruption was about 5, 000 years ago. Scientists could not understand what caused all these eruptions in a region of the world in which almost no other volcanic activity is observed.
Researchers have now uncovered this secret. Most volcanoes on our planet are located at the edges of tectonic plates, which constantly move a short distance (about a few centimeters per year) along the surface of the earth's mantle. But in Australia, changes in the thickness of the continent have led to unique conditions in which heat from the mantle travels to the surface. Combined with Australia's northward drift (it travels about 7 cm annually), this led to a magma-creating hotspot on the continent.
"There are about 50 other similar isolated volcanic regions around the world, and the emergence of some of them we cannot currently explain, " said Rodri Davis of the National University of Australia.
6. Fish living in polluted water
From 1940 to 1970, factories dumped waste containing polychlorinated biphenyls (PCBs) directly into New Bedford Harbor in Massachusetts. In the end, the Environmental Protection Agency declared this harbor an ecological disaster zone, because the level of PCBs there many times exceeded all permissible norms.
The harbor is also home to a biological mystery that the researchers say has finally been solved.
Despite severe toxic pollution, a fish called the Atlantic hazelnut continues to thrive and thrive in New Bedford Harbor. These fish remain in the harbor throughout their life. Usually, when fish digest PCBs, the toxins contained in this substance become even more dangerous under the influence of the fish's metabolism.
But the filbert was able to genetically adapt to the poison, and as a result, toxins do not appear in its body. The fish have fully adapted to the pollution, but some scientists believe that these genetic changes could make the hazelnuts more susceptible to other chemicals. It is also possible that the fish will simply not be able to live in normal, clean water when the harbor is finally cleared of pollution.
7. How did the “underwater waves” originate?
Underwater waves, also called "internal waves", are located under the surface of the ocean and are hidden from our eyes. They raise the ocean surface by only a few centimeters, so they are extremely difficult to detect, and only satellites can help here.
The largest internal waves occur in the Luzon Strait, between the Philippines and Taiwan. They can climb 170 meters and travel long distances, moving only a few centimeters per second.
Experts believe that we must understand how these waves arise, since they can be an important factor in global climate change. The water of the inner waves is cold and salty. It mixes with water, which is warmer and less salty. Internal waves carry large volumes of salt, heat and nutrients across the ocean. It is with their help that heat is transferred from the surface of the ocean to its depths.
Researchers have long wanted to understand how huge internal waves originate in the Luzon Strait. They are difficult to see in the ocean, but instruments can detect the difference in density between the internal wave and the water that surrounds it. For a start, the specialists decided to simulate the process of the appearance of waves in a 15-meter reservoir. It was possible to obtain internal waves by applying a stream of cold water under pressure to two "mountain ranges" located at the bottom of the reservoir. So it seems that huge internal waves are generated by the chain of mountain ranges located at the bottom of the strait.
8. Why do zebras have stripes
There are many theories about why zebras are striped. Some people think that the stripes act as camouflage, or they are such a way to confuse predators. Others believe the stripes help the zebra regulate its body temperature or choose a mate.
Scientists from the University of California decided to find the answer to this question. They studied where all the species (and subspecies) of zebras, horses and donkeys live. They collected a wealth of information about the color, size and location of the stripes on the bodies of zebras. They then mapped the habitats of tsetse flies, horseflies, and deer flies. Then they took a few more variables into account, and finally did a statistical analysis. And they had an answer.
“I was amazed at our results. Again and again, stripes on the body of animals were observed in those regions of the planet where there were most problems associated with fly bites. "
Zebras are more prone to fly bites because their hair is shorter than that of a horse, for example. Blood-sucking insects can carry deadly diseases, so zebras need to avoid this risk in any way they can.
Other scientists from the University of Sweden have found that flies avoid zebras because their stripes are the correct width. If the stripes were wider, the zebra would not be protected. The study showed that flies are most attracted to black surfaces, less attractive to white surfaces and the striped surface is least attractive to them.
9. Mass extinction of 90% of the Earth's species
252 million years ago, about 90% of the animal species on our planet were destroyed. This period is also known as the "Great Extinction" and is considered the most massive extinction on Earth. It is like an ancient detective novel, the suspects of which were very different - from volcanoes to asteroids. But it turned out that the only way to see the killer is through a microscope.
According to researchers from MIT, the culprit for the extinction was a single-celled microorganism called Methanosarcina, which consumes carbon compounds to form methane. This microbe still exists today in landfills, in oil wells and in the intestines of cows. And in the Permian period, scientists believe, Methanosarcina underwent a genetic transformation from a bacterium, which allowed Methanosarcina to process acetate. Once this happened, the microbe was able to consume a bunch of organic matter containing acetate found on the ocean floor.
The microbial population literally exploded, spewing huge amounts of methane into the atmosphere and acidifying the ocean. Most of the plants and animals on land died along with fish and shellfish in the ocean.
But to multiply at such a wild rate, the microbes would need nickel. After analyzing the sediments, the researchers suggested that the volcanoes operating in the territory of what is now Siberia erupted large amounts of nickel, which is necessary for microbes.
10. Origin of Earth's oceans
Water covers about 70% of the surface of our planet. Previously, scientists thought that at the time of the emergence of the Earth, there was no water on it, and its surface was melted due to collisions with various cosmic bodies. It was believed that water appeared on the planet much later, as a result of collisions with asteroids and wet comets.
However, new research shows that water was on the surface of the Earth even at the stage of its formation. The same may be true for other planets in the solar system.
To determine when the water hit the Earth, the researchers compared two groups of meteorites. The first group were carbonaceous chondrites, the oldest meteorites ever discovered. They appeared at about the same time as our Sun, even before the planets of the solar system appeared.
The second group is meteorites from Vesta, a large asteroid that formed in the same period as Earth, that is, about 14 million years after the birth of the solar system.
These two types of meteorites have the same chemical composition and contain a lot of water. For this reason, researchers believe that the Earth was formed with water on the surface, carried there by carbonaceous chondrites about 4.6 billion years ago.