Uncover the mysteries of ten natures
A sail stone that can "walk"
A flat, dry lake bed in Death Valley National Park at California's Racetrack is home to sail stones that "walk." From the 1840s to the present, the phenomenon of the sailstone "walking" occurs every few years or decades, and an unforeseen force has caused hundreds of rocks to cross the earth at the same time, leaving parallel trajectories on the dry mud. And these sail stones, each weighing up to 300 kilograms.
In 2011, a group of American researchers decided to launch an investigation. They set up a time-lapse camera and a weather station to measure wind gusts, then installed dynamic sensing GPS trackers on 15 pieces of limestone.
In December 2013, the mystery was finally solved as the rocks moved — heavy rain and snowfall left 7mm of precipitation on the salt lake. At night, the water freezes into thin flakes of ice that shatter into large floating sheets of ice in the midday sun. The breeze, which is about 15 km/h, blows these accumulated ice plates, which push the rocks to leave trails on the dirt below the ice surface. After a few months the lake bed dried up, and these trajectories were revealed.
That is, the rock can only move if the conditions are perfect. Wind, sunlight, water, ice, none of this can be too much or too little.
How giraffes stay upright
Giraffes weigh about 1,000 kilograms, but compared to their size, the bamboo pole-like legs are incredibly thin. However, they never fall or get injured.
To find out why, researchers at the Royal Veterinary College studied giraffe limbs donated from ZOOs in the European Union. The researchers placed the limbs in a steel frame and then simulated the weight of the giraffes on the giraffes' legs with a mass of 250 kilograms. Each leg is stable and there is no problem at all standing upright.
In fact, giraffes' legs can successfully withstand greater weight – thanks to the suspensory ligaments (fibrous tissue used to hold bones together) that are trapped longitudinally in the giraffe's leg bones. These leg bones are similar to the metatarsal bones in human feet and the metacarpal bones in the hands. But these bones of giraffes are much longer than in humans. The suspensory ligament itself does not produce any force, it provides a passive support simply because it is elastic tissue, not muscle. It reduces the fatigue of the animal because it does not require a large amount of muscle to bear its own weight. These suspensory ligaments also protect the giraffe's foot joints and prevent it from collapsing on both feet.
The unique origin of Australia's only active volcano
Australia has only one active volcanic area, which stretches from Melbourne to Mount Gambian for 500 kilometres. In the previous 4 million years, there were about 400 volcanic eruptions, and the last eruption was about 5,000 years ago. Scientists have been puzzled by the question: What caused these eruptions to be concentrated in one time period and almost no eruptions in another?
Today, researchers have solved the puzzle. The vast majority of volcanoes on Earth form on crust tectonic plates, while crust tectonic plates located on the mantle always move small distances (a few centimeters per year). But in Australia, differences in land thickness cause a flow under the mantle, directing heat to the surface. Coupled with Australia's annual drift northwards of about 7 centimeters, the area evolved into a hot spot, resulting in magma.
Carrier pigeon Bermuda Triangle
In the 1860s, researchers at Cornell University began studying an extraordinary ability of carrier pigeons: they could find their way home from places they hadn't known before. The researchers released pigeons in different parts across New York State, except for the pigeons released on Mount Jersey, the rest of the pigeons did well.
Professor Jonathan Hagstrum, from the U.S. Geological Survey, believes that while his theory is still controversial, he may have solved the mystery. "The way the birds look for directions is to use a compass and a map. Compasses usually refer to the position of the Sun or the Earth's magnetic field, and they use sound as a map, which will tell them the location of their relative home. ”
Hagstrum believes that pigeons use infrasound waves, which are sounds of lower frequency that humans cannot hear. Birds may be using infrasound waves (in this case, caused by small vibrations on the Earth's surface caused by deep-sea waves) as beacons of home.
A dune that "sings"
There are currently 35 sand dunes known to make a loud rumbling sound, like the low chant of a cello. These sounds last about 15 minutes and can be transmitted for about 10 kilometers. Some dunes sing occasionally, while others sing every day. This phenomenon occurs when sand grains slide down the dunes.
At first, scientists thought these sounds came from vibrations on the subsurface of the dunes. But the researchers found through experimental simulations that it was sand, not dunes, that made sounds — when grains of sand slid down the dunes or a beveled structure.
Next, the researchers investigated why some singing dunes can make multiple tones at once. They studied sand from two dunes — one from southwestern Morocco, where sand always emits a sound of about 105 Hz, similar to a liter G two octaves below middle C; and another from a sand dune in southeastern Oman, where sand emits sounds in the range of 9 notes, from liter F to D, with frequencies between 90 and 150 Hz.
It turns out that the size of the sand grains is a factor that determines the pitch of the notes. The grains of sand in Morocco are almost the same size, about 150 to 170 microns. They consistently emit a tone similar to a liter of G. Oman's grains range in size from 150 to 310 microns, which allows them to emit tones in the range of 9 notes.
