How the Grand Canyon (大峡谷) was created remains one of the geology's greatest mysteries. Some evidence suggests that the process was a gradual one in which the Colorado River (which runs through the canyon) slowly cut deeper and deeper into the ground over millions of years. But volcanic rock samples taken from the canyon now suggest that the canyon was down-cut instead.

    Down-cutting is when a flood of water rushes over a landscape (地形) with enough force to cut deeply into the ground and leaves behind a canyon. Such a flood is usually released when a natural or man-made dam (堤坝) bursts.

    Robert Webb, a research geologist, says natural dams seem to have formed and broken across the Colorado River several times during the last million years. The dams were built when lava(熔岩) from the eruptions of nearby volcanoes flowed into the river. The lava hardened into hard rocks and blocked the river, causing it to back up and form a lake. Each time the lake grew so huge that it broke the rock dam, releasing a flash flood that furthered the down-cutting process and deepened the canyon.

    Down-cutting is not just an earthly event. Satellite photos sent back from Mars suggest that the process has happened there, too, say many other researchers.

    The photos, taken by the Mars Global Surveyor, indicate that an enormous lake existed on Mars 3.5 billion years ago. The lake spilled into a large nearby hole. One edge of the hole broke, releasing a flash flood that quickly carved out a grand canyon.

    The existence of down-cutting on Mars is just one more piece of evidence that the cold, dry planet was once warm and wet.

    When the residents of Buenos Aires want to change the pesos they do not trust into the dollars they do, they go to an office that acts as a front for thriving illegal exchange market.

    As the couriers carry their bundles of pesos around Buenos Aires, they pass grand buildings like the Teatro Colon, an opera house that opened in 1908, and the Retiro railway station, completed in 1915. In the 43 years leading up to 1914, GDP had grown at an annual rate of 6%, the fastest recorded in the world. In 1914 half of Buenos Aires's population was foreign-born. Its income per head was 92% of the average of 16 rich economies.

    It never got better than this. Its income per head is now 43% of those same 16 rich economies; it trails Chile and Uruguay in its own backyard.

    The country's dramatic decline has long puzzled economists. “If a guy has been hit___shots it's hard to work out which one of them killed him.” says Rafael di Tella. But three deep-lying explanations help to throw light on the country's decline. Firstly, Argentina may have been rich 100 years ago but it was not modern. The second theory stresses the role of trade policy. Thirdly, when it needed to change, Argentina lacked the institutions to create successful policies.

    Argentina was rich in 1914 because of commodities; its industrial base was only weakly developed. The landowners who made Argentina rich were not so bothered about educating it: cheap labor was what counted.

    Without a good education system, Argentina struggled to create competitive industries. It had benefited from technology in its Belle Epoque period, but Argentina mainly consumed technology from abroad rather than inventing its own.

    Argentina had become rich by making a triple bet on agriculture, open market and Britain, its biggest trading partner. If that bet turned sour, it would require a severe adjustment. The First World War delivered the initial blow to trade. Next came the Depression, which crushed the open trading system on which Argentina depended. Dependence on Britain, another country in decline, backfired(失败) as Argentina's favored export market signed preferential deals with Commonwealth countries.

    After the Second World War, when the rich world began its slow return to free trade with the negotiation of the General Agreement on Tariffs and Trade in 1947, Argentina had become a more closed economy. An institution to control foreign trade was created in 1946; the share of trade as a percentage of GDP continued to fall. High food prices meant big profits for farmers but empty stomachs for ordinary Argentines. Open borders increased farmers' taking but sharpened competition from abroad for domestic industry. Heavy export taxes on crops allow the state to top up its decreasing foreign-exchange reserves; limits on wheat exports create surpluses(过剩) that drive down local prices. But they also dissuade farmers from planting more land, enabling other countries to steal market shares.

    There's been a lot of talking about white-and-blue collar workers, and you may have even heard of gold collar workers, but lately a new color of collar is making its way into China's urban vernacular(土话)—green. Green collars say no when work is life and life is work. They choose to get out of the fast lane(车道), and explore new ways of living "green".