In addition, the speed at which the grains of sand move is also a factor. When all grains of sand are about the same size, they all move at similar speeds, always making the same tone sound. When the sand grains are different in size, they move differently, so that the sound they emit has a wider range of tones.
Fish thriving in the Super Fund Clean Farm
From the 1840s to the 1870s, manufacturing plants dumped polychlorinated biphenyls (PCBs) as scrap into New Bedford Harbor, Massachusetts. The EPA announced that it would use the port as a superfund clean-up site because the PCB contamination here has exceeded safety standards by more than 4 times.
However, in the midst of such toxic substances polluting the environment, the Atlanta medaka grows wildly.
Usually, when a fish digests a PCB, some of the chemicals produced by its metabolism are more toxic to the fish than the original PCB. But the study found that medaka triggered a switch on the genetic pathway, preventing the formation of metabolic toxins. They have adapted to PCB contamination, but some scientists believe that this genetic alteration may make medaka more sensitive to the harmful effects of other pollutants, and it is possible that when the water is cleared, the fish will not be able to survive in a healthy environment.
It is worth noting that medaka is a food for striped perch, horse mackerel and some of the other fish we usually eat. So, although medaka appears to be immune to PCB toxins, they can still pass these contaminants upward through the food chain to us.
How underwater waves are generated
Underwater waves, also known as submerged waves, reside beneath the surface of the ocean and are hidden from our line of sight. These submersible waves raise water on the surface of the ocean by several inches, making it often difficult for us to detect them except using satellites. The largest submersible waves occur in the Luzon Strait, located between Taiwan and the Philippines, where they can rise up to 170 meters and move long distances at a speed of just a few centimeters per second.
Scientists believe we must understand how these submersible waves are generated, because these submersible waves can have a very large impact on global climate change. Submersible waves mix the low-salinity, warm, upper water of the ocean with the salinity, icy, lower water and push large amounts of salt, heat, and nutrients throughout the ocean, which is the main way heat is transferred from the ocean surface to the lower water.
To solve the mystery of how submerged waves in the Luzon Strait are generated, scientists conducted simulation experiments in a 15-meter-high wave tank. Submerged waves are obtained by pushing icy bottom water towards two ridges that simulate the seafloor. The study found that these huge submersible waves were generated by the gaps between the ridges of the Luzon Strait, rather than by the ridge's similarity to the high mountains.
Why do zebras have stripes
There are many theories about why zebras have stripes on them, some of which suggest that stripes act as a role in regulating body temperature or choosing a partner. Scientists at the University of California, Davis, decided to find this answer by studying where zebra, wild horse, and wild donkey populations (and subpopulations) live, and collecting information about the color, location, and size of the stripes on zebras. They then mapped the location of tsetse flies (an African blood-sucking fly) and flies such as horseflies and deer flies, plus some other variables, some statistical analysis.
Eventually, they found the answer: Where there are more blood-sucking flies in the world, zebras also have more stripes on their bodies — which can keep them from being attacked by blood-sucking flies. Zebras are more susceptible to blood-sucking flies because they have shorter hair than other similar animals. These blood-sucking flies carry deadly diseases, so it is important for zebras to avoid this danger.
Permian species mass extinction
About 252 million years ago, about 90% of the species on our planet were completely destroyed in extinction at the end of the Permian. Scientists have been looking for the culprit that triggered the extinction of species.
Researchers at the Massachusetts Institute of Technology in the United States said that the culprit is a single-celled microorganism called "Methane Octococcus", which feeds on carbon compounds and produces methane as waste. This microbiome is found today in garbage dumps, oil wells and the internal organs of cows. In the Permian, scientists believe that Octococcus methane underwent a genetic transfer from a bacterium that could acetate Methane Octococcus acetogenesis. Once the gene transfer occurs, the microbe can eat a large amount of organic matter.
Microbial numbers explode, producing large amounts of methane in the atmosphere and acidifying the oceans. Most of the flora and fauna on land are dead, as are the fish and crustaceans in the sea. But these microbes need to get nickel to multiply so wildly. Based on an analysis of the sediments, the researchers believe that volcanic eruptions in Siberia provided large amounts of nickel needed for microbial reproduction.
The origin of the Earth's oceans
About 70% of our earth's surface is covered by water. It is generally believed that the fall of asteroids and comets has brought water to our planet. Scientists feel that the water on the Earth's surface must have come very late — millions of years after the Earth formed.
But a new study suggests that the Earth already had water on its surface as early as its formation, enough water for life to evolve earlier than we originally thought it would be.
To determine when water reaches Earth, the researchers compared two groups of meteorites. The first group is carbonaceous chondrite meteorites, which are the oldest meteorites that have been identified. It appears almost at the same time as the Sun. The second group of meteorites is thought to have come from Vesta, a large planetary belt in the same large region as Earth that formed 14 million years after the formation of the solar system. Both meteorites contain the same chemical composition and contain large amounts of water. Therefore, researchers believe that when the Earth formed 4.6 billion years ago, there was water from carbonaceous chondrite meteorites on its surface.