    Living green doesn't mean someone is working as an environmentalist, biologist or scientist. Instead it is more of a lifestyle choice. A typical green collar is well educated like a white-collar but physically tough like a blue-collar, likely born in the 70s or 80s of the last century and living in one of China's big cities, with a monthly income well above 5,000 yuan(about US $700).

    The life of a green collar may go something like this: Turn off the mobile phone after work, eat only healthy food rich in vitamins, go on hikes every weekend, and like to help the underprivileged.

    Green collars even have their own club. In Beijing, the Green Collar Club is for people who share a "be happy, healthy and helpful" spirit. The club often holds charity parties and uses the donations for environmental protection and poverty relief(摆脱贫困) projects in China.

    "They are successful in their careers, but do not miss the pleasures in life. They have a lot of money, but do not fall slave to it." said Zuo Shiguang, one of the founding members of the club.

    Research shows that some orchestral(管弦乐的) instruments are in a danger of dying out.YouGov research, asked by the Royal Philharmonic Orchestra (RPO) to find the most popular instruments among schoolchildren, has revealed the increasing popularity of the ukulele(尤克里里琴), with one in eight expressing a desire to learn, making it the highest ranked instrument behind the typical rock-band grouping of the guitar, piano, keyboards, drums and bass guitar.

    But younger generations' interest in"more complex instruments"is decreasing, with the three least popular being the French horn, the double bass and the trombone.

    James Williams, managing director of the RPO, believed the changes reflect the increasing pressure schools are under to provide music education, and went on to say that more needs to be done to interest secondary school students in the wider range of instruments. His concern was for the composition(构成) of future orchestras if the trend towards instruments like rock-band grouping were allowed to continue. But there may be yet another death, one that few would be quick to sorrow over：the recorder(竖笛).

    Cheap, convenient, easy to learn, and suitable for individual and group performances, the recorder was once the go-to instrument for children's early musical education.But in many schools it has been replaced by the ukulele, which, for teachers, offers many of the same benefits with none of the lasting damage to hearing. Plus, from a student's viewpoint: you can play Metallica on one.

    Not all hope is lost for the cream-colored, 10-pound Yamaha recorder with a long history, however. About 13% of girls and 4% boys surveyed by YouGov said they wanted to learn the recorder.Surprisingly high! Unlikely as it may be, these children's interest in the recorder must be encouraged.

Socially, few things are more annoying than someone repeatedly checking their phone in the middle of your conversation with them. Soon enough, you're having unhappy thoughts, thinking of their way like, I'm boring you; you're more concerned with whoever's on that phone than me; you don't care about me. None of that is necessarily true, but this is: "If someone is engaged in a great conversation, they wouldn't care about their phones," says Leslie, a psychologist and researcher at NYU.

Do you sometimes wonder: What should I have said to a rude person like this? What if we have to talk to such maddening persons? Experts have advice about how to deal with this.

Whether you say something or not, remember that the cell-addict's annoying habits aren't about you. "It's rude, for sure, but sometimes we mistake the behavior for more than what it is," says Leslie. "It's possible that they are facing something tough and merely experiencing nervousness or anxiety," he adds. It's also possible that their partner is stuck with a flat tyre (轮胎) or their kid is sick in hospital. The point is that you don't know.

So before you become angry at the cell-addict's open rudeness, focus instead on building a better conversation than whatever's going down on Instagram. You might never be able to achieve this, given the power of today's social media, so if you're close enough to a person, Leslie advises you to directly ask them: "What's on that thing that's so interesting?" Chances are that they will apologise at once and quickly put the phone away. But if the answer is something real, talk about it. Better yet, you can avoid the situation in advance by saying something like, "I'm really interested in catching up properly, so how about we leave our phones in the car?" If they indeed have that flat tyre or sick kid, at least you won't have to assume that it's because your stories are boring